Relevance of topographic control on hydrogeological properties of the
weathered granite gneiss aquifer in watershed perspective -- Usri
sub-basin, Giridih, India
Abstract
Usri, a southward sloping fourth order drainage sub-basin of Barakar
river, is located in the northern margin of Chhotanagpur plateau,
Giridih, India. Gently sloping undulating landforms devoid of hills and
outcrops is main characteristics of this sub-basin. Topographic
elevation varies between 310 to 390 m MSL. Geographically it is located
between lat 24.38° N to 24.54° N long and 86.07° E and 86.28° E
longitudes. Thick weathered horizon developed over homogenous Archean
granite-gneiss is the principal unconfined aquifer system. Basement
topographic (weathering depth) and water table have been correlated with
the surface topographic features (landforms). Presence of considerably
thick weathered horizons, devoid of rock exposures, regional uniformity
in geomorphic characters and its location at fringe of plateau provides
favorable condition for correlation of surface topography with basement
topography and water table. It has been observed that basement surface
is replica of ground surface only in regional or watershed perspective
with reference to common datum. The basement surface is not always exact
replica of ground surface at micro watershed scale. In many cases,
basement surface is reverse of ground surface. The depth basement has
remained constant along the basin water-divide situated near the margin
of the plateau. The depth of basement (weathered horizon) is higher in
upper reaches than lower reaches on the micro water-divides (upland) as
well as in the drainage depressions (channels) within the sub-basin. The
upper reaches of the sub-basin mainly along the basin water-divide has
better groundwater prospects than lower reaches. There is no definite
trend of water table with respect to ground and basement topography.
Many places water table is shallow on the micro water-divides (upland)
and deep in drainage depressions (channels). The established
correlations are likely to be applicable in the other geographical area
where similar watershed and geological characteristics exits.