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Design of small dams

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Design of small dams

Design of small dams

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  • 1. UNITED STATES DEPARTMENT OF THE INTERIOR BUREAU OF RECLAMATION DESIGN OFSMALL DAMS A Water Resources Technical Publication First Edition, 1960 Second Edition, 1973 Revised Reprint, 1977 Third Edition, 1987
  • 2. As the Nation’s principal conservation agency, the Department of theInterior has responsibility for most of our nationally owned publiclands and natural resources. This includes fostering the wisest use ofour land and water resources, protecting our fish and wildlife, preserv-ing the environmental and cultural values of our national parks andhistorical places, and providing for the enjoyment of life through out-door recreation. The Department assesses our energy and mineralresources and works to assure that their development is in the bestinterests of all our people. The Department also has a major respon-sibility for American Indian reservation communities and for peoplewho live in Island Territories under U.S. Administration. For sale by the U.S. Government Printing OtTice Superintendent of Documenta, Mail Stop: SSOP. Washington, DC 20402-9323
  • 3. III Mission of the Bureau of ReclamationThe Bureau of Reclamation of the U.S. Department of the Interior isresponsible for the development and consarvation of the Nationswater resources in the Western United States. The Bureau’s original purpose “to provide for the reclamation of aridand semiarid lands in the West” today covers a wide range of interre-la ted functions. These include providing municipal and industrial watersupplies; hydroelectric power generation; irrigation water for agricul-ture; water quality improvement; flood control; river navigation; riverregulation and control; fish and wildlife enhancement; outdoor recrea-tion; and research on water-related design, construe tion, materials,atmospheric management, and wind and solar power.Bureau programs most frequently are the result of close cooperationwith the U.S. Congress, other Federal agencies, States, local govern-men ts, academic institutions, water-user organizations, and otherconcerned groups.
  • 4. Preface to the Third Edition The second edition of’ Design of Small Dams has siderations,” has been revised to include a discus-been very popular throughout the world; it has been sion on the management of fish and wildlif’epublished in a number of different languages and resources at, completed project,s, in addition to newused extensively in the United Stat,es. Since the design considerations. An expanded section onsecond edition was published in 1974, there have water quality implications to dam design and opbeen significant revisions in the approaches and erat,ion is also included.procedures related to the design of dams. Because Chapter 3, “Flood Hydrology Studies,” has beenof these revisions and the continued demand for this complet,ely revised, including incorporating t,he pre-manual, it was decided that, this new third edition vious appendix A, “EsGmating Rainfall Runoff’be prepared and published. from Soil and Cover Data,” int,o the chapt,er. Ref- The purpose of this third edition has been erence to t,he Soil Conservation Services’ curvechanged in scope and intent from that of the second number approach for assigning infiltration losses,edition. The title Design of Small Dams has been the triangular unit-hydrograph approach, and allretained even though some of the information in discussions and plates providing guidance for es-the third edition relates to large dams. Many of the timating probable maximum precipitation havetheoretical concepts presented can be applied to been eliminated. These topics have been replacedlarge or small structures; however, it is recom- by a treatment of infiltration losses as actually apmended that the procedures and methods presented plied by the Bureau of Reclamation, expanded con-be used only as guidelines. When preparing the de- sideration and guidance relative t,o the developmentsign of large or complicated structures, especially of unit, hydrographs using the dimensionless uni-those located where they create a high hazard, the graph and S-graph approaches, and specific ref-owner should rely on experienced dam engineers, erence to the Nat,ional Weather Service’sexperienced consultants, or refer to more detailed Hydrometeorological Report series as the basis forreferences. developing probable maximum precipitation esti- Some of the chapters and appendixes have been mates for the contiguous United Statues.revised extensively, while others reflect only minor Chapter 5, “Foundation and Const,ruction Ma-revisions. Chapter 1, “Plan Formulation,” has been terials,” has been updated t,o incorporate currentcondensed to briefly cover only the basic concepts standards in foundation and construction mat,erialsof plan formulation. The authors of this chapter investigations. A reservoir studies section has beenconcluded that a detailed discussion of plan for- added to the section on scope of investigations. Themulation was not appropriate because the primary sections on soil and rock classification have beenfocus of this manual is on design, not project plan- updated to reflect current standards, and a new sec-ning. Also, a discussion of plan formulation, par- tion on engineering geophysics has been added toticularly with an emphasis on Federal plan summarize the capabilities of these methods. Theformulat,ion requirements, would not be of interest sections on subsurface explorations and samplingto a majority of dam designers. The chapter thus have been revised extensively to represent, new tech-provides a brief discussion of the steps of plan for- nology. The logging of explorations has also beenmulation and some of the fundamental tests for the revised to reflect current standards, and t,he fieldviability of proposed plans. and laboratory test section has been updated. Chapter 2, “Ecological and Environmental Con- Changes in soil mechanics terminology and soil V
  • 5. vitesting procedures generated by revision of the Bu- modified low Froude number basin as an alternativereau’s Earth Manual are reflected in this chapter. to basin 4 design, and modifications in the designThe previous table 8, “Average Properties of Soils,” criteria for baffled apron spillways to permit theirwhich is now table 5-1, was recompiled to include use for higher unit discharges. Other contemporarylaboratory test results obtained since the last edi- spillway concepts are introduced, although designtion. Figure 5-14, “Permeability of Soils,” was added criteria are not included because they are still underto this edition to illustrate ranges of permeability development. Included in this category are laby-measured on compacted soil specimens tested at the rinth weirs where large flows must be discharged inBureau’s laboratory in Denver. The bibliography a limited space such as a narrow canyon, and thehas been updated to include selected sources of in- use of air slots (aerators) in spillways where thereformation for foundation and construction mate- is high potential for cavitation damage. Plunge-poolrials investigation. design criteria have been somewhat improved by the Chapter 6, “Earthfill Dams,” has been revised to addition of several references to recent research.update terminology and reflect design philosophy, The suggested method for calculating the dischargeprocedures, and standards that have evolved since under radial gates has been revised to reflect1974. The major change is greater emphasis on in- up-to-date criteria developed by the U.S. Armyternal filtering and drainage to control seepage and Corps of Engineers, Waterways Experiment Sta-internal erosion within embankment dams. New tion. The section on siphon spillways has beenfigures have been added that show current dam em- omitted from this edition because they are seldombankments that have been designed and con- used as fibw control structures for dams. The bib-structed by the Bureau of Reclamation. Other liography has been revised by the removal of ref-illustrations have been replaced or revised to reflect erences that were hard to obtain and by the additioncurrent thinking and technology. Liberal reference of many new references that reflect the currentis made to design standards that have been devel- state-of-the-art.oped as guides for Bureau engineers. Chapter 12, “Operation and Maintenance,” now Chapter 7, “Rockfill Dams,” required only minor includes additional topics, clarification, and morerevisions; however, the Bureau does not have ex- detail. The new topics added are “Changes in Op-tensive experience with the design and construction erating Plan,” which addresses modification to aof rockfill dams. Design and construction proce- structure to add additional storage or to change thedures for rockfill dams have changed over the last purpose of allocation of storage; “Emergency Pre-two or three decades and continue to do so. The paredness Plan,” which addresses instructions to anchapter gives a good general background for the operator during emergency situations; and “Damdesign of rockfill dams; however, the designer Operators Training,” which outlines the require-should also refer to the literature on the subject. ments for the training of operators to assure that Chapter 8, “Concrete Gravity Dams,” now in- operation and maintenance of a facility are per-cludes additional topics, clarification, and more de- formed in an accurate and responsible manner.tail. This chapter has also been revised to address Chapter 13 is a new chapter dealing with damconcerns for concrete dams of any height. Sections safety. Although dam safety is always an underlyingon material properties and foundation considera- consideration in the design, construction, opera-tions have also been added. More complete discus- tion, and monitoring of a dam, the passage of leg-sions are now included for forces acting on the dam, islation on Safety of Dams has placed addit,ionalrequirements for stability, and stress and stability emphasis on dam safety; and the inclusion of aanalyses. Discussions addressing the analysis of chapter on this subject was believed to be impor-cracked dams have been clarified and expanded to tant. This chapter presents procedures and refer-include analysis during an earthquake. Also, a gen- ences to other procedures for the evaluation anderal iterative approach for cracked dam analysis, analyses of dam safety issues for both new and ex-applicable for static and dynamic conditions, is now isting dam structures.included. The appendix designations have been revised. The “Spillways” and “Outlet Works” chapters, 9 The previous appendix A is now part of chapter 3,and 10, respectively, now include two new hydraulic and the original appendix H, “Sedimentation,” isdesigns for energy dissipators. These designs are a now appendix A. A new appendix H, “Operation
  • 6. viiand Maintenance,” presents a checklist for Oper- have been added.ation and Maintenance inspections. The intent of this third edition is to expand dis- Appendix D, “Soil Mechanics Nomenclature,” cussion of concepts for design of small to large damswas updated to reflect current terminology in use and to update the different approaches and pro-from ASTM Designation D-653, “Standard Defi- cedures being employed in the current state-of-the-nitions of Terms and Symbols Relating to Soil and art of planning, design, construction, operation, andRock Mechanics,” and from USBR 3900, “Standard evaluation processes. The text is not intended inDefinitions of Terms and Symbols Relating to Soil any way to encourage assumption of undue respon-Mechanics.” The latter reference is from the Bu- sibility on the part of unqualified personnel, butreau’s recently revised Earth Manual, volume 2, rather to point out the importance of specialized“Test Designations.” training. Engineers who do not have specialized Appendix E, “Construction of Embankments,” training in dam engineering should seek advicehas been revised to emphasize and more fully de- from experienced consultants.scribe construction control philosophy and proce- This manual was prepared by personnel of thedures. Several photographs of more modern Bureau of Reclamation, U.S. Department of the In-equipment and construction techniques have been terior, Denver, Colorado, under the direction ofadded. The “Rapid Method of Compaction Con- Darrell Webber, Assistant Commissioner, Engi-trol” has been eliminated; the reader is now referred neering and Research, with contributions from theto the Bureau’s Earth Manual for that procedure. staff of other Assistant Commissioners. Neil Par-Terminology has been updated to that currently rett, Chief, Division of Dam and Waterway Design,used within the Bureau of Reclamation. established a three-man team to coordinate the as- A discussion on concrete erosion has been added, sembly of this new edition: Harold K. Blair, Chair-and the discussion on abnormal set of concrete has man, Head, Design Section No. 2 of the Concretebeen expanded in appendix F, “Concrete in Con- Dams Branch; Thomas N. McDaniel, Design Man-struction.” The design of concrete mixes has been ager, Embankment Dams Branch; and Ronald D.revised and includes revisions to tables, forms, and Mohr, General Engineer, Document Systems Man-the steps involved in concrete mix design. agement Branch. Numerous engineers, technicians, Appendix G, “Sample Specifications,” has been and support personnel participated with this teamupdated to include guide specifications currently in the preparation of this third edition and theirused by the Bureau of Reclamation. efforts are greatly appreciated. Special recognition Throughout the third edition, figures and illus- to the many authors, both current and past, istrations have been revised and many new figures appropriate: Current Author(s) Past Author(s) Chapter 1 W.C. Dunkin, C.W. Huntley A.F. Johnson Chapter 2 J.C. Hokenstrom E.A. Seamen, L.W. Davidson Chapter 3 A.G. Cudworth, Jr. D.L. Miller, R.A. Clark, S. Schamach Chapter 4 T.N. McDaniel, H.K. Blair H.G. Arthur Chapter 5 S.R. Bartlett, R.C. Hatcher J.W. Hilf Chapter 6 T.N. McDaniel H.G. Arthur Chapter 7 T.N. McDaniel R.W. Bock, L.W. Davidson Chapter 8 H.L. Boggs, C.C. Hennig A.T. Lewis, J.S. Conrad, E.L. Watson, L.M. Christiansen Chapter 9 H.K. Blair, T.J. Rhone C.J. Hoffman Chapter 10 H.K. Blair, T.J. Rhone C.J. Hoffman Chapter 11 T.N. McDaniel, H.K. Blair E.R. Lewandowski Chapter 12 W.P. Gersch, L.J. Yocom H.G. Arthur Chapter 13 H.J. Warren, D.G. Achterberg, D.J. Trieste Appendix A R.I. Strand, E.L. Pemberton R.I. Strand
  • 7. *.*VIII Current Author(s) Past Author(s) Appendix B R.I. Strand, T.J. Rhone C.J. Hoffman, J.M. Lara, R.I. Strand Appendix C R.A. Simonds, H.K. Blair P.K. Bock, C.J. Hoffman Appendix D R.A. Young J.W. Hilf Appendix E T.N. McDaniel J.W. Hilf Appendix F J.L. Hart J.E. Backstrom, L.C. Porter, E.L. Ore, G.B. Wallace Appendix G J.L. Hart, R. Wright, R.E. Fink, N.F. Larkins, R.H. Restad, T.N. McDaniel E.R. Lewandowski Appendix H W.P. Gersch, L.J. Yocom Preparation of the manuscript for publication sional references to proprietary materials or prod-was performed by the personnel of the Planning ucts in this publication. These references are notand Editing Section, Document Systems Manage- to be construed in any way as an endorsement be-ment Branch, A. J. Huber, Branch Chief. cause the Bureau does not endorse proprietary The Bureau of Reclamation expresses apprecia- products or processes of manufacturers or the ser-tion to the organizations who have permitted the vices of commercial firms.use of their material in this text. There are occa-
  • 8. Preface to the Second Edition The first edition of “Design of Small Dams” was discussion of the slurry trench method of cutoffpublished to serve primarily as a guide to safe prac- construction, earthquake considerations, soil-tices for those concerned with the design of small cement design criteria, additional design details,dams in public works programs in the United and a more extensive reference list. The discussionStates. Its publication was warmly received and, in of rockfill dam design has been considerably ex-the intervening years since then, it has been widely panded in chapter VII to reflect the recent interestused in the United States, reprinted numerous in rockfill dams and the growth of available infor-times, and translated into many foreign languages, mation on this subject. Baffled spillway design pro-including Korean, Spanish, Japanese, and Chinese. cedures have been incorporated in chapter IX, and Since publication of the first edition of “Design additional information on tunneling has been pre-of Small Dams,” a large body of new literature has sented in chapter X. Appendix A includes new in-become available to dam designers, and many new formation on the estimation of rainfall runoff fromdesign procedures used at the Bureau of Recla- soil cover data, and an expanded discussion of flowmation have been changed to reflect more.modern in natural channels is contained in appendix B. Ap-techniques. As the number of changes in design pendix C includes new tables for the design of bothtechniques increased, it became apparent that their reinforced concrete pressure pipe and cast-in-placeincorporation in a second edition would be bene- conduits, and appendix E has a more complete dis-ficial to those individuals and agencies concerned cussion of the rapid method of compaction control.with small dams. Appendix G has been expanded to include speci- The purpose of the second edition remains es- fications concerning air and water pollution, andsentially the same as for the first edition. Many of each specification has been updated to reflect cur-the design procedures proposed in the first edition rent Bureau requirements. A new appendix on res-remain virtually unchanged. However, a number of ervoir sedimentation is presented in appendix H,new procedures have been developed by the Bureau which outlines current procedures used to estimateand are currently in use. To make this new infor- the rate of sedimentation and the period of timemation available generally, it is included in the sec- before sediment will interfere with the useful func-ond edition. The increased concern of the Bureau tions of the reservoir. A convenient list of conver-of Reclamation with environmental problems is re- sion factors is presented in appendix I to facilitateflected by the inclusion of chapter II, “Ecological the increased utilization of metric units. Many mi-and Environmental Considerations.” This chapter nor changes have been made throughout the text tooutlines some of the practical measures which may reflect current design and construction techniques.be t.aken to reduce the environmental and ecological It is intended that this book will provide the de-impact of a project. Chapter III has been extensively signer with an important source of information.revised’to include current methods of design flood However, this text is not intended in any way tocomputation and to incorporate new graphical data. encourage the assumption of undue responsibility Chapter V has been revised to reflect the avail- on the part of unqualified personnel, and the useability of current information concerning founda- or application of the methods and data containedtion design and to include supplemental foundation herein is strictly the responsibility of the personinvestigation procedures. Chapter VI contains ad- utilizing the material. Designs should reflect theditional material on the design of earth dams, a actual site conditions and should not merely be pat- ix
  • 9. Xterned after a successful design used at another recognition is given to H. G. Arthur, Director oflocation. Design and Construction, for his overall guidance Periodically, the names of Bureau of Reclamation in preparation of the text and to Dr. J. W. Hilf,projects and features are changed by acts of Con- Chief of the Division of Design, for his technicalgress, Federal agencies, etc., and therefore there advice.may be a few inconsistencies in the project and fea- The second edition of the text was coordinated,ture names referred to in the text. edited, and much supplemental technical informa- Some recent changes include the following: tion provided by L. W. Davidson, Civil Engineer, Earth Dams Section. Detailed editorial guidance, Cachuma Dam to Bradbury Dam final review, and preparation of the manuscript for Wasco Reservoir to Clear Lake publication was performed by W. E. Foote of t,he Soap Park Reservoir to Milly K. Goodwin Lake Technical Services Branch. Missouri River Basin Project to Pick-Sloan The Bureau of Reclamation again expresses Missouri Basin Program. grateful appreciation to those organizations which have permitted the use of material from their pub- There are occasional references to proprietary lications, especially the National Oceanic and At-materials or products in this publication. These mospheric Administration, U.S. Department ofmust not be construed in any way as an endorse- Commerce, for material used in chapter III; the Soilment since the Bureau cannot endorse proprietary Conservation Service, U.S. Department of Agri-products or processes of manufacturers or the ser- culture, whose material was used in appendix A; thevices of commercial firms for advertising, publicity, U.S. Geological Survey of the Department of thesales, or other purposes. Interior, who supplied material used in chapter V, The second edition was prepared by the engineers and the Corps of Engineers, U.S. Department ofof the Bureau of Reclamation, U.S. Department of the Army, whose report on slurry trench construc-the Interior, at its Engineering and Research Center tion was used in the preparation of chapter VI. Ac-in Denver, Colo. A number of engineers and tech- knowledgments to other organizations whichnicians participated in the preparation of the sec- furnished lesser amounts of material are givenond edition and in its critical review, and the efforts throughout the text.of these persons are greatly appreciated. Special
  • 10. Preface to the First Edition This book presents instructions, standards, and earthfill dams because they are the most commonprocedures for use in the design of small dams. It type. For the purpose of this book, small dams in-is intended to serve primarily as a guide to safe clude those structures with heights abovepractices for those concerned with the design of streambed not exceeding 50 feet except for concretesmall dams in public works programs in the United dams on pervious foundations. For the latter struc-States. The book will serve this purpose in three tures, the maximum height is further limited toways: (1) It will provide engineers with information dams whose maximum net heads (headwater to tail-and data necessary for the proper design of small water) do not exceed 20 feet. The text is not in-dams, (2) it will provide specialized and highly tech- tended to cover dams of such large volumes thatnical knowledge concerning the design of small significant economies can be obtained by utilizingdams in a form that can be used readily by engineers the more precise methods of design usually reservedwho do not specialize in this field, and (3) it will for large dams. In recognition of the limited engi-simplify design procedures for small earthfill dams. neering costs justified for small dams, emphasis is An earlier publication, “Low Dams” which was placed on efficiency and relatively inexpensive pro-prepared in 1938 by the National Resources Com- cedures to determine the necessary design data.mittee,, presented much useful information on the Simplified design methods are given to avoid thedesign of small dams. In the 20 years that have complex procedures and special investigations re-elapsed since the printing of that book, however, quired for large dams or for unusual conditions. Ad-there have been many technical advances in the equate but not unduly conservative factors of safetydesign of dams, and the need for a new work in- are used in the simplified design methods.corporating the latest design techniques has become Small dams are properly considered to be asso-increasingly evident. It is believed that this book, ciated with small streams and drainage areas of lim-“Design of Small Dams,” will fill that need. The ited extent. For these situations or for those innew book retains much of the format of “Low which spillway capacity is obtainable at relativelyDams” and some of the material from the earlier low cost, a sufficient approximation of the inflowpublication has been incorporated in the new one, design flood discharge may be determined by pro-but most of the text is wholly new. cedures given in this- text. For important projects, Although this text is related almost exclusively particularly where the spillway cost is a major itemto the design of small dams and appurtenant struc- of project cost and thus may have an importanttures, it is important that the designer be familiar bearing on project feasibility, more exact and com-with the purposes of the project, the considerations plex studies which are beyond the scope of this textinfluencing its justification, and the manner of ar- may be justified.riving at the size and type of structure to be built. This text is addressed to the designer of the struc-For these reasons, an outline discussion of a desir- ture and does not include in its scope the field ofable project investigation has been included in construction practices or methods. However, as thechapter I. integrity of the design requires adherence to lim- Only the more common types of small dams now iting specifications for materials and to the practicebeing constructed are discussed. These include con- of good workmanship in construction, appendixescrete gravity, earthfill (rolled-type), and rockfill are included on “Construction of Embankments,”dams. Emphasis is placed on the design of rolled “Concrete in Construction,” and “Sample Speci- xi
  • 11. xiifications.” More detailed specifications will be re- or in its critical review, and the efforts of all of thesequired to ensure proper construction of any specific are gratefully acknowledged. Special recognition isdam. given to 0. L. Rice, Chief of the Dams Branch, for This text is not intended in any way to encourage his guidance and counsel, especially in determiningassumption of undue responsibility on the part of the scope and treatment of the text.unqualified personnel, but rather to point out the The text was coordinated and edited by H. G.importance of specialized training and to stimulate Arthur, Supervisor, Design Unit, Earth Dams Sec-wider use of technically trained and experienced tion, and final review and preparation of the man-consultants. uscript for the printer was by E. H. Larson, Head, This text should be of service to all concerned Manuals and Technical Records Section.with the planning of small water storage projects, The Bureau of Reclamation expresses gratefulbut in no way does it relieve any agency or person appreciation to those organizations which have per-using it of the responsibility for safe and adequate mitted the use of material from their publications,design. The stated limitations of the design pro- especially the Soil Conservation Service, U.S. De-cedures should be heeded. partment of Agriculture, whose material was used This book was prepared by the engineers of the in appendix A; and the Corps of Engineers, U.S.Bureau of Reclamation, U.S. Department of the In- Department of the Army, whose Technical Manualterior, at Denver, Colo., under the direction of TM 5-545 was freely used in the preparation of partGrant Bloodgood, Assistant Commissioner and D of chapter V. Acknowledgments to other organ-Chief Engineer, and L. G. Puls, Chief Designing izations furnishing a lesser amount of material areEngineer. More than 30 engineers and many tech- given throughout the text.nicians participated in the preparation of the book
  • 12. Section CONTENTS PagePrefaces .. ... ... ... .... .. .... .. ... ... ... ... ... .. ... ... ... .. .... .. ... ... ... .. ... ... ... .. .... .. .... .. ... ... ... .. .... .. ... ... ... ... .....................................CHAPTER 1. PLAN FORMULATIONGeneral ... ... .... .. .... .. .... .. ... ... ... ... ... .. .... .. ... ... ... .. .... .. ... .. .... .. .... .. ... ... ... .. .... .. ... .. .... .. .... .. .... ......................................... 1CHAPTER 2. ECOLOGICAL AND ENVIRONMENTAL CONSIDERATIONS A. INTRODUCTION2.1. Planning ... .. .... .. .... .. .... .. .... .. ... .. .... .. .... .. ... ... ... .. .... .. .... .. ... ... ... .. .... .. ... ... ... .. .... .. .... .. ... ... ... ........................... 3 B. GENERAL ENVIRONMENTAL ISSUES2.2. Requirements .. .... .. .... ... ... ... .... .. .... .. .... .. .... .. .... .. .... .. .... .. .... ... ... ... ... ... .... .. .... .. .... .. .... .. .... ... .... .. .... .. .... .. .... .. 42.3. Categories of resources ... ... .... .. .... .. .... .. .... .. .... .. .... .. .... .. .... ... ... ... ... ... ... ... .... .. .... .. .... .. .... ... ... ... .... .. .... .. .... . 4 C. FISH AND WILDLIFE CONSIDERATIONS2.4. General ... .. .... ... ... ... ... ... .... .. .... .. .... ... ... ... ... ... ... ... ... ... ... ... .... .. .... .. .... .. .... .. .... .. .... ... ... ... .... .. .... .. .... .. .... ... ... ... 42.5. Ecological and environmental considerations for fish . .... ... ... .. .... ... ... ... .... .. .... .. .... ... ... ... ... ... ... ... .... .. 42.6. Ecological and environmental considerations for wildlife . .... .. .... .. .... .. .... .. .... ... ... ... .... .. .... .. .... .. .... .. . 8 D. WATER QUALITY2.7. General . .. .... ... .... .. .... .. .... .. .... ... ... ... ... ... ... ... .... .. .... .. .... .. .... .. .... .. .... .. .... .. .... ... ... ... .... .. .... .. .... ... ... ... ... ... ... ... .. 14 (a) Water quality analysis .. .. .... .. .... .. .... .. .... .. .... .. .... ... ... ... ... .. .... ... ... ... .... .. .... .. .... .. .... ... ... ... .... .. .... .. .. 14 (b) Effects of design and operating criteria .. ... .... .. .... .. .... .. .... .. .... .. .... .. .... ... ... ... .... .. .... .. .... .. .... .. ... 16 (c) Design considerations ... ....*....................................................................................... .. ... ... ... ... ... 17 E. ARCHEOLOGICAL AND HISTORICAL CONSIDERATIONS2.8. Requirements ... .. .... .. .... .. .... .. .... .. .... ... ... .. .... ... ... ... ... ... ... ... ... ... ... ... ... ... .... .. .... .. .... .. .... ... ... ... ... ... ... ... ... ... ... . 18 F. RECREATION CONSIDERATIONS2.9. Planning for recreation facilities . ... ... ... ... .... .. ... ... .... .. .... .. .... .. .... .. .... .. .... .. .... ... ... ... ... ... .... .. .... .. .... .. .... .. 19 G. BIBLIOGRAPHY2.10. Bibliography ... .. .... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... .... .. .... .. .... .. .... .. .... .. .... .. .... .. .... ... ... ... ... ... ... ... ... ... 21CHAPTER 3. FLOOD HYDROLOGY STUDIES 3.1. Purpose and scope................................................................................................................................. 23 3.2. Background ............................................................................................................................................ 23 ... XIII
  • 13. xiv DESIGN OF SMALL DAMSSection Page (a) PMF hydrograph ....................................................................................................................... 23 (b) Specific-frequency flood hydrograph ...................................................................................... 233.3. Basic hydrologic and meteorologic data.. ........................................................................................... 233.4. Hydrologic data ..................................................................................................................................... 23 (a) Recorded streamflow data ........................................................................................................ 23 (b) Peak discharge data .................................................................................................................. 243.5. Meteorologic data.. ................................................................................................................................ 243.6. Field reconnaissance of drainage basins for flood hydrology studies.. .......................................... 24 (a) Drainage network ...................................................................................................................... 24 (b) Soil and geologic conditions.. ................................................................................................... 25 (c) Vegetative cover ......................................................................................................................... 25 (d) Land use ..................................................................................................................................... 25 (e) Significant nearby basins.. ........................................................................................................ 253.7. Field reconnaissance report.. ............................................................................................................... 263.8. Development of probable maximum storms.. .................................................................................... 26 (a) Hydrometeorological reports 51 and 52 .................................................................................. 26 (b) Regionalized procedures west of the Continental Divide .................................................... 273.9. Flood runoff from rainfall .................................................................................................................... 28 (a) Basic unit hydrograph theory.. ................................................................................................ 28 (b) Unit hydrograph lag time ......................................................................................................... 29 (c) Temporal distribution of unit runoff.. .................................................................................... 33 (d) Development of synthetic unit hydrographs.. ........................................................................ 34 (e) Infiltration and other losses..................................................................................................... 39 (f) Base flow and interflow ............................................................................................................ 42 (g) Design-flood hydrographs ......................................................................................................... 513.10. Flood runoff from snowmelt ................................................................................................................ 523.11. Envelope curves of prior flood discharges ......................................................................................... 533.12. Estimates of frequency of occurrence of floods ................................................................................ 543.13. Flood hydrology reports ....................................................................................................................... 563.14. Bibliography ........................................................................................................................................... 57CHAPTER 4. SELECTION OF TYPE OF DAM A. CLASSIFICATION OF TYPES4.1. General ................................................................................................................................................... 594.2. Classification according to use ............................................................................................................ 594.3. Classification by hydraulic design ...................................................................................................... 594.4. Classification by materials ................................................................................................................... 594.5. Earthfill dams ........................................................................................................................................ 604.6. Rockfill dams ......................................................................................................................................... 614.7. Concrete gravity dams .......................................................................................................................... 624.8. Concrete arch dams .............................................................................................................................. 634.9. Concrete buttress dams.. ...................................................................................................................... 644.10. Other types.. ........................................................................................................................................... 64 B. PHYSICAL FACTORS GOVERNING SELECTION OF TYPE4.11. General ................................................................................................................................................... 644.12. Topography ............................................................................................................................................ 644.13. Geology and foundation conditions .................................................................................................... 65 (a) Rock foundations ....................................................................................................................... 65 (b) Gravel foundations .................................................................................................................... 65
