Reservior planning

RESERVOIR PLANNING
Prof.M.B CHOUGULE DKTE’S YCP Ichalkaranji

What is a Reservoir-
• It is an area developed by water body due to
construction of dam.
• TYPE:
• Storage Reservoirs.
• Flood Control Reservoirs.
• Retarding Reservoirs.
• Detention Reservoirs.
• Distribution Reservoirs.
• Multipurpose Reservoirs.
• Balancing Reservoirs.

Reservoir Planning
For the best and efficient design of
Irrigation project the investigation is must
so it is carried out in three stages
Surveys for Irrigation project :
1. Reconnaissance Survey
2. Preliminary Survey
3. Detailed Survey / Construction Survey

Reconnaissance Survey :-
In reconnaissance survey the find out number of
project sites where storage of water can be done.
In this survey inspection of region is done and
data collected physically without using precise
survey instrument.
In reconnaissance survey following information is
collected.
The size of catchment area, vegetation in the
catchment area, soil type, slopes, existing ponds,
Command area, Dam site, rainfall, river gauge data,
population supporting the scheme, history of other
nearby scheme.

Preliminary Survey :-
This survey is carried out by experienced
supervision with modern instruments it may
take few month to one or two year depending
on size of project. It is carried out in dry season
with careful planning.
Preliminary survey divided into parts
1. Engineering survey
2. Hydrological survey
3. Geological survey

1. Engineering Survey :-
In this type of survey various types of surveys are carried out
such as Plane table survey, Traverse survey, aerial and
photographic survey etc. the aim of this survey is to
prepare a contoured map of the site.
Contour map gives the following information.
1. Water spread. 6. Area elevation curve
2. Capacity of the reservoir. 7.Storage elevation curve
3. Suitable dam site.
4. Site for waste weir and outlets.
5. Arrangement of lines of communication
6. Map of the area to indicate the land property to be
surveyed

2. Hydrological Survey :-
Whenever any storage work is constructed, it is very
essential to ascertain that required amount of
water will be available at the site for storage.
Therefore hydrological survey is of catchment area
is done to collect the data for determining
availability of water for the reservoir.
It is necessary for
1. To study runoff pattern and to estimate yield.
2. To determine maximum discharge.
3. Determination of hydrograph of worst flood to
determine spillway capacity and its capacity.

3. Geological/Exploration Survey :-
It is done in two stages
i) Survey inspection and surface mapping.
ii) Sub surface exploration.
Sub surface exploration gives information
1. Water tightness of the basin
2. Stability of foundation for the dam.
3. Faulty structure in the basin.
4. Type and depth of overburden.
5. Ground water condition of region.
6. Location of quarry sites for construction materials.

Detailed Survey :-
After the preliminary survey only a few sites are
selected for further consideration. In this type
of survey office studies and estimates for each
of the selected site is prepared.
Detailed designs of various storage structures are
prepared in the drawing office and the cost is
worked out. So the relative merits and demerits
of two or more sites are take into consideration
so as to adopt one site finally.

.
• Data collected in detailed survey
• 1)survey of command area.
• 2)type of suitable dam.
• 3)boring/trial pits at dam site.
• 4)detailed report of soil .
• 5)detail of area under submergence.
• 6)details of people comes under influence.
• 7)existing sediment problem if any.
• 8) material available, quarry sites available nearby
the project.
• 9)gauging of river.

Points to be considered for the site
selection of reservoir :-
1. Stable foundation for the dam should be
available.
2. At the selected site, the river valley should be
narrow so that the length of the dam may be
short.
3. The proposed reservoir basin should be water
tight and free from cracks, fissures so that there
is no loss of water due to percolation.
4. The reservoir basin should not submerged
valuable land properties.

Points to be considered for the site
selection of reservoir :-
5. The tributaries which carry high content of
sediments should be avoided.
6. The site should be such that the optimum
storage capacity is available for the desired
purpose.
7. The site should be easily accessible by road and
railway.
8. The construction materials should be available
in nearby area.

Data to be collected for irrigation
project :-
The preliminary investigation consists of
1. Approximate quantity of water.
2. Period of deficient water supply.
3. Technical feasibility of project such as
i) command area, ii) nature of soil, iii) types of
crops, iv) demand for water at present and in
future.
4. Approximate cost of all proposed works.

Data to be collected for irrigation
project :-
The detailed investigation consists of
1. Soil survey
2. Field work for availability of water
3. Gauging of river
4. Fixing dam site
5. Availability of materials of construction
6. Sedimentation problem
7. Contour survey of reservoir basin
8. Types of dams
9. Alignment of main canals

Area Elevation and Storage Elevation
Curve
Area – Capacity Curve :-
The area capacity curve is useful in:
1) Deciding capacity of reservoir.
2) Water spread of reservoir.
3) Elevation of water at any point can be calculated.
4) Determining control levels of dam.

