Evaluation of simulating daily discharge flow using SWAT model, case study: Kasilian catchment area

Lack of hydrometric data is the main issue for research and executive plans. In thepresent study in order to solve this issue, the capability of SWAT model has beenstudied in terms of daily discharge simulation in un-gauged watersheds. This model cansimulate six hydrological and biological processes such as daily discharge, dailysediment, yearly and monthly water balance, water quality, agricultural products andestimation of vegetative cover for different animal grazing management systems.Simulation has been done for both gauged and un-gauged basins in Kasilian catchmentfor two time periods as calibration and validation of model. Calibration has been doneusing data derived from 4 years recording data (1987-1981) while validation has beendone using 6 years data (1981-1986). Results show that, ABF, CN2 and REVAPCparameters are most sensitive and also Z and T-Laps parameters are low sensitiveamong other parameters. The model simulated runoff reasonable with r2=0.69, PBIAS=-2.5, and NS=0.72, whereas, the validation of model for the same data showed thatr2=0.57, PBIAS=4.3, and NS=-0.54, which indicates that the performance this model isnot quite valid for low stream flows because of sensitivity of hydrological parameters.The new version of SWAT model, modified during 2000 to 2005, has a capability inusing GIS, thus it can be used in the same study area.