  • 14. CONTENTS xvSection Page (c) Silt or fine sand foundations.. .................................................................................................. 65 (d) Clay foundations ........................................................................................................................ 65 (e) Nonuniform foundations.. ......................................................................................................... 654.14. Materials available ................................................................................................................................ 654.15. Hydrology ............................................................................................................................................... 664.16. Spillway .................................................................................................................................................. 664.17. Earthquake.. ........................................................................................................................................... 66 C. LEGAL, ECONOMIC, AND ESTHETIC CONSIDERATIONS4.18. Statutory restrictions ............................................................................................................................ 664.19. Purpose and benefit-cost relation.. ..................................................................................................... 674.20. Appearance.. ........................................................................................................................................... 67CHAPTER 5. FOUNDATIONS AND CONSTRUCTION MATERIALS A. SCOPE OF INVESTIGATIONS5.1. General ................................................................................................................................................... 695.2. Foundations.. .......................................................................................................................................... 695.3. Embankment soils.. ............................................................................................................................... 715.4. Riprap and rockfill.. .............................................................................................................................. 745.5. Concrete aggregate ................................................................................................................................ 745.6. Reservoir studies ................................................................................................................................... 76 (a) General.. ...................................................................................................................................... 76 (b) Reservoir maps.. ......................................................................................................................... 76 (c) Investigation methods ............................................................................................................... 77 6. COLLECTION AND PRESENTATION OF DATA5.7. General ................................................................................................................................................... 785.8. Presentation of data ............................................................................................................................. 78 C. SOURCES OF INFORMATION5.9. Topographic maps ................................................................................................................................. 795.10. Geologic maps ........................................................................................................................................ 805.11. Agricultural soil maps ........................................................................................................................... 815.12. Remote sensing.. .................................................................................................................................... 82 D. SOIL CLASSIFICATION5.13. General ................................................................................................................................................... 865.14. Soil components .................................................................................................................................... 87 (a) Size .............................................................................................................................................. 87 (b) Gradation.. .................................................................................................................................. 87 (c) Angularity ................................................................................................................................... 88 (d) Shape ........................................................................................................................................... 885.15. Soil moisture .......................................................................................................................................... 885.16. Properties of soil components ............................................................................................................. 88 (a) Gravel and sand ......................................................................................................................... 88 (b) Silt and clay ............................................................................................................................... 90 (c) Organic material ........................................................................................................................ 94
  • 15. xvi DESIGN OF SMALL DAMSSectic vz Page5.17. Unified soil classification system.. ...................................................................................................... 94 (a) General.. ...................................................................................................................................... 94 (b) Field classification ..................................................................................................................... 945.18. Engineering characteristics of soil groups.. ....................................................................................... 95 (a) General.. ...................................................................................................................................... 95 (b) Shear strength.. .......................................................................................................................... 95 (c) Permeability ................................................................................................................................ 95 E. ROCK CLASSIFICATION AND DESCRIPTION OF PHYSICAL PROPERTIES OF ROCK5.19. General ................................................................................................................................................... 98 (a) Definition and types .................................................................................................................. 98 (b) Mineral identification ............................................................................................................... 98 (c) Common rock-forming minerals .............................................................................................. 995.20. Igneous rocks ......................................................................................................................................... 100 (a) General ........................................................................................................................................ 100 (b) Classification.. ............................................................................................................................ 101 (c) Primary structural features.. .................................................................................................... 1015.21. Sedimentary rocks.. ............................................................................................................................... 102 (a) General ........................................................................................................................................ 102 (b) Characteristics ........................................................................................................................... 103 (c) Primary structural features ...................................................................................................... 1035.22. Metamorphic rocks ............................................................................................................................... 105 (a) General ........................................................................................................................................ 105 (b) Classification .............................................................................................................................. 1055.23. Rock classification ................................................................................................................................ 107 (a) Unit names and identification ................................................................................................. 108 (b) Descriptors and descriptive criteria for physical characteristics.. ...................................... 111 F. SURFACE EXPLORATIONS5.24. General ................................................................................................................................................... 1135.25. Fluvial-lacustrine soils .......................................................................................................................... 113 (a) Definition .................................................................................................................................... 113 (b) Outwash deposits ....................................................................................................................... 113 (c) Flood plain deposits.. ................................................................................................................. 114 (d) Lacustrine deposits .................................................................................................................... 1165.26. Glacial deposits.. .................................................................................................................................... 116 (a) General ........................................................................................................................................ 116 (b) Glacial till.. ................................................................................................................................. 116 (c) Glacial outwash .......................................................................................................................... 1165.27. Aeolian deposits.. ................................................................................................................................... 1195.28. Residual soils ......................................................................................................................................... 119 G. GEOPHYSICAL EXPLORATION METHODS5.29. General ................................................................................................................................................... 1215.30. Surface geophysical techniques ........................................................................................................... 122 (a) Seismic refraction surveys ........................................................................................................ 123 (b) Seismic reflection surveys ........................................................................................................ 123 (c) Shear-wave surveys .................................................................................................................... 124 (d) Surface waves ............................................................................................................................. 125 (e) Vibration surveys ....................................................................................................................... 125 (f) Electrical-resistivity profiling surveys .................................................................................... 126
  • 16. CONTENTS xviiSe& 3n Page (g) Electrical-resistivity soundings ................................................................................................ 127 (h) Electrical-resistivity, dipole-dipole surveying ........................................................................ 127 (i) Electromagnetic-conductivity profiling surveys.. ................................................................... 128 (j) Electromagnetic-conductivity sounding surveys.. .................................................................. 128 (k) Ground-probing radar ............................................................................................................... 128 (1) Self-potential surveying.. .......................................................................................................... 128 H. SUBSURFACE EXPLORATORY METHODS5.31. Accessible exploratory methods .......................................................................................................... 129 (a) Test pits ...................................................................................................................................... 130 (b) Large-diameter borings.. ........................................................................................................... 130 (c) Trenches ...................................................................................................................................... 130 (d) Tunnels ....................................................................................................................................... 1315.32. Nonaccessible exploratory methods.. .................................................................................................. 132 (a) Cone-penetrometer testing.. ..................................................................................................... 132 (b) Standard penetration testing.. ................................................................................................. 132 (c) Auger drilling.. ............................................................................................................................ 133 (d) Rotary drilling.. .......................................................................................................................... 140 (e) Core drilling.. .............................................................................................................................. 148 I. SAMPLING METHODS5.33. General ................................................................................................................................................... 1505.34. Disturbed samples (hand-sampling methods) ................................................................................... 151 (a) Accessible test pits, trenches, and large-diameter borings .................................................. 151 (b) Stockpiles and windrows .......................................................................................................... 151 (c) Hand-auger borings ................................................................................................................... 151 (d) Concrete aggregate sources ...................................................................................................... 151 (e) Riprap sources ............................................................................................................................ 1525.35. Disturbed samples (mechanical sampling methods) ........................................................................ 153 (a) Power auger drills.. .................................................................................................................... 153 (b) Reverse-circulation drills.. ........................................................................................................ 1555.36. Protection and preparation of disturbed samples for shipping.. .................................................... 1555.37. Undisturbed hand-sampling methods.. ............................................................................................... 155 (a) Procedures for obtaining hand-cut samples.. ......................................................................... 155 (b) Protection and shipping preparation for hand-cut undisturbed samples.. ........................ 1555.38. Undisturbed mechanical sampling methods.. .................................................................................... 155 (a) Soft, saturated cohesive or noncohesive soils.. ...................................................................... 156 (b) Soft to moderately firm cohesive soils ................................................................................... 158 (c) Medium to hard soils and shales.. ........................................................................................... 1595.39. Rock coring methods ............................................................................................................................ 160 J. LOGGING EXPLORATIONS5.40. Identification of holes ........................................................................................................................... 1615.41. Log forms ............................................................................................................................................... 1625.42. Information on log forms ..................................................................................................................... 164 (a) Drilling notes column ................................................................................................................ 165 (b) Center column.. .......................................................................................................................... 170 (c) Classification and physical conditions column.. .................................................................... 1705.43. Description of soils ............................................................................................................................... 1715.44. Description of rock cores ..................................................................................................................... 172 (a) Objectives of geologic logging ................................................................................................... 173 (b) Data required for geologic logs of drill holes ......................................................................... 173
  • 17. . ..XVIII DESIGN OF SMALL DAMSSection Page K. FIELD AND LABORATORY TESTS5.45. General ................................................................................................................................................... 1755.46. Field permeability tests ........................................................................................................................ 175 (a) General ........................................................................................................................................ 175 (b) Open-end tests ........................................................................................................................... 176 (c) Packer tests ................................................................................................................................ 1775.47. Inplace unit weight tests (sand replacement method). .................................................................... 1785.48, Vane shear test.. .................................................................................................................................... 1795.49. Laboratory tests on soils ...................................................................................................................... 179 (a) Gradation .................................................................................................................................... 179 (b) Moisture content ....................................................................................................................... 181 (c) Atterberg limits .......................................................................................................................... 181 (d) Specific gravity ........................................................................................................................... 183 (e) Laboratory compaction ............................................................................................................. 183 (f) Relative density .......................................................................................................................... 1835.50. Laboratory tests on riprap and concrete aggregate .......................................................................... 185 (a) Specific gravity and absorption ............................................................................................... 185 (b) Abrasion.. .................................................................................................................................... 185 (c) Soundness ................................................................................................................................... 185 L. BIBLIOGRAPHY5.51. Biliography .. .... ... ... ... .... .. .... ... .... .. .... ... .... .. .... ... .... .. .... ... .... .. .... .. .... ... .... .. .... ... .... .. .... ... .... .. ....................... 186CHAPTER 6. EARTHFILL DAMS A. INTRODUCTION6.1. Origin and development ....................................................................................................................... 1876.2. Scope of discussion ............................................................................................................................... 1876.3. Selection of type of earthfill dam ....................................................................................................... 188 (a) General ........................................................................................................................................ 188 (b) Diaphragm type ......................................................................................................................... 189 (c) Homogeneous type.. ................................................................................................................... 189 (d) Zoned embankment type .......................................................................................................... 192 B. DESIGN PRINCIPLES6.4. Design data ... ... .... .. .... ... .... .. .... ... .... .. .... ... .... .. .... ... ... ... .... ... ... ... .... .. .... ... ... ... .... .. .... ... .... ... .... .................... 1926.5. Design criteria . .... ... ... ... .... ... ... ... .... .. .... ... .... .. .... ... .... .. .... ... .... .. .... .. .... ... .... .. .... ... .... .. .... ... .... ... .... .. .... ... .... 192 C. FOUNDATION DESIGN6.6. General ................................................................................................................................................... 1936.7. Rock foundations.. ................................................................................................................................. 1946.8. Methods of treating rock foundations.. .............................................................................................. 1946.9. Sand and gravel foundations ............................................................................................................... 202 (a) General.. ...................................................................................................................................... 202 (b) Amount of underseepage .......................................................................................................... 203 (c) Seepage forces ............................................................................................................................ 2046.10. Methods of treating sand and gravel foundations ............................................................................ 205 (a) General ........................................................................................................................................ 205
  • 18. CONTENTS xixSectia Page (b) Cutoff trenches .......................................................................................................................... 206 (c) Partial cutoff trenches .............................................................................................................. 206 (d) Sheet piling cutoffs ................................................................................................................... 207 (e) Cement-bound and jet-grouted curtain cutoffs ..................................................................... 208 (f) Slurry trench cutoffs ................................................................................................................. 209 (g) Grouting.. .................................................................................................................................... 212 (h) Upstream blankets .................................................................................................................... 212 (i) Downstream embankment zones for pervious foundations.. ............................................... 215 (j) Toe drains and drainage trenches.. ......................................................................................... 219 (k) Pressure-relief wells .................................................................................................................. 2206.11. Designs for sand and gravel foundations.. ......................................................................................... 224 (a) General.. ...................................................................................................................................... 224 (b) Case 1: Exposed pervious foundations (shallow depth) ....................................................... 225 (c) Case 1: Exposed pervious foundations (intermediate depth) .............................................. 225 (d) Case 1: Exposed pervious foundations (great depth) ........................................................... 227 (e) Case 2: Covered pervious foundations .................................................................................... 228 (f) Summary of pervious foundation treatments ........................................................................ 2286.12. Methods of treating silt and clay foundations.. ................................................................................ 229 (a) General ........................................................................................................................................ 229 (b) Saturated foundations ............................................................................................................... 231 (c) Relatively dry foundations.. ...................................................................................................... 2326.13. Designs for silt and clay foundations.. ............................................................................................... 234 (a) Saturated foundations.. ............................................................................................................. 234 (b) Relatively dry foundations ....................................................................................................... 234 D. EMBANKMENTS6.14. Fundamental considerations ................................................................................................................ 2396.15. Pore water pressure .............................................................................................................................. 2406.16. Seepage through embankments ........................................................................................................... 2416.17. Stability analyses .................................................................................................................................. 2436.18. Embankment design ............................................................................................................................. 244 (a) Use of materials from structural excavation .......................................................................... 244 (b) Embankment slopes, general ................................................................................................... 245 (c) Diaphragm type .......................................................................................................................... 246 (d) Homogeneous type ..................................................................................................................... 249 (e) Zoned embankments .................................................................................................................. 2496.19. Seismic design.. ...................................................................................................................................... 253 E. EMBANKMENT DETAILS6.20. Crest design ............................................................................................................................................ 253 (a) General ........................................................................................................................................ 253 (b) Width .......................................................................................................................................... 253 (c) Drainage ...................................................................................................................................... 253 (d) Camber ........................................................................................................................................ 253 (e) Surfacing.. ................................................................................................................................... 255 (f) Safety requirements ................................................................................................................... 255 (g) Zoning .......................................................................................................................................... 255 (h) Typical crest details .................................................................................................................. 2556.21. Freeboard ................................................................................................................................................ 2556.22. Upstream slope protection ................................................................................................................... 258 (a) General ........................................................................................................................................ 258 (b) Selecting the type of protection .................................................... . ......................................... 258
  • 19. xx DESIGN OF SMALL DAMSSection Page (c) Dumped rock riprap .................................................................................................................. 260 (d) Hand-placed rock riprap.. ......................................................................................................... 262 (e) Concrete paving.. ........................................................................................................................ 262 (f) Soil-cement ................................................................................................................................. 2636.23. Downstream slope protection.. ............................................................................................................ 2656.24. Surface drainage.. .................................................................................................................................. 2666.25. Flared slopes at abutments.. ................................................................................................................ 267 F. DESIGN EXAMPLES OF SMALL EARTHFILL DAMS6.26. General ................................................................................................................................................... 2676.27. Maximum sections ................................................................................................................................ 268 (a) Amarillo Regulating Reservoir.. ............................................................................................... 268 (b) Cawker City Dike ...................................................................................................................... 268 (c) Big Sandy Dike .......................................................................................................................... 268 (d) Carpinteria Reservoir Dike ...................................................................................................... 268 (e) Carter Lake Dam No. 3.. .......................................................................................................... 270 (f) Crane Prairie Dam.. ................................................................................................................... 270 (g) Crescent Lake Dam.. ................................................................................................................. 270 (h) Dickinson Dam.. ........................................................................................................................ 270 (i) Dry Falls Dam ............................................................................................................................ 272 (j) Fruitgrowers Dam ...................................................................................................................... 272 (k) Howard Prairie Dam.. ............................................................................................................... 272 (1) Lion Lake Dikes ......................................................................................................................... 272 (m) Lovewell Dam ........................................................................................................................... 272 (n) Eklutna Dam.. ............................................................................................................................ 272 (0) Lower Two Medicine Dam ....................................................................................................... 272 (p) Olympus Dam ............................................................................................................................ 274 (q) Picacho North Dam .................................................................................................................. 274 (r) Picacho South Dam.. ................................................................................................................. 274 (s) Pishkun Dikes ............................................................................................................................ 276 (t) Lubbock Regulating Reservoir ................................................................................................. 276 (u) Shadow Mountain Dam.. .......................................................................................................... 276 (v) Soda Lake Dike .......................................................................................................................... 276 (w) Stubblefield Dam ...................................................................................................................... 276 (x) Tiber Dike .................................................................................................................................. 276 (y) Sheep Creek Barrier Dam.. ...................................................................................................... 276 (z) Wasco Dam ................................................................................................................................. 276 (aa) Ute Dam Dike .......................................................................................................................... 276 (bb) San Justo Dike ........................................................................................................................ 278 (cc) Calamus Dam ........................................................................................................................... 278 G. BIBLIOGRAPHY6.28. Bibliography . .... .. .... ... .... .. .... ... ... ... .... .. .... ... .... .. .... ... ... ... .... .. .... ... ... ... .... .. .... ... .... .. .... ... .... .. .... ................... 283CHAPTER 7. ROCKFILL DAMS A. GENERAL7.1. Origin and usage.. .................................................................................................................................. 2877.2. Definition and types of rockfill dams ................................................................................................ 287
