Chapter 7 dams and reservoirs


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Chapter 7 dams and reservoirs

  1. 1. Chapter 7 Dams and reservoirs Prof. Dr. Ali El-Naqa Hashemite University June 2013
  2. 2. Dams Definition of Dams Advantages and Disadvantages of Dams Classification of Dams Types of Dams
  3. 3. What is a Dam? A dam is a structure built across a stream, river or estuary to retain water. Dams are made from a variety of materials such as rock, steel and wood.
  4. 4. Dams
  5. 5. Dams
  6. 6. Structure of Dam Toe Heel Sluiceway Spillway Freeboard Gallery
  7. 7. Definitions Heel contact with the ground on the upstream side Toe contact on the downstream side Abutment Sides of the valley on which the structure of the dam rest Galleries small rooms like structure left within the dam for checking operations Diversion tunnel Tunnels are constructed for diverting water before the construction of dam This helps in keeping the river bed dry Spillways It is the arrangement near the top to release the excess water of the reservoir to downstream side Sluice way An opening in the dam near the ground level, which is used to clear the silt accumulation in the reservoir side
  8. 8. Advantages of Dam Irrigation Water Supply Flood Control Hydroelectric Recreation Navigation Dams gather drinking water for people. Dams help farmers bring water to their farms. Dams help create power and electricity from water. Dams keep areas from flooding. Dams create lakes for people to swim in and sail on.
  9. 9. Disadvantages of Dam Dams detract from natural settings, ruin nature's work Dams have inundated the spawning grounds of fish Dams have inhibited the seasonal migration of fish Dams have endangered some species of fish Dams may have inundated the potential for archaeological findings Reservoirs can foster diseases if not properly maintained Reservoir water can evaporate significantly Some researchers believe that reservoirs can cause earthquakes
  10. 10. Three Gorges Dam
  11. 11. Three Gorges Dam
  12. 12. Three Gorges Dam Type: Concrete Gravity Dam Cost: Official cost $25bn - actual cost believed to be much higher Work began: 1993 Due for completion: 2009 Power generation: 26 turbines on left and right sides of dam. Six underground turbines planned for 2010 Power capacity: 18,000 megawatts Reservoir: 660km long, submerging 632 sq km of land. When fully flooded, water will be 175m above sea level Navigation: Two-way lock system became operational in 2004. One-step ship elevator due to open in 2009.
  13. 13. Three Gorges Dam Sluice Gates
  14. 14. Three Gorges Dam Shipping Locks Shipping Locks
  15. 15. Hoover Dam
  16. 16. Hoover Dam Location: Arizona and Nevada, USA Completion Date 1936 Cost 165 million Reservoir Capacity 1.24 trillion cubic feet Type Arch/ Gravity Purpose: Hydroelectric power/flood control Reservoir: Lake Mead Materials: Concrete Engineers: Bureau of Reclamation The Hoover Dam is a curved gravity dam. Lake Mead pushes against the dam, creating compressive forces that travel along the great curved wall. The canyon walls push back, counteracting these forces. This action squeezes the concrete in the arch together, making the dam very rigid. This way, Lake Mead can't push it over. Today, the Hoover Dam is the second highest dam in the country and the th highest in the world. It generates more than four billion kilowatt-hours a year, that's enough to serve . million people!
