reservoir planning ajitha miss

RESERVOIR PLANNINGRESERVOIR PLANNING

NECESSITY OF CREATING RESERVOIRSNECESSITY OF CREATING RESERVOIRS

Retain excess water from periods of high flows for use during periods of low flows

– Irrigation

– Development of hydroelectric power

– Water supply for domestic and industrial use

Storage of flood water reduce flood damage

– Flood control

Single purpose reservoir Multi-purpose reservoir

INVESTIGATIONS FOR RESERVOIR INVESTIGATIONS FOR RESERVOIR PLANNINGPLANNING

1. Engineering surveys

2. Geological investigations

3. Hydrological investigations

ENGINEERING SURVEYSENGINEERING SURVEYS

Area of the site (dam site, reservoir and associated works) surveyed and contour map of the entire area is prepared

From contour map, storage capacity and water spread area of reservoir at various elevations can be determined

– Water spread area at any elevation determined by measuring the area enclosed by the contour corresponding to that elevation with a planimeter

– Storage capacity of reservoir determined by taking contour areas at equal interval and summing up by trapezoidal formula, cone formula or prismoidal formula

GEOLOGICAL INVESTIGATIONSGEOLOGICAL INVESTIGATIONS

Geological investigations required to determine

– Suitability of foundation for dam

– Water tightness of the reservoir basin

– Location of quarry sites for obtaining suitable construction materials

HYDROLOGICAL INVESTIGATIONSHYDROLOGICAL INVESTIGATIONS

To estimate the quantity of water likely o be available in river

– Study of runoff pattern of river at the proposed dam site to determine the storage capacity of reservoir

– Determination of hydrograph of the worst flood to determine the spillway capacity and design

SELECTION OF SITE FOR A SELECTION OF SITE FOR A RESERVOIRRESERVOIR

1. Suitable dam site must be available

2. River valley at site

– Narrow so that the length of dam is less

– Open out at u/s to provide large basin for reservoir storage

3. Surrounding hills must be watertight

4. Reservoir basin should be water tight

5. Site should be such that minimum land and property is submerged in the reservoir

6. Site should be such that it should avoid those tributaries which carries unusually high sediment content

7. Site should be such that adequate reservoir capacity must be made available

SELECTION OF SITE FOR A SELECTION OF SITE FOR A RESERVOIR…RESERVOIR…

8. As far as possible a deep reservoir must be formed

– Land cost per unit capacity is low

– Less evaporation loss

– Less weed growth

9. No minerals and objectionable salts present

10.Quality of water available in reservoir should be of good

SELECTION OF SITE FOR A SELECTION OF SITE FOR A RESERVOIR…RESERVOIR…

ZONES OF STORAGE IN A ZONES OF STORAGE IN A RESERVOIRRESERVOIR

Normal pool level (N.P.L)

– Maximum elevation to which water surface will rise in the reservoir during normal operating conditions

– Also called as full reservoir level (F.R.L) or full tank level (F.T.L)

Minimum pool level

– Lowest elevation to which water is drawn from reservoir under normal conditions

ZONES OF STORAGE IN A ZONES OF STORAGE IN A RESERVOIR…RESERVOIR…


Maximum pool level

– Maximum elevation to which water surface will rise in reservoir during design flood (worst flood)

– Also known as maximum water level (M.W.L)

Useful storage

– Volume water stored between normal pool level and minimum pool level

– Also known as live storage as it can be used for various purposes

Dead storage

– Volume of water held below the minimum pool level

– It cannot be used for any purpose under normal conditions


Surcharge storage

– Volume water stored between normal pool level and maximum pool level of reservoir

– Uncontrolled storage as it exists only during floods and cannot be retained for later use


RESERVOIR YIELDRESERVOIR YIELD

Reservoir yield

– The amount of water that can be supplied from a reservoir in a specified interval of time

– Depend upon inflow and vary from year to year

Safe yield of firm yield

– The maximum quantity of water which can be supplied from the reservoir during a critical dry period

– The period of lowest natural flow of the stream is taken as the critical period

Secondary yield– Quantity of water available in excess of safe yield

during periods of high flows

Average yield3

– Average of safe yield and secondary yield over a period of time

Design yield– Value of yield adopted for design of a reservoir– Should be such that the demands of consumers are met

with and storage is not unduly depleted

RESERVOIR YIELD…RESERVOIR YIELD…

RELATIONSHIP BETWEEN YIELD AND RELATIONSHIP BETWEEN YIELD AND STORAGESTORAGE

Inflow – Yield = Change in storage

If inflow is more than yield

– Storage will increase

If inflow is less than yield

– Storage will be depleted

MASS CURVEMASS CURVE

DEMAND CURVEDEMAND CURVE

1. Prepare a mass curve from flow hydrograph for a number of consecutive years

2. Corresponding to the given rate of demand, prepare a demand curve

3. Draw lines parallel to the demand curve and tangential to the high points of the mass curve (points at the beginning of dry periods)

DETERMINATION OF RESERVOIR DETERMINATION OF RESERVOIR CAPACITY FOR A SPECIFIED YIELD CAPACITY FOR A SPECIFIED YIELD OR DEMAND USING MASS CURVEOR DEMAND USING MASS CURVE

4. Measure the maximum vertical intercepts between the tangential lines and mass curve

– Vertical intercepts indicate the volume by which the total flow in the stream falls short of the demand and required to be provided from reservoir storage

5. Determine the largest of the vertical intercept measured in step 4 and this represents the reservoir capacity required to satisfy the given demand


1. Prepare a mass curve in the same manner as in the previous case

2. Draw tangents at high points in such a manner that their maximum departure from the mass curve does nit exceed the given capacity of reservoir

DETERMINATION OF YIELD FROM A DETERMINATION OF YIELD FROM A RESERVOIR OF GIVEN CAPACITYRESERVOIR OF GIVEN CAPACITY

3. Measure the slopes of these tangents and which represents the yield which can be obtained in each year from the reservoir of given capacity

– Slope of the fattest tangent is the safe yield


RESERVOIR LOSSESRESERVOIR LOSSES

Reservoir losses due to– Evaporation– Absorption– Percolation

MEASURES TO REDUCE MEASURES TO REDUCE EVAPORATION LOSS IN RESERVOIRSEVAPORATION LOSS IN RESERVOIRS

By constructing reservoirs of less surface area

By growing tall trees on the windward side of reservoir which act as wind breakers

By spraying certain chemicals which form thin film above the water surface

By removing weeds and plants from periphery of the reservoir

By providing coverings of thin polythene sheets for water surface

By developing underground reservoirs

By growing huge trees and forest around reservoir so that a cooler environment is formed

MEASURES TO REDUCE MEASURES TO REDUCE EVAPORATION LOSS IN RESERVOIRSEVAPORATION LOSS IN RESERVOIRS

reservoir planning ajitha miss

Engineering

reservoir storage

yield storage

area of reservoir

azones of storage

deep reservoir

reservoir planningplanning

reservoir level f

live storage