  • 20. CONTENTS xxiSection Page B. FOUNDATION DESIGN7.3. Foundation requirements and treatment ... .... .. .... ... ... ... .... .. .... ... .... .. .... ... .... .. .... ... .... .. .... ... .... ... ... ... .... 2897.4. Membrane cutoffs ... .... ... ... ... .... .. .... .. .... ... .... .. .... .. .... ... .... .. .... ... ... ... .... .. .... ... .... ... ... ... .... ... ... ... .... ... .......... 289 C. EMBANKMENT DESIGN7.5. Selection of rock materials .. ... ... .... .. .... ... ... ... .... .. .... ... .... .. .... ... ... ... .... ... ... ... .... ... ... ... .... ... .... ... ... ... .... ... .. 2917.6. Embankment sections . .. .... .. .... ... .... .. .... ... .... .. .... .. .... ... .... ... ... ... .... .. .... ... .... .. .... ... .... ... .... .. .... ... .... .. ..... .. .. 2927.7. Placement of rockfill materials . .... .. .... ... .... .. .... ... .... .. .... ... .... .. .... ... ... ... .... ... .... .. .... ... .... ... .... .. .... ... .... ... . 2977.8. Seismic design .. .. .... ... .... .. .... ... .... .. .... ... .... .. .... ... ... ... .... .. .... ... .... .. .... ... .... ... .... .. .... ... .... ... .... .. .... ................. 299 D. MEMBRANE DESIGN7.9. Impervious central core.. ...................................................................................................................... 3007.10. Reinforced concrete.. ............................................................................................................................. 3007.11. Asphaltic concrete.. ............................................................................................................................... 3027.12. Steel ........................................................................................................................................................ 3077.13. Timber planking.. .................................................................................................................................. 308 E. BIBLIOGRAPHY7.14. Bibliography . ... .... ... .... .. .... ... ... ... .... ... ... ... .... .. .... ... ... ... .... ... ... ... .... .. ..... .. .... ... .... .. .... ... .... ... .... .................... 312CHAPTER 8. CONCRETE GRAVITY DAMS A. INTRODUCTION8.1. Origin and development .. .. .... ... ... ... .... .. .... ... ... ... .... .. .... ... .... .. .... ... ... ... .... ... .... .. .... ... .... ... .... .. .... ... .... .. .... . 3158.2. Scope of discussion .... ... ... ... .... .. .... ... ... ... .... .. .... ... ... ... .... .. .... ... .... .. .... ... .... .. .... ... .... .. .... ... .... ... .... .. .... ....... 315 B. CONCRETE PROPERTIES8.3. Strength .................................................................................................................................................. 3158.4. Elastic properties .................................................................................................................................. 3168.5. Thermal properties ............................................................................................................................... 3168.6. Average properties ................................................................................................................................. 316 (a) Basic considerations .................................................................................................................. 316 (b) Criteria ........................................................................................................................................ 316 C. FORCES ACTING ON THE DAM8.7. General ................................................................................................................................................... 3178.8. External water pressure ....................................................................................................................... 318 (a) Basic considerations .................................................................................................................. 318 (b) Criteria ........................................................................................................................................ 3188.9. Temperature ........................................................................................................................................... 318 (a) Basic considerations .................................................................................................................. 318 (b) Criteria.. ...................................................................................................................................... 3208.10. Internal water pressures ...................................................................................................................... 320 (a) Basic considerations .................................................................................................................. 320 --- (b) Criteria .... ... .... .. .... .. .... ... ... ... .... .. .... ... ... ... .... .. .... .. .... ... ... ... .... .. .... ... .... ... .... .. .... ... .... .. .... ................. 321
  • 21. xxii DESIGN OF SMALL DAMSSection Page8.11. Dead load ................................................................................................................................................ 321 (a) Basic considerations.. ................................................................................................................ 321 (b) Criteria ........................................................................................................................................ 3218.12. Ice ............................................................................................................................................................ 321 (a) Basic considerations .................................................................................................................. 321 (b) Criteria.. ...................................................................................................................................... 3218.13. Silt pressure ........................................................................................................................................... 322 (a) Basic considerations.. ................................................................................................................ 322 (b) Criteria ........................................................................................................................................ 3228.14. Earthquake.. ........................................................................................................................................... 322 (a) Basic considerations .................................................................................................................. 322 (b) Criteria.. ...................................................................................................................................... 3258.15. Load combinations ................................................................................................................................ 326 (a) Basic considerations.. ................................................................................................................ 326 (b) Criteria.. ...................................................................................................................................... 326 D. FOUNDATION CONSIDERATIONS8.16. Deformation modulus ........................................................................................................................... 326 (a) Basic considerations.. ................................................................................................................ 326 (b) Criteria.. ...................................................................................................................................... 3278.17. Shear strength.. ..................................................................................................................................... 327 (a) Basic considerations.. ................................................................................................................ 327 (b) Criteria.. ...................................................................................................................................... 3288.18. Foundation configuration.. ................................................................................................................... 328 (a) Basic considerations .................................................................................................................. 328 (b) Criteria.. ...................................................................................................................................... 328 E. REQUIREMENTS FOR STABILITY8.19. Safety factors.. ....................................................................................................................................... 328 (a) Basic considerations .................................................................................................................. 328 (b) Criteria.. ...................................................................................................................................... 328 F. STRESS AND STABILITY ANALYSES8.20. Sliding stability ..................................................................................................................................... 329 (a) Basic considerations .................................................................................................................. 329 (b) Criteria.. ............................................................. .;. ...................................................................... 3308.21. Internal stresses-untracked sections ............................................................................................... 330 (a) Basic considerations .................................................................................................................. 330 (b) Criteria.. ...................................................................................................................................... 3318.22. Internal stresses and sliding stability-cracked sections ................................................................ 331 (a) Basic considerations .................................................................................................................. 331 (b) Static method of analysis.. ....................................................................................................... 331 (c) Pseudostatic method of analysis .............................................................................................. 332 (d) General iterative method of analysis.. .................................................................................... 334 (e) Criteria ........................................................................................................................................ 334 G. ADDITIONAL TOPICS8.23. Dams on pervious foundations ............................................................................................................ 3348.24. Details of layout and design ................................................................................................................ 335 (a) Nonoverflow sections ................................................................................................................ 335
  • 22. . CONTENTS XXIIISection Page (b) Overflow sections.. ..................................................................................................................... 335 (c) Contraction joints.. .................................................................................................................... 335 H. COMPUTER METHODS8.25. General .. .. .... ... .... .. .... ... .... .. .... .. .... ... .... .. .... ... ... ... .... .. .... ... .... .. .... ... ... ... .... .. .... ... .... .. .... ... ........................... 336 I. BIBLIOGRAPHY8.26. Bibliography .. .... ... ... ... .... .. .... ... ... ... .... .. .... ... .... .. .... ... ... ... .... .. .... ... .... .. .... ... ... ... .... ... .... ... .... .. ..................... 336CHAPTER 9. SPILLWAYS A. GENERAL9.1. Function .................................................................................................................................................. 3399.2. Selection of inflow design flood .......................................................................................................... 339 (a) General considerations .............................................................................................................. 339 (b) Inflow design flood hydrographs ............................................................................................. 3409.3. Relation of surcharge storage to spillway capacity .......................................................................... 3419.4. Flood routing ......................................................................................................................................... 3419.5. Selection of spillway size and type ..................................................................................................... 344 (a) General considerations .............................................................................................................. 344 (b) Combined service and auxiliary spillways.. ............................................................................ 345 (c) Emergency spillways .................................................................................................................. 346 B. SERVICE SPILLWAYS9.6. Selection of spillway layout ................................................................................................................. 3479.7. Spillway components ............................................................................................................................ 35: (a) Control structure ....................................................................................................................... (b) Discharge channel ..................................................................................................................... 351 (c) Terminal structure.. ................................................................................................................... 351 (d) Entrance and outlet channels.. ................................................................................................ 3529.8. Spillway types.. ...................................................................................................................................... i%X& (a) General ........................................................................................................................................ (b) Free overfall (straight drop) spillways .................................................................................... 352 (c) Ogee (overflow) spillways .......................................................................................................... 353 (d) Side channel spillways .............................................................................................................. 353 (e) Labyrinth spillways ................................................................................................................... 354 (f) Chute (open channel or trough) spillways.. ............................................................................ 355 (g) Conduit and tunnel spillways ................................................................................................... 357 (h) Drop inlet (shaft or morning glory) spillways ....................................................................... 357 (i) Baffled chute spillways.. ........................................................................................................... 358 (j) Culvert spillways.. ...................................................................................................................... 3629.9. Controlled crests ................................................................................................................................... 363 (a) General.. ...................................................................................................................................... 363 (b) Flashboards and stoplogs ......................................................................................................... 363 (c) Rectangular lift gates ................................................................................................................ i$ (d) Wheel- or roller-mounted gates.. ............................................................................................. (e) Radial gates ................................................................................................................................ 364
  • 23. xxiv DESIGN OF SMALL DAMS Section Page C. HYDRAULICS OF CONTROL STRUCTURES9.10. Shape for uncontrolled ogee crest.. ..................................................................................................... 3659.11. Discharge over an uncontrolled overflow ogee crest.. ...................................................................... 365 (a) General ........................................................................................................................................ 365 (b) Pier and abutment effects ........................................................................................................ 3659.12. Discharge coefficient for uncontrolled ogee crests ........................................................................... 369 (a) Effect of depth of approach ..................................................................................................... 369 (b) Effect of heads different from design head ........................................................................... 369 (c) Effect of upstream face slope.. ................................................................................................. 369 (d) Effect of downstream apron interference and downstream submergence.. ....................... 3699.13. Examples of designs of uncontrolled ogee crests.. ............................................................................ 370 (a) Example 1 ................................................................................................................................... 370 (b) Example 2 ................................................................................................................................... 3749.14. Uncontrolled ogee crests designed for less than maximum head.. ................................................. 3759.15. Gate-controlled ogee crests.. ................................................................................................................ 3769.16. Discharge over gate-controlled ogee crests.. ...................................................................................... 3769.17. Side channel spillways.. ........................................................................................................................ 376 (a) General ........................................................................................................................................ 376 (b) Design example.. ........................................................................................................................ 381 D. HYDRAULICS OF FREE-FLOW DISCHARGE CHANNELS9.18. General ................................................................................................................................................... 3839.19. Open channels ....................................................................................................................................... 384 (a) Profile .......................................................................................................................................... 384 (b) Convergence and divergence .................................................................................................... 385 (c) Channel freeboard.. .................................................................................................................... 385 E. HYDRAULICS OF TERMINAL STRUCTURES9.20. Deflector buckets ................................................................................................................................... 3879.21. Hydraulic-jump basins.. ........................................................................................................................ 387 (a) General ........................................................................................................................................ 387 (b) Basin design in relation to Froude numbers ......................................................................... 388 (c) Rectangular versus trapezoidal stilling basin ........................................................................ 394 (d) Basin depths versus hydraulic heads.. .................................................................................... 394 (e) Tailwater considerations ........................................................................................................... 394 (f) Stilling basin freeboard.. ........................................................................................................... 3989.22. Submerged bucket dissipators ............................................................................................................. 3989.23. Examples of designs of a stilling basin and an alternative submerged bucket dissipator .......... 4009.24. Plunge basins ......................................................................................................................................... 402 F. HYDRAULICS OF SPILLWAYS9.25. Free overfall (straight drop) spillways ............................................................................................... 403 (a) General ........................................................................................................................................ 403 (b) Hydraulic-jump basins.. ............................................................................................................ 404 (c) Impact block type basins.. ........................................................................................................ 404 (d) Slotted-grating dissipators ....................................................................................................... 404 (e) Example of design of a free overfall spillway ........................................................................ 4069.26. Drop inlet (shaft or morning glory) spillways.. ................................................................................. 407 (a) General characteristics.. ............................................................................................................ 407 (b) Crest discharge.. ......................................................................................................................... 407
  • 24. CONTENTS xxvSection Page (c) Crest profiles .............................................................................................................................. 409 (d) Transition design ....................................................................................................................... 409 (e) Conduit design............................................................................................................................ 415 (f) Design example .......................................................................................................................... 4169.27. Culvert spillways ................................................................................................................................... 421 (a) General ........................................................................................................................................ 421 (b) Circular conduit with vertical headwall ................................................................................. 424 (c) Box culvert with vertical or warping inlet walls.. ................................................................. 426 (d) Conduit pressures ...................................................................................................................... 427 (e) Antivortex devices ..................................................................................................................... 428 (f) Energy dissipators.. .................................................................................................................... 428 (g) Design examples......................................................................................................................... 428 G. STRUCTURAL DESIGN DETAILS9.28. General ................................................................................................................................................... 4299.29. Crest structures and walls ................................................................................................................... 4299.30. Open channel linings.. .......................................................................................................................... 4309.31. Miscellaneous details.. .......................................................................................................................... 433 (a) Cutoffs.. ....................................................................................................................................... 433 (b) Backfill.. ...................................................................................................................................... 433 (c) Riprap.. ........................................................................................................................................ 433 H. BIBLIOGRAPHY9.32. Bibliography .. .... .. .... ... .... .. .... ... .... .. .... ... .... .. .... ... ... ... .... .... .. ... .... .. .... .. .... ... .... .. .... ... ... ... .... ... ..................... 434CHAPTER 10. OUTLET WORKS A. GENERAL10.1. Functions ................................................................................................................................................ 43510.2. Determination of required capacities ................................................................................................. 43510.3. Outlet works position in relation to reservoir storage levels.......................................................... 43710.4. Conditions that determine outlet works layout ................................................................................ 44310.5. Arrangement of outlet works ............................................................................................................... 44510.6. Location of outlet works controls ....................................................................................................... 446 (a) General ........................................................................................................................................ 446 (b) Control at upstream end of conduit ....................................................................................... 446 (c) Control at intermediate point along conduit ......................................................................... 447 B. OUTLET WORKS COMPONENTS10.7. General ................................................................................................................................................... 448 (a) Tunnels ........................................................................................................................................ 448 (b) Cut-and-cover conduits ............................................................................................................. 44910.8. Controls .................................................................................................................................................. 449 (a) Control devices........................................................................................................................... 449 (b) Arrangement of controls ........................................................................................................... 450 (c) Control and access shafts ......................................................................................................... 450 (d) Control houses ........................................................................................................................... 45110.9. Intake structures ................................................................................................................................... 45110.10. Terminal structures and dissipating devices ..................................................................................... 45210.11. Entrance and outlet channels ............................................................................................................. 453
  • 25. xxvi DESIGN OF SMALL DAMSSection Page C. HYDRAULIC DESIGN10.12. Nature of flow in outlet works.. .......................................................................................................... 45310.13. Open-channel flow in outlet works.. ................................................................................................... 45310.14. Pressure flow in outlet conduits ......................................................................................................... 45510.15. Pressure flow losses in conduits .......................................................................................................... 456 (a) General.. ...................................................................................................................................... 456 (b) Friction losses ............................................................................................................................ 456 (c) Trashrack losses.. ....................................................................................................................... 457 (d) Entrance losses .......................................................................................................................... 458 (e) Bend losses ................................................................................................................................. 458 (f) Transition losses ........................................................................................................................ 458 (g) Gate and valve losses ................................................................................................................ 460 (h) Exit losses ................................................................................................................................... 46010.16. Transition shapes .................................................................................................................................. 460 (a) Entrances.. .................................................................................................................................. 460 (b) Contractions and expansions.. ................................................................................................. 460 (c) Exit transitions .......................................................................................................................... 46110.17. Terminal structures .............................................................................................................................. 463 (a) General.. ...................................................................................................................................... 463 (b) Impact-type stilling basin ......................................................................................................... 463 (c) Stilling wells ............................................................................................................................... 46310.18. Design examples.. .................................................................................................................................. 263 (a) Example 1 ................................................................................................................................... 465 (b) Example 2.. ................................................................................................................................. 467 D. STRUCTURAL DESIGN DETAILS10.19. General ................................................................................................................................................... 47010.20. Tunnel details.. ...................................................................................................................................... 47110.21. Cut-and-cover conduit details ............................................................................................................. 474 (a) General ........................................................................................................................................ 474 (b) Cutoff collars.. ............................................................................................................................ 474 (c) Conduit joints.. ........................................................................................................................... 478 (d) Design loads ............................................................................................................................... 47910.22. Details of typical structures ................................................................................................................ 481 E. BIBLIOGRAPHY10.23. Bibliography ... .... .. .... .. .... ... .... .. .... ... ... ... .... ... ... ... .... .. .... ... .... .. .... .. .... .. .... ... .... .. .... ... ... ... .... ... ..................... 489CHAPTER 11. DIVERSION DURING CONSTRUCTION A. DIVERSION REQUIREMENTS11.1. General ................................................................................................................................................... 49111.2. Streamflow characteristics ................................................................................................................... 49111.3. Selection of diversion flood ................................................................................................................. 491 B. METHODS OF DIVERSION11.4. General ... .... .. .... ... ... ... .... ... ... ... .... .. .... ... ... ... .... .. .... .. .... ... .... .. .... .. .... ... ... ... .... .. .... .. .... .. ............................... tii11.5. Tunnels . .. .... ... .... .. .... ... ... ... .... .. .... ... .... .. .... .. .... .. .... ... ... ... .... .. .... ... ... ... ... ... .... .. .... .. .... .. ..... .. .... .. .... ... .... .. .... .
