WATER LOSSES FROM RESERVOIR AND ITS
CONTROL
Surface evaporation, seepage into the surrounding
soil or rocks, and seepage through dam foundations
are all ways that water in a reservoir might be lost.
Evaporation losses are frequently of significant
importance, whereas seepage losses may typically be
avoided.
Reservoir losses may be classified under the
following three heads.
1. Evaporation losses
2. Absorption losses
3. Reservoir leakage or percolation losses.
Evaporation Losses.
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These are the major losses from a reservoir.
This loss is affected by exposure of surface
area of the reservoir, wind velocity,
temperature, relative humidity etc.
This loss is express in cm of water depth and
varies from place to place depending upon
the local conditions such temperatures,
relative humidity, wind etc.
Absorption Losses.
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This loss of water is considerable in the
beginning, but falls to very small values after
some time when pores get saturated
These losses depend upon the soil forming
the reservoir.
These losses are not consider while planning
a reservoir.

Hence while selecting the site of the
reservoir, this aspect of the site is investigated
in great length and if any such fault is noticed,
it is rectified before reservoir is constructed
CONTROL OR MINIMIZATION OF WATER
LOSSES FROM RESERVOIR
Under normal circumstances, it is impossible to
manage the climatic elements that cause evaporation,
as well as the absorption losses and percolation
losses. However, attempts are made to restrict
evaporation by controlling the passage of wind over
water surfaces or by protecting the water surface.
area by physical or chemical methods.
An amount of 495,000 cubic kilometers of water are
thought to evaporate each year and enter the
atmosphere. Reservoirs of fresh water lose around
990 cubic kilometers, or 261,530 billion gallons,
through evaporation. The restocking of aquifers,
lakes, and rivers would be possible even if only a
portion of this evaporative loss could be stopped. To
protect water resources in certain locations, it is
crucial to cover reservoirs in drought-prone regions
and huge water bodies in dry and semi-arid climates.
Modern modular coverings that can stop up to 98%
of evaporation losses are cost-effective instruments
that can help us preserve our fresh water supply.
The methods generally used are as follows:
1. Wind breakers
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Reservoir Leakage or Percolation Losses.
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Reservoirs being very large, their banks are
permeable.
But the permeability of the soil is generally
very low and hence these losses do not carry
any importance.
But in certain cases the banks of the reservoir
may be made of badly fractured rocks or
having continuous seams of porous strata.
Such conditions may cause serious leakage.
To stop such leaks grouting with cement may
have to be resort.
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These structures are used to control
erosion,
produce
agricultural
products, save energy consumption,
develop the environment, manage
waves and turbulence, etc.
Reducing evaporation is one of the
most important uses of windbreaks
done through the change in wind
velocity and direction and air
turbulence.
2. Covering the water surface
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Covering an open water body has
many
advantages: Reduces
evaporation of water by up to 90%

Reduces algae growth and therefore
filter
clogging.
Reduces
concentration of salts in the water.
3. Reduction of exposed water surface
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Reducing the exposed water
surface works best if some shallow
portions in the reservoirs can be
easily separated from the rest of the
lake.
The method consists in building dikes
to isolate the shallow portion of the
reservoir and divert the water to
deeper area and is somewhat effective
in drought prone areas.
4. Integrated operation of reservoirs
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The operation of the reservoirs not
only guarantees the flood control
safety of the river, but also plays
various roles in power generation,
water supply, ecological environment
maintenance, and navigation.
5. Treatment
with
chemical
evaporetardants (WERs).
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Major Reservoirs in Philippines
1. San Roque Dam
Year of operation: 2003
Purpose – Power generation, Irrigation, flood
control
Installed Capacity – 345MW
Reservoir capacity – 800 MCM
2. Magat Dam
water
These retardants significantly aid
in lowering the plastic shrinkage,
wind crusting, stickiness and
sponginess eradicating all the
possibilities of uneven surface
texture. Evaporation Retardant is
used in cement works, dams, ponds,
and lakes.
RESERVOIR IN PHILIPPINES
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located in Cotabato, Agusan, Central Luzon,
and Cagayan.
There are 423 minor and 438 larger dams.
The major purposes of dams and reservoirs
are hydropower generation, irrigation, flood
control, and water supply.
Rivers, lakes, river basins, and groundwater
reservoirs are the principal water sources in
the Philippines. The Cagayan River, which is
both the longest and greatest river, releases
over 53,943 million cubic meters of water
each year. Rainfall and seepage from rivers
and lakes replenish the 47,895 million cubic
meters of groundwater reserves there. The
lakes are mostly used for fish farming. The
four major groundwater reservoirs are
Year of operation: 1970s
Purpose – Power generation, irrigation
Installed Capacity – 100MW
Energy Capacity – 232 GWh
Reservoir capacity – 1250 MCM
3. Ambuklao Dam
Year of operation: 1950s
Purpose – Power generation, irrigation
Installed Capacity – 74MW
Energy Capacity -400 GWh
Reservoir capacity – 217 MCM
4. Binga Dam
Year of operation: 1960
Purpose – Power generation
Installed Capacity – 100MW
Energy Capacity -516 GWh
Reservoir capacity – 87.4 MCM
5. Pantabangan Dam
Year of operation: 1970s
Purpose – Power generation, Irrigation
Installed Capacity – 100MW
Energy Capacity -232 GWh
Reservoir capacity – 3,000 MCM