The document discusses reservoir planning and gravity dams. It covers topics like reservoir investigations, site selection, zones of storage, yield and capacity calculations. It also discusses types of dams, selection of dam type and site, and forces acting on gravity dams. Gravity dams are described as structures that resist forces through their own weight. Key forces on gravity dams include water pressure, uplift pressure, earthquake pressure, and more.

1. FABRIKAM
UNIT-5
RESERVOIR PLANNING…

2. FABRIKAM
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2
SUB-TOPICS
1. RESERVOIR PLANNING
--- Investigations
--- Site selection
--- Zones of Storage
--- Yield and Storage Capacity of Reservoir
--- Reservoir Sedimentation
2. Dams
--- Types of dams
--- Selection of type of dam
--- Selection of site of a dam
3. Gravity dams
--- Forces acting on a gravity dam
--- Causes of failure of a gravity dam
--- Elementary and practical profile
--- Limiting height of a dam
--- Stability Analysis
--- Drainage Galleries
--- Grouting

3. FABRIKAM 3
INTRODUCTION:
Dams are constructed across rivers or streams to create an artificial lake or reservoir.
 Storage works are constructed to serve many purposes
1. Storage and control of water for irrigation
2. Storage and diversion of water for domestic uses
3. Water supplies for industrial uses
4.Development of hydroelectric power
5.Increasing water depths for navigation
6.Storage space for flood control
7.Reclamation of low-lying lands
8.Debris control
9.Preservation and cultivation of useful aquatic life

4. FABRIKAM 4
1. Storage or conservation Reservoirs
2. Flood Protection Reservoirs
3. Distribution Reservoirs
4. Multipurpose Reservoirs
A storage reservoir is constructed to store
the excess water during the period of
large supplies, and release it gradually.
A Flood control reservoirs are those which
store water during flood and release it
gradually at a safe rate when flood reduces.
A Distribution reservoir is a small storage
reservoir used for water supply in a city.
Depending upon the purposes served,
Reservoirs

5. FABRIKAM 5
INVESTIGATIONS FOR RESERVOIR PLANNING:
1. Engineering Surveys
2. Geological investigations
3. Hydrological Investigations
1.ENGINEERING SURVEYS:
From the contour plan, the following physical characteristics are prepared
1. Area-Elevation curve
2. Storage-Elevation curve
3.Map of the area to indicate the land property to be surveyed.
4.Suitable site selection for the dam
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6. FABRIKAM 6
2.GEOLOGICAL INVESTIGATIONS:
1.Water tightness of reservoir basin
2.Suitability of foundations for the dam
3.Geological and Structural features – folds, faults, fissures etc,.
4.Type and depth of over burden (superficial deposits)
5.Location if permeable and soluble rocks, if any.
6.Ground water conditions in the region
7.Location of quarry sites for materials.
3.HYDROLOGICAL INVESTIGATIONS:
1. Capacity of irrigation canals, Installed capacity of power houses.
2.Study of Run-off pattern at the proposed site – determine the storage capacity
3.Determine the hydrograph of the worst flood – spillway capacity and design.

7. FABRIKAM 7
SELECTION OF SITE FOR A RESERVOIR:
1. The geological condition of the catchment area – Percolation losses are minimum, maximum runoff
2. The reservoir site – quantity of leakage through it is minimum.
3. The dam should be founded on sound watertight rock base.
4. The percolation below the dam should be minimum.
5. The reservoir basin should have narrow opening in the valley
6. The cost of real estate for the reservoir as less as possible.
7. It has adequate capacity without submerging excessive land.
8. Less evaporation losses because if reduction in the water spread area.
9. Avoids or excludes water from those tributaries which carry a high percentage of silt in water
10. Water stored in it is suitable for the purpose for which project is undertaken.

8. FABRIKAM 8
ZONES OF STORAGE IN A RESERVOIR:
1.Useful Storage
2.Surcharge Storage
3.Dead Storage
4.Bank Storage
5.Valley Storage
Normal Pool Level : Maximum Level – water will rise in the reservoir during ordinary
operation condition
--- Level of the spillway crest
--- Top level of spillway gates
Maximum Pool Level: Level to which water rises during the design flood
Minimum Pool Level: Lowest elevation – ordinary operating condition
Useful storage : Normal Pool Level – Minimum Pool Level
Dead Storage : Below the minimum pool Level, not useful under ordinary
operating conditions
Surcharge Storage : Normal Pool Level – Maximum level corresponding to flood
--- Usually uncontrollable
Bank storage & Valley storage: stored in previous formation of the river banks
--- Depends upon geological conditions of river banks.

