Abstract:
In this study the SWAT model was verified on monthly basis and used for developing management scenarios for the critical sub-watersheds of a small agricultural watershed (Arang) in Chhattisgarh, India. Various thematic maps including watershed and sub-watershed boundaries, drainage networks, slope and soil texture maps were generated using Arc GIS. Supervised classification method was adopted for land use/cover classification from satellite imageries using ERDAS Imagine. The calibrated values of Manning's 'n' for overland flow and channel flow were referred and used for monthly validation of the SWAT model for the years 2004 to 2005. Validation results revealed that the model was predicting the monthly surface runoff and sediment yield satisfactorily. Comparison between observed and simulated values of organic N and P, NO3—N and soluble P showed good agreement for several events during the years 2003 to 2005. The model simulated daily rainfall was having close agreement with that of observed rainfall. Also the model predicted and monthly runoff and sediment yield using generated daily rainfall compared well with observed runoff and sediment yield during simulation period of 2003 through 2005. The critical sub-
watersheds were identified on the basis of average annual sediment yield and nutrient losses during the study period . Out of ten sub-watersheds only two sub-watersheds (SW5 and SW7) were found to be critical. Several combinations of treatment options were considered which included four crops (rice, maize, groundnut and soybean), five tillage (zero, conservation, field cultivator, M.
B. plough and conventional) and three levels of fertilizer (existing, half of recommended and recommended). The existing management practice was considered as the base for evaluating other management practices for rice. The results showed that the other crops could not replace rice since these crops resulted in higher sediment yield as compared to rice. Considering both sediment and nutrient losses collectively 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 for rice therefore, recommended for the management of critical subwatersheds of Arang watershed.
