Assessment of Water Availability in Chennai Basin under Present and Future Climate Scenarios

Abstract

Rivers are sensitive to changes in tectonic deformation, and adjust themselves on different scales of time periods depending on the physical properties of the host rocks and climatic effects. The resultant changes are exhibited by the geomorphic indices and landform assemblages within a river basin. This paper presents the results of integrated quantitative geomorphic analysis conducted for understanding the prevalent tectonic activities in a medium sized drainage basin, the Thoppaiyar sub-basin, India. The major part of the study area is covered by gneisses and granites. The sub-basin is divided into fourteen fourth order micro basins (FOMBs) for quantitative geomorphic analysis. Prior to quantitative analysis, longitudinal river profile and channel morphology were studied. The channel morphology includes cross sections, width-to-depth ratio, entrenchment ratio, bank height ratio were measured during field investigation. Various geomorphic indices namely, the basin shape index (Bs), drainage basin asymmetry factor (Af), hyp-sometric integral (Hi), hypsometric curve (Hc), valley floor width-to-height ratio (Vf), transverse topographic symmetry (T) and stream length gradient index (SL) were derived using topographic maps and SRTM satellite data. The spatial distri-butions of these parameters were represented as thematic layers using. The results obtained from these indices were combined by ArcGIS 9.3 software to generate an index of relative active tectonics (I RAT) in the sub-basin. It indicated the prevalence of differences among the FOMBs and an overall relatively low tectonic activity in the Thoppaiyar sub-basin.