  • 26. CONTENTS xxviiSection Page11.6. Conduits.. ................................................................................................................................................ 49511.7. Temporary diversion channels-earthfill dams ................................................................................ 49611.8. Multiple-stage diversion for concrete dams ...................................................................................... 49911.9. Cofferdams ............................................................................................................................................. 499 C. SPECIFICATIONS REQUIREMENTS11.10. Contractor’s responsibilities.. .............................................................................................................. 50111.11. Designer’s responsibilities.. .................................................................................................................. 502 D. BIBLIOGRAPHY11.12. Bibliography ... .... .. .... ... ... ... .... .. .... .. .... ... .... .. .... .. .... ... ... ... .... .. .... ... .... .. .... .. .... .. .... ... .... .. .... ... ...................... 503CHAPTER 12. OPERATION AND MAINTENANCE A. GENERAL12.1. Operation and maintenance program .. .... ... ... ... ... ... .... .. .... .. .... ... .... .. .... ... ... ... .... .. .... ... .... .. .... ... .... .. .... .. 505 B. INSPECTION AND MAINTENANCE OF DAMS12.2. General information.. ............................................................................................................................ 50612.3. Earthfill embankments.. ....................................................................................................................... 50612.4. Concrete dams ....................................................................................................................................... 50612.5. Structures and mechanical equipment.. ............................................................................................. 507 C. OPERATION12.6. Storage dams .......................................................................................................................................... 50712.7. Diversion dams ...................................................................................................................................... 50912.8. Flood detention reservoirs ................................................................................................................... 50912.9. Changes in operating plan.. ................................................................................................................. 50912.10. Emergency preparedness plan ............................................................................................................. 51012.11. Dam operator’s training ....................................................................................................................... 510 D. BIBLIOGRAPHY12.12. Bibliography .... .. .... .. .... ... .... .. .... .. .... ... .... .. .... .. .... ... ... ... .... .. .... ... ... ... ... ... .... .. .... ... ... ... .... ... ... ... ................... 510CHAPTER 13. DAM SAFETY A. INTRODUCTION13.1. Purpose ................................................................................................................................................... 51113.2. Scope ....................................................................................................................................................... 51113.3. Definitions .............................................................................................................................................. 51113.4. Federal guidelines for dam safety ....................................................................................................... 512 B. PRINCIPLES AND CONCEPTS13.5. New dams ............................................................................................................................................... 512 (a) Planning and design .................................................................................................................. 512
  • 27. ...XXVIII DESIGN OF SMALL DAMS Section Page (b) Construction ............................................................................................................................... 51313.6. Existing dams ........................................................................................................................................ 513 (a) Operation and maintenance ..................................................................................................... 513 (b) Periodic examinations and evaluations .................................................................................. 51313.7. Documentation on dams ...................................................................................................................... 513 C. PERIODIC DAM SAFETY EVALUATIONS13.8. General . .... ... .... .. .... ... .... .. .... ... ... ... .... .. .... ... .... .. .... ... ... ... .... .. .... ... ... ... .... .. .... ... .... .. .... .. ............................... 51413.9. Examinations .. .. .... ... .... .. .... ... ... ... .... .. .... ... .... .. .... .. .... ... .... .. .... ... ... ... .... .. .... ... .... .. .... ... .... .. .... ... ................. 514 D. TECHNICAL ANALYSES13.10. General ................................................................................................................................................... 51513.11. Overall safety classification.. ............................................................................................................... 51613.12. Downstream hazard assessment.. ........................................................................................................ 51613.13. Analyses of hydrologic/hydraulic issues.. ........................................................................................... 52113.14. Analyses of seismotectonic issues.. ..................................................................................................... 52213.15. Analyses of geologic issues.. ................................................................................................................. 52313.16. Analyses of geotechnical issues ........................................................................................................... 52313.17. Analyses of structural issues ............................................................................................................... 525 E. CORRECTION OF DAM SAFETY DEFICIENCIES13.18. Responsibility ........................................................................................................................................ 52713.19. Basis for dam safety corrections.. ....................................................................................................... 527 F. BIBLIOGRAPHY13.20. Bibliography ... ... .... .. .... ... .... .. .... ... ... ... .... .. .... ... .... .. .... ... .... .. .... ... ... ... .... .. .... ... .... .. .... ... .... ... ... .................... 528APPENDIX A. RESERVOIR SEDIMENTATIONA.l. General ................................................................................................................................................... 529A.2. Methods of determining sediment inflow.. ........................................................................................ 530A.3. Reservoir sediment deposition.. ........................................................................................................... 540A.4. Downstream channel effects.. .............................................................................................................. 553A.5. Bibliography.. ......................................................................................................................................... 563APPENDIX B. HYDRAULIC COMPUTATIONS A. HYDRAULIC FORMULASB.l. Lists of symbols and conversion factors.. .......................................................................................... 565B.2. Flow in open channels.. ........................................................................................................................ 567B.3. Flow in closed conduits.. ...................................................................................................................... 576B.4. Hydraulic jump.. .................................................................................................................................... 583 B. FLOW IN NATURAL CHANNELSB.5. General ................................................................................................................................................... 590B.6. Collection of data.. ................................................................................................................................ 593B.7. Slope-area method of computing streamflow.. .................................................................................. 594
  • 28. CONTENTS xxixSection PageB.8. Development of rating curves.. ............................................................................................................ 600B.9. Critical flow.. .......................................................................................................................................... 606B.lO. Computer applications.. ........................................................................................................................ 608 C. BIBLIOGRAPHYB.ll. Bibliography .... ... ... ... .... .. .... ... .... .. .... ... .... .. .... .. .... ... .... .. .... ... .... .. .... ... ... ... .... .. ..... .. .... ... .... .. ....................... 609APPENDIX C. STRUCTURAL DESIGN DATAc.1. Introduction ........................................................................................................................................... 611C.2. Earth pressures on retaining walls.. ................................................................................................... 611C.3. Earthquake loads on retaining walls.. ................................................................................................ 611C.4. Allowable bearing values for structure footings ................................................................................ 611C.5. Precast concrete pipe conduits.. .......................................................................................................... 611C.6. Cast-in-place concrete conduits .......................................................................................................... 620C.7. Bibliography ........................................................................................................................................... 622APPENDIX D. SOIL MECHANICS NOMENCLATURED.l. Introduction .. ... .... ... ... ... .... ... ... ... .... .. .... ... .... .. .... ... .... .. .... .. .... ... .... .. .... ... .... .. .... ... .... .. .... ... .... ... .... .. .... ... .... 623D.2. Definitions, symbols, and units .. ... ... ... .... ... ... ... .... .. .... ... .... .. .... ... ... ... .... .. .... ... .... .. ..... ... ... ... .... ... .... ... .... 623APPENDIX E. CONSTRUCTION OF EMBANKMENTSE.l. General ................................................................................................................................................... 641E.2. Soil mechanics of compaction ............................................................................................................. 642E.3. Preparation of foundations .................................................................................................................. 644E.4. Earthfill .................................................................................................................................................. 648E.5. Pervious fill ............................................................................................................................................ 651E.6. Rockfill and riprap.. .............................................................................................................................. 653E.7. Miscellaneous fills.. ............................................................................................................................... 653E.8. Records and reports .............................................................................................................................. 654E.9. Control criteria.. .................................................................................................................................... 654E.lO. Bibliography.. ......................................................................................................................................... 657APPENDIX F. CONCRETE IN CONSTRUCTION A. CONCRETE AND CONCRETE MATERIALSF.l. Important properties of concrete ........................................................................................................ 659F.2. Workability ............................................................................................................................................ 659F.3. Durability ............................................................................................................................................... 659F.4. Effects of curing on strength.. ............................................................................................................. 662F.5. Effects of entrained air on the properties of concrete ..................................................................... 662F.6. Types of portland cement .................................................................................................................... 663F.7. Abnormal set of portland cement.. ..................................................................................................... 665F.8. Use of pozzolans .................................................................................................................................... 666F.9. Quality and gradation of aggregates.. ................................................................................................. 667F.lO. Quality of mixing and curing water .................................................................................................... 668F.ll. Use of admixtures ................................................................................................................................. 668F.12. Field control ........................................................................................................................................... 668
  • 29. xxx DESIGN OF SMALL DAMSSection Page B. DESIGN OF CONCRETE MIXESF.13. Introduction ........................................................................................................................................... 670F.14. Estimate of water requirement.. .......................................................................................................... 671F.15. Estimate of cement requirement.. ....................................................................................................... 671F.16. Estimate of admixture requirement.. .................................................................................................. 671F.17. Estimate of aggregate requirement.. ................................................................................................... 672F.18. Computations of proportions.. .......................................................................................................... .:. 673F.19. Batch mass computations .................................................................................................................... 673F.20. Adjustments to trial mix.. .................................................................................................................... 674F.21. Mixes for small jobs.. ............................................................................................................................ 677 C. MANUFACTURE, PLACEMENT, CURING, AND INSPECTION OF CONCRETEF.22. Aggregate production and control.. ..................................................................................................... 678F.23. Batching methods and facilities at concrete mixing plants.. .......................................................... 678F.24. Production of quality concrete.. .......................................................................................................... 679F.25. Preparations preliminary to placing.. ................................................................................................. 679F.26. Transporting .......................................................................................................................................... 679F.27. Placing.. .................................................................................................................................................. 681F.28. Curing ... ... .... ... ... ... .... .. ..... .. .... .. .... ... .... .. .... ... ... ... .... .. .... ... ... ... .... .. .... ... .... .. .... ... ... ... .... .............................. 683 D. BIBLIOGRAPHYF.29. Bibliography . ... .... .. .... ... .... .. .... .. ..... .. .... .. .... ... .... .. .... .. .... ... .... .. .... ... ... ... .... .. .... ... .... .. ..... .. .... ... ................... 686APPENDIX G. SAMPLE SPECIFICATIONSG.l. Introduction . ... .... .. .... ... .... .. .... ... .... .. .... ... ... ... .... .. .... ... ... ... .... .. .... ... ... ... .... .. .... ... .... .. .... ... .... .. .................... 687 A. ENVIRONMENTAL QUALITY PROTECTIONG.2. Landscape preservation.. ...................................................................................................................... 687G.3. Preservation of vegetation ................................................................................................................... 688G.4. Prevention of water pollution .............................................................................................................. 689G.5. Abatement of air pollution .................................................................................................................. 690G.6. Dust abatement ..................................................................................................................................... 691G.7. Noise abatement .................................................................................................................................... 691G.8. Light abatement .................................................................................................................................... 691G.9. Preservation of historical and archeological data ............................................................................. 691G.lO. Vegetation control.. ............................................................................................................................... 691G.ll. Pesticides ................................................................................................................................................ 692G.12. Cleanup and disposal of waste materials ........................................................................................... 692 B. EXCAVATIONG.13. Clearing at damsite ............................................................................................................................... 693G.14. Classification of excavation ................................................................................................................. 694G.15. Classification of excavation (alternate). ............................................................................................. 694G.16. Definitions of materials.. ...................................................................................................................... 695G.17. Opencut excavation, general ................................................................................................................ 696G.18. Drilling line holes for rock excavation ............................................................................................... 699G.19. Excavation for grout cap ...................................................................................................................... 699
  • 30. CONTENTS xxxiSection PageG.20. Excavation for dam embankment foundation.. ................................................................................. 699G.21. Stripping.. ............................................................................................................................................... 701G.22. Excavation, in opencut, for structures ............................................................................................... 701G.23. Protective coating for structure foundations .................................................................................... 701G.24. Borrow areas.. ........................................................................................................................................ 702G.25. Rock deposits (rock furnished by contractor). .................................................................................. 706G.26. Rock source (source furnished by Contracting Officer) .................................................................. 706G.27. Disposal of excavated materials .......................................................................................................... 707 C. EMBANKMENTG.28. Embankment construction, general.. .................................................................................................. 708G.29. Earthfill in dam embankment, zone 1 ............................................................................................... 711G.30. Specially compacted earthfill, zone 1. ................................................................................................ 718G.31. Test pits in compacted earthfill.. ........................................................................................................ 719G.32. Earthfill in dam embankment, zone 2 ............................................................................................... 720G.33. Earthfill in dam embankment, drainage material, zone 3 .............................................................. 722G.34. Sand, gravel, and cobble fill in dam embankment, zone -. ........................................................ 724G.35. Miscellaneous fill in dam embankment, zone ............................................................................ 725G.36. Rockfill in dam embankment, zone - ............................................................................................ 726G.37. Impervious backfill ................................................................................................................................ 727G.38. Compacting impervious backfill.. ........................................................................................................ 727G.39. Pervious backfill.. .................................................................................................................................. 727G.40. Rock backfill .......................................................................................................................................... 728G.41. Filters.. .................................................................................................................................................... 729G.42. Bedding for riprap ................................................................................................................................. 729G.43. Riprap ..................................................................................................................................................... 729 D. TUNNEL AND SHAFT CONSTRUCTIONG.44. Tunnel construction, general ............................................................................................................... 732G.45. Draining, lighting, and ventilating tunnel during construction ..................................................... 733G.46. Tunnel excavation ................................................................................................................................. 733G.47. Shotcrete for protective coatings ........................................................................................................ 734G.48. Structural-steel tunnel support system.. ............................................................................................ 735G.49. Foot blocks, lagging, blocking, and spreaders ................................................................................... 736G.50. Rock bolt tunnel supports ................................................................................................................... 736G.51. Chain link fabric tunnel supports ...................................................................................................... 738G.52. Shotcrete tunnel support system ........................................................................................................ 739G.53. Preparation for placing concrete lining ............................................................................................. 741G.54. Concrete in outlet works tunnel lining and gate chamber .............................................................. 742G.55. Backfill grouting .................................................................................................................................... 743 E. PRESSURE GROUTINGG.56. Requirements for pressure grouting, general .................................................................................... 744G.57. Drilling foundation grout holes ........................................................................................................... 746G.58. Pipe for foundation grouting ............................................................................................................... 747G.59. Hookups to grout holes ........................................................................................................................ 748G.60. Pressure grouting foundations and outlet works.. ............................................................................ 748G.61. Slush grouting foundations .................................................................................................................. 753G.62. Dental concrete.. .................................................................................................................................... 754
  • 31. xxxii DESIGN OF SMALL DAMSSection Page F. CONCRETE SPECIFICATIONSG.63. Introduction ... .... .. .... ... ... ... .... .. .... ... .... .. .... ... .... .. .... ... ... ... .... .. .... ... ... ... .... ... ... ... .... .. .... ... .... ... .................... 755 1. Concrete Specifications for Small JobsG.64. Source ..................................................................................................................................................... 756G.65. Materials ................................................................................................................................................. 756G.66. Composition ........................................................................................................................................... 757G.67. Batching, mixing, and transporting .................................................................................................... 758G.68. Concrete placement, curing, and protection ...................................................................................... 758G.69. Repair of concrete.. ............................................................................................................................... 758G.70. Payment.. ................................................................................................................................................ 759G.71. cost ......................................................................................................................................................... 759 2. Concrete Specifications for large JobsG.72. Source ..................................................................................................................................................... 759G.73. Composition ........................................................................................................................................... 759G.74. Concrete quality control measures and concrete quality assurance program ............................... 760G.75. Cementitious materials ......................................................................................................................... 761G.76. Admixtures.. ........................................................................................................................................... 765G.77. Water ...................................................................................................................................................... 766G.78. Sand ........................................................................................................................................................ 766G.79. Coarse aggregate.. .................................................................................................................................. 768G.80. Batching ................................................................................................................................................. 769G.81. Mixing.. ................................................................................................................................................... 771G.82. Temperature of concrete ...................................................................................................................... 772G.83. Forms ...................................................................................................................................................... 773G.84. Reinforcing bars and fabric ................................................................................................................. 775G.85. Tolerances for concrete construction ................................................................................................. 779G.86. Preparations for placing.. ..................................................................................................................... 782G.87. Placing .................................................................................................................................................... 783G.88. Finishes and finishing .......................................................................................................................... 786G.89. Repair of concrete.. ............................................................................................................................... 787G.90. Protection.. ............................................................................................................................................. 788G.91. Curing ..................................................................................................................................................... 788G.92. Measurement of concrete.. ................................................................................................................... 791G.93. Payment for concrete ............................................................................................................................ 792 G. MISCELLANEOUSG.94. Diversion and care of stream during construction ........................................................................... 792G.95. Removal of water from foundations ................................................................................................... 793G.96. Concrete or cement-bound curtain.. ................................................................................................... 794G.97. Steel sheet piling.. ................................................................................................................................. 795G.98. Saturation of dam foundation by flooding to promote consolidation ........................................... 795G.99. Topsoil for seeding.. .............................................................................................................................. 796G.lOO. Water for seeded areas ......................................................................................................................... 796G.lO1. Seeding .................................................................................................................................................... 797G.102. Joints and edges in concrete.. .............................................................................................................. 799G.103. Rubber waterstops.. ............................................................................................................................... 800
