HYDROLOGICAL STUDIES OF A SMALL WATERSHED IN INDIA USING ANSWERS MODEL

Abstract

Soil erosion is a serious problem which if left unchecked can have disastrous consequences on our environment. Every year millions of tonnes of top soil is are washed away into the rivers and sea by erosion. Proper and effective management of land and water resources demands. a quantitative assessment of runoff and soil erosion. Soil is naturally removed by the action of water or wind. Soil erosion by water is the result of rain detaching and transporting vulnerable soil, either directly by means of rain splash or indirectly by rill and gully erosion. Four basic factors influence runoff and soil erosion by water: climate, soil properties, topography and land use practices. Spatial variability of these parameter must be taken into account during runoff and sediment outflow simulation. Distributed parameter models are applicable for these kinds of simulations. The mapping and management of such spatial information require the use of new technologies such as satellite remote sensing and geographical information system (GIS). In the present study, a spatially distributed model, the Areal Nonpoint Source Watershed Environment Response Simulation (ANSWERS) has been used to simulate runoff and erosion in Karso watershed in the Hazaribagh district of Jharkhand state. The watershed is discretized into square elements assumed to have all hydrologically significant parameters uniform. The GIS techniques have been utilized to spatial discretization of the Karso catchment in to grids. The integration of GIS with distributed parameter reduces the time needed for generating large number of input data associated with these models as compared to conventional methods. Slope and aspect information were generated in GIS from Survey of India Toposheets. Information of input parameters such as land forms, drainage, soil, land use/land cover was derived from digital analysis of Landsat Thematic Mapper data with limited ground truth. Values of variables such as slope; aspect, soil variables (porosity, moisture content, field capacity, infiltration capacity and erodibility factor), surface variables (roughness and surface retention) and channel variables (Width and roughness) are defined for each element. The continuity equation is used to route flow to the catchment outlet. Three erosion processes are iii considered: detachment of soil particles by raindrop impact, detachment of soil particles by overland flow, and transport of soil particles by overland flow.