  17. 17. Dams in Thailand Bhumibol Dam The Largest Concrete Arch Dam in Thailand Name Bhumibol Dam Location On Ping river at Sam Ngao district, Tak province Type Concrete Arch Gravity Dam (largest in Thailand of this type) Size 154 meters high and 486 meters long at the crest Year Completed 1964 Storage Capacity 13,462 million cubic meters Electricity Generating Capacity 535 MW Annual Energy 1,200 GWh
  18. 18. Dams in Thailand Sirikit Dam Name Sirikit Dam Location On Nan River at Tha Pla district, Uttaradit province Type Earth fill dam Size 113.6 meters high and 800 meters long at the crest Year Completed 1974 Storage Capacity 9,510 million cubic meters Electricity Generating Capacity 500 MW Annual Energy 1,000 GWh
  19. 19. Dams in Thailand Srinagarind Dam Name Srinagarind Dam Location On Kwae Yai river at Ban Chao Nen subdistrict, Si Sawat district, Kanchanaburi province Type Rockfill dam with impervious core Size 140 meters high and 610 meters long at the crest Year Completed 1980 Storage Capacity 17,745 million cubic meters (largest storage capacity in Thailand) Electricity Generating Capacity 720 MW Annual Energy 1,140 GWh
  20. 20. Dams in Thailand Vajiralongkorn Dam Name Vajiralongkorn Dam Location On Kwae Noi river at Tha Khanun subdistrict, Thong Pha Phum district, Kanchanaburi province Type Rockfill dam with facing slab Size 92 meters high and 1,019 meters long at the crest Year Completed 1984 Storage Capacity 8,860 million cubic meters Electricity Generating Capacity 300 MW Annual Energy 760 GWh
  21. 21. Dams in Thailand Lam Takong Dam Name Lam Takong Dam Location On Lam Takong river at Sikiew district, Nakorn Ratchasima province Type Earth fill dam Size 92 meters high and 1,019 meters long at the crest Year Completed 1969 Storage Capacity 310 million cubic meters Irrigation Command Area 100,000 rai
  22. 22. Classification of Dams Storage Dam Detention Dam Diversion Dam Coffer Dam Debris Dam Classification based on function
  23. 23. Typical Storage Dam Srinagarind Dam Vajiralongkorn Dam
  24. 24. Typical Storage Dam Maeklong Dam Tha Thung Na Dam
  25. 25. Classification of Dams Classification based on hydraulic design Classification based on material of construction Overflow Dam/Overfall Dam Non-Overflow Dam Rigid Dam Non Rigid Dam
  26. 26. Classification of Dams Classification based on structural behavior Gravity Dam Arch Dam Buttress Dam Embankment Dam
  27. 27. Gravity Dam Gravity dams are dams which resist the horizontal thrust of the water entirely by their own weight. Concrete gravity dams are typically used to block streams through narrow gorges.
  28. 28. Gravity Dam Cross Section Plain View Material of Construction: Concrete, Rubber Masonry
  29. 29. Arch Dam An arch dam is a curved dam which is dependent upon arch action for its strength. Arch dams are thinner and therefore require less material than any other type of dam. Arch dams are good for sites that are narrow and have strong abutments.
  30. 30. Arch Dam Cross Section Plain View Material of Construction: Concrete
  31. 31. Buttress Dam Buttress dams are dams in which the face is held up by a series of supports. Buttress dams can take many forms - the face may be flat or curved.
  32. 32. Buttress Dam Cross Section Plain View Material of Construction: Concrete, Timber, Steel
  33. 33. Embankment Dam Embankment dams are massive dams made of earth or rock. They rely on their weight to resist the flow of water.
  34. 34. Embankment Dam Cross Section Plain View Material of Construction: Earth, Rock
  35. 35. Types of Dam Factors governing selection of types of dam A Narrow V-Shaped Valley : Arch Dam A Narrow or Moderately with U-Shaped Valley : Gravity/Buttress Dam A Wide Valley : Embankment Dam Topography-Valley Shape
  36. 36. Types of Dam Factors governing selection of types of dam Solid Rock Foundation : All types Gravel and Coarse Sand Foundation : Embankment/Concrete Gravity Dam (H≤15 m) Silt and Fine Sand Foundation : Embankment/Gravity Dam (H≤8 m) Non-Uniform Foundation : - Geology and Foundation Condition
  37. 37. Types of Dam Factors governing selection of types of dam Climate conditions Availability of construction materials Spillway size and location Environmental considerations Earthquake zone Overall cost General considerations
  38. 38. Gravity Dam
  39. 39. Gravity Dam Forces on Gravity Dam Gravity or weight of dam Hydrostatic force Uplift force Ice force Earthquake forces
  40. 40. Gravity Dam Forces on Gravity Dam Free-body diagram of cross section of a gravity dam
  41. 41. Gravity Dam Forces on Gravity Dam Gravity or weight of dam W When W = Weight of dam = Specific weight of material = Volume of dam Weight of Dam
  42. 42. Gravity Dam Forces on Gravity Dam Hydrostatic Force xwh AhH I. Horizontal hydrostatic force II. Vertical hydrostatic force wwv H Hydrostatic Force
  43. 43. Gravity Dam Forces on Gravity Dam Uplift Force Uplift Force Uplift Force 2 t)hh( U 21w
  44. 44. Gravity Dam Forces on Gravity Dam Ice Force Ice Force Ice Force
  45. 45. Gravity Dam Forces on Gravity Dam Earthquake Force )g0.1tog5.0(mE d 2 ww hk555.0E Earthquake Force
  46. 46. Arch Dam
  47. 47. Arch Dam I. Constant radius arch dams for U-shaped valleys have vertical US face constant extrados radii for U-shaped valley suitable to install gates at the US face II. Constant angle arch dams for V-shaped valleys have curved US face no possibility for gate installment
  48. 48. Arch Dam Section
  49. 49. Arch Dam Section
  50. 50. Arch Dam Reaction Forces on Arch Dam Arch Dam with an Overflow Spillway allow hr t 2 )2/(Sin2 B k
  51. 51. Arch Dam Example Profiles of Existing Dam
  52. 52. Embankment Dam Earth-Fill Embankment Dam A earth-fill dam in Australia.