  • 32. ... CONTENTS XXXMSection PageG.104. PVC waterstops.. ................................................................................................................................... 803G.105. Sponge rubber filler for concrete joints ............................................................................................. 806G.106. Metal seals ............................................................................................................................................. 806G.107. Metal waterstops.. ................................................................................................................................. 807G.108. Anchor bars.. .......................................................................................................................................... 807G.109. Drainage, general .................................................................................................................................. 808G.llO. Dam embankment toe drains .............................................................................................................. 808G.lll. Structure underdrains.. ......................................................................................................................... 810G.112. Drilling drainage holes ......................................................................................................................... 811G.113. Cast iron pipe drains.. .......................................................................................................................... 812G.114. Dry-rock paving for open drains.. ....................................................................................................... 812G.115. Blasting for rock.. .................................................................................................................................. 813G.116. Information as to subsurface investigations.. .................................................................................... 814G.117. Soil-cement slope protection ............................................................................................................... 815 H. BIBLIOGRAPHYG.118. Bibliography.. ......................................................................................................................................... 820APPENDIX H. TYPICAL CHECKLIST OF DAMS AND STRUCTURES FOR ON-SITE INSPECTIONS Operations.. ............................................................................................................................................ 821APPENDIX I. CONVERSION FACTORS International system (SI metric)/U.S. customary conversion factors .. ... ... ... .... ... .... .. .... ... .... .. .... .. 827 TABLES3-l. Unit hydrograph lag data, Great Plains ............................................................................................ 333-2. Unit hydrograph lag data, Rocky Mountains ................................................................................... 353-3. Unit hydrograph lag data, Southwest Desert, Great Basin, and Colorado Plateau.. .................. 383-4. Unit hydrograph lag data, Sierra Nevada, California.. .................................................................... 403-5. Unit hydrograph lag data, Coast and Cascade ranges.. ................................................................... 423-6. Unit hydrograph lag data, urban basins ............................................................................................ 433-7. Dimensionless unit hydrograph data, Great Plains ......................................................................... 443-8. Dimensionless S-graph data, Great Plains ........................................................................................ 443-9. General storm dimensionless unit hydrograph data, Rocky Mountains.. ..................................... 453-10. General storm dimensionless S-graph data ....................................................................................... 453-11. Thunderstorm dimensionless unit hydrograph data, Rocky Mountains.. ..................................... 463-12. Thunderstorm dimensionless S-graph data, Rocky Mountains ..................................................... 463-13. Dimensionless unit hydrograph data, Southwest Desert, Great Basin, and Colorado Plateau .............................................................................................................................. 473-14. Dimensionless S-graph data, Southwest Desert, Great Basin, and Colorado Plateau.. ............. 473-15. Dimensionless unit hydrograph data, Sierra Nevada, Coast, and Cascade ranges.. .................... 483-16. Dimensionless S-graph data, Sierra Nevada, Coast, and Cascade ranges .................................... 483-17. Dimensionless unit hydrograph data, urban basins ......................................................................... 493-18. Dimensionless S-graph data, urban basins.. ...................................................................................... 493-19. Synthetic unit hydrograph data .......................................................................................................... 515-l. Average engineering properties of compacted soils .......................................................................... 96
  • 33. xxxiv DESIGN OF SMALL DAMS Table Page5-2. Igneous textural descriptors ................................................................................................................. 1035-3. Bedding, foliation, and flow texture descriptors.. ............................................................................. 1115-4. Durability index descriptors ................................................................................................................ 1125-5. Rock hardness and strength descriptors ............................................................................................ 1145-6. Identification and sizes of samples.. ................................................................................................... 1525-7. Checklist for description of soils ........................................................................................................ 1715-8. Description of soils ............................................................................................................................... 1725-9. Values of C, for permeability computations ...................................................................................... 1796-l. Comparison of slurry trench cutoffs .................................................................................................. 2136-2. Treatment of pervious foundations ..................................................................................................... 2306-3. Recommended slopes of stabilizing fills for dams on saturated silt and clay foundations ........ 2356-4. Properties of loess in Medicine Creek Dam foundation .................................................................. 2386-5. Recommended slopes for small homogeneous earthfill dams on stable foundations.. ................ 2506-6. Recommended slopes for small zoned earthfill dams on stable foundations ............................... 2526-7. Wave height versus fetch and wind velocity ..................................................................................... 2586-8. Fetch versus recommended normal and minimum freeboard.. ....................................................... 2586-9. Thickness and gradation limits of riprap on 3:l slopes .................................................................. 2637-l. Gradations of asphaltic-concrete aggregates.. ................................................................................... 3047-2. Results of tests on asphaltic concrete ................................................................................................ 3079-l. Flood routing computations ................................................................................................................. 3439-2. Design of an uncontrolled overflow ogee crest ................................................................................. 3759-3. Side channel spillway computations ................................................................................................... 3839-4. Computations for hydraulic-jump basin design ................................................................................ 4029-5. Coordinates of lower nappe surface for different values of HJR, when P/R, = 2.0.. ................. 4119-6. Coordinates of lower nappe surface for different values of H,/R, when P/R, = 0.30 ................. 4129-7. Coordinates of lower nappe surface for different values of H,/R, when P/R, = 0.15 ................. 4139-8. Water surface profile computations for case 1 ................................................................................. 4209-9. Computations for discharge curve for case 1, R, = 7.0 feet.. .......................................................... 4219-10. Water surface profile computations for case 2 ................................................................................. 4229-11. Computations for discharge curve for case 2, R6 = 11.75 feet ........................................................ 4229-12. Allowable subatmospheric pressures for conduits flowing full ....................................................... 42710-l. Discharge and loss coefficients for conduit entrances.. ................................................................... 45810-2. Computation of total loss coefficients-example 1.. ........................................................................ 46810-3. Hydraulic computation for free flow portion of tunnel-example 1 (maximum losses) ............. 46910-4. Hydraulic computation for free flow portion of tunnel-example 1 (minimum losses). ............ 46910-5. Computation of total loss coefficient-example 2.. .......................................................................... 47013-1. Hazard classification.. ........................................................................................................................... 517A-l. Weighting values of factors affecting sediment yield.. ..................................................................... 530A-2. Sediment load computations for Rio Toa Vaca ................................................................................ 538A-3. Bedload correction ................................................................................................................................ 539A-4. Modified Einstein procedure computations.. ..................................................................................... 539A-5. Design type curve selection ................................................................................................................. 547A-6. Reservoir area and capacity data, Theodore Roosevelt Lake ......................................................... 548A-7. Determination of sediment elevation at Theodore Roosevelt Dam.. ............................................. 552A-8. Elevation of sediment at Theodore Roosevelt Dam.. ....................................................................... 554A-9. Theodore Roosevelt Lake, type II reservoir sediment deposition study (English units) ............ 554A-10. Theodore Roosevelt Lake, type II reservoir sediment deposition study (SI-metric units) ... .. ... 555B-l. Conversion factors and formulas .... ... ... ... .... .. .... ... ... ... ... ... .... .. .... ... ... ... .... .. .... .. .... ... .... .. .... ... .... .. .... .. ... 568B-2. Velocity head and discharge at critical depths and static pressures in circular conduits partly full . .... .. .... ... .... .. .... .. .... ... ... ... .... .. .... ... ... ... .... .. .... .. .... .. .... ... .... .. .... ... ... ... .... .. .... ... ... ..... 578B-3. Uniform flow in circular sections flowing partly full ... .. .... .. .... .. .... ... .... .. .... ... ... ... .... .. .... ... ... ... .... .. .. 578B-4. Velocity head and discharge at critical depths and static pressures in horseshoe conduits partly full .. .... .. .... ... ... ... .... .. .... .. .... ... ... ... .... .. .... ... ... .. .... ... .... .. .... ... ... ... .... .. .... ... .... .. .... .. .... .... 580
  • 34. CONTENTS xxxvTable PageB-5. Uniform flow in horseshoe sections flowing partly full.. ................................................................. 581B-6. Coefficient of roughness, average channels ....................................................................................... 595B-7. A method of computing mean n value for a channel.. ..................................................................... 595B-8. Computations for tailwater rating curve ........................................................................................... 603B-9. Water surface profile computations-method A .............................................................................. 609C-l. Suggested allowable bearing values for footings of structures appurtenant to small dams.. ..... 614c-2. Reinforcement and wall thicknesses for 12- through 108-inch reinforced concrete pressure pipe ..................................................................................................................................... 617E-l. Criteria for control of compacted dam embankments ..................................................................... 657F-l. Attack on concrete by soils and waters containing various sulfate concentrations.. .................. 661F-2. Allowable maximum net water-cement plus pozzolan ratios for durability of concrete subjected to various degrees of exposure.. ..................................................................................... 664F-3. Approximate air and water contents per volume of concrete, and proportions of fine and coarse aggregate ........................................................................................................................ 670F-4. Recommended slumps for various types of construction ................................................................ 671F-5. Approximate strength of concrete (containing good aggregate) for various water-cement ratios.. ........................................................................................................................ 671F-6. Example of trial mix computation using percentage of sand method.. ......................................... 674F-7. Average strength that must be maintained to meet design requirements .................................... 675F-8. Typical trial computations for concrete mix.. ................................................................................... 676F-9. Concrete mixes for small jobs ............................................................................................................. 678G-l. Gradation for zone 2 material.. ........................................................................................................... 720G-2. Requirements of specified test designations.. .................................................................................... 731G-3. Riprap gradation requirements-size of rock fragments.. ............................................................... 731G-4. Minimum cementitious materials content.. ....................................................................................... 758G-5. Additional cementitious materials requirements .............................................................................. 758G-6. Total air content ................................................................................................................................... 766G-7. Allowable percentages of deleterious substances in sand.. .............................................................. 767G-8. Sand grading requirements.. ................................................................................................................ 767G-9. Allowable percentages of deleterious substances in coarse aggregate.. .......................................... 769G-10. Coarse aggregate grading requirements ............................................................................................. 769G-11. Additional cement or cementitious materials requirements ........................................................... 770G-12. Form sheathing or lining material requirements.. ............................................................................ 774G-13. Variations from specified lines, grades, and dimensions ................................................................. 780G-14. Tolerances for concrete surface irregularities ................................................................................... 782G-15. Rubber waterstop physical characteristics ........................................................................................ 801G-16. Number of test units ............................................................................................................................ 802G-17. PVC waterstop physical characteristics.. ........................................................................................... 805 FIGURES2-l. Several types of check dams.. .............................................................................................................. 62-2. Construction schematics for artificial overhead cover structures .................................................. 72-3. Artificial spawning channels along the Tehama-Colusa Canal ...................................................... 72-4. Alaska steep pass fishway, fish ladder ............................................................................................... 82-5. Horizontal drum-screen, fish-passage structure ............................................................................... 92-6. Fences passable for antelope and an antelope pass structure ........................................................ 112-7. Typical food and cover planting scheme.. .......................................................................................... 122-8. Details for constructing a goose-nesting platform ........................................................................... 132-9. Constructed nesting islands.. ............................................................................................................... 142-10. Typical water-level manipulation plan for a warm-water reservoir.. ............................................. 152-11. Fenced wildlife crossing over Tiger Creek Canal, California.. ........................................................ 16
  • 35. xxxvi DESIGN OF SMALL DAMSFigure Page2-12. Revised Richmond deer-escape ramp.. ............................................................................................... 172-13. Multipurpose intake structure with multilevel outlet potential.. ................................................... 182-14. Diffused-air reservoir aeration system ............................................................................................... 192-15. Floating dock, functional at various water levels ............................................................................. 203-l. Unit hydrograph principles.. ................................................................................................................ 293-2. Unit hydrograph application ............................................................................................................... 303-3. Unit hydrograph lag relationships, Great Plains ............................................................................. 323-4. Unit hydrograph lag relationships, Rocky Mountains.. ................................................................... 343-5. Unit hydrograph lag relationships, Southwest Desert, Great Basin, and Colorado Plateau.. ... 373-6. Unit hydrograph lag relationships, Sierra Nevada, California.. ..................................................... 393-7. Unit hydrograph lag relationships, Coast and Cascade ranges of California, Oregon, and Washington.. .............................................................................................................................. 413-8. Unit hydrograph lag relationships, urban basins ............................................................................. 433-9. Dimensionless unit hydrograph and sample computations.. ........................................................... 503-10. Typical dimensionless S-graph.. .......................................................................................................... 503-11. Apical components of total flood runoff hydrograph ..................................................................... 523-12. Typical envelope curve ......................................................................................................................... 554-l. Crescent Lake Dam, a small earthfill storage dam on Crescent Creek in Oregon ..................... 604-2. Black Canyon Dam, a concrete gravity storage and diversion structure on the Payette River in Idaho ..................................................................................................................... 614-3. Knight Diversion Dam, a small diversion structure on the Duchesne River near Duchesne, Utah ........................................................................................................................ 624-4. Olympus Dam, a combination earthfill and concrete-gravity structure on the Big Thompson River in Colorado .................................................................................................. 635-1. Geologic map and cross section of a damsite.. .................................................................................. 725-2. Exploration for embankment materials-borrow area location map and typical cross section ...................................................................................................................................... 735-3. Typical talus deposit suitable for riprap.. .......................................................................................... 755-4. Soil triangle of the basic soil textural classes.. ................................................................................. 835-5. Rock strata illustrating folding in sedimentary rocks ..................................................................... 855-6. Sinkhole plain indicating deep plastic soils over cavernous limestone, developed in humid climate ............................................................................................................................... 865-7. Typical soil gradation curve ................................................................................................................. 895-8. Typical angularity of bulky grains.. .................................................................................................... 905-9. Test for liquid limit ............................................................................................................................... 90S-10. Test for plastic limit ............................................................................................................................. 905-11. Dilatancy test for silt ............................................................................................................................ 915-12. Soil classification chart (laboratory method). ................................................................................... 925-13. Shear strength of compacted soils ...................................................................................................... 975-14. Permeability of soils ............................................................................................................................. 985-15. Mineral cleavage.. .................................................................................................................................. 995-16. Intrusive igneous masses ... ................................................................................................................... 1005-17. Three dikes cutting sedimentary beds ............................................................................................... 1015-18. Blocky type of solidified lava flows .................................................................................................... 1025-19. Textures of igneous rocks.. ................................................................................................................... 1035-20. Field classification of igneous rocks ................................................................................................... 1045-21. Scoriaceous structure in extrusive lava rock ..................................................................................... 1055-22. Field classification of sedimentary rocks.. ......................................................................................... 1065-23. Conglomerate ......................................................................................................................................... 1075-24. Fossiliferous limestone ......................................................................................................................... 1075-25. Foliation in metamorphosed sedimentary rocks.. ............................................................................. 1085-26. Field classification of metamorphic rocks ......................................................................................... 1095-27. Field classification of pyroclastic rocks ............................................................................................. 1105-28. Aerial view and topography of an alluvial fan .................................................................................. 115
  • 36. CONTENTS xxxviiFigure Page5-29. Aerial view and topography of stream deposit showing river alluvium and three levels of gravel terraces.. .................................................................................................................. 1175-30. Aerial view and topography of terminal moraine of continental glaciation.. ............................... 1185-31. Aerial view and topography of loess................................................................................................... 1205-32. A go-foot nearly vertical cut in a loess formation in Nebraska.. ................................................... 1215-33. Importance of geophysical methods in civil engineering.. ............................................................... 1225-34. Seismograph setup and readings.. ....................................................................................................... 1255-35. Qpes of surface waves ......................................................................................................................... 1265-36. Dipole-dipole resistivity array.. ........................................................................................................... 1275-37. Schematic diagram of ground-penetrating radar.. ............................................................................ 1295-38. Trench excavation showing hydraulic trench jack shoring ............................................................. 1315-39. Cone-penetrometer testing using a conventional drill rig.. ............................................................. 1335-40. Self-contained, truck-mounted electrical cone-penetration apparatus.. ........................................ 1335-41. Example of output data from an electrical cone penetrometer.. .................................................... 1345-42. Standard split-barrel sampler .............................................................................................................. 1355-43. Disassembled split-barrel sampler.. .................................................................................................... 1355-44. Making a standard penetration test using a drill rig.. .................................................................... 1365-45. Continuous-flight auger mounted on an all-terrain carrier ............................................................ 1365-46. Hollow-stem auger with center plug ................................................................................................... 1385-47. Large disk auger with ripper teeth ..................................................................................................... 1395-48. Bucket drill rig in drilling position with a 24-foot triple Kelly and 36-inch bucket ................... 1405-49. Top-head drive drill with head in mast for drilling.. ....................................................................... 1425-50. Fluted Kelly drill setup ........................................................................................................................ 1435-51. Horizontal rotary drill .......................................................................................................................... 1465-52. Diamond-core drill rig used in exploration of a dam foundation ................................................... 1485-53. Types of hand augers ............................................................................................................................ 1535-54. Auger sampling ...................................................................................................................................... 1535-55. Blasting a rock ledge at the riprap source for Stampede Dam, California .................................. 1545-56. Initial steps to obtain a hand-cut undisturbed block sample ......................................................... 1565-57. Final steps to obtain a hand-cut undisturbed block sample ........................................................... 1575-58. Chain saw equipped with carbide-tipped blade being used to cut block sample ......................... 1585-59. Double-tube core barrel used for obtaining samples of rock .......................................................... 1615-60. Nomenclature for diamond-core drill equipment .............................................................................. 1625-61. Size variations for core-drill casing .................................................................................................... 1635-62. Nominal dimensions for drill casings and accessories..................................................................... 1645-63. Standard coring-bit sizes...................................................................................................................... 1645-64. Standard drill-rod sizes........................................................................................................................ 1655-65. Example geologic log of a drill hole ................................................................................................... 1665-66. Example log of test pit or auger hole.. ............................................................................................... 1685-67. Drill-hole log and penetration resistance data.. ................................................................................ 1695-68. Logging of core obtained from rotary drilling.. ................................................................................. 1745-69. An open-end pipe test for soil permeability that can be made in the field.. ................................ 1765-70. Packer test for rock permeability ....................................................................................................... 1785-71. Determining inplace unit weight by replacing soil with a sand of known unit weight.. ............ 1795-72. Procedure for inplace unit weight test ............................................................................................... 1805-73. Example gradation analysis curves ..................................................................................................... 1825-74. Laboratory compaction test curves ........................................................... ......................................... 1846-1. Upstream face of clam and fishscreened inlet structure.. ................................................................ 1886-2. Fruitgrowers Dam, an earthfill storage clam at an offstream location in Colorado.. .................. 1896-3. Shadow Mountain Dam, an earthfill structure on the Colorado River in Colorado .................. 1906-4. Seepagethrough a completely homogeneous clam............................................................................ 1916-5. Seepagethro’ugh modified homogeneous dams ................................................................................. 1916-6. Grout curtain used on the abutment of Granby Dam, Colorado ................................................... 1956-7. Packers used for grouting by the Bureau of Reclamation: (A) leather cup, (B) mechanical ..... 197
