This document discusses reservoirs and dams. It covers why water is stored in reservoirs, such as to raise head for hydroelectric power and smooth flows for irrigation. It describes methods for determining reservoir size, dam design considerations like forces and types of dams, and technical issues like silting and failure modes. The social impacts of dams are also addressed, such as displacement of local populations and changes to downstream economies. Examples of good and bad dam projects are provided for analysis of who benefits from and makes decisions about dams.

1. 4/20/2016 1
•RESERVOIRS

2. RESERVOIR
• Why store?
– Raise head, smooth flow, conflicts and trade offs
• Determination of reservoir volume/height
– Mass curve approach, simulation approach
• Dam design
– Forces on a dam, Types of dam, Seepage, Spillways
• Technical problems with dams
– Silting, failure
• Social impact of dams

3. Reservoir
On the web (not necessarily on dams.org)
– Find an example of a “bad” dam project
– Find an example of a “good” dam project
We will be discussing
– Who benefits and who loses when a dam is built?
– Who makes the decisions?
– What makes a dam good or bad?

4. Reservoir: Why store ?
• Raise head
– Hydro power
– Allow greater flow to irrigation
• Smooth flow
– Reliable Hydro power
– Off season irrigation
– Flood control
– Domestic Water supply
• Other reasons
– Fishing
– Leisure

5. Reservoirs; Why store: Conflicts
• Maximising head vs. Maximising storage
–If the storage is used, the head is reduced
• Water use vs. flood control
–Water use prefers a full reservoir (for use later)
–Flood control the reservoir should be empty (so floodwater
can fill it)

6. THE ANATOMY OF A RESERVOIR

7. RESERVOIRS: HOW MUCH TO STORE
3 2
( ) ( )h f V f A 

8. RESERVOIRS: HOW MUCH TO STORE
n in outQ Q Q 
in stream precipitationQ Q Q 
......out used spill evaporation leakage seapageQ Q Q Q Q Q     
precipitationQ AP

9. Reservoirs: how much to store: mass curve

10. RESERVOIRS: DAM DESIGN: FORCES
ON A DAM
2
2
h
F


2
h
F W t 
W
 is the specific weight of water

11. Reservoirs: Dam design: Types of Dam
Type Materials Typical cross section Plan view
Gravity Concrete, rubble
masonry
Arch Concrete
Buttress Concrete,
ferrocement,
timber, steel
Embankment Earth, rock

12. Reservoirs Dam design: Seepage: Flow nets
 Lines of constant potential, and constant flow
– Perpendicular
– Should form a series of squares

13. reservoirs: seepage: typical flow nets

14. Reservoirs: Typical flow nets: Earth dams

15. reservoirs: zoned earth dams: piping

16. Toe drain
Blanket drain
Chimney and blanket
drain
Impermeable core and
blanket
Reservoirs: Seepage: Earth dams

17. Reservoirs: Seepage: Zoned earth dams

18. Seepage: Zoned earth dams
Ramganga project

19. Reservoirs: Zoned earth dams
Kishan rockfill dam

20. Reservoirs: Spillways: Types
Side channel
Chute
Shaft
Syphon
Ogee

21. Reservoirs: Spillways: Side channel

22. Reservoirs: Spillways: Chute spillways

23. Reservoirs: Spillways: Shaft spillways

24. Reservoirs: Spillways: Ogee spillways

25. Reservoirs: Spillways: Ogee spillways

26. Reservoirs: Spillways: Hydraulic jump

27. Reservoirs: Spillways: Hydraulic jump

28. V = Stream velocity (m s-1)
R = Hydraulic radius
S = Slope
n =Manning roughness
Spillways: Hydraulic jump Manning's equation
2 3 1 2
R S
V
n


29. p = pressure (Pa)
r = Density (kg m-3)
g =Gravity (m s-2)
v =velocity (m s-1)
z = elevation (m)
Spillways: Hydraulic jump Bernoulli's equation
2
constant
2
p v
z
g gr
  

30. Spillways: Hydraulic jump: Sums: Critical depth
E
h
2
2
v
E h
g
 
crith
minE
Tranquil
Rapid
E = Specific Energy (m)
h = head (m)
g = Gravity (m s-2)
v = velocity (m s-1)

31. Spillways: Hydraulic jump: Sums: Head loss
 
2
2
2
2
L d
v
h H h h
g
 
    
 
Hd
h1
h2
2
2
2
v
g
2
1
2
v
g
h
hL

32. Hd
h1
h2
2
2
2
v
g
2
1
2
v
g
h
hL
Spillways: Hydraulic jump: Height of jump
1 2
2 2
1 1 1 1
2
2
2 4
h h v h
h
g
 
   
 

33. Spillways: Hydraulic jump: Location of the
hydraulic jump

34. Spillways: Encouraging a jump

35. Technical problems with dams: Silting

36. Technical problems with dams: Silting

37. Technical problems with dams: Failure modes
 Overtopping – inadequate spillways (1/3)
 Foundation failure (1/3)
– Excess seepage through foundation
– Piping – insufficient drainage/grading
 Wave action
 Erosion of downstream face
 Slump
 Bank stability
 Seismic activity
 Degradation – lack of maintenance
 Material supplies sub specification

38. Reservoirs: Technical problems with dams:
Failure:

39. Technical problems with dams: Failure:

40. TECHNICAL PROBLEMS WITH DAMS:
FAILURE: PIPING DAM
Dec 22 3:00 pm Dec 23 7:00 am
Dec 23 9:30 am Dec 23 3:30 pm

41. TECHNICAL PROBLEMS WITH DAMS:
FAILURE: DAM SLIDE

42. TECHNICAL PROBLEMS WITH DAMS:
FAILURE: DAM EARTHQUAKE DAMAGE

43. Technical problems with dams: Failure: dam
bank slip

44. Reservoirs: Social impact of dams
 Climate change
 Fertility of downstream banks
 Displacement
 Changes in local economy
 Deforestation
 Possibility of financial collapse
 Possibility of failure

45. Reservoirs: Summary
• Storage needs may conflict
• Mass balance and the mass curve are useful ways to size reservoirs
• Seepage is an issue with earth dams but can be dealt with by zoning
• There are several varieties of spillway, including side channel, chute, shaft, syphon,
and ogee
• Hydraulic jump is a useful technique to reduce spillwater levels
• Dams can fail by silting, overtopping, foundation failure wave action, erosion and lack
of maintenance
• Dams can have social and environmental impacts