9. FABRIKAM 9
STORAGE CAPACITY & YIELD:
 Yield: Amount of water that can be supplied from the reservoir in a specified interval of time
For example, if 25,000 cubic.m of water is supplied from a reservoir in one year= Yield = 25,000 cubic.m/year
Safe Yield or Firm yield: Maximum quantity of water that can be guaranteed during a critical dry period.
 Secondary Yield: Quantity of water available in excess of safe yield during periods of high flood.
Average Yield: Arithmetic average of the Safe and the Secondary yield over a long period of time.
The reservoir capacity corresponding to a specified yield is determined by Mass Inflow Curve and Demand Curve.
Mass Inflow Curve: Plot between the cumulative inflow in the reservoir with time.
Demand Curve: Plot between accumulated demand with time.
DEMAND CURVEMASS INFLOW CURVEFLOOD HYDROGRAPH

10. FABRIKAM 10
CALCULATION OF RESERVOIR CAPACITY FOR A SPECIFIED YIELD, FROM THE FLOW MASS INFLOW CURVE
STEP-1: From the flood hydrograph of several years – prepare the mass inflow curve
- also Demand Curve (same scale)
STEP-2: From A1, A2 & A3… of mass inflow curve, draw the tangents parallel to demand curve
STEP-3: Measure the E1D1, E2D2 & E3D3… between tangent and mass inflow curve.
The vertical intercepts indicate the
volume by which the inflow falls
short of demand
C1D1 = Net Inflow
C1E1 = Demand
Reservoir Capacity = C1E1 – C1D1
STEP-4: Biggest of the vertical ordinates represents the required reservoir
capacity.
NOTE: --- Vertical distance between successive tangents represents water
wasted over the spillway
1. The required reservoir capacity is 2100 ha-m.
2. Assuming @ A1 - the reservoir to be full ,
@ D1 =depleted to 1300 ha-m, (2100-800) ---- again full @ B1.
3. Assume @ A2 – Reservoir is to be full
@ D2 – Reservoir became empty
4. B/w B1 & A2 – Quantity of spill – 800 ha -m

11. FABRIKAM 11
DETERMINATION OF SAFE YIELD FROM A RESERVOIROF A GIVEN CAPACITY
 Determining the safe yield from a reservoir of a given storage capacity, with the help of mass inflow curve
STEP-1: --- Prepare the mass inflow curve
-- demands at various rates, varying from 0 to 5000 ha-m per year
STEP-2: --- From A1, A2, A3…. Draw tangents – maximum departure from the mass
inflow curve doesn't exceed the specified reservoir capacity.
NOTE: The E1D1, E2D2, E3D3… are all equal to the reservoir capacity.
STEP-3: --- Measure the slopes of each of these tangents.
--- slope indicates the yield which can be attained in each year from
reservoir of given capacity.
--- The slope of the flattest demand line is firm yield or safe yield.

12. FABRIKAM 12
RESERVOIR SEDIMENTATION:
The extent of erosion and silt load in the stream depends upon following factors:
1. Nature of soil of the catchment area
2. Topography of the catchment area
3. Vegetation Cover
4. Intensity of rainfall
LIFE OF A RESERVOIR:
 The ultimate destiny of a reservoir is to be filled with silt deposits.
Time passes, more and more silting takes place and live or effective storage is gradually reduced
The useful life of reservoir is terminated when capacity reduced to 20% of designed capacity.
RESERVOIR SEDIMENT CONTROL:
 Proper selection of Reservoir site
Control of sediment inflow
Proper designing and reservoir planning
Control of sediment deposit
Removal of sediment deposit
Erosion control in the catchment area.

13. FABRIKAM 13
2.DAMS:
 A dam – Hydraulic structure constructed across a river to store water on its u/s side.
 An impervious or fairly impervious barrier put across a natural stream, a reservoir is formed.
CLASSIFICATION OF DAMS:
Basis of Classification Types Common Examples
1. Classification according to
use
I. Storage Dam
II. Diversion Dam
III. Detention Dam
 Gravity dam, Earth dam, Rockfill dam. Arch dam
etc.
 Weir, Barrage
 Dike, water spreading dam, debris dam
2. Classification by hydraulic
design
I. Overflow Dam
II. Non-Overflow Dam
 Spillway
Gravity dam, earth dam, rockfill dam
3. Classification by Materials I. Rigid Dams
II. Non-Rigid Dams
 Gravity dam, arch dam, buttress dam, steel dam,
timber dam
Earth dam, rockfill dam

14. FABRIKAM 14
1. Gravity dam
2. Earth dam
3. Spillway
4. Rockfill dam
5. Weir
6. Barrage

15. FABRIKAM 15
S.No Type Definition
1 Storage Dam •To impound water to its u/s side during the periods of excess supply in the river (i.e. during rainy season) and is used
in periods of deficient supply
2 Diversion Dam • Raises water level slightly in the river and thus provides head for carrying or diverting water into ditches, canals or
other conveyance systems.
3 Detention Dam •To store water during floods and release it gradually at a safe rate, when flood recedes.
•Flood damage d/s is reduced
4 Non-Overflow
Dam
• Top of the dam is kept at higher elevation than the maximum expected high flood level.
• Water is not permitted to overtop the dam.
5 Overflow Dam • One which is designed to carry surplus discharge (including floods) over its crest.
6 Rigid Dam •Constructed of Rigid materials such as masonry, concrete, steel or timber.
7 Non-Rigid Dams •Constructed of non-rigid materials such as earth or rockfil.

