This document provides information about dams and reservoirs. It begins with definitions of dams and describes their basic components and structure. It then classifies different types of dams such as gravity dams, arch dams, buttress dams, and embankment dams. Details are given about specific dams like the Three Gorges Dam, Hoover Dam, and dams in Thailand. The document discusses the advantages and disadvantages of dams. It also covers dam failure case studies and provides statistics on dams. In the end, it discusses benefit-cost analysis of dams and their impact.

1. Chapter 7
Dams and reservoirs

2. Dams
Definition of Dams
Advantages and Disadvantages of Dams
Classification of Dams
Types of Dams

4. 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.

5. Dams

6. Dams

7. Structure of Dam
Toe
Heel
Sluiceway
Spillway
Freeboard
Gallery

8. 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.

9. 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.

10. 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

11. Three Gorges Dam

12. Three Gorges Dam

13. 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.

14. Three Gorges Dam
Sluice Gates

15. Three Gorges Dam
Shipping Locks
Shipping Locks

16. Hoover Dam

17. 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 18th highest in the world. It generates more
than four billion kilowatt-hours a year, that's enough to
serve 1.3 million people!

18. 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

19. 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

20. 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

21. 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

22. 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

23. Classification of Dams
Storage Dam
Detention Dam
Diversion Dam
Coffer Dam
Debris Dam
Classification based on function

24. Typical Storage Dam
Srinagarind Dam
Vajiralongkorn Dam

25. Typical Storage Dam
Maeklong Dam
Tha Thung Na Dam

26. 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

27. Classification of Dams
Classification based on structural behavior
Gravity Dam
Arch Dam
Buttress Dam
Embankment Dam

28. 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.

29. Gravity Dam
Cross Section Plain View
Material of Construction:
Concrete, Rubber Masonry

30. 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.

31. Arch Dam
Cross Section Plain View
Material of Construction:
Concrete

32. 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.

33. Buttress Dam
Cross Section Plain View
Material of Construction:
Concrete, Timber, Steel

34. Embankment Dam
Embankment dams are massive
dams made of earth or rock.
They rely on their weight to
resist the flow of water.

35. Embankment Dam
Cross Section Plain View
Material of Construction:
Earth, Rock

36. 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

37. 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

38. 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

39. Gravity Dam

40. Gravity Dam
Forces on Gravity Dam
Gravity or weight of dam
Hydrostatic force
Uplift force
Ice force
Earthquake forces

41. Gravity Dam
Forces on Gravity Dam
Free-body diagram of cross
section of a gravity dam

42. 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

43. Gravity Dam
Forces on Gravity Dam
Hydrostatic Force
xwh AhH 
I. Horizontal hydrostatic force
II. Vertical hydrostatic force
wwvH 
Hydrostatic Force

44. Gravity Dam
Forces on Gravity Dam
Uplift Force
Uplift Force
Uplift Force
2
t)hh(
U 21w



45. Gravity Dam
Forces on Gravity Dam
Ice Force
Ice Force
Ice Force

46. Gravity Dam
Forces on Gravity Dam
Earthquake Force
)g0.1tog5.0(mEd 
2
ww hk555.0E 
Earthquake Force

47. Arch Dam

48. 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

49. Arch Dam
Section

50. Arch Dam
Section

51. Arch Dam
Reaction Forces on Arch Dam
Arch Dam with an Overflow
Spillway
allow
hr
t






2
)2/(Sin2
B
k

52. Arch Dam
Example Profiles of Existing Dam

53. Embankment Dam
Earth-Fill Embankment Dam
A earth-fill dam in
Australia.

54. Embankment Dam
Rock-Fill Embankment Dam

55. Embankment Dam
Earth Dams:
are the most simple and economic (oldest dams)
Types:
1.Homogeneous embankment type
2.Zoned embankment type
3.Diaphragm type

56. Embankment Dam
Homogeneous Embankment Dam

57. Embankment Dam
Zone-Based Embankment Dam

58. Embankment Dam
Diaphragm Earth Dam

59. Embankment Dam
Rock fill Dam with RC facing

60. Embankment Dam
Slip Failure of Earth Dam

61. Buttress Dam

62. 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.

63. Buttress Dam
Typical Sections of
Buttress Dams
Shapes of Buttress Dam

64. Buttress Dam
Multiple-Arch Dam
(Buttress Dam)

65. Miscellaneous Types of Dam
Timber Crib Dam
A timber crib dam in
Michigan.

66. Miscellaneous Types of Dam
Steel Dam
Red Ridge steel
dam in Michigan.

67. Miscellaneous Types of Dam
Stone Masonry Dam
Stone Masonry dam.

68. A coffer dam during the
construction of locks at
the Mongomery Point
Lock and Dam.
Miscellaneous Types of Dam
Coffer Dam

69. 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.

70. Types of Dam
Earthfill 58%
Timber Crib 2%
Other 16%
Rockfill 3%
Concrete 11%
Stone Masonry 10%

71. 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

72. 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

73. 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

75. 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

76. Figure 7.1 Primary purposes of dams in the United States.

77. Figure 7.2 Age of dams in the United States.

78. Figure 7.3 Principal parts of a dam.

79. 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

80. 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.

81. Figure 7.5 Classification of principle storage zones in a cross section of a
multipurpose reservoir.

83. 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.

84. Figure 7.7 The dramatic concrete arch design of Hoover Dam securely
holds the impounded waters of Lake Mead.

85. Figure 7.9 Grand Coulee Dam is a gravity concrete dam.

86. Figure 7.10 Hydroelectric turbines at Grand Coulee Dam.

87. Workers inspect a hydroelectric turbine runner blade at Fort Loudoun Dam,
near Lenoir City, Tennessee.

88. 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

89. 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

90. 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.

91. 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

92. 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.

93. 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”).

94. 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.

95. 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.

96. Figure 7.14 Main-river dams form a staircase of reservoirs that stretch the
entire length of the Tennessee River.

100. Figure 7.15 Chickamauga Lock and Dam, located on the Tennessee River
near Chattanooga, Tennessee, is a major lock in the TVA navigation system.

101. Rhine - Danube Canal

102. Main (Rhine) - Danube Canal: Elevations on the section from
Würzburg to Passau going through 53 stepwise locks

103. Interesting Websites
 Panama Canal Video
 Canal Video

104. By Alex Otto
Buford Dam
Allatoona
Dam
Nantahala Dam

107. 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.

108. Atlanta, Georgia
“the fastest-spreading human
settlement in history"
Time Magazine
March 22, 1999

109. Lake Lanier
Carter’s Lake
Lake Allatoona
Atlanta

111. 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

112. Lake Purposes
1. Flood control
2. Navigation
3. Hydroelectric power generation
4. Water supply
5. Water quality
6. Recreation
7. Fish and wildlife management

117. Lake Water Quality Issues
• Lake Sedimentation
– Reduction in storage capacity
– Impairment of
• navigation
• recreation
• aquatic habitats
• Regulatory Controls
– Stormwater regulations
– Erosion and sediment laws

118. 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

122. Lake Allatoona Tributaries

123. 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

126. 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

128. 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)

129. 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).

130. Reservoirs

131. 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).

132. 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)

133. 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).

134. 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.

135. 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.

136. Reservoirs

137. 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.

138. 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.

139. 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)

140. 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.

141. 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..