  • 37. ...XXXVIII DESIGN OFSMALLDAMSFigure Page6-8. Packers used for grouting by the Bureau of Reclamation: (C) pneumatic, (D) cone-type ......... 1986-9. Types of grout hole packers used by the Bureau of Reclamation.. ................................................ 1996-10. Circulating grouting system.. ............................................................................................................... 2016-11. Grouting plant used at Ruedi Dam, Colorado .................................................................................. 2016-12. Placing concrete grout cap at Navajo Dam, New Mexico.. ............................................................. 2026-13. Example computation of seepage by Darcy’s formula.. ................................................................... 2046-14. Seepage force components ................................................................................................................... 2056-15. Cutoff trench excavation and backfill ................................................................................................ 2076-16. Placement of compacted fill in the cutoff trench.. ........................................................................... 2086-17. Cement-bound curtain cutoff .............................................................................................................. 2096-18. Sequence of operations for the construction of a slurry trench.. ................................................... 2106-19. Excavation of a slurry trench.. ............................................................................................................ 2106-20. Airlifting sand from bottom of slurry trench.. .................................................................................. 2126-21. Right abutment blanket construction at Ochoco Dam.. .................................................................. 2166-22. Upstream slope of Ochoco Dam ......................................................................................................... 2166-23. Downstream embankment sections for pervious foundations ........................................................ 2176-24. Typical filter design .............................................................................................................................. 2206-25. Typical toe drain installation .............................................................................................................. 2216-26. Toe drain construction at Calamus Dam, Nebraska.. ...................................................................... 2216-27. Pressure-relief wells and appurtenances.. .......................................................................................... 2236-28. Treatment of case 1: exposed pervious foundations.. ....................................................................... 2266-29. Treatment of stratified foundations ................................................................................................... 2276-30. Treatment of case 2: covered pervious foundations ......................................................................... 2296-31. Appearance and identification of Missouri River Basin loess.. ...................................................... 2336-32. Typical compression curves for Missouri River Basin loess ........................................................... 2336-33. Design of dam on saturated fine-grained foundation ...................................................................... 2356-34. Foundation design criteria for relatively dry fine-grained soils ..................................................... 2366-35. Alternative foundation design criteria for relatively dry fine-grained soils.. ................................ 2366-36. Geology of right abutment of Medicine Creek Dam.. ...................................................................... 2376-37. Ponding on foundation of Medicine Creek Dam.. ............................................................................ 2386-38. Record of loess foundation settlement at Medicine Creek Dam.. .................................................. 2396-39. Position of phreatic line in a zoned embankment.. .......................................................................... 2416-40. Effect of rapid drawdown on pore pressures.. ................................................................................... 2426-41. Locations of random zones of fill materials within embankment sections .................................. 2456-42. Materials distribution chart for San Justo Dike.. ............................................................................ 2476-43. Size range of impervious cores used in zoned embankments ......................................................... 2506-44. Seismic risk map of the conterminous United States ..................................................................... 2546-45. Examples of crest details at maximum camber.. .............................................................................. 2566-46. Riprap on upstream slope of an earthfill dam ................................................................................. 2596-47. Paved upstream slope of an earthfill dam.. ....................................................................................... 2606-48. Placing riprap on an upstream slope ................................................................................................. 2616-49. Displacement of riprap on a low dike by wave action.. ................................................................... 2626-50. Completed riprap slope protection on upstream face of Blue Mesa Dam, Colorado.. ................ 2646-51. Hand-placed rock riprap on Indian Creek Dike.. ............................................................................. 2656-52. Concrete paving blocks on the upstream slope of Belle Fourche Dam.. ....................................... 2656-53. Soil-cement paving on the upstream slope of Cheney Dam, Kansas ............................................ 2656-54. Typical section of soil-cement slope protection.. .............................................................................. 2656-55. Placement of soil-cement slope protection.. ...................................................................................... 2666-56. Downstream slope of Belle Fourche Dam protected by grass ........................................................ 2676-57. Mica1 sections of a contour ditch and an open drain.. ................................................................. 2676-58. Amarillo Regulating Reservoir ............................................................................................................ 2696-59. Cawker City Dike.. ................................................................................................................................ 2696-60. Typical section, Big Sandy Dam.. ....................................................................................................... 2696-61. Carpinteria Reservoir Dike.. ................................................................................................................ 270
  • 38. CONTENTS xxxixFigure Page6-62. Construction of concrete lining at Carpinteria Reservoir.. ............................................................. 2706-63. Carter Lake Dam No. 3 ....................................................................................................................... 2716-64. Crane Prairie Dam.. .............................................................................................................................. 2716-65. Crescent Lake Dam .............................................................................................................................. 2716-66. Dickinson Dam ...................................................................................................................................... 2726-67. Dry Falls Dam ....................................................................................................................................... 2736-68. Fruitgrowers Dam ................................................................................................................................. 2736-69. Howard Prairie Dam ............................................................................................................................ 2736-70. Lion Lake Dikes .................................................................................................................................... 2746-71. Lovewell Dam ........................................................................................................................................ 2746-72. Eklutna Dam, Alaska ........................................................................................................................... 2746-73. Lower Two Medicine Dam, Montana ................................................................................................. 2756-74. Olympus Dam ........................................................................................................................................ 2756-75. Picacho North Dam .............................................................................................................................. 2756-76. Picacho South Dam .............................................................................................................................. 2776-77. Pishkun Dikes ....................................................................................................................................... 2776-78. Lubbock Regulating Reservoir ............................................................................................................ 2776-79. Shadow Mountain Dam ....................................................................................................................... 2776-80. Soda Lake Dike.. ................................................................................................................................... 2786-81. Stubblefield Dam.. ................................................................................................................................. 2786-82. Sections of Tiber Dike ......................................................................................................................... 2796-83. Sheep Creek Barrier Dam .................................................................................................................... 2796-84. General plan for Wasco Dam .............................................................................................................. 2806-85. Sections for Wasco Dam ...................................................................................................................... 2816-86. Dike section of Ute Dam, New Mexico ............................................................................................. 2826-87. San Justo Dike ...................................................................................................................................... 2826-88. Calamus Dam ......................................................................................................................................... 2837-l. Resistance to sliding for embankments ............................................................................................. 2887-2. Detail of concrete membrane at cutoff wall.. .................................................................................... 2907-3. Detail of asphaltic-concrete membrane at cutoff wall ..................................................................... 2907-4. Detail of steel-plate membrane at cutoff wall .................................................................................. 2907-5. Doweled cutoff slab used with upstream concrete membrane ........................................................ 2917-6. Granite rockfill on downstream face of Montgomery Dam, Colorado .......................................... 2927-7. Grain size distribution for modeled rockfill materials.. ................................................................... 2937-8. Effect of maximum particle size on the angle of internal friction ................................................ 2947-9. Typical maximum section of an earth-core rockfill dam using a central core ............................. 2957-10. Typical maximum section of a decked rockfill dam.. ....................................................................... 2967-11. Typical rockfill sluicing operation ...................................................................................................... 2987-12. Maximum section of Upper Blue River Dam, Colorado ................................................................. 2997-13. Placement of fine and coarse filter material ..................................................................................... 3017-14. Placement of concrete by the use of slip forms.. .............................................................................. 3037-15. Placement of shotcrete on the upstream face of Taum Sauk Dam, Missouri ............................. 3047-16. Completed rockfill embankment at Upper Blue River Dam, Colorado, before membrane placement ........................................................................................................... 3057-17. Placing asphaltic concrete on the face of Montgomery Dam, Colorado ....................................... 3067-18. Foundation cutoff used at Montgomery Dam, Colorado.. ............................................................... 3067-19. Completed asphaltic-concrete facing at Upper Blue River Dam, Colorado ..................... . .......... 3087-20. Steel facing on the upstream slope of El Vado Dam, New Mexico.. ............................................. 3097-21. Details of steel membrane used at El Vado Dam, New Mexico.. ................................................... 3107-22. Details of steel membrane used at Rio Lagartijo Dike, Venezuela.. .............................................. 3117-23. Details of steel membrane used at Sirinumu Dam, New Guinea ................................................... 3128-1. Forces acting on a concrete gravity dam ........................................................................................... 3178-2. Water surface designations .................................................................................................................. 3198-3. Water pressures acting on an overflow concrete dam ..................................................................... 320
  • 39. Xl DESIGN OF SMALL DAMSFigure Page8-4. Need for earthquake analyses based on Richter magnitude and distance from causative fault ................................................................................................................................... 3238-5. Site estimate of peak ground acceleration.. ....................................................................................... 3248-6. Coefficients for pressure distribution for constant sloping faces.. ................................................. 3258-7. Shear resistance on an existing joint in rock foundation of a gravity dam ................................. 3278-8. Static pressure diagrams along the base or any horizontal section of a gravity dam ................. 3328-9. Pseudostatic pressure diagrams along the base or any horizontal section of a gravity dam.. ... 3339-l. Small chute spillway in operation.. ..................................................................................................... 3409-2. Inflow and outflow hydrographs ......................................................................................................... 3429-3. Reservoir capacity curve ...................................................................................................................... 3449-4. Spillway discharge-elevation curve ..................................................................................................... 3449-5. Spillway capacity-surcharge relationship.. .......................................................................................... 3469-6. Comparative costs of spillway-dam combinations.. .......................................................................... 3479-7. Plan and sections of a typical bathtub service spillway and an auxiliary spillway.. ................... 3489-8. Aerial view of service spillway.. ........................................................................................................... 3509-9. Aerial view of service and auxiliary spillways.. ................................................................................. 3509-10. Semicircular overflow crest for small chute spillway.. ..................................................................... 3519-11. Typical straight drop spillway installation for small heads.. .......................................................... 3549-12. Typical side channel and chute spillway arrangement .................................................................... 3559-13. Ute Dam 14-cycle labyrinth spillway ................................................................................................. 3569-14. Chute spillway for Scofield Dam, Utah ............................................................................................. 3579-15. Drop inlet spillway for a small dam.. ................................................................................................. 3589-16. Conduit and stilling basin for drop inlet spillway.. .......................................................................... 3599-17. Baffled chute drop spillway ......... -....................................................................................................... 3609-18. Basic proportions of a baffled chute spillway.. ................................................................................. 3619-19. Fujimoto entrance for baffled chutes ................................................................................................. 3619-20. Recommended baffle pier heights and allowable velocities for baffled chute spillways .............. 3629-21. Factors for definition of nappe-shaped crest profiles ...................................................................... 3669-22. Ogee crest shape defined by compound curves.. ............................................................................... 3689-23. Discharge coefficients for vertical-faced ogee crest.. ........................................................................ 3709-24. Discharge coefficients for other than the design head .................................................................... 3719-25. Discharge coefficients for ogee-shaped crest with sloping upstream face.. ................................... 3719-26. Effects of downstream influences on flow over weir crests ............................................................ 3729-27. Ratio of discharge coefficients resulting from apron effects.. ......................................................... 3739-28. Ratio of discharge coefficients caused by tailwater effects.. ........................................................... 3749-29. Subatmospheric crest pressures for Ho/H, = 0.75............................................................................ 3779-30. Subdtmospheric crest pressures for undershot gate flow ................................................................ 3789-31. Discharge coefficient for flow under gates.. ....................................................................................... 3799-32. Side channel flow characteristics.. ...................................................................................................... 3809-33. Comparison of side channel cross sections ....................................................................................... 3829-34. Example of hydraulic design for side channel spillway.. ................................................................. 3829-35. Flow in open channels.. ........................................................................................................................ 3849-36. Flare angle for divergent or convergent channels ............................................................................ 3869-37. Characteristic forms of hydraulic jump related to the Froude number ........................................ 3879-38. Relations between variables in hydraulic jump for rectangular channel ...................................... 3899-39. Stilling basin characteristics for Froude numbers between 2.5 and 4.5.. ...................................... 3909-40. Characteristics for alternative low Froude number stilling basins ................................................ 3929-41. Stilling basin characteristics for Froude numbers above 4.5 where incoming velocity, V, 5 60 ft/s ....................................................................................................................... 3939-42. Stilling basin characteristics for Froude numbers above 4.5 .......................................................... 3959-43. Stilling basin depths versus hydraulic heads for various channel losses ...................................... 3969-44. Relationships of conjugate depth curves to tailwater rating curves .............................................. 3979-45. Submerged buckets ............................................................................................................................... 3989-46. Hydraulic action of solid and slotted buckets.. ................................................................................. 399
  • 40. CONTENTS xliFigure Page9-47. Scour patterns downstream from a solid bucket dissipator for an ogee overflow crest.. ........... 3999-48. Flow characteristics of a slotted bucket ............................................................................................ 3999-49. Limiting criteria for slotted bucket design.. ...................................................................................... 4019-50. Definition of symbols for submerged buckets.. ................................................................................. 4029-51. Example of design of stilling device for overflow spillway.. ............................................................ 4029-52. Plunge basin energy dissipator ............................................................................................................ 4039-53. Hydraulic characteristics of straight drop spillways with hydraulic jump or with impact blocks ........................................................................................................................... 4059-54. Slotted-grating dissipator.. ................................................................................................................... 4069-55. Nature of flow and discharge characteristics of a morning glory spillway.. ................................. 4089-56. Elements of nappe-shaped profile for circular weir.. ....................................................................... 4099-57. Relationship of circular crest coefficient C, to H,,/R, for different approach depths (aerated nappe) ................................................................................................................................. 4109-58. Circular crest discharge coefficient for other than design head.. ................................................... 4109-59. Relationship of H,/H, to Ho/R, for circular sharp-crested weirs.. ............................................... 4149-60. Upper and lower nappe profiles for circular weir (aerated nappe and negligible approach velocity) ............................................................................................................................. 4159-61. Comparison of lower nappe shapes for circular weir for different heads ..................................... 4159-62. Increased circular crest radius needed to minimize subatmospheric pressure along crest ......... 4169-63. Comparison of drop inlet profiles for various flow conditions.. ..................................................... 4179-64. Drop inlet spillway profile ................................................................................................................... 4189-65. Drop inlet crest, transition, and conduit plottings .......................................................................... 4199-66. Drop inlet spillway discharge curves .................................................................................................. 4219-67. Typical flow conditions for culvert spillways on mild and steep slopes........................................ 4239-68. Head-discharge curves for square-edged and rounded inlets for circular culverts on steep slopes.. ................................................................................................................................ 4249-69. Hydraulic characteristics of full pipe flow for culvert spillways .................................................... 4259-70. Discharge coefficient for submerged box culvert spillways with square-edged top opening ....... 4279-71. Floor lining details for spillway channels .......................................................................................... 43210-l. Typical low-head outlet works installations.. .................................................................................... 43610-2. Typical free-flow conduit outlet works installations ........................................................................ 43710-3. Typical pressure conduit and tunnel outlet works installations .................................................... 43810-4. Typical combined pressure and free-flow conduit outlet works installations .............................. 43910-5. Typical tunnel outlet works installations.. ........................................................................................ 44010-6. Typical outlet works installations for concrete dams ...................................................................... 44110-7. Typical precast pipe outlet works installations ................................................................................ 44210-8. Relation of minimum design head to conduit size ........................................................................... 44310-9. Combined spillway and outlet works, and structures with common stilling devices................... 44410-10. Flow through submerged tubes ........................................................................................................... 45410-11. Head losses in conduit flowing under pressure.. ............................................................................... 45710-12. Bend loss coefficients ........................................................................................................................... 45910-13. Typical conduit transition .................................................................................................................... 46210-14. Dimensional criteria for impact-type stilling basin ......................................................................... 46410-15. Impact-type stilling basin in operation.. ............................................................................................ 46510-16. Stilling well energy dissipator installation ........................................................................................ 46610-17. Stilling well energy dissipator with a 54-inch sleeve valve.. ........................................................... 46710-18. Typical supports for an outlet works tunnel.. ................................................................................... 47310-19. Sections and details for circular tunnels ........................................................................................... 47510-20. Sections and details for horseshoe tunnels ....................................................................................... 47610-21. Sections and details for modified horseshoe and miscellaneous tunnels ...................................... 47710-22. Definitions of “A” line and “B” line dimensions for different shapes of tunnels ....................... 47810-23. Typical cutoff collars on an outlet works conduit ............................................................................ 47910-24. Typical control joint and cutoff collar details.. ................................................................................. 48010-25. Typical joint details for precast concrete pipe.. ................................................................................ 481
