Water Resources Management 15: 41–54, 2001. © 2001 Kluwer Academic Publishers. Printed in the Netherlands. 41 Estimation of Soil Erosion for a Himalayan Watershed Using GIS Technique SANJAY K. JAIN 1∗ , SUDHIR KUMAR 1 and JOSE VARGHESE 2 1 National Institute of Hydrology, University of Roorkee, Roorkee, India; 2 Department of Earth Sciences, University of Roorkee, Roorkee, India ( ∗ author for correspondence, e-mail: sanjay@nih.ernet.in, fax: 0091-1332-72123) (Received: 20 June 2000; accepted: 21 April 2001) Abstract. The fragile ecosystem of the Himalayas has been an increasing cause of concern to en- vironmentalists and water resources planners. The steep slopes in the Himalayas along with depleted forest cover, as well as high seismicity have been major factors in soil erosion and sedimentation in river reaches. Prediction of soil erosion is a necessity if adequate provision is to be made in the design of conservation structures to offset the ill effects of sedimentation during their lifetime. In the present study, two different soil erosion models, i.e. the Morgan model and Universal Soil Loss Equation (USLE) model, have been used to estimate soil erosion from a Himalayan watershed. Parameters required for both models were generated using remote sensing and ancillary data in GIS mode. The soil erosion estimated by Morgan model is in the order of 2200 t km -2 yr -1 and is within the limits reported for this region. The soil erosion estimated by USLE gives a higher rate. Therefore, for the present study the Morgan model gives, for area located in hilly terrain, fairly good results. Key words: erosion, GIS, Morgan, remote sensing, USLE 1. Introduction Soil erosion is a complex dynamic process by which productive surface soils are detached, transported and accumulated in a distant place resulting in exposure of subsurface soil and sedimentation in reservoirs. It is estimated that out of the total geographical area of 329 Mha of India, about 167 Mha is affected by serious water and wind erosion. This includes 127 Mha affected by soil erosion and 40 Mha degraded through gully and ravines, shifting cultivation, waterlogging, salinity and alkalinity, shifting of river courses and desertification (Das, 1985). Narayan and Babu (1983) have estimated that in India about 5334 Mt (16.4 t ha -1 ) of soil is detached annually, about 29% is carried away by the rivers into the sea and 10% is deposited in reservoirs resulting in the considerable loss of the storage capacity. The entire Himalayan region is afflicted with a serious problem of soil erosion and rivers, flowing through this region, transport a heavy load of sediment. The Himalayan and Tibetan regions cover only about 5% of the Earth’s land surface, but supply about 25% of the dissolved load to the world oceans (Raymo and Rud- diman, 1992). In the Himalayan mountains, as a consequence of loss of forest