16. FABRIKAM 16
S.No Type Pic Advantages Disadvantages
1 GRAVITY DAMS  Relatively more strong & stable
Use as overflow spillway crest
Constructed of any height
Specially suited for heavy downpour
Failure is not sudden
Deep sluices to retard sedimentation
or silt deposits
Cheaper in long run, more permanent
Constructed only on sound rock foundations.
 Initial cost is very high
Manufacturing and transporting mass concrete
More time to construct
 Required skill labour & mechanised plants
Under specific provisions – allow subsequent
height of gravity dam
2 ARCH DAMS Particularly adapted to gorges
Much lesser than corresponding
gravity dam
Requires less material, it is cheaper
Problems of uplift pressure is minor
 Small part of water load is
transferred to foundations
 Moderate foundations
 Skilled labour and sophisticated form work
 slow rate of construction
 Requires very strong abutments of solid rock
capable of resisting arch thrust.
Few sites are suitable for this type of dam.
3 BUTTRESS DAM  Less massive than gravity dam
Foundation pressures are less.
Water load acts normal to inclined
deck
 Stabilizes both overturning and
sliding
 Further raising of height is possible
 Concrete amount is 33 to 50% of
gravity dam
 Skilled labour requirements
 Shuttering concrete ratio are greater
Deterioration of u/s concrete surface has
serious effects
 More susceptible to willful damage.

17. FABRIKAM 17
S.No Type Pic Advantages Disadvantages
4 STEEL DAMS  Modern method of steel fabrication
 Construction completes in less
duration
Cheaper than other rigid dams
 Stresses are more determinate
 greater flexibility to resist unequal
settlement
 Not affected by frost action
Leaky joints – repair more easily
Steel dams are lighter
 Can’t absorb the shock from vibrations of
spilling water
 More constant maintenance than concrete
 anchored at foundation – difficult and
precarious
 considerable concentration of bearing stresses
5 TIMBER DAMS  Low initial cost
 Suitable for any type of foundation
 Temporary dams
 Greater speed in construction
High maintenance cost
Life is short
Suitable only for small heights
 greater seepage loss..

18. FABRIKAM 18
S.No Type Pic Advantages Disadvantages
4 EARTH &
ROCKFILL DAMS
Earth dams - any type of available
foundations
 Rockfill dam – restriction on quality
of foundation
 Constructed rapidly
 Unskilled labour and with materials
available
Generally cheaper than other types
 Subsequently raised in height
without much difficulty
 More vulnerable to damage by floods
 Fail suddenly without sufficient warning
 Can’t be used as overflow dams
 Not suitable at the locations where heavy
downpour is more common
 Requires heavy maintenance cost and
constant supervision.

19. FABRIKAM 19
SELECTION OF TYPE OF A DAM
1. Topography
2. Geology & Foundation conditions
3. Materials of Construction
4. Spillway size and Location
5. Roadway
6. Length and Height of dam
7. Life of a dam
SELECTION OF SITE OF A DAM
1. Foundations
2. Topography
3. Site for spillway
4. Materials
5. Reservoir and Catchment area
6. Communication
7. Locality

20. FABRIKAM 20

21. FABRIKAM 21
3.GRAVITY DAMS
 A gravity dam – structure so proportioned that its own weight resists the force exerted upon it.
 Most ancient gravity on record was built in Egypt more than 400 years of B.C of uncemented masonry, and in perfect
condition for many centuries.
Gravity dams can also known as Straight gravity dam, solid gravity dams and hollow gravity dams.
Gravity dams are particularly suited across gorges with very steep side slopes.
The highest dams in the world are of gravity type.
FORCES ACTING ON A GRAVITY DAM
1. Water Pressure
2. Weight of a dam
3. Uplift Pressure
4. Pressure due to Earthquake
5. Ice Pressure
6. Wave Pressure
7. Silt Pressure
8. Wind Pressure

22. FABRIKAM 22
1.WATER PRESSURE:
 Major external force acting on dam.
 U/s face is Vertical:
--- Water pressure acts horizontally
--- Intensity of pressure varies triangularly.
 U/s face is partly vertical and partly inclined
--- Resultant water pressure can be resolved into two components
i)Horizontal component – PɤH - Horizontal force
ii) Vertical component - PɤV - Weight of water supported by
inclined face
Horizontal force :
---Horizontal force acts at a height of H/3 from the base of dam.
 Vertical force: PɤV = weight of water contained by column AA’C’B
Similarly for tail water on the D/s side
---Horizontal Pressure,
--- Vertical Pressure, PɤV ‘ = weight of water contained by column FF’E’
2
2
H
PH

