Morphometric analysis of watersheds in Kelani river basin for soil and water conservation

Geomorphic behaviour of watersheds influences the soil erosion characteristics in river basins and is used to prioritise the watersheds for soil and water conservation. There is evidence of higher rates of soil erosion occurring in the Kelani river basin. Thus, soil conservation in this basin is crucial at present. This study was carried out to identify the priority within the Kelani river basin for soil and water conservation using GIS spatial environment. Kelani river basin was first delineated on the digital elevation model (DEM) of 15 x 15 m resolution. It was further sub divided into 20 watersheds (KB1 to KB20) using spatial analysis techniques in GIS. Morphometric parameters such as areal, linear and relief were calculated for the 20 watersheds and ranked considering the susceptibility to erosion. Final priority was assessed based on the compound value. Hypsometric integral was also calculated for the 20 watersheds, and the watersheds were classed as young, mature and old. The results showed that upstream sub watersheds KB 18 and KB20 fell under very high priority for soil and water conservation and they were further sub divided (KB18.1 to KB18.6 and KB 20.1 to KB 20.8, respectively) to investigate the most prioritised areas for soil and water conservation. The results showed that KB18.5 and KB18.6, and KB20.1, KB20.2 and KB20.3 are the most susceptible areas for soil erosion in KB18 and KB20 watersheds, respectively. Significant higher correlation (- 0.529 at significant level 0.01) between the compound value and observed turbidity data validated the morphometric base priority for soil and water conservation in Kelani river basin. Results of the study can be utilised in watershed prioritisation for soil and water conservation in Kelani river basin in Sri Lanka.