Area elevation curve:-
From the contour plan of reservoir site the area of
successive contours A1,A2,A3………An are
determined with the help of planimeter. The
area A1 is minimum at the bottom of the basin
and area An is maximum at the top of the
basin. This curves gives the area submerged at
different elevation.

Storage - elevation or
volume elevation curve:-
The volume of the storage of water between
successive contours is calculated by
prismoidal formula. The volume of storage
between successive contours, goes on
increasing from bottom of the basin
towards its top.

Silting of reservoirs :-
Silting of reservoirs means the deposition of silt
and clay. This mainly occurs when runoff occurs
Runoff contain smaller soil particles such as silt
clay, fine sand which may deposited at the bed
of reservoir which reduces the storage capacity
of reservoir.
When these particles reaches into reservoir tries
to settle down due to action of gravity, coarser
one settle down while fine remain suspension
therefore it is very essential to check silting of
dam and water stored in reservoir.

Method to reduces the entry of silt:-
Pre- constructing method
1. Selection of proper dam site such that
catchment area has less erodable portion.
2. Constructing the dam in stages.
3. Providing vegetation screens.
4. Proper reservoir design causing silt water to
escape.

.
• 1. Pre-constructing measures:
• i. Selection of dam site: Silting can be reduced by choosing the reservoir site in such
a way as to exclude the run off from easily erodible catchment. As silting reduces it
increases capacity of reservoir.
• ii. Construction of the dam in stages: The dam should be built lower, and raised
subsequently when some of its capacity gets silted up. Therefore the life of a
reservoir can be prolonged by constructing the dam in stages.
• iii. Construction of check dams: The sediment inflow can be controlled by
constructing smaller check dams across the river contributing major sediment load
and trap large amount of coarser sediments.
• iv. Vegetation screens: Vegetation’s trap large amount of sediments which reduces
entry of silt in reservoir and helps to increase life of dam.
• v. Construction of under sluices in the dam: The dam is provided with openings that
is under sluices in its base, so as to remove the more silted water on the
downstream side.
•

.
• 2. Post-constructing measures
• i. Removal of post flood water: The sediment content
increases just after the floods; therefore attempts are
generally made not to collect this water, which reduces
sediment load on reservoir.
• ii. Mechanical stirring of the sediment: The deposited silt is
scoured and disturbed by mechanical mean, so as to keep it
in a moving state, thus helps in pushing it towards the
sluices.
• iii. Erosion control and soil conservation: this includes all
those general methods which are adopted to reduce
erosion of soil. Because when the soil erosion is reduced,
automatically, the sedimentation problem is reduced
•

Post constructing method
• Removal of post flood water.
• Dredging.
• Mechanical stirring.
• Soil conservation method.

Factor affecting Silting :-
1. Catchment Area : - In case of fan shaped
catchment the amount of deposition of finer
soil fractions will be more as compared to fern
shaped catchment.
2. Slope of country : - If the slope is steep more
particles are deposited through runoff
3. Climatic condition :- climatic condition also
affect the production of silting like dryness,
rain, heat helps in production of silting.
4. Nature of surface soil :- If soil is loose, silting is
more along with runoff.

.
• 1. Catchment area: If catchment area is more, silting will
be more. If catchment area is less, silting will be less.
• 2. Shape of catchment: If catchment area is fan shaped,
siltingwill be more. If catchment area is fern shaped, silting
will be less.
• 3. Slope of country: If slope is steep, more particles will be
erodes because of high velocity of runoff & will be
deposited in reservoir basin and vice versa.
• 4. Climatic condition: Dry and rainy climate helps in
production of more silt material.
• 5. Nature of surface soil: If soil is weathered or loose it can
be easily flow with runoff and deposited in reservoir.

Control Level in Dam :-
1. Top Bund Level (TBL) : - This is RL of dam top which
depends on capacity, storage flood lift & free board.
The height of dam at any section is difference
between TBL & GL.
2. High Flood Level (HFL) : - It is the maximum RL up to
which water can rise in the reservoir.
3. Full Tank Level (FTL) :- Water in reservoir is stored up
to a level known as FTL or FRL. Usually the crest of
spillway is kept at this level.
4. Lowest Water Level (LWL) :- It is the lowest RL of
water surface in the reservoir. If water goes below LWL
then water can not be drawn out of the reservoir.

