DAMS AND RESERVOIR DESIGN

(10B71CE412)
CREDIT 3
• COURSE CODE: 10B71CE412
• BOOK: DESIGN OF HYDRAULIC STRUCTURES
BY DR. S K GARG
• CODES:
• IS 6512: Criteria for design of solid gravity
dams
 COURSE DETAIL
• 1.Planning of project, Purpose of
development, Project study, Ecological and
environmental considerations.
• 2. Flood studies, Economic considerations,
Selection of types of dam.
• 3. Dams Classification, Physical factor
governing selection of types of dams, legal,
economic, aesthetic considerations.
• 4. Concrete gravity dam:
• Introduction, Origin and development, Forces
acting on dam, Requirements for stability,
Design of gravity dam
• 5. Earthfill dam:
• Origin, Selection of type, Design principles,
Foundation design, Embankments,
Embankment details
• 6. Rockfill dam :
• Origin and usage, Definition and types,
Foundation design, Embankment design,
Membrane design
Elements of Dam Engineering
• Introduction
• A dam is an impervious barrier constructed across a river
or stream to store water on its upstream side. The side of
barrier on which water is stored is called upstream side
and the other side of the barrier is called downstream
side.
 Purpose of Dam
• Dam is generally most suitable in hilly areas
where deep valleys are available which gives a
deep storage of water. The stored water on its
upstream side serves various purpose such as:
• Flood Mitigation
• Irrigation
• Water Supply
• Navigation
• Fishery and wild life Preservation
• Hydro-electric Power Generation
• Recreation
 Classification of Dams
• Classification as per function and use
Storage dam
• This is the most common type of dam
normally constructed to store excess flood
water which can be utilized later when
demand exceeds the flow in river. The Storage
dams may be constructed for various purposes
such as irrigation, water supply, hydro-power
generation etc. they may be made of concrete,
stone or earth or rock fill etc.
Storage Dam
• Detention Dams
• This type of dams are mainly constructed to
control flood. This type of dam stores water
temporarily and releases it gradually at a safe
rate when the flood recedes. Detention dam
provides safeguard against possible damage
due to flood on the downstream side of it.
Sometimes a detention dam may also be used
as storage dam.
Detention Dams
• Diversion Dam
• The purpose of diversion dam is necessarily
different. It is constructed to divert the river
water into canal, conduit etc. For this purpose,
mostly a weir or low level dam is constructed
across the river to raise the water level which can
be diverted as per the needs. This type of dam
may be used for water supply, irrigation or some
other purposes.
Diversion Dam
Classification as per hydraulic
design
• Overflow Dam: An overflow dam is built to
allow the overflow of surplus discharge above the
top of it. They are generally built of masonry or
concrete and they are gravity type of dam.
Usually dams are not designed as overflow for
their entire length. Only few meters of its length
is kept as overflow section.
Overflow Dam
 Classification of Dams
• Non-Overflow Dam:
• In this type of dam, water is not allowed to overtop the
dam. The top of the dam is fixed at a higher elevation
than the expected maximum flood level. Since water is
not allowed to overtop, it can be constructed of large
variety of materials such as earth, rock fill, masonry,
concrete etc.
Non-Overflow Dam
 Classification as per Structural
Design
• Gravity Dam:
• It is a solid concrete or masonry dam that all
external forces are resisted by its own weight
or gravity forces.
• Arch Dam:
• An arch dam is curved masonry or concrete
dam which has convex portion facing
upstream. It resists major portion of water
pressure by arch action.
• The self weight of the dam is comparatively
lesser than gravity dam.
Gravity Dam & Arch Dam
• Buttress Dam:
• It consists of sloping membrane or deck on
upstream which is supported by number of
buttress or piers. These buttress are
constructed of reinforcements concrete
and supported by struts or bracings.
Buttress Dam
 Buttress Dam
Shapes of Buttress Dam

Typical Sections of
Buttress Dams
 Buttress Dam

Multiple-Arch Dam
(Buttress Dam)
 Classification as per Structural
Design
• Embankment Dams
• They are constructed of locally available soils, gravels
and sands, which resists all external forces by it shear
strength. These types of dams are more suitable up to
moderate height. They are generally trapezoidal in
section. Earth dam, earth and rock fill dam are the
example of this type of dam.
Embankment Dams
Miscellaneous Types of Dam
Timber Crib Dam

A timber crib dam in

Michigan.
Miscellaneous Types of Dam
Steel Dam

Red Ridge steel dam

in Michigan.
Miscellaneous Types of Dam
Stone Masonry Dam

Stone Masonry dam.

