EXTRACTION OF PARAMETERS AND MODELLING SOIL EROSION USING GIS IN A GRID ENVIRONMENT

摘要

Soil erosion assessment for watershed management is one of the major concerns because in reality it is not possible to conserve all areas under the threat of erosion because of the financial constraints. Geographic Information Systems are becoming a popular tool when seeking solutions to issues of these kinds, which are spread over large spatial extents. However it is of utmost importance to ensure a reasonable assessment of soil erosion because this is the core to any such decision making. Use of USLE for erosion assessment using GIS poses concerns since some parameters are polygon specific. This could be overcome easily by the use of grid-based data layers and selecting appropriate size of grids for a particular data set. The most common problem is the computation of the slope length and slope class parameters of a particular grid of a DEM. The present study describes a different methodology to compute these factors using a digital elevation model of the study area. A watershed from Sri Lanka covering an area of 23,000ha was selected for modelling. Field survey results recognised the need to calibrate the model for planning purposes. Model calibration used a weighting scheme. A comparative analysis of results for the same project area from the grid-based model and a model that did not use grid-based data indicated an almost same value of mean annual erosion level for the watershed. This paper also carries a discussion of the key issues that need to be considered when modelling in different environments. Suitably developing a model in a grid data environment provides better flexibility to compute erosion levels for different spatial scales. Grid based method also enables the meaningful use of pixel based remotely sensed land cover information for modelling soil erosion.