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Title
Application of remote sensing and GIS for sustainable development

81
CASE STUDY
A watershed covering an area of 650 sq. km in
southern part of Tamil Nadu, India was selected for
study with the following objectives.
The main objective of the study was to model the
watershed by assessing various land and water
requirements necessary for the watershed and test the
sustainability of watershed considering the various
resources and constraints available in the watershed.
This was achieved by :
(i) quantifying the total quantity of water required for
various activities like agriculture, industry and
domestic consumption etc.
(ii) quantifying the total quantity of surface water
available in the watershed using USDA-SCS
method.
(iii) quantifying the total quantity of ground water
available by developing ground water model for
the watershed.
(iv) optimize the agricultural production through linear
programming model and assess the sustainability
status of the watershed.
Even though the study covers a wide spectrum of
sustainability factors, this paper deals with the methods
and results obtained on quantifying the ground water
through the modelling techniques.
By using the satellite data of Landsat 5 TM FCC
and IRS-1A LISS 11 FCC the resource maps were
prepared. The collateral data like daily rainfall data for
10 years, meteorological data like temperature,
humidity, sunshine, wind velocity, well census, pumping
data, demographic data, agricultural data on cropping
pattern, crops cultivated, bore hole details, well
extraction details, fodder requirement for animal
population, water requirement for different crops were
used in the modelling study. The area was divided into
grids of 1 km x 1 km size for the analysis.
Computation of available water resources consists
of (i) computation of surface run off using land use, land
cover and hydrological soil group maps (ii) computation
of sub surface potential by developing a mathematical
model through partial differential equation using mainly
field measurements (iii) computation of various inflow
components in the hydrologic process like rainfall
recharge, river bed recharge, return flow from irrigation,
sub surface inflow etc. (iv) computation of various
outflow components include extraction for human and
animal population, agricultural extraction, sub surface
outflow, loss due to evapotranspiration through natural
vegetation.
After computation of various inflows and outflows
to each grid, the net discharge or recharge to each grid
has been computed using the equation :
Qnet = I - Q where Qnet is the net charges in
storage of all inflows and outflows, 1 is the total volume
of inflow components and Q is the total volume of
outflow components.
The simulation of model was carried out at IRS,
Chennai using basic aquifer simulation program with
various inputs of net storage (NQ) with time interval of
15 days (t), the boundary conditions, the available
piezometric heads and the aquifer parameters.
The model was calibrated with the data for the year
1983-84 to 1988. The calibrated model was tested with
the input values pertaining to the period of 1988-89 to
1992-93. The results from the test runs were compared
with the observed values and the difference between
them was obtained. After calibrating the model it was
used for assessing the quantity of ground water
available. The watershed boundary was super imposed
over the ground water level contour drawn taking into
account the minimum and maximum ground water
available in the acquifer. Final computation of total
quantity of water was calculated for each micro
watershed by adding surface runoff or overland flow
with the available groundwater.
RESULTS OBTAINED
The available groundwater in each micro water
shed was computed from the distributed groundwater
model by aggregating the potentials available in all the
grid segments in a particular watershed for period of ten
years 1983-92. The minimum quantity of ground water
that can be extracted is 31.62 mm\ The maximum and
average quantity of ground water that can be harnessed
during the ten year period was assessed as 238.24 and
136.30 mm 3 respectively for the entire aquifer of the
study area. The average surface water quantity of
surface water that can be harnessed are 2 mm’ and 25
mm 3 respectively during thg 10 years period. The
average total quantity of water i.e. both surface and sub
surface available in the entire watershed was assessed as
147.65 mm 3 . The minimum quantity of water available
during the year 1988-89 works out to be around 33 mm 3
and the maximum quantity of water available during the
year 1987-93 for both surface and ground water in the
watershed is given in Table 1.