  53. 53. Embankment Dam Rock-Fill Embankment Dam
  54. 54. Embankment Dam Earth Dams are the most simple and economic (oldest dams) Types: 1 Homogeneous embankment type 2 Zoned embankment type 3 Diaphragm type
  55. 55. Embankment Dam Homogeneous Embankment Dam
  56. 56. Embankment Dam Zone-Based Embankment Dam
  57. 57. Embankment Dam Diaphragm Earth Dam
  58. 58. Embankment Dam Rock fill Dam with RC facing
  59. 59. Embankment Dam Slip Failure of Earth Dam
  60. 60. Buttress Dam
  61. 61. Buttress Dam Buttress Dam : is a gravity dam reinforced by structural supports. Buttress :a support that transmits a force from a roof or wall to another supporting structure. This type of structure can be considered even if the foundation rocks are little weaker.
  62. 62. Buttress Dam Typical Sections of Buttress Dams Shapes of Buttress Dam
  63. 63. Buttress Dam Multiple-Arch Dam (Buttress Dam)
  64. 64. Miscellaneous Types of Dam Timber Crib Dam A timber crib dam in Michigan.
  65. 65. Miscellaneous Types of Dam Steel Dam Red Ridge steel dam in Michigan.
  66. 66. Miscellaneous Types of Dam Stone Masonry Dam Stone Masonry dam.
  67. 67. A coffer dam during the construction of locks at the Mongomery Point Lock and Dam. Miscellaneous Types of Dam Coffer Dam
  68. 68. Dam Failure Tailing Dam at Aznalcollar Mine, Spain April 25, 1998: the tailings dam at the Aznalcollar mine near Sevilla, Spain failed. This has had BIG societal implications -- the toxic waste has killed many fish and birds and flooded thousands of hectacres of farmland. February 26, 1999 marks the 27th anniversary of the failure of another tailings dam on Buffalo Creek, West Virginia 125 peoople were killed and 4,000 were left without homes. The dam failure was compounded by the fact that it was waste that was escaping; the waste caught fire and an explosion eventually occured.
  69. 69. Types of Dam Earthfill 58% Timber Crib 2% Other 16% Rockfill 3% Concrete 11% Stone Masonry 10%
  70. 70. Dam Failure June 5, 1976: the failure in the Teton Dam led to flooding in the cities of Sugar City and Reburg in Idaho. The dam failure killed 14 people and caused over $1 billion in property damages. The dam failed because the bedrock was not strong enough to support the structure. Currently the dam is once again used for hydroelectric power. Teton Dam, Idaho
  71. 71. Dam Failure July 17 1995 : a spillway gate of Folsom Dam failed, increasing flows into the American River significantly The spillway was repaired and the USBR carried out an investigation of the water flow patterns around the spillway using numerical modelling No flooding occured as a result of the partial failure, but flooding is still a major concern for this area It seems that the Folsom Dam may be due for a height increase as an answer to this concern Folsom Dam, USA
  72. 72. Chapter 7. Dams • Dam Basics – Purposes of Dams – Components of Dams – Types of Dams – Dam Operations • Benefit-Cost Analysis • Impact of Dams • Dams and Locks for Navigation
  73. 73. Purposes of Dams  A management tool used to control, regulate, and deliver water for a variety of purposes:  Store water for dry periods  Prevent flooding  Increase river depth to aid navigation  Stock watering and irrigation  Fish farming
  74. 74. Figure 7.1 Primary purposes of dams in the United States.
  75. 75. Figure 7.2 Age of dams in the United States.
  76. 76. Figure 7.3 Principal parts of a dam.
