Effective Management of Critical Sub-watersheds Using SWAT Model, Remote Sensing and GIS

Soil and Water Assessment Tool (SWAT) was tested on monthly and seasonal basis and used for developing management scenarios for the critical sub-watersheds of a small agricultural watershed of Chhattisgarh. The watershed and sub-watershed boundaries, drainage networks, slope and soil texture maps were generated using Geographic Information System. Supervised classification method was adopted for land use/cover classification from satellite imagery. Manning's ‘n’ for overland and channel flow and Fraction of Field Capacity (FFC) were calibrated for monsoon season of the years 2002 to 2003. The model was validated for the years 2004 to 2005. Results revealed that the model was predicting the monthly and seasonal surface runoff and sediment yield satisfactorily. Simulation results of nutrients including organic N and P in sediment and NO₃-N and soluble P in runoff were also compared with observed data for several events and found satisfactory. The critical sub-watersheds were identified on the basis of average annual sediment yield and nutrient losses. Out of ten subwatersheds, SWS-5 and SWS-7 were found to be critical. Several combinations of treatment options were considered which included four crops, five tillage and three levels of fertilizer. The existing management practices were considered as the base for evaluating other management practices for rice. The results showed other crops couldn't replace rice since these crops resulted in higher sediment yield as compared to rice. Considering both sediment and nutrient losses together the zero tillage, conservation tillage and field cultivator with half dose of fertilizer (40:30 of N:P kg/ha) were found to be better than the other treatments considered for evaluating their impact on sediment yield and nutrient losses for sub-watershed (SWS-5).