1. Dead storage: - The storage below lowest sill level
(LSL) can not be used and hence it is called as dead
storage. LSL is a upstream sill level is kept 50cm to
100cm below LWL. This is generally equal to volume of
silt.
2. Live storage : - the storage between LWL and FTL is
called as live storage.
Live storage = irrigation requirement + Tank losses
3. Gross storage :- It is the storage at FTL in the
reservoir.
Gross storage = Dead storage + Live storage
4. Free Board :- It is the vertical distance between TBL
and HFL. It is clear margin kept as a measure of safety
so that wave form should not cross dam.
5. Parent stream:- it is the river across which dam is
constructed.

FIXING CONTROL LEVELS
• The procedure for fixing the control levels of
reservoir is called water planning and data
required for this is as follows.
• The catchment area (A.Km2) its classification and
rainfall data.
• The command area , proposed crop pattern, delta
or duty losses and intensity of irrigation.
• area capacity curve.
• The rate of silting, life of reservoir, L section.
• The rate of tank losses.

PROCEDURE
• 1 yield is determined from catchment area
and rainfall data which gives dependable
yield.
• 2 crop water requirement (CWR) find out crop
water requirement per month, per season,
per year from gross command area for
respective projects.
• I.e. large, small, medium etc. while finding out
CWR transit losses are included at head of
canal

FIXING LWL
• The dead storage is decided depending upon the quantity
of silt coming through runoff, its size, its shape and type of
soil, shape of catchment.
• The life of reservoir is considered to be equal to the
number of years required to fill up the reservoir by silt up
to LSL.
• these years are generally taken as 100 years, it is fixed as
the highest of below.
• 1) RL corresponding to silt storage capacity.
• Silt capacity= rate of silting x CA (Km2) x life (years)
• 2) RL of sill of sluice at under section calculated from- tail
end of distribution system.
• 3)RL of corresponding to 10% of gross storage.

Fixing FTL
• For fixing FTL annual demand and available yield is
calculated and compared the lesser of two is adopted as
value of gross storage and from this FTL is obtained.
• The various control levels of reservoir are fixed as follows
• TO FIX L.S.L/L.W.L/D.S.L.
• It is highest of following:
• 1)R.L. corresponding to silt storage capacity.
• =rate of silting x catchment area x life of dam
• (m3/km2/year) (km2) (year)
• rate of silting is = 200 to 500 m3 / km2/year
• 2) R.L. corresponding to 10% of gross storage or C.W.R
• 3) R.L. of bed of cannel at head + full supply depth of canal.

FIXING OF H.F.L, F.R.L and T.B.L
• F.R.L is fixed at gross storage. The gross storage is
taken as lesser of demand and supply.
• H.F.L= F.R.L+ Flood Lift (H)
• H is assumed between 2 to 3 M
• T.B.L = H.F.L + Free board
• Free board is assumed depending upon the height
of dam.

WATER SPREAD AREA:
• Water spread area is spread of reservoir on
upstream side at high flood level. All land within
high flood level contour comes under water spread
area.
• FLOOD ABSORPTION CAPACITY: It is volume of
water in reservoir between HFL and FTL.
• COMMAND AREA SURVEY:
1) to find out the culturable command area.
2) to fix the alignment of canal in distribution work.
3) To decide number of water shed.
4) To know about unculturable command area.For this
purpose spot level contouring method is adopted

PROCEDURE FOR COMMAND AREA SURVEY:
• 1) the village map should be made with the preliminary
survey as gross command area which is taken as horizontal
control.
• 2)and vertical control is established by fixing TBM on
plinths, parapet ( i.e. of bridges and well )
• 3) then village maps are taken to field and positions of
leveling staff is marked and readings are taken
simultaneously and RL is calculated and should be marked
on map directly other than this the while doing command
area survey the other info should be collected which is
• 1)strata type, its depth 4) Existing irrigation.
• 2) population and their occupation.
• 3) number of wells and ground water table.

PROJECT REPORT
• The executive engineer is the in charge of project and he
should prepare project report which consist of following
points:
• 1) HISTORY: any past history available with respect to
previous in that catchment area and its comparison with
proposed project.
• 2) IRRIGATION DETAIL: it include the following items:
canal, required for proposed project, lay out of canal cross
drainage work and other structure required for irrigation
work.
• 3) CONSTRUCTION DETAIL: it include , material required for
project, if special equipment, tools are to be required then
these must be included in it, total planning of work,
duration of work, its completion time etc.

ECONOMY:
• Total cost of project with current bye laws. Total
estimation item wise with abstract sheet, details of
total revenue generation after completion of
project, it should include provision of maintenance
cost per year etc.
• APPENDICES:
• 1) important points of project. 6) schedule of rate.
• 2) site plan. 7) any communication
• 3) photographs. Made w.r.t project
• 4) different tables and datas. with other
• 5) estimation quantity in detail.
dept, there Suggestion , and important views etc.

Reservior planning

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