Assessment of Runoff and Erosion using GIS

Abstract

A study has been carried out on the Gayathri sub basin of Barathapuzha river basin, one of the major rivers of Kerala, with focus on runoff and erosion generating process of the watershed. The geographical area of the watershed is 1042 km 2 and GIS techniques are made use of to incorporate special variability more thoroughly and effectively. Specific objectives of the study included characterisation of watershed from the stand point of runoff and erosions process and the quantification of these physical processes. The digital elevation modal of the Gayathri watershed shows that about 85 % of the geographical area lies in the slope range of 0to 25 %. Major textural classes of the soil are loamy and clayey. Vegetation comprises mixed crops in garden land, paddy, rubber and forest. Surface runoff has been computed by SCS curve number method and the result indicate that 38 % of annual rainfall flows out as surface runoff. Gross erosion predicted by USLE indicate that 31 % of the total area is subjected to severe erosions of the order of 40-100 t/ha/yr and 34.5 % of the area experiences an erosions rate of 10-40 t/ha/yr. High surface runoff potential of the watershed throws light on the need of the augmentation of water harvesting measures. In areas with high rate of erosion, an appropriate erosions control practice has to be adopted to book the erosion under sustainable limits.