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The ground water resources and
balance available were computed based on the "Ground Water Estimation
Methodology - 1997". The salient features are given below :
Unit
of Computation
The unit of computation proposed in the methodology is 'Watershed'.
Watershed with well-defined hydrogeological boundaries is an appropriate
hydrogeological unit for ground water estimation. However, it also
recommends 'block/Tehsil' as the unit of computation for the first few
years since there can be non-availability of data. In the present
report 'block' is taken as the unit of computation as in the earlier
cases. This is mainly due to lack of data, especially on number of
structures, draft, population, and other vital figures on watersheds.
Recharge during monsoon and non-monsoon season
The methodology recommends computation of 'recharge' figures separately
for monsoon and non-monsoon seasons. The monsoon season is taken
as June to September end and the remaining part as non-monsoon. The NE
monsoon, which accounts for more than 10% of the total rainfall
contributes to he aquifer and hence, recharge is worked out separately
as the 'non-monsoon recharge'.
Sub-units
The following sub-units are recommended for the computation of various
figures.
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Hilly areas
Areas with more than 20% slope were removed from the recharge
computation. This was done by using the physiographic map and
the block boundary map of the State.
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Poor ground water
quality area
There are no areas which can be mapped as 'poor' ground water
quality area. The poor ground water quality is seen as
isolated pockets close to backwater and lagoons and is mostly during
summer months. Since this is negligible, it is not considered
for computation of the dynamic resources. However, it was
taken care during the computation of the static resource since
brackish water is evaluated in many bore holes drilled along the
coastal sedimentaries and crystalline close to back water channels.
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Command and non-command
area The methodology
envisages computation of various figures 'command' and
'non-command' areawise. However, it could not be done since
the data of the command area and the details of various structures
in it were not available. In Kerala, all the surface water
projects except Kallada are planned to irrigate paddy and the
irrigation canals are contour canals. Due to the
non-availability of map showing the canal network and area irrigated
in the command and non-command areas, recharge from the irrigation
canals could not be computed for each bloc
For the computation of various
figures the units were divided into sub-units as decided above to the
extent possible. Afterwards the areas underlined by various
formations were demarcated and the areas were measured separately.
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