Estimation of Ground Water Runoff by SWAT Model in Golgol Catchment

The biggest restriction of natural resources in Iran is dry and semi-dry climate and deficit of water resources. Non-normative use of natural resources causes imbalance between water components and demand. The main objective of this study is to test the performance and usability of the simulation model to estimate water balance and groundwater flow in 223.9 km2 of Golgol catchment in Ilam Province using Soil and Water Assessment Tools (SWAT) model and SUFI2 Program. The input data model include topographic, land use and soil maps and also climatologically data, including daily precipitation, temperature, relative humidity and stream flow. In order to determine the important parameters of the model, the parameter sensitivity analysis using "One At a Time " (OAT) was performed and the effect of various parameters such as stream flow, lateral flow and ground water flow on water balance evapotranspiration was examined. In order to calibrate the model SUFI2 algorithm was used.Simulation model for 13 years from 1997 to 2009, was the first of eight years (2004, 1997) for model calibration and the next five years (2009-2004) were selected for validation of model results. Statistical indices P-factor, d-factor, Nash Sutcliffe (NS) and the coefficient of determination (R2) on a monthly basis for the evaluation model was chosen.The Nash-Sutcliff coefficient for calibration and validation period is 0.65 and 0.49 respectively. The results show satisfactory performance of the SWAT model to simulate the water balance components in the Golgol catchment. The obtained values of R2 in both calibration and validation are 0.66 and 0.51 respectively which is indicating the relative desirability of the model. The results of simulation show that the average annual rainfall of 503 mm, the maximum amount is belong to evapotranspiration that equal 366 mm (72%) of the total precipitation in the catchment. The total groundwater and lateral flow is equal 77 mm (15.3 %), the surface runoff is 47.8 mm (9.5 %