  77. 77. Important Terms and Concepts  Types:  Gravity Concrete Dam  Buttresses  Concrete Arch Dam  Earthfill Dam  Core of large rocks  Clay cutoff walls  Stone surface (rip rap)  Storage (pools):  Dead Pool (not PC...)  Inactive Pool  Conservation Pool  active or joint-use  Flood Pool  Surcharge Pool  Freeboard  Other Terms:  Face: Exposed surface of dam  Abutments: sides of dam  Appurtenances: pipes, gates, etc.  Dam Crest: Top of dam  Toe: base of dam  Parapet wall: along top  Spillway: for emergency releases  Outlet Gate: Adjustable spillway  Firm Yield: dependable capacity  Powerhouse: location of generators  Headrace: Canal leading up to powerhouse  Tailrace: Canal leading away from powerhouse
  78. 78. Figure 7.4 Basic dam designs. Note the rip-rap placed on the upstream face of the earthen embankment dam to prevent erosion from waves.
  79. 79. Figure 7.5 Classification of principle storage zones in a cross section of a multipurpose reservoir.
  80. 80. Figure 7.6 Notice the cement blocks that are being poured during construction of Hoover Dam and the tremendous width of the structure at its base.
  81. 81. Figure 7.7 The dramatic concrete arch design of Hoover Dam securely holds the impounded waters of Lake Mead.
  82. 82. Figure 7.9 Grand Coulee Dam is a gravity concrete dam.
  83. 83. Figure 7.10 Hydroelectric turbines at Grand Coulee Dam.
  84. 84. Workers inspect a hydroelectric turbine runner blade at Fort Loudoun Dam, near Lenoir City, Tennessee.
  85. 85. Benefit - Cost Study  Costs  Land Purchase  Dam Construction  Dam Operation  Power lines  Irrigation systems  Navigation aids  Environmental impacts  Benefits  Cheaper electricity  Fewer floods  More irrigation water  More recreation  Easier navigation  Increased property values
  86. 86. Benefit - Cost Analysis  Benefit - Cost Ratio:  Ratio of Benefits to Costs: r = B / C  r > 1 means more benefits than costs  Net Value:  Benefits minus costs: NV = B - C  NV > 0 means more benefits than costs  Rate of Return:  Discount rate that makes B(rr) = C  rr > market rate is a good investment
  87. 87. Issues:  Time-Value of Money  Today’s Costs vs. Tomorrow’s Benefits  Must Discount the value of future benefits  The Discount rate is like the interest rate  Incorporates the risk of the project, and the alternative uses of the money, such as investing the money somewhere else.
  88. 88. Impacts of Dams  Barriers to fish and boat movement  Salmon in the west, Shad in the east  Must build locks to move boats around dams  Sediments build up in reservoir  Farmland along the Nile and Mississippi Rivers depended on these for soil improvement, and the Delta needs these to keep the ocean out  Many cities, farms, and people must be relocated
  89. 89. FERC Relicensing  The Federal Energy Regulatory Commission (FERC) regulates private dams (such as Georgia Power dams).  In order to get or renew a permit, the operator has to explain how the dam benefits the public.  FERC can give the original permit to anyone.  When renewing a permit, FERC can give it to the builder, or to anyone else they choose.  Many Georgia Power dams must have their permits renewed, and are finding ways to improve their performance so they can get their permit renewed.
  90. 90. Figure 7.12 This scene in Wanxian, the largest of the relocation cities affected by Three Gorges Dam, called Sanxia Ba in China (San meaning “three,” Xia meaning “Gorge,” and Ba meaning “Dam”).
  91. 91. Figure 7.13 This tributary of the Yangtze River flows through the narrow canyon called Xiao Sanxia (Lesser Three Gorges) and will be flooded after completion of the Three Gorges Dam.
  92. 92. Dams and Locks for Navigation  Problem with dams blocking rivers  Historical use of rivers by boats to transport goods.  With a new dam in the way, the barge operators are put out of business.  Protests build for providing a way around the obstruction.
  93. 93. Figure 7.14 Main-river dams form a staircase of reservoirs that stretch the entire length of the Tennessee River.
  94. 94. Figure 7.15 Chickamauga Lock and Dam, located on the Tennessee River near Chattanooga, Tennessee, is a major lock in the TVA navigation system.
  95. 95. Rhine - Danube Canal
  96. 96. Main (Rhine) - Danube Canal: Elevations on the section from Würzburg to Passau going through 53 stepwise locks
  97. 97. Interesting Websites  Panama Canal Video  Canal Video
  98. 98. By Alex Otto Buford Dam Allatoona Dam Nantahala Dam
  99. 99. Athens Poultry Industry  Employs  150 workers per shift (three shifts) at about $10/hr  Several dozen supervisors at about $20/hr  This is a payroll of over $15,000,000 per year  Water Use  They process about 200,000 birds per day  This requires about 7 gallons per bird  Which is 500 million gallons per year  Water value  is 3 cents per gallon  not counting taxes and other community benefits.