  • 41. DESIGN OF SMALL DAMSFigure Page10-26. Intake tower arrangement.. .................................................................................................................. 48210-27. Typical drop inlet intake.. .................................................................................................................... 48310-28. ‘&pica1 trashracked box intake.. ......................................................................................................... 48410-29. Typical front-entrance intake structures.. ........................... .............................................................. 48510-30. Intake with sloping entrance.. ............................................................................................................. 48610-31. Typical shaft for slide gate control.. ................................................................................................... 48710-32. Gate chamber and shaft with high-pressure gates ........................................................................... 48810-33. Typical hydraulic-jump stilling basin.. ............................................................................................... 48911-l. Temporary diversion flume through an earthfill damsite ............................................................... 49211-2. Temporary diversion flume used during construction of a concrete dam.. ................................... 49311-3. Diversion through an auxiliary stream-level conduit.. ..................................................................... 49411-4. Diversion of the American River during construction of Folsom Dam and Powerplant ............ 49511-5. Diversion adit and upstream cofferdam at Seminoe Dam.. ............................................................ 49611-6. Concrete plug in diversion adit for Causey Dam.. ............................................................................ 49711-7. Upstream side of slide gate for closure of river outlet works.. ....................................................... 49811-8. Temporary diversion channel through an earthfill dam.. ................................................................ 49911-9. Flows through diversion opening and over low blocks of a concrete dam.. .................................. 50011-10. Cofferdam at Ridgway Dam, Colorado.. ............................................................................................. 50111-11. Upstream cofferdam of steel sheet piling and earthfill diverting streamflow into tunnel ......... 502A-l. Area and capacity curves for Lake Mead.. ........................................................................................ 531A-2. Sediment distribution from reservoir surveys.. ................................................................................. 532A-3. Lake Mead sediment deposition profile.. ........................................................................................... 533A-4. Average annual sediment yield rate versus drainage area size.. ..................................................... 534A-5. Suspended sediment sampler DH-48.. ................................................................................................ 535A-6. Suspended sediment rating curve for Rio Toa Vaca ........................................................................ 536A-7. Flow duration curve for Rio Toa Vaca.. ............................................................................................. 537A-8. Schematic diagram of reservoir allocations and sediment deposition.. ......................................... 541A-9. Trap efficiency curves.. ......................................................................................................................... 542A-10. Comparison of densities on Lake Mead ............................................................................................ 544A-11. Sediment deposited in flood control pool.. ........................................................................................ 545A-12. Sediment distribution design curves .................................................................................................. 546A-13. Sediment distribution for Theodore Roosevelt Lake.. ..................................................................... 549A-14. Area and capacity curves for Theodore Roosevelt Lake ................................................................. 550A-15. Depth versus capacity for Theodore Roosevelt Lake.. ..................................................................... 551A-16. Curves to determine the depth of sediment at Theodore Roosevelt Dam.. .................................. 553A-17. Typical sediment deposition profile .................................................................................................... 555A-18. Topset slope versus original stream slope for existing reservoirs .................................................. 556A-19. Armoring definitions.. ........................................................................................................................... 558A-20. Tractive force versus transportable sediment size ........................................................................... 560A-21. Degraded channel by the three-slope method ................................................................................... 561B-l. Characteristics of open-channel flow ................................................................................................. 570B-2. Depth of flow and specific energy for a rectangular section in open channel ............................. 571B-3. Energy-depth curves for rectangular and trapezoidal channels ..................................................... 572B-4. Critical depth in trapezoidal sections ................................................................................................ 574B-5. Approximate losses in chutes for various values of water surface drop and channel length ..... 577B-6. Characteristics of pressure flow in conduits ..................................................................................... 583B-7. Headwater depth for concrete pipe culverts with entrance control.. ............................................. 584B-8. Headwater depth for corrugated-metal pipe culverts with entrance control.. .............................. 585B-9. Head for concrete pipe culverts flowing full, n = 0.012 .................................................................. 586B-10. Head for corrugated-metal pipe culverts flowing full, n = 0.024.. ................................................. 587B-11. Headwater depth for box culverts with entrance control ............................................................... 588B-12. Head for concrete box culverts flowing full, n = 0.013 ................................................................... 589B-13. Hydraulic jump symbols and characteristics ..................................................................................... 590B-14. Hydraulic jump properties in relation to Froude number.. ............................................................. 591
  • 42. CONTENTS xliiiFigure PageB-15. Relation between variables in the hydraulic jump.. ......................................................................... 592B-16. Energy of open-channel flow.. ............................................................................................................. 596B-17. Sample slope-area computation, plan view of reach.. ...................................................................... 598B-18. Sample slope-area computation, cross sections ................................................................................ 599B-19. Sample slope-area computation, high-water profile.. ....................................................................... 600B-20. Sample slope-area computation, discharge.. ...................................................................................... 601B-21. Plan and cross section of Elk Creek Dam site ................................................................................. 602B-22. Tailwater rating curve for Elk Creek Dam.. ...................................................................................... 603B-23. Cross sections used to establish a rating curve by method A ........................................................ 605B-24. Area and hydraulic radius curves-section 3, Red Fox River ........................................................ 606B-25. Conveyance (I&) curves-section 3, Red Fox River ........................................................................ 607B-26. Rating curve-section 1 ....................................................................................................................... 608C-l. Earth pressures on retaining walls.. ................................................................................................... 612c-2. Precast concrete pipe on concrete base for conduit under or through embankment dams.. ..... 615c-3. Location of critical sections in design of precast concrete pressure pipe.. ................................... 616c-4. n-pica1 cast-in-place, single-barrel conduits.. ................................................................................... 621c-5. Typical reinforcement pattern for cast-in-place conduits.. ............................................................. 622E-l. Embankment placing operations ........................................................................................................ 643E-2. Average field and laboratory compaction curves for three dam embankment soils.. .................. 644E-3. Cleanup of foundation rock ................................................................................................................. 645E-4. Use of formed dental concrete to fillet steep, rough rock.. ............................................................. 646E-5. Pneumatic-tire front-end loader being used for compaction .......................................................... 647E-6. Vibratory plate being used for special compaction adjacent to conduit ....................................... 648E-7. Placing, leveling, and compacting the fill at Olympus Dam.. ......................................................... 649E-8. Removal of oversize rock by screening pit-run material ................................................................. 651E-9. Borrow area operation at Ridgway Dam ........................................................................................... 652E-10. Statistical analysis of field unit weight tests for compaction control.. ......................................... 655E-11. Statistical analysis of field unit weight tests for moisture control.. .............................................. 656F-l. Typical pattern cracking on the exposed surface of concrete affected by alkali-aggregate reaction .................................................................................................................. 660F-2. Disintegration of concrete caused by sulfate attack ........................................................................ 661F-3. Cavitation erosion of concrete on and adjacent to a dentate in the Yellowtail Afterbay Dam spillway stilling basin ............................................................................................. 663F-4. Abrasion erosion of concrete in the dentates, walls, and floor of the Yellowtail Afterbay Dam sluiceway stilling basin .......................................................................................... 663F-5. Compressive strength of concrete dried in laboratory air after preliminary moist curing ......... 665F-6. Effects of air content on durability, compressive strength, and required water content of concrete.. ......................................................................................................................... 665F-7. Strength in relation to water-cement ratio for air-entrained and non-air-entrained concrete .............................................................................................................. 666F-8. Apical size distribution of suitably graded natural aggregate.. ..................................................... 669F-9. Methods of stockpiling aggregates ...................................................................................................... 680F-10. Methods of handling concrete at ends of conveyors and chutes.. .................................................. 682F-11. Methods of vibrating and of working concrete ................................................................................. 683F-12. Methods of handling concrete with buckets, hoppers, and buggies.. ............................................. 684F-13. Placing concrete in forms .................................................................................................................... 685F-14. Placing unformed concrete on slopes ................................................................................................. 686
  • 43. Chapter 1 Plan Formulation The plan formulation process consists of iden- f. Analysis and comparison of the rough mone-tifying water-related needs and opportunities, de- tary and nonmonetary estimates, and selec-veloping alternative plans that provide for those tion of those alternatives justifying furtherneeds and opportunities, and selecting the plan study.from among those alternatives that most effectively g. Progressive refinements in physical, eco-and efficiently provides for those needs and oppor- nomic, environmental, and social evaluations;tunities. Identification of the needs and opportu- and selection of the more promising alter-nities is done primarily through public involvement, natives for more detailed study.which includes the client and interested agencies. h. Progressive reexamination of problems and,Plan formulation includes economic, social, envi- opportunities, alternative plans previouslyronmental, engineering, hydrologic, land classifi- considered, and new alternatives that may becation, legal, and institutional considerations. conceived in light of the results and refine- Some of the more common water-related needs ments of progressive investigations andand opportunities are agricultural irrigation, mu- analyses.nicipal and industrial uses, power generation, flood i. Selection among the few remaining alterna-control, instream flow augmentation, groundwater tives, giving consideration to more detailedrecharge, recreation, fish and wildlife habitat, and studies, to comparative benefits and costs inpollution abatement. monetary terms, and to differences among al- Plan formulation is an iterative process of com- ternatives that are not readily reducible toparing and selecting from alternative plans until the monetary terms.most acceptable plan is identified. j. Selection of a single plan from the surviving The following sequence of steps can serve as a alternatives, with further analysis using pro-helpful guide in plan formulation for a water re- gressive levels of development to determinesources study: the optimum project size, and with consider- a. Preliminary identification of needs and ation given to such concerns as pertinent laws, opportunities. interstate compacts, and fiscal and adminis- b. Preliminary decisions on possible alternative trative policies of- relevant governing and fi- plans for providing for the needs and nancing organizations. opportunities. In practice, the relationships of engineering, eco- c. Preliminary estimate of prospective differ- nomic, hydrologic, environmental, and social prin- ences among the alternatives, expressed in ciples and criteria of plan formulation should be physical or nonmonetary terms. well understood. These relationships should he ap- d. Translation of descriptions of the differences plied at all stages of the planning investigations and among the alternatives into rough estimates analyses from the beginning resource inventories of the benefits and costs in monetary terms, and field inspections, through the increasing stages their times of occurrence, and their conver- of refinement, to the time that one plan is selected sions to approximately equivalent values for for detailed investigation and evaluation. a common time period. The viability of proposed plans can be tested to e. Evaluation of nonmonetary effects of the a substantial degree by applying four tests: plan, such as expected environmental and so- (1) completeness, (2) effectiveness, (3) efficiency, cial effects. and (4) acceptability. These four tests are set out
  • 44. 2 DESIGN OF SMALL DAMSin the “Economic and Environmental Principles plans are crucial to realization of the con-and Guidelines for Water and Related Land Re- tributions to the objective.sources Implementation Studies,” dated March 10, (2) Effectiveness.-The extent to which an al-1983, as published by the U.S. Water Resources ternative plan alleviates the specified prob-Council. While the tests, as extracted from that lems and achieves the specifieddocument and stated below, are intended for guid- opportunities.ance for Federal agencies, they are appropriate for (3) Efficiency.-The extent to which an alter-the evaluation of any plan for use of water native plan is most cost effective in alle-resources. viating the specified problems and realizing The four tests are: the specified opportunities, consistent with (1) Completeness.-The extent to which a given protecting the nation’s environment. alternative plan provides and accounts for all (4) Acceptability.-The workability and viability necessary investments or other actions to en- of the alternative plan with respect to ac- sure the realization of the planned effects. ceptance by State and local entities and the This may require relating the plan to other public; and compatibility with existing laws, types of public and private plans if the other regulations, and public policy.
  • 45. Chapter 2 Ecological and Environmental Considerations A. INTRODUCTION 2.1. Planning.-Proper planning of dams re- pertise, including economics, engineering, design,quires a heightened awareness of our natural and biology, recreation, hydrology, and sociology. Thehuman environment. Concern for environmental disciplines involved in each study should be basedquality includes concern for the air and water, our on the natural and physical resources involved innatural ecological systems, and our cultural re- that study. It is through the effective interactionssources. Many laws and regulations now reflect this of the team members that arrangements are madeconcern and require the consideration of environ- to accommodate environmental concerns early inmental factors in planning. the planning rather than through mitigating ac- Recent legislation and public concern require tions after the project is completed.agencies to provide detailed statements of the sig- The enhancement of existing resources and thenificant environmental impacts of the proposed ac- complete avoidance of adverse environmental ef-tions that can affect the quality of the environment. fects are not always possible. In addition, benefitsReports meeting this requirement have become to one resource may result in the loss of anotherwidely known as EIS’s (Environmental Impact resource; e.g., impounding a stream may create aStatements). The demand for these reports has re- dependable water supply but eliminate terrestrialsulted in the establishment of numerous companies resources within the permanent pool area. It is thewhose primary purpose is to develop technically ad- job of a planning team to develop plans that resultequate EIS’s and extensive literature on environ- in impacts that are more positive than negative. Inmental assessment methods [l, 2, 3, 4, 5, 61’. In many cases, adverse environmental impacts can bemany instances, the objective appears to be the de- reduced significantly through the careful design,velopment of an EIS; however, the goal is not better construction, and operation of project features.documents but decisions that better balance the use The purpose of this chapter is to describe waysof water resources with the protection and enhance- to plan for environmental resources and to identifyment of environmental quality. some practical solutions to the common environ- Legislation and public concern have fostered a mental problems that frequently confront projectmultiobjective approach to water development and planners and designers. Because each project pre-more serious consideration of the potential envi- sents unique problems, the reader is encouraged toronmental consequences of development. Environ- consult the publications referenced in the bibliog-mental aspects must be considered from the initial raphy at the end of this chapter (sec. 2.10) and otherplanning and design of a project through its con- publications on this subject. Designers and plannersstruction and operation [7, 81. This requires the are encouraged to consult experts in the environ-actions of an interdisciplinary (and in some cases mental sciences to identify the opportunities forinteragency) team representing a wide range of ex- enhancing natural resources and to develop creative solutions for lessening adverse impacts.‘Numbers in brackets refer to entries in the bibliography (sec. 2.10). 3
  • 46. 4 DESIGN OF SMALL DAMS 6. GENERAL ENVIRONMENTAL ISSUES 2.2. Requirements.-Subsequent sections of vice, National Marine Fisheries Service, and thethis chapter deal with the environmental issues Environmental Protection Agency. State agenciesgenerally encountered in all water resource devel- include game and fish, recreation, public hea!th,opment projects. A list of environmental factors historic preservation, and water resource organi-that might be important in a specific project would zations. Each study should involve a unique com-be extensive. Therefore, each study should identify, bination of agencies, depending on the resourcesor “scope,” the environmental issues that could sig- involved.nificantly affect planning. In many instances, these 2.3. Categories of Resources.-The generalissues are specific legal requirements (local, State, categories of resources that should be consideredor Federal regulations) that must be addressed. The include air quality, water quality, prime and uniqueappropriate agencies should be consulted for com- farmlands, wild and scenic rivers, endangered spe-pliance procedures. In the United States, the ap- cies, wetlands, unique natural areas, wildernesspropriate Federal agencies include the Fish and areas, sound quality, visual quality, and geologic for-Wildlife Service, Forest Service, National Park Ser- mations [9]. C. FISH AND WILDLIFE CONSIDERATIONS 2.4. Genera/.-Experience in Federal water re- quirements of these species are considered duringsources development indicates that fish and wildlife the planning, design, and operation of the reservoirresources may represent a major portion of the en- project. The following sections discuss how fish andvironmental concerns that should be addressed be- wildlife may be affected by dams and reservoirs, andfore project construction and operation. These describe certain features that can be incorporatedresources include animal species with economic im- into a project design to reduce adverse impacts orportance because of their uses as food and for com- to directly benefit certain groups of species.merce, species with recreational importance 2.5. Ecological and Environmental Considera-because of their uses in hunting and fishing, and tions for Fish.-Impacts to fish and other aquaticendangered species with ecological importance be- life resulting from the construction of a dam andcause of the concern for their protection. Species subsequent impoundment of water can be causedthat are indicators of environmental health and by the change from flowing to standing water con- species with esthetic appeal should also be ditions, by the modification of downstream flows,considered. by changes in temperature and water quality con- Because of the complexity of fish and wildlife ditions, or by the addition of physical barriers toresource problems that, on the surface, appear sim- both usptream and downstream movements.ple, it is imperative that professional fish and wild- The most dramatic impact is caused by the con-life biologists be actively involved in project version of a portion of a free-flowing stream or riverplanning and design. Those professionals familiar system to a standing-water system. Depending onwith the resources in the planning area should be the numerous physical and chemical variables of theconsulted early in the planning phase. The appro- site, the temperature and water quality conditionspriate agencies can supply valuable information on could change so as to significantly affect projectlocal wildlife habitats and populations. Their in- uses, including fish and wildlife and recreation.volvement can result in the avoidance of critical Water quality issues in reservoir design are dis-resource areas, and their suggestions can help en- cussed in greater detail in part E of this chapter.hance particular resources. Where adverse impacts In most instances, either the species of fish thatare unavoidable, they can recommend actions (de- occupy the new reservoir are different from thosesigns and management methods) that can partially in the stream, or the ratio of the various speciesor completely mitigate project impacts. contributing to the total population is significantly Reservoirs can be of significant benefit to certain changed. If a significant fishery exists in the streamfish and wildlife species when the biological re- or if the project is to provide fishing opportunities,
  • 47. ECOLOGICAL AND ENVIRONMENTAL CONSIDERATIONS 5the planning study needs data accurate enough to spawning channels and riffle areas have sometimesassist in the design of alternatives that will maxi- been beneficial (fig. 2.3).mize fishery benefits in the new reservoir, but will When the construction of a dam will create aavoid adverse impacts downstream. The agencies barrier to upstream and downstream fish move-responsible for fish management should be con- ments where fish populations are an important re-sulted for such a project. source (e.g., salmon), the design should include Assessment of existing and potential fishery re- facilities for fish passage. Several design featuressources may, depending on the significance of the are possible alternatives. Although none of theseresource. and the amount of available data, require are completely effective in passing fish, they cansophisticated population or habitat studies. Where reduce adverse impacts significantly. The types ofmigratory species(salmon, trout, shad, striped bass, structures include fishways (or ladders), conduits,etc.) are important, tagging or radio-tracking tech- and turbine bypasses [14]. At some facilities, trap-niques may be necessary. In recent years, there has ping and hauling have been selected as the mostbeen an increased emphasis on more accurate de- cost-effective solution.termination of the flow conditions that optimize The fish ladder is perhaps the most commonfish habitat for the various life stages (spawning, method used to facilitate fish passage. These struc-fry, juvenile, and adult) [lo, 11, 121.Depending on tures generally consist of a series of stepped poolsthe resource involved, the study methods can vary separated by weirs. Another type of passage struc-in the amount of time, money, and technical ex- ture, the Denil-type fishway, consists of a chutepertise needed to obtain adequate information. Pre- with energy dissipating vanes in the sides and bot-dictions of reservoir populations are often made by tom that reduce the water velocity enough to permitcomparing the physical and chemical properties fish to ascend. Figure 2-4 shows yet another design,with those of other reservoirs in the same area [ 131. the Alaska steep pass fishway, at Ice Harbor Dam In cases where stored water will be used to gen- in Alaska. [ 141.erate hydroelectric power in a peaking pattern, the To direct fish to passage areas and to reduce theinstallation of a reregulation dam downstream from possibility of their entry into intake structures, sev-the discharge point should be considered if a sig- eral types of excluding devices have been used.nificant fishery resource exists, or high recreational These devices include stationary and movinguse is expected. This reregulation structure should screens (fig. 2-5), louvered deflectors, and electricbalance high and low flow conditions which, if un- weirs [ 141.Where specific requirements for fish pas-regulated, could strand fish and recreationists, ex- sage or exclusion are required, designs may be de-pose spawning areas, and scour the stream bottom, veloped with the help of the U.S. Fish and Wildlifepossibly reducing the production of aquatic food. Service or the State fishery agency. In relatively small rivers and streams, it is often Within the reservoir, there are several factorspossible to create habitat conditions that increase that should be considered and evaluated to enhancefish populations. Where pools are limiting, the con- the value of the anticipated fishery. Results fromstruction of bank deflectors or small dams can di- water quality and temperature studies should in-rect the current so that scour holes are developed dicate whether the reservoir will thermally stratify.[14, 151 (see fig. 2-l). These structures can be very If stratification is expected, the reservoir may beeffective, yet they require little maintenance if suitable for management as a “two-story” fishery,properly located and constructed. Wing deflectors with warm-water species occupying the upper layercan be placed to direct the stream current to avoid (epilimnion), and cool or cold-water species estab-excessive erosion, permitting the area to stabilize lished in the lower layer (hypolimnion). Manage-and reducing the amount of sediment entering the ment of the hypolimnion assumes that oxygen willstream. Riprap and rock-filled gabions can also ef- be available in an acceptable concentration, whichfectively control erosion. Underbank (escape) cover is determined in the water-quality studies. In strat-can be developed through the construction of ified reservoirs, the installation of a multilevel in-overhanging structures: using logs securely an- take structure may be desirable for both reservoirchored into the bank and covered by planking and and downstream management.sod (fig. 2-2). Where spawning habitat is limited or When preparing the reservoir area, it is ofteninaccessible because of the dam, construction of advantageous to leave some trees and shrubs in the
  • 48. 6 DESIGN OF SMALL DAMS - Orynal channel level - - Pool scoured below dam Rocks placed on stapled woven wire and mudsllls to hold gravel seal Use log knee braces set against large boulder or tree downstream to anchor ma/n dam log. ks coverlng gravel seal Pool scoured below no natural rocks ,n 2x1 xl m gabion Figure 2-1 .-Several types of check dams. Scour holes developed by these doms create habitat conditions thot increase fish populations. 103-D- 1793.
