Spatial Characters of a Tropical River Basin, South-West Coast of India

Abstract

An evaluation of drainage network of Mahe river basin (394 km2), Kerala, India, with a humid tropical setting is carried out using geospatial techniques. The streams of the basin generally conform to Horton’s laws. However, the correlation between mean stream length and stream order is low (r = +0.55), probably due to an abrupt increase in mean stream length in the highest orders of the subwatersheds. The Subwatersheds in the extreme eastern part of the basin are characterized by maximum relief, and gradients exhibit highest runoff and susceptibility to flooding and inundation. The lineament zones and associated tectonic activity control the drainage patterns and disposition of subwatersheds. The various linear and spatial morphometric parameters of each subwatershed are ranked based on their susceptibility to flooding. Subwatersheds III–VI are environmental hot spots, where implementation of flood control and mitigation measures should be urgently focused. The other subwatersheds steady are found to be in steady state equilibrium with components like climate, lithology, tectonics and topography that determine origin and development of a drainage basin. Major flooding rarely occurs in Mahe, in spite of favourable morphometric characters in other parts of the basin, and is attributed to permeable lateritic nature and dominant areal extent of SW IX in the western most extreme.