  100. 100. Atlanta, Georgia “the fastest-spreading human settlement in history" Time Magazine March 22, 1999
  101. 101. Lake Lanier Carter’s Lake Lake Allatoona Atlanta
  102. 102. Lake Allatoona Northwest Atlanta, Bartow and Cherokee Counties  Created by U.S. Army Corps of Engineers  Filled in December 1950  Watershed area is 1,110 mi2  Lake volume is 367,500 acre-feet  Lake area is 12,010 acres  Maximum depth is 145 ft
  103. 103. Lake Purposes 1. Flood control 2. Navigation 3. Hydroelectric power generation 4. Water supply 5. Water quality 6. Recreation 7. Fish and wildlife management
  104. 104. Lake Water Quality Issues • Lake Sedimentation – Reduction in storage capacity – Impairment of • navigation • recreation • aquatic habitats • Regulatory Controls – Stormwater regulations – Erosion and sediment laws
  105. 105. 1 10 100 1,000 10,000 0.1 1 10 100 Normalized Discharge, Q / Qo SuspendedSolidsConcentration,mg/L West Fork Little River near Clermont Chestatee River near Dahlonega Chattahoochee River at Cornelia Chattahoochee River at Norcross Sediment Rating Curve Lake Lanier
  106. 106. Lake Allatoona Tributaries
  107. 107. Sediment Budget Annual sediment loads, w/o bedload  Etowah River: 25,300 tons  Little River: 10,000 tons  Noonday Creek: 1,100 tons  Blankenship Sand  Operates on the Etowah and Little Rivers  Removes over 120,000 tons of sand and silt  85% are sand product  15% are silt materials
  108. 108. Sand Removal Each semi load contains: 23 tons of sediment 98% sand 2% clays 253 pounds of organic matter 10 pounds of nitrogen 5 pounds of phosphorus 2 pounds of regulated metals (mostly Ba, Cr) This frees up almost 4000 gallons of storage
  109. 109. Silt Removal Each semi load contains: 23 tons of sediment 35% sand 55% silt 10% clays 2600 pounds of organic matter (10x sands) 50 pounds of nitrogen (5x sands) 12 pounds of phosphorus (2.5x sands) 12 pounds of regulated metals (5x sands)
  110. 110. Reservoirs  A reservoir is an artificial lake called man-made reservoir. It can be formed by building a dam across a valley, by excavating the land or by surrounding a piece of land with dykesand diverting a part of the river flow into the reservoir. The water is stored in the reservoir and can be used for irrigation, hydro-power or as a water source for domesticor industry use. Man-made reservoirs are also very effective constructions to control unexpected floods (see also stormwater management).  A reservoir is fed by precipitation, rainwater runoff or from a constant flow of a river. Water loss can occur due to evaporation (especially in arid regions) and depending on the reservoir bottom due to percolation (small reservoirs are often lined). Sediments from rivers or surface runoff can reduce the storage volume of a man-made reservoir significantly (FAO 1992).
  111. 111. Reservoirs
  112. 112. Reservoirs  Water stored in a valley usually has a higher level than the valley bottom downstream of the dam. Because of this difference in level, the valley can be irrigated by a gravity system or other distribution systems. Water can be taken from the reservoir via a concrete or steel pipe.  This pipe connects the reservoir to an irrigation canal downstream. A valve is usually located on the upstream end of the pipe to control the discharge of water into the canal (FAO 1992). The kinetic energy of reservoirs is often used to produce electricity (see also hydropower small-scale and hydropower large-scale).
  113. 113. Comparison of the riverbed landscape between upstream and downstream reaches of the Yasugawa Dam in the Yasu River in central Japan. The dam is as old as 53 years and the distinctive riverbed armouring can be observed. White part of rocks indicates thick accumulation of organic matter originated from the reservoir. Source: TAKEMON (2006)
  114. 114. Reservoirs  Where no such water-body previously existed the presence of a reservoir in a drainage basin and the abstraction of significant water amounts for storage upstream significantly impacts the watercourse, the flora and fauna, and the human inhabitants in the drainage basin.  These potential impacts should be identified and thoroughly examined prior to reservoir construction, in order to comprehensively assess the total value of the reservoir project.  Procedures to identify and properly evaluate potential environmental, social and economic consequences of reservoir construction involve so- called „Environmental Impact Assessment‟ (EIA). Such an assessment is now obligatory by law in many countries for all new dam constructions (UNEP 2000).
