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What is meant by a Reservoir?
A reservoir is natural or artificial lake or storage pond where water is
stored as a source of water supply.

Reservoir
Usually, a barrier is constructed across the stream in the form of a dam, water
gets stored on the upstream side of the barrier forming a pool of water.
In the rainy season, water gets stored and saves the downstream are from being
overflowed.
In the dry season, the stored water is supplied.

Classification (Depending upon the
purpose served)
❑Storage or Conservation reservoirs
❑Flood Control reservoirs
❑Multipurpose reservoirs
❑Distribution reservoirs

Storage or Conservation reservoirs
➢Definition:
A storage or a conservation reservoir can retain excess supplies
during periods of peak flows and can release them gradually during low
flows and when the need arises.
➢Purpose:
❑Ensure full water supply throughout the year.
❑In addition to conserving water for later use, the storage of flood
waters may also reduce flood damage below the reservoir

Example of Storage or Conservation reservoirs

Flood Control reservoirs
A flood control reservoir , generally called a flood-mitigation reservoir , stores a
portions of the flood flows in such a way as to minimize the flood peaks at the areas
to be protected downstream.
The entire inflow entering the reservoir is discharged till the out flow reaches the safe
capacity of the channel downstream.
The inflow in excess of this rate is stored in the reservoir, which is then gradually
released , so as to recover the storage capacity for the next flood
A flood control reservoir differs from a conservation reservoir only in its need for a
large sluiceway capacity to permit rapid drawdown before or after a flood.

Example: Flood Control reservoirs

Types: Flood Control reservoirs
There are two basic types of flood mitigation reservoirs;
▪Storage reservoir: A reservoir having gates and valves installation at its spillway and at its sluice
outlets is known as storage reservoir.
▪Retarding reservoir: A reservoir with uncontrolled and ungated outlets is known as a retarding
basin or retarding reservoirs.
❑Purpose: The sole purpose of Flood Control reservoirs are to CONTROL FLOODS.

Multipurpose reservoirs
A reservoir planned and constructed to serve various purpose together is called a multipurpose
reservoir.
Purpose: Multipurpose reservoirs may be managed to balance some or all of the following activities:
▪Flood control
▪Soil erosion
▪Environmental management
▪Hydroelectric power generation
▪ Navigation
▪Recreation
▪Irrigation

Distribution reservoir
A distribution reservoir connected with the conduits of a primary water
supply; used to supply water to consumers according to fluctuations in
demand over short time periods and serves for local storage in case of
emergency.
Such a reservoir can be filled by pumping water at a certain rate and can
be used to supply water even at rate higher than inflow rate during
period of maximum demands called critical periods of demand.
Purpose:
➢Works as vast storage tank

Different storage zones of a reservoir
01. Normal Pool Level or
Maximum Conservation Level
02. Minimum Pool Level
03. Useful & Dead Storage
04. Maximum Pool Level or
Full Reservoir Level
05. Surcharge Storage
06. Bank Storage
07. Valley Storage

Normal Pool Level or Maximum Conservation Level-
-It is the maximum elevation to which the reservoir water surface will rise during normal operating
condition.
-Most of the cases, it is equivalent to the elevation of the spillway crest or the top of the spillway gates.

Minimum Pool Level-
-The lowest water surface elevation, which has to be kept under normal operating
condition in a reservoir, is called the minimum pool level.

Useful & Dead Storage-
The volume of water stored in a reservoir between the minimum pool and normal pool
levels is called the Useful Storage.
-Water stored in the reservoir below the minimum pool level is known as the Dead
Storage.

Maximum Pool Level or Full Reservoir Level-
-The maximum level to which the water rises during the worst design flood is known as the
Maximum Pool Level.

Surcharge Storage-
-The volume of water stored between the normal pool level and the maximum pool level is called
surcharge storage.

Bank Storage-
When the reservoir is filled up, certain amount of water seeps into the permeable
reservoir banks.
This water comes out as soon as the reservoir gets depleted. This volume of water is
known as the Bank Storage.

Valley Storage-
-Before a dam is constructed, certain variable amount of water is stored in the stream
channel, called Valley Storage.

Dam reservoir
SELECTION OF A SUITABLE SITE

Selection Of A Suitable Site For A Dam
Reservoir
Selection of a proper dam site is important. Because it would be helpful to
❑Construct a strong dam.
❑Reduce risk due to natural disaster .
❑Store maximum amount of water.

Reservoir
Factors that should be kept in mind while selecting a suitable site for dam reservoir:
1. Good topographical location:
❑ dam can be constructed along the path of river.
❑ at the location where there is narrowing of the river.
❑ basin above the dam should be properly calculated to store maximum amount of water.
❑ wide and flat valley will be perfect for a dam site.

Reservoir
2. Right geological structure:
❑ Rock structure on which dam will be constructed should be strong enough to sustain all visible
and invisible forces acting on it such as
⇒weight of the dam. ⇒water stored in it.
❑The region of site will be such that there should be least occurrence of earthquake.
❑There should be minimum leakage of the reservoir bank.
❑It should avoid seepage of water and should be waterproof.
❑General bed level at dam site should be higher than that of the river basin.
❑Silting should be avoided as far as possible. .

Reservoir
3. Sufficient Water:
❑The reservoir site should have adequate capacity
❑The flow of water should be sufficient enough to fill the dam.
❑Minimum water losses of the catchment area through absorption and percolation.
❑Water flow of river should be able to accommodate the loss due to evaporation.
❑Soluble material must not be present at site which cause change in odor, taste and color of
water.

Reservoir
4. Accessibility:
❑Site should be easily accessible.
❑Land and property submerged by the proposed land should be as low as
possible.
❑It should be connected to important town and cities.
❑Site should provide enough space for labor colonies.
❑Healthy environment should be available near the site.
❑The land should be cheap and there should be less population.

Reservoir
5. Quick Reconnaissance Survey:
Survey should be carried out to check if dam can be built both from technical and economic
points of view.

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about reservoir details Lecture 12,13.pdf

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about reservoir details Lecture 12,13.pdf