Geology Reference
In-Depth Information
of the saprolite zone and the fracturing and interconnectivity between the
various fractures allow a potential aquifer.
Mean annual rainfall is about 750 mm, the mean annual temperature is
about 26 °C, although in summer, the maximum temperature can reach
45 °C. The resulting potential evaporation transpiration is 1,800 mm/year.
The annual rainfall is around 750 mm and the recharge around 10-15 %.
NUMERICAL MODELLING OF AQUIFER FLOW
IN MAHESHWARAM WATERSHED
The Maheshwaram watershed was modelled with the MARTHE software
developed at the BRGM (French Geological Survey, Thiery, 1993). MARTHE
is a transient hydrodynamic modelling code, representing three-dimensional
and/or multi-layer flow in aquifers. The solution method uses finite differences
with a rectangular grid and offers the possibility of having a free surface in
a mesh of any layer.
Model Fabrication
The studied aquifer was represented by a two-layer aquifer flow system. The
upper layer for the weathered zone, the lower one in the weathered-fractured
granite represented as an equivalent porous medium. Each layer was divided
into 5,272 square meshes with a 100-m side (Fig. 3). Layer 1 is unconfined
and layer 2 is confined but may become unconfined when layer 1 becomes
dry. The MARTHE code is used with its coupled climatic-balance model
(GARDENIA: Thiéry and Boisson, 1991). The groundwater flow in the
Maheshwaram watershed is simulated in transient regime in order to represent
the piezometric variations observed in the wells in the studied area from
January 2001 to July 2003.
The thickness of the weathered layer was estimated by kriging from the
measurements made in the 25 existing lithologs and the Vertical Electrical
Sounding (VES) interpretations (Krishnamurthy et al., 2000). The geometry
of the weathered-fractured granite layer was deduced jointly from the total
depth of the 900 inventoried wells in the watershed after removing the wells
with a total depth of more than 70 m and from the result of the VES.
Figure 4 shows the aquifer geometry with bottom of each layer above mean
sea level.
Boundary Conditions
The topographical limits of the watershed were taken as the groundwater
divides (no-flow boundaries), except at the northern limit where a non-
perennial stream at the outlet of the watershed can evacuate the surface