  115. 115. Reservoirs  Ecological impacts of reservoir dams have been reported from various aspects such as barrier for migratory animals like anadromous fish, eutrophication of reservoirs by plankton blooming, decreasing flow volumes in tail waters, stabilisation of flow regimes by flood peak cut, changes in thermal regimes of river water, river bed degradation and increase in substrate grain size by sediment trapping, etc. (TAKEMON 2006).  Furthermore big dams and extraction of water (e.g. for spate irrigation) can create riparian conflicts (see water conflicts). Also read the paragraph “Impact on Environment” in the rivers factsheet.
  116. 116. Basic Design Principles Adapted from UNEP (2000)  Like lakes, reservoirs range in size from pond-like to very large water-bodies (e.g. Lake Powell, U.S.A.). The variations in type and shape, however, are much greater than for lakes. The term „reservoir‟ includes several types of constructed water-bodies and/or water storage facilities:  1. Valley reservoirs – created by constructing a barrier (dam) perpendicular to a flowing river.  2. Off-river storage reservoirs – created by constructing an enclosure parallel to a river, and subsequently supplying it with water either by gravity or by pumping from the river.
  117. 117. Reservoirs
  118. 118. Basic Design Principles Adapted from UNEP (2000)  The latter reservoirs are sometimes called embankment or bounded reservoirs, and have controlled inflows and outflows to and from one or more rivers.  In addition to single reservoirs, reservoir systems also exist, and include cascade reservoirs - consisting of a series of reservoirs constructed along a single river, and inter-basin transfer schemes – designed to move water through a series of reservoirs, tunnels and/or canals from one drainage basin to another.
  119. 119. Pumping from a Reservoir for Irrigation  The fields located around the reservoir upstream of a dam or surrounding a natural lake are higher than the reservoir or lake's water table. Here irrigation is only possible with the help of pumping stations, manual or motorised pumping.  The water level in the reservoir is usually highest at the end of the rainy season, and lowest at the end of the dry season or the irrigation season. Pumps installed at reservoirs and lakes must be able to handle these fluctuations, which are not only vertical, but even more pronounced horizontally, because the water recedes back to the lowest parts of the reservoir.  A dead branch of a river can also be made to function as a reservoir. The branch is filled with water during the wet season and closed off during the dry season so that the stored water may be used. Due to the low water level, pumps are normally needed to irrigate fields from such a reservoir.
  120. 120. Pumping from a Reservoir for Irrigation  A small reservoir in the hills of Tepoztlán (Morelos, Mexico), which is mainly filled by precipitation catchment. The water is extracted by gravity and is protected by a fence to avoid contamination from animals or unauthorised use. The reservoir is sealed with an impermeable liner. Source: B. STAUFFER (2009)
  121. 121. Operation and Maintenance  Because reservoirs are man-made water-bodies, they are more amenable to artificial operation and regulation than lakes. As previously noted, operational possibilities unique to reservoirs include the ability to discharge known volumes of water at predetermined times, and selective discharge of water from different water layers within the reservoir. This must be planned carefully as it directly impacts the environment as described above. Also read the document “Reservoir Operations and Managed Flows” (WMO and GWP 2008).  Dams, especially the very large ones, must be checked regularly to ensure their stability and security. Furthermore, many man-made water reservoirs are affected by high sedimentation rates.  The accumulation of sediments in the reservoir reduces the main reservoir asset i.e. its volume capacity. Moreover sediments can negatively affect pumping and hydropower equipment. Therefore the designers should consider the soil erosion and sediment transport (CHANSON and JAMES 1998). There are several approaches to minimize or deal with sedimentation.
  122. 122. Operation and Maintenance  When a reservoir serves different functions it is nearly impossible to operate each function at its maximum level. For example, a reservoir that provides irrigation, power generation (see small scale and large scale hydropower), flood control, and recreational use may cause conflicting demands by its users (WATERENCYCLOPEDIA 2011).  Health Aspects  Faecal pollution and other contamination of reservoirs has to be prevented by wastewater treatment and buffer zones in case of non-point sources of pollution (see also the factsheets on lakes or invalid link). If the reservoir is also used as a source of drinking water, please also check water purification as a measure to protect human health.  It should also be considered, that surface water sources can lead to mosquito breeding..