 
2
21
1
H
PH




23. FABRIKAM 23
2.WEIGHT OF THE DAM:
 Major resisting force.
 Analysis purposes, generally unit length of dam is considered.
 The total weight of dam acts at the C.G of its section.
3.UPLIFT PRESSURE:
The uplift pressure is defined as the upward pressure of water as it flows or seeps through the body of the dam or its
foundation.
Water has a tendency to seep through the pores and fissures of foundations.
 Seeps through the joints between the body of dam and its foundation.
 The seeping water exerts pressure and must be accounted for in stability analysis.
--- The Uplift pressure at heel, A=
--- The Uplift pressure at toe, F =
--- The Uplift pressure at gallery =
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1
H
)](
3
1
[ 11
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4.PRESSURE DUE TO EARTHQUAKE:
 The earthquake sets up primary, secondary, Raleigh and Love waves in the earth’s crust and in any direction.
 The waves impart accelerations to the foundations under the dam and causes its movement.
 In order to avoid rupture the dam must move also move along with the accelerations.
 This accelerations introduces an inertia force in the body of the dam .
 Setup stresses initially in lower layers and gradually in the whole body of the dam.

24. FABRIKAM 24
5.ICE PRESSURE:
 More important for dams constructed in cold countries or at higher elevations.
 Water surface of the reservoir is subjected to expansion and contraction due to temperature variations.
 The coefficient of thermal expansion of ice being 5 times more than that of concrete.
 The dam face has to resist the force due to expansion of ice.
IS 6512-1984 recommends that it may be provided for at the rate of 250kN/m2 to the face of dam.
6.WAVE PRESSURE:
 Wave are generated on the reservoir surface because of wind blowing over it.
 Wave pressure depends on the height of the waves developed.
 Wave height may be calculated from the following formula given by D.A.Molitor.
The pressure intensity due to waves is given by
Where: h=height of waves in m, between trough and crest
V = Wind velocity in km/hr
F = Fetch or straight length of water expanse in km
ww whP 4.2
FVh
FFVh
w
w
.0322.0
271.0763.0.0322.0 4
1

 for F<32km
for F>32km

25. FABRIKAM 25
7.SILT PRESSURE:
 The silt load gets deposited to an appreciable extent when dam is constructed.
 The dam is, therefore, subjected to silt pressure in addition to the water pressure.
 The silt pressure is given by
Where: ɤs
1 = submerged unit weight of silt
ϕ = angle of internal friction
hs = height to which the silt is deposited
--- U/s face is inclines – vertical weight of silt supported on the slope also acts as vertical force.



sin1
sin1
2
1 21


 sss hP
8.WIND PRESSURE:
 Minor force and need hardly to be taken into account for the design dams.
 Considered only on that portion of the superstructure.
 Normally, it is taken as 1 to 1.5kN/m2 for the area exposed to the wind pressure.

26. FABRIKAM 26
3.1 COMBINATION OF LOADING FOR DESIGN:
a) U.S.B.R Recommendations:
--- All the forces acting on a dam do not act simultaneously
--- Various combinations of loads which may act simultaneously.
--- The U.S.B.R specifies the normal and extreme load combinations as below.
1.Normal Load Combination:
i) Normal water surface elevation Ice pressure Silt pressure Normal uplift
ii) Normal water surface elevation Earthquake force Silt pressure Norma Uplift
iii) Maximum water surface elevation Silt Pressure Normal uplift
2. Extreme Load combination:
i) Maximum water
surface elevation
Silt pressure Extreme uplift with no drain in operation to
release the uplift

27. FABRIKAM 27
b) Indian Standard Recommendations (IS 6512-1984):
 Gravity dam design shall be based on the most adverse load conditions A,B,C,D,E,F & G.
Depends upon scope and details of the various project components, site conditions and construction programme.
S.No LOAD COMBINATION LOADS
1 A (Construction condition) Dam completed but no water in reservoir and no tailwater
2 B (Normal operating condition) Full Reservoir Level
(top of crest gate)
Normal dry weather
tail water
Normal Uplift Ice & Silt
(if applicable)
3 C (Flood discharge condition) Maximum Flood Level
(All gate open)
Tail water at flood
elevation
Normal Uplift Ice & Silt
(if applicable)
4 D A + Earthquake
5 E B + Earthquake but no ice
6 F C + Extreme uplift (drainage inoperative)
7 G E + Extreme uplift (drainage inoperative)

28. FABRIKAM 28
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