  • 49. ECOLOGICAL AND ENVIRONMENTAL CONSIDERATIONS 7 Sod cover over rock and fill , , ,. ~ I ~ Ii 1111 t ..ri ~ Y-, Ii I lJ : .~,~~ ~ ~ II Rock foundation in trench I ,bak pilings used in lieu lof rock foundations Figure 2-2.-Construction schemotics for ortificial overhead cover structures. From [16]. 103-D-1794.Figure 2-3.-Artificial spawning channels along the Tehama-Colusa Canal. Part of the Central Valley Project, California. PBO1-D-Bl027
  • 50. DESIGN OF SMALL DAMS Figure 2-4.-Alaska steep pass fishway , fish ladder. Ice Harbor Dam, Alaska. P80 l-D-81 028permanent pool area as cover and feeding areas for strand eggsof undesirable species,such as carp. Atfish [16]. This should be balanced with the recre- other times, the fish manager may recommend in-ational objectives of boating and water skiing. Ar- creasing the water level, then holding it constanttificial spawning areas can also be developed with to enhance the spawning of desirable species.successful results in certain situations (e.g., using 2.6. Ecological and Environmental Considera-stone substitutes). tions for Wildlife.-Impacts to wildlife resulting It may be desirable to eradicate fish from drain- from the construction and operation of a reservoiragescontributing to the reservoir to reduce the in- can be causedby the loss and modification of theirfluence of undesirable species on a new reservoir habitat and the disruption of movement patterns.and to provide stocked sport fish with at least a These impacts may be caused by direct and by in -temporary advantage. The use of fish toxicants, direct actions. Certain impacts, such as inundationsuch as rotenone, is usually the preferred method. of habitat within the reservoir area, are unavoidableThe decision to use fish toxicants should be made if project purposes are to be met. Nevertheless,after consultation with Federal and State fish agen- other impacts can be reduced through design con-cies as part of an overall fish-management plan. siderations, and still others can be offset only by Where possible, the reservoir should contain a including separable wildlife features.permanent conservation pool to ensure the contin- Ecological complexities and legal requirementsued survival of fish species. When pool levels are make it imperative that wildlife agencies be in-lowered in response to other project purposes, the volved from the initial project planning. An im-changes should generally be gradual to avoid portant contribution of these agencies can be thestranding desirable species.However, it may be ad- identification of important or critical wildlife areas.vantageous at times to effect a rapid drawdown to Foreknowledge of this kind can often be used to
  • 51. ECOLOGICAL AND ENVIRONMENTAL CdNSlDERATlONS Bypass to river I/Sprocket and iron Bypass weir -l-F+ flow+H I u I PLAN Drum screen, wheel SECTION A-A Figure 2-5.-Horizontal drum-screen, fish-passage structure. From [ 141. 103-D-1795.avoid adverse impacts to these resource areas. of application. The methods now used include pop- In the past, the importance of a wildlife resource ulation census, remote sensing, radio telemetry,was measured, to a large extent, by its significance habitat analysis, and mathematical models [17, 18,as a recreation base (hunting, nature study, etc.). 19, 201.However, in the past 10 to 12 years, the emphasis To offset the loss of inundated wildlife habitat,has shifted to methods that measure various eco- the wildlife value of noninundated areas may belogical factors. These methods vary in both the type increased (increase carrying capacity). Perhaps theof information developed and their time and cost most widely used practice to increase the value of
  • 52. 10 DESIGN OF SMALL DAMSan area for wildlife is to exclude livestock (and hu- maintenance, but will benefit many species ofmans in some instances) by fencing, while allowing wildlife.wildlife to pass. Fencing is also used to exclude wild- Operation (storage and release of water) of thelife from hazardous areas and from areas where reservoir can usually be modified to benefit wildlifewildlife could interfere with project operations (e.g., and fish without affecting other project purposes.canals) or could be a hazard to humans (e.g., in an Figure 2-10 presents a graphic representation ofautomobile collision). The kinds of animals to be typical seasonal water-level fluctuations at a warm-excluded must be considered in the design of the water reservoir. In such reservoirs, operationalfence. By varying the fence design, livestock can be plans can be devised that increase game and forageexcluded while permitting antelope to pass over or fish product,ion and waterfowl use, while decreasingunder the fence (fig. 2-6). turbidity and rough fish populations. Wildlife habitat can also be improved through Canals associated with many reservoir projectsthe selective planting of the trees, shrubs, and pose special problems to wildlife and wildlife man-grasses that provide needed food and cover (fig. agers [24, 251. Although canals may not cause a2-7). Depending on the frequency and length of in- significant loss of habitat, they can trap thirsty orundation, areas within the boundaries of the fluc- migrating animals unless certain design features aretuating pool can be managed effectively for wildlife. incorporated. The problem occurs when wildlife areThe types of plants selected are of critical impor- attracted to open canals for water or try to cross atance and should be selected by experienced wildlife canal that has interrupted a seasonal or daily mi-managers [al, 221. Where project lands are already gration route. An animal can become trapped andunder agricultural development or where lands are eventually drown in a canal because of its steep orsuitable for cropping, wildlife benefits can be ob- smooth sides or its high water velocity. This prob-tained through a share-cropping arrangement, in lem can be especially critical in areas with largewhich the user is required to leave a portion of each populations of deer and antelope.year’s crop to provide winter food and cover. Pro- To reduce the severity of this problem, canalsceeds from the lease of the land can be used to help can be fenced or even covered in certain critical,offset annual wildlife operation and management high-use areas. Where canals are fenced, drinkingcosts. access areas should be provided. This usually in- Enhancement of the habitat for some species volves a simple flattening of the side slopes. To per-may occur as a result of dam construction. Addi- mit crossing, bridges should be constructed attional nesting sites for certain wildlife species (e.g., specified intervals and at regular crossing pointsducks, geese, and raptors) can be developed through (fig. 2-11). In areas where fencing or covering arethe use of constructed nesting devices (fig. 2-8). impractical, the canal side slopes should be rough-Constructed islands can also serve as excellent nest ened or provided with cleats *to allow escape. Insites provided water-level fluctuations are not great addition, turnouts and deflectors can be installedduring the nesting season (fig. 2-9). The construc- to direct animals into the areas of reduced currenttion of subimpoundments within the main pool area where escape ramps are located (fig. 2-12). Once acan provide pair and brood habitat for waterfowl project is operational, it may be necessary to addand habitat for other marsh species. These sub- certain escape or access restriction features afterimpoundments can also serve as sediment and nu- problem areas have been empirically identified.trient traps in areas on the contributing watershed Nevertheless, animal drowning cannot be com-where erosion is a problem. pletely avoided. At projects where power is produced, high- Wildlife and water resource development can ex-voltage towers, poles, and transmission wires can ist in harmony if there is a commitment on the partpose serious obstacles for birds. In addition to of developers and environmental groups to com-strikes (flying into a structure), large birds, such as promise. The important point is that a wildlifeeagles and hawks, risk electrocution. The careful management plan should be developed by profes-design of these features can greatly reduce their sional wildlife managers. A well-formulated planpotential for adverse impacts [23]. In addition, can benefit wildlife resources, generate revenues totransmission-line rights-of-way can be planted with help offset management costs, and help create avegetation that will not interfere with operation or positive public image.
  • 53. ECOLOGICAL AND ENVIRONMENTAL CONSIDERATIONS 11 t ,RBED WIRE e the smooth ottom strand Three-strand fence Four-strand fence WOVEN WIRESheep, cattle and horses ANTELOPE PASS Figure 2-6.-Fences passable for antelope and an antelope pass structure. From [ 141. 103-D- 1796.
  • 54. 12 DESIGN OF SMALL DAMS Prop1 Multi-flora rose Native rose Buffaloberry Russian olive ROCK Mtn. red cedar ,y Ponderosa pine man eln i (Ulmus pumlla) Cottonwood Wild plum Caragana Chokecherry Sweet clover Figure 2-7.-Typical food and cover planting scheme. Angostura Reservoir, South Dakota. From 114). 103-D-1797.
  • 55. ECOLOGICAL AND ENVIRONMENTAL CONSIDERATIONS 13 c -I I-L 7 IIhi I --!-t-lna II II 1 I II -111 l-l TOP VIEW BOLT 2- BY 4-INCH BOARD TO STEEL POSTS ,2- BY 4-INCH BOARD J/ ,/WIRE ,TlTl jbAPP.OX. 7 FEET FNn b.. Y /lFW . IL 1- BY a-INCH BOARD ?$? =-TRUCK OR TRACTOR TIRE TIED S1ECUREL Y TO TOP OF PLATFO IRM WITH WIRE LOOSE HAY OR STRAW ANGLE-TYPE STEEL POSTS/ TOP VIEW WITH TIRE PLACEMENT Figure 2-8.-Details for constructing a goose-nesting platform. From [ 141. 103-D- 1798.
  • 56. 14 DESIGN OF SMALL DAMS Figure 2-9.-Constructed nesting islands. Canyon Ferry Reservoir, Montana. From [141. PSO1-D-Sl029 D. WATER QUALITY 2.7 Genera/.-The quality of the water im- problems, the project should be reexamined to de-pounded by a dam must be considered in the plan- termine whether changescan reducethese problemsning and design of a project. If the water is of to an acceptable level.inferior quality for intended users (irrigators, mu- (a) Water Quality Analysis.-The suitability ofnicipalities, industry), if it unnecessarily impairs the water quality for the intended uses should bethe habitat for the fish and wildlife in the reservoir determined. A sufficient number of water samplesor downstream, or if the reservoir is subject to ex- should be collected and analyzed to accurately char-cessivealgal growth that reduces the attractiveness acterize the water to be stored. The number of sam-of the area for recreation, then the reservoir should ples and the extent of laboratory analysis requiredbe considered a partial failure becauseanticipated depends somewhat on the intended uses.project benefits will not be fully realized. Water intended solely for irrigation may be de- In the past, water quality issueswere seldom con- scribed adequately by the analysis of 12 to 20 rep-sidered except as an afterthought. More recently, resentative samples collected over a typical annualattempts have been made to evaluate these effects cycle and analyzed for common ions and boron.as part of the environmental impact analysis. Like However, water for human consumption should beother environmental issues, water quality consid- analyzed for all contaminants listed in the appro-erations should be an integral part of the planning priate drinking water standard (e.g., "Environmen-and design process to avoid water quality-related tal Protection Agency National Primary andfailures. In general, the analyses described in the Secondary Drinking Water Regulations"). Severalfollowing paragraphs should be completed for each years of data may be required to properly evaluatereservoir. If any of these analyses indicate potential the suitability of potable water. For aquatic life,
  • 57. ECOLOGICAL AND ENVIRONMENTAL CONSIDERATIONS 15 Calenda Level Habitat and Population Improvement Meters above conservation poo Period Manioulatiol Purooses j- Jan 1 Hoid low Provide spring runoff and flood capa cjtv, allow weather to clean rocky shorellnes of algae, slit. Feb 28 Mar 1 Increase Inundate vegetation and rocks for gradually Improved spawning, reduce walleye losses through darn outlets. May 15 MaylG Hold 111gtl Maintain fish nursery habltat; decom- pose vegetation for nutrients and turbi.ddlty control. Jun 30 Jul Decrease Expose shorelines for revegetation; Jul 15 abruptly dessicate rough fish spawn. Jul 16 Hold low Expose forage fish to predation; allow vegetation to mature. Sep 30 Ott Increase Partially inundate vegetation for in gradually creased waterfowl food and cover. Nov 15 Nov 16 Hold Maintain for maximum waterfowl use. intermediate Dee 15 Dee Decrease Reduce ice and wave damage to vege Dee 31 araduallv tation; prepare for next season.Figure 2-lo.-Typical water-level manipulation plan for a warm-water reservoir. From [26]. 103-D-1799.
  • 58. 16 DESIGN OF SMALL DAMS Figure 2-11.-Fenced wildlife crossing over Tiger Creek Canal, California. From [14]. PSO1-D-S10JO other water-quality parameters are important: an location (latitude, longitude, and elevation), appropriate sampling program generally focuses on amount and location of inflows and discharges,and common ions, physical properties, dissolved gasses, the depth, surface area, and volume of the reservoir. trace metals, pesticides, and nutrients. The extent The temperature regime influences many of the of sampling for each of the above groups depends other measures of water quality both in the reser- on the intended uses of the water and the results voir and below the dam. of initial analyses. Someof these other parameters, such as the TDS (b) Effects of Design and Operating Criteria.- (total dissolved solids), dissolved oxygen, and nu-The effects of proposed design and operating cri- trients, can be also modeled [28]. However, exceptteria on the water quality should be evaluated both for the TDS and to a lesser extent dissolved oxygen,in the reservoir and downstream. Various tools are mathematical simulations of these parameters foravailable to perform some of the required analyses. planned reservoirs are generally less reliable thanOne of the basic factors that affects most water- temperature simulation models. Other tools usefulquality parameters is the temperature regime. For- in water quality analysesinclude physical modeling,tunately, fairly reliable temperature simulation algal assay tests, and anaerobic lake-bottom sim-models are available to predict temperature profiles ulations. The procedures for assessing the eutro-in reservoirs [27, 28, 29]. From the temperature sim- phication potential of planned reservoirs have beenulation, it is possible to determine the time of initial described in other texts [30].stratification, the strength of the thermocline, and Water quality can be affected by the design andthe temperature profile. Someof the significant fac- operational features of the reservoir. The obvioustors affecting the thermal regime are solar radia- impacts are those associated with the location oftion, air temperature, sky cover, wind speed, outlets. Bottom withdrawals result in cooler water
  • 59. ECOLOGICAL AND ENVIRONMENTAL CONSIDERATIONS 17 Figure 2-12. .Revised Richmond deer-escape ramp. Water flow is from left to right. From [14]. PSO1-D-Sl031downstream and warmer water in the reservoir. water. Obvious sources of pollution, such as con-Withdrawals from the epilimnion (from near the taminated tributaries, old mine spoils rich in heavysurface) result in warmer water downstream and metals, and saline springs, should be avoided. Oncecooler water in the reservoir. Bottom withdrawals the site is selected, water quality can be controlledalso tend to flush nutrients and sediment out of the somewhat by designing the outlet works, as dis-reservoir. The timing of releasescan also influence cussedpreviously in section 2.7(b). It is importantthe water quality. Other effects may be more subtle. to specify the water-quality goals of the project inIt is clear, however, that water quality aspects advance because of the possible tradeoff betweenshould be evaluated for various reservoir and outlet water quality in the reservoir and water qualityconfigurations. downstream. Other design factors include the ex- Once the reservoir models are operational, it is tent to which vegetation is removed from the res-fairly easyto evaluate the effects on the water qual- ervoir and the possibility of eliminating potentiality of changesin the reservoir-its size, outlet con- sourcesof pollution, e.g.,excavation of mine tailingsfiguration, or operating procedures. The analysis of in the watershed or pool area.those constituents not subject to direct simulation The design should provide some flexibility tois usually aided by temperature and dissolved ox- deal with water quality problems. For example, mul-ygen models. tilevel outlets can be provided so that water from (c) Design Considerations.-Water quality is af- different elevations can be blended to controlfected by various elements of the design. The pri- (within limits) the quality of the outflows (fig. 2.13).mary factor in controlling water quality is the Nevertheless, if a reservoir does not stratify,selection of the damsite. Ideally, the dam should be multilevel outlets are ineffective. In the early 1960s,located on a reach of stream that has high quality a reservoir was constructed in Kansas with a four-
  • 60. 18 DESIGN OF SMALL DAMS /Upstream face of dam Outlet works conduit / Figure 2-13.--Multipurpose intake structure with multilevel outlet potential. 103-D-1800.level outlet structure. However, because its reser- constructed before the reservoir was filled. The restvoir is wide, shallow, and subject to considerable of the reaeration system (motors and compressorswind action, the waters are consistently well-mixed; to provide air to the underwater pipes) will be in-therefore, the multiple outlets have little effect on stalled, if needed, when the reservoir is operational.the water quality. Thus, a thorough understanding A reaeration system could also be designed and in-of stratification is vital for an effective design. stalled after the reservoir is completed. Some res- An aeration system can be designed to improve ervoirs in California have been successfullythe quality of the reservoir water by destratifying retrofitted with diffused-air systems, which providethe water column and increasing the dissolved ox- partial destratification and control the temperatureygen content (fig. 2-14). An aeration system can and dissolved oxygen in the reservoir. These sys-also reduce the concentrations of many contami- tems have improved the water quality substantially.nants, which remain in solution only under the an- Other designs that benefit water quality includeaerobic (no oxygen) conditions that occur in the the modification of turbines to increase the dis-hypolimnion of a stratified reservoir. solved oxygen in discharges through powerplants At a reservoir in Colorado, which may have a and the installation of deflectors on outlet workstendency to develop excessive concentrations of to reduce nitrogen supersaturation below the dam.heavy metals at certain times of the year, the un- However, these problems do not normally affectderwater portion of a reaeration system (perforated small dams.pipes and the necessary supports) was designed and E. ARCHEOLOGICAL AND HISTORICAL CONSIDERATIONS 2.8. Requirements.-During the planning of a ously undiscovered sites. Emphasis should bewater development project, a professional archeol- placed on those areas that are to be physically mod-ogist should conduct a thorough search of the rec- ified (e.g., the reservoir area, damsite, and recrea-ords relating to the location of known historic and tion sites). Before construction, the entire projectarcheological sites within the project area. The area should be subjected to a complete ground sur-Government agencies responsible for the preser- vey [31]. If historical or archeological sites are dis-vation of such resources should be consulted about covered during construction, activity should bethe legal requirements. Furthermore, the entire stopped and a professional archeologist should beproject area should be surveyed to identify previ- contacted.
  • 61. ECOLOGICAL AND ENVIRONMENTAL CONSID