Hypsometry and Landform Evolution: a Case Study in the Banas Drainage Basin, Rajasthan, with Implications for Aravalli Uplift

The hypsometry (area-elevation analysis) of drainage basins is a useful method to decipher the stages of landform evolution and assess the influence of geologic and tectonic factors on topography. Various parameters of hypsornetric curve have been identified and defined here, and their implications discussed. An empirical relation involving the mean elevation and the hypsometric integral has, been derived to determine the relative tectonic uplift of the subcatchments.

The hypsometry of the 6^th order Banas drainage basin in Rajasthan, and its nine 5^th and 4^th order subcatchments have been analysed. In the Mashi and Morel subcatchments, catchment widening is accompanied by significant channel networking and high erosion, leading to mass accumulation and elevation increase at the lower reaches. Other subcatchments show 2D stream branching without significant valley incision and downstream mass accretion. The subcatchment aspect ratio has influenced the hypsometric curve shape. The landform age of the subcatchments appears to increase in the following order: Dhil, Dai, Kothari, Chandrabhaga, Mashi, Morel, Berach, Khari and Galwa.The hypsometry of the studied subcatchments distinguishes two landform development trends. Two landform evolution models, one based on discharge-dominant fluvial process and the other on slope-dominant diffusive process, have been derived.

Tectonic uplift deduced from hypsometry is relatively greater in the SW part of the Banas drainage basin than in the N and NW parts. This is because of differential vertical movement of several tectonic sub-blocks, bounded by reactivated old dislocation zones and active faults. Tectonic uplift seems to have either defeated or matched the denudation in the Aravalli hill range, and the Banas catchment landform has approached a stage of steady-state equilibrium.