Abstract

Soil erosion is one of the most serious environmental problems since the fertile soil which is rich in nutrients gets removed.  This erosion of soil reduces the capacity and life span of rivers and reservoirs. This has become severe problem which is a challenging management task for the water resource department. Thus soil resource need to be conserved for optimal land use for maintaining and improving soil productivity. Since mathematical models have great potential to support land use planning with the goal of improving water and land quality.  In  this  study,  the  Soil  and  Water  Assessment  Tool (SWAT)  model  having  an  interface  with Arc View GIS software is used for estimation of sediment yield for Kesem watershed. The model is calibrated and validated using observed runoff and sediment yield data. The SWAT model was used to estimate the runoff and sediment yield of Kesem watershed. The model was calibrated, validated, and assessed for evaluation to model ambiguity using Nash–Sutcliffe coefficient (NSE) and coefficient of determination (R2). Ten highly sensitive parameters were recognized for stream flow simulation of which CN2 (Initial SCS CN II value) factor was the most sensitive one and four highly sensitive parameters were recognized for sediment yield simulation of which SPCON (Linear parameters for sediment re-entrainment) was most sensitive one. The model was calibrated for a time period between 1995 to 2004 and validated from 2005 to 2009 for flow and sediment yield. During flow calibration the R2 and NS give as value of 0.68 and 0.67 respectively, and similarly for validation the R2 and NS give as value of 0.65 and 0.60, respectively. For sediment calibration the R2 and NS coefficient give as 0.77 and 0.64, respectively and sediment validation R2 and NS give as 0.65 and 0.54, respectively. The calibration and validation results found were good and satisfactory for both flow and sediment. The total observed flow for study area at gauged station was 15.52m3/s and the simulated flow by SWAT model was 14.15m3/s and observed annual sediment yield generated from rating curve at selected gauging station was found 29.62ton/ha/yr and the simulated yield by SWAT model was 25.75ton/ha/yr. From the model simulated output, sub-basins 2, 7, 5, and 18 were found to be the severely eroded sub-basins with annual average sediment yield of 22.01ton/ha, 19.29ton/ha, 19.09ton/ha and 18.93ton/ha, respectively. While, sub-basins 12 and 13 were found to be the least sediment sources with annual average sediment yield of 0.03 ton/ha and 0.06ton/ha respectively. Six scenarios were developed to decrease sediment yield in the catchment and sediment management approach were proposed in the Kesem catchment. By this study we come to know that the SWAT model is competent of predicting sediment yields and hence can be used as a tool for water resources planning and management in the study watershed.