Miscellaneous Types of Dam
Coffer Dam

A coffer dam during the

construction of locks at the
Mongomery Point Lock and
Dam.
Classification as per material of
construction
• Rigid Dams
• These dams are built of rigid materials such as
masonry, concrete, steel or timber. In earlier
times dams were mostly built of stone
masonry which have been replaced
now-a-days by concrete.
• Non-Rigid Dams
• These dams are built of non-rigid materials
such as earth, rock fill etc. Earth Dam, Rock
fill Dam etc are the examples of this type.
Rigid Dams & Non-Rigid Dams
 Embankment Dams
• They are the most ancient type of dams that can be build
by naturally available materials with minimum of
processing. These dams are not suited for sites where
good foundations is not available at a reasonable depth
for concrete or masonry dam to construct.
• Earth Dam:
• Earth dams are made of locally available soils, sands and
gravel with trapezoidal in section. They are economical
and suitable for almost all type of available foundation.
Factors to be considered for dam construction:

1. Topography of division i.e. deep valley and low

submergence area is preferred
2. Base of foundation materials should be impervious.
3. Regions should be free from earthquake activities.
4. Materials should be easily available.
5. Rivers should be perrenial in nature
Reservoir
 RESERVOIR
• A reservoir is a large, artificial lake created by
constructing a dam across a river.
• In water resources engineering it is used in a
restricted sense for a comparatively large body
of water stored on the upstream of a dam
constructed for this purpose.
• Thus a dam and a reservoir exist together.
 Types of reservoir

• 1. Single purpose reservoir: serves only single

purpose

• 2. Multipurpose reservoir: serves more than

one purposes
 Classification of reservoir

• According to the purpose served reservoir is

broadly classified into five types
• 1. storage reservoir
• 2. flood control reservoir
• 3. multipurpose reservoir
• 4. distribution reservoir
• 5. balancing reservoir
 Storage reservoir
• i) Also known as conservation reservoir as it is used
to conserve water.
• ii) Storage reservoirs are constructed to store the
water in the rainy season and to release it later when
the river flow is low.
• iii)Storage reservoirs in India are usually
constructed for irrigation, the municipal water
supply and hydropower.
 Flood control reservoir
• i) A flood control reservoir is constructed for the
purpose of flood control
• ii) It protects the areas lying on its downstream
side from the damages due to flood.
• iii) A flood control reservoir is designed to moderate
the flood and not to conserve water
• Iv) they are of two types
• a) detention reservoir
• b) retarding reservoir
• Detention reservoirs:
• A detention reservoir stores excess water during
floods and releases it after the flood
• The effect of reservoir on a flood is to reduce the peak
discharge by absorbing a volume of flood water when
the flood is rising, and releasing the same later
gradually when the flood is receding.
• Advantages:
• a) The detention reservoirs provide more flexibility of
operation and better control of outflow than
retarding reservoirs
• b) The discharge from various detention
reservoirs on different tributaries of a river can be
adjusted according to the carrying capacity of the
d/s channel.
• Disadvantages:
• a) The detention reservoirs are more expensive than
the retarding reservoirs because of high initial cost
and maintenance cost of gates and the lifting
machinery.
Retarding reservoir:
A retarding reservoir is provided with spillways and
sluiceways which are ungated. The maximum
combined discharging capacity of all spillways and
sluiceways is limited to the safe-carrying capacity
of the channel downstream.
The retarding reservoir stores a portion of the flood
when the flood is rising and releases it later when
the flood is receding.
• Advantages:
• A) The retarding reservoirs are relatively less
expensive than detention reservoirs.
• B) As the outflow is automatic, there is no possibility
of a disaster due to human error or negligence.
• Disadvantages:
• The retarding reservoirs do not provide any flexibility
of operation as the outflow is automatic.
 Multipurpose reservoir
• A multipurpose reservoir is designed and
constructed to serve two or more purposes. In
India, most of the reservoirs are designed as
multipurpose reservoirs to store water for irrigation
and hydropower, and also to effect flood control.
 Distribution reservoir
• i) A distribution reservoir is a small storage reservoir
to tide over the peak demand of water for
municipal water supply or irrigation.
• ii) The distribution reservoir is helpful in permitting
the pumps to work at a uniform rate. It stores water
during the period of lean demand and supplies the
same during the period of high demand
• Water is pumped from a water source at a uniform
rate throughout the day for 24 hours but the
demand varies from time to time.
• When the demand of water is less than the pumping
rate, the water is stored in the distribution reservoir.
On the other hand, when the demand of water is
more than the pumping rate, the distribution
reservoir is used for supplying water at rates
greater than the pumping rate. Distribution
reservoirs are rarely used for the supply of water for
irrigation. These are mainly
used for municipal water supply.
 Balancing reservoir
• A balancing reservoir is a small reservoir
constructed d/s of the main reservoir for
holding water released from the main
reservoir.
 Storage capacity of reservoir
• Most important characteristics of a reservoir is its
storage capacity
• The available storage capacity of a reservoir
depends upon the topography of the site and the
height of dam.
• To determine the available storage capacity of a
reservoir upto a certain level of water,
engineering surveys are usually conducted.
• In addition to finding out the capacity of a reservoir,
the contour map of the reservoir can also be
used to determine the land and property which
would be submerged when the reservoir is filled up
to various elevations.
 Area elevation curve

