1. Rivers
and their tributaries - The quantity of water flowing through the rivers
can be computed by knowing the cross-section of river bed, the height of water
level and the rate of flow. In fact for a definite cross-section of a given
site the height of river stage can be a direct measure of the water quantity
flowing through the stream by using suitably calibrated stage-discharge-relation
curve (Hammer & Mackichan, 1981).
2. Mine water - The
quantity of water being pumped out of the mines can be computed by knowing the
rate of pumping and the time for which pumping is being done. This water comes
out from confined and unconfined aquifer as the case may be. It forms a water
source only if it is re-used. But if it is thrown off the area (as run-off or
evaporation) it is rather to be substracted to calculate the actual water availability.
Similarly water discharged from any place of water use, should be analysed and
studied how it can be treated and recycled so that forms a source, otherwise
if it is allowed to flow away uselessly it creates a series of additional problems,
like pollution of land and water resources etc.
To assess the suitability of water for various uses it is necessary to determine
the quality of water available from each source and then compare it with the
suitability criteria. If the quality of water available does not conform to
the suitability criteria, necessary arrangements may have to be made for treatment
of water to achieve the desired quality.
Quality Criteria: Permissible limits for the pollutants
for various uses of water and effluent discharges have been defined by the Bureau
of Indian Standards (BIS) under IS 10500 for drinking water, IS2490 for effluent
discharges on inland surface and water for different purposes, and IS2296 for
sewerage discharge.
By analysing the water from the various sources to assess the contaminants present
and comparing the extent of contamination with the various water quality standards,
the quality of water available from the sources can be defined. However, there
may be seasonal variation of water quality, which can be ascertained by assessing
the quality in all the seasons.
Water Inventory: With the information on quality
and quantity of water from various sources available, an inventory can be drawn
in respect of water availability.
Water Availability Forecast: The data on water
availability in the past can be used to forecast its availability in future
by trend analysis. Since the past data may not be available in most cases in
Indian scenario it may not be possible to do the trend analysis. The forecast
in such cases may have to be made on the basis of the available data and the
data generated during the water balance study.
It may be mentioned here that the water holding capacity of the surface storages,
unconfined and confined aquifers may reduce with time. In case of surface storages,
the capacity decreases due to silting; while in case of groundwater, recharge
decreases due to compaction of the soils, and the aquifers' capacity decreases
due to its compaction as a result of ground water withdrawal.
Water Requirement: In any inland area water is
required for various purposes, e.g., domestic, agriculture, horticulture, industries,
recreation poultry, dairy etc.
Requirements are to be calculated for the present time, after 5 years, 10 years
and 15 years; calculation is to be based on the following.
Requirements of population: including ethnic, other supporting services
and even floating population, e.g. those coming at the time of sowing, harvesting,
etc. As per Indian standard, requirement is 50 gpd per head as against the international
standards of 100 gpd and even more.
Requirements for irrigation/watering: Water is
required for agriculture (for crops), horticulture (for fruits & vegetables)
and pisciculture (for fisheries). Land-use information will give the area for
each variety, while crop pattern will give the requirement of water/unit area.
Further irrigation requirement depends upon climatic factors e.g. evaporation
potential and quantity and distribution of rainfall in "time".
While considering the long time requirement, expected land-use changes are also
to be taken care of considering the fact that population-pressure and mining
activities effect other land-uses, e.g. agricultural/forest land is converted
to settlement area.
Requirements for industries: Water requirement
for industries is to be calculated considering input, output and discharge quantity
and quality. Thermal power stations require water for energy generation. Central
Pollution Control Board (CPCB) specifications are to be considered (as per IS
2490).
Recreational requirement: This is to be calculated
considering quantity as well as quality.
The water quality and quantity required for various purposes can be assessed
by having an inventory of the planned activities and water requirement for them.
Depending upon the nature of the activity there may be variation in the requirement
of water quantity and quality.
The requirement for domestic consumption: This may not vary much round
the year, while for agriculture it will be seasonal and will depend upon the
crop pattern and rainfall pattern. In case of the industries the requirement
will depend on the nature of the activities in the industries and recycling
provisions.
In case of water requirement if the data is available from the past, a trend
analysis can be done for forecast of water requirement on the basis of the present
level of activities. However, in forecasting the water requirement, both in
terms of quality and quantity, for any area the activities planned for future
should be taken into account.
With the help of the data it should be possible to assess and forecast the qualitative
and quantitative requirement of water for various purposes in any given area.