SOIL EROSION MODELLING IN WATERSHED - A CASE STUDY

Abstract

Soil erosion is a natural physical process of detachment and subsequent removal of soil particles from the surface of land due to rainfall and runoff. Soil erosion modelling is nothing but the process of mathematical description of soil particle detachment and transportation on land surfaces. These models are useful in prediction of soil erosion for conservation planning and planning of water resources projects. The soil erosion modelling is the best tool for understanding erosion processes and for setting research priorities. There are mainly three types of soil erosion estimation models; empirical models, conceptual and physical models. The conventional methods of soil erosion estimation may not be accurate and time effective. Remote sensing in conjunction with the Geographical Information System (GIS) has emerged as a powerful tool in estimating soil erosion more accurately. In the present study a Geographical Information System (GIS) based distributed rainfall-runoff and soil erosion estimation has been carried out. The event based runoff generated from watershed is estimated using SCS-CN method. The model parameters, Curve Number (CN) and Surface retention (S) are evaluated under different Antecedent Moisture Condition (AMC), Hydrological Soil Group (HSG) and landuse conditions. Runoff is estimated on both distributed and lumped basis using GIS and conventional methods. A distributed approach has been adopted in the event based soil erosion estimation using Universal Soil Loss Equation (USLE). This erosion modelling is carried out to estimate soil erosion by rainfall-runoff in Deshgaon and Ozarkhed watershed. The required input data is geographic in nature such as landuse/land cover, soil type so they are modeled in GIS. Using Digital Elevation Model (DEM), erosion from each of the discretized cells have been calculated in GIS enviornment. MMF conceptual model is also applied to estimate soil erosion in both the •watersheds. The GIS database used for soil erosion estimation using USLE, has been utilized in this method. The computation for fifteen different parameters has been performed. The sensitivity analysis for GIS based USLE model is performed in order to know the change in models performance with. changing input parameters. The sensitivity analysis indicates that soil erodibility factor (K), crop/cover management factor (C) are not contributing any noticeable change in soil erosion. In the rainfall-runoff-soil erosion 1 analysis on one of the event in both watersheds, soil erosion is observed even when the runoff is zero with less rainfall indicating that rainfall is the main influencing factor in soil erosion. It is found that the conservation practices are very important and sensitive in soil erosion from both watersheds. The different types of conservation practices are applied to study their effect on soil erosion in watershed. As both the watersheds are showing higher erosion rates, there is need to apply some conservation practices to reduce soil erosion rate. In Deshgaon watershed contour type and contour strip type conservation practices are applied and it is found that on all the events in contour strip type conservation practice rate of soil erosion is lower than contour strip type conservation practice. In case of Ozarkhed watershed which is having severe erosion rate some more types of conservation practices are applied. The contour type of conservation practice is not showing any major reduction in erosion rate as it is noticed in case of bench terrace type of conservation practice. In bench terracing type of conservation practice the soil erosion rate is very low as compare to other conservation practices. The conservation practices are selected on the basis of topograpical and geological characteristics of watershed.