• From the contour plan, the water spread area of the

reservoir at any elevation is determined by
measuring the area enclosed by the corresponding
contour. Generally, a planimeter is used for
measuring the area. An elevation-area curve is
then drawn between the surface area as
abscissa and the elevation as ordinate.
Elevation-Capacity-Area Curve
 Elevation capacity curve
• The storage capacity of the reservoir at any
elevation is determined from the water spread
area at various elevations. An
elevation-storage volume is plotted between the
storage volume as abscissa and the elevation
as ordinate.
• The following formulae are commonly used to
determine the storage capacity (i.e. storage
volumes)
• Trapezoidal formula:
• According to the trapezoidal formula, the storage
volume between two successive contours of areas
A1 and A2 is given by
• ∆V=(A1+A2)h/2
• where h is the contour interval. Therefore the total
storage volume V is
• V=h/2(A1+2A2+2A3+2A4+-----------------2An-1+An)
• n= total no of areas
• Cone formula:
• The storage volume between two successive
contours of areas A and A is given by
• V=h/3(A1+A2+√(A1A2)
• Prismoidal formula:
• V=h/6(A1+4A2+A3)
• Integration method:
• A general equation of the area elevation curve is
assumed as
• A=α+βh+γh2+..................ηhn-1 where
• A= area at any elevation h and
• α, β,γ,are constants
• Let y= height of water surface in the reservoir
above assumed datum , over which the
storage capacity is to be worked out
• Ay =represents symbolically the area of the
contour at this height then
• Ay=α+βy+γy2+..................ηyn-1
• The storage capacity Sy is given by
intergrating the above equation
• S y = ʃ0 y A y
• Sy = ʃ0y ( α+βy+γy2+..................ηyn-1)

• Sy = ( αy+βy2+γy3+..................ηyn) + K
• K= constant of integration
 Important definitions
• Full Reservoir Level (FRL): It is the level
corresponding to the storage which includes both
inactive and active storages and also the flood
storage, if provided for. In fact, this is the highest
reservoir level that can be maintained without
spillway discharge or without passing water
downstream through sluice ways.
• Minimum Drawdown Level (MDDL): It is the level
below which the reservoir will not be drawn down so
as to maintain a minimum head required in power
projects.
• Dead Storage Level (DSL): Below the level, there are
no outlets to drain the water in the reservoir by
gravity.
Maximum Water Level (MWL): This is the water level
that is ever likely to be attained during the passage
of the design flood. It depends upon the specified
initial reservoir level and the spillway gate operation
rule. This level is also called sometimes as the
Highest Reservoir Level or the Highest Flood Level.
• Live storage: This is the storage available for the
intended purpose between Full Supply Level and the
Invert Level of the lowest discharge outlet. The Full
Supply Level is normally that level above which over
spill to waste would take place. The minimum
operating level must be sufficiently above the lowest
discharge outlet to avoid vortex formation and air
entrainment. This may also be termed as the volume
of water actually available at any time between the
Dead Storage Level and the lower of the actual water
level and Full Reservoir Level.
• Dead storage: It is the total storage below the invert
level of the lowest discharge outlet from the
reservoir. It may be available to contain
sedimentation, provided the sediment does not
adversely affect the lowest discharge.
•.
• Freeboard: It is the margin kept for safety between
the level at which the dam would be overtopped and
the maximum still water level. This is required to
allow for settlement of the dam, for wave run up
above still water level and for unforeseen rises in
water level, because of surges resulting from
landslides into the reservoir from the peripheral hills,
earthquakes or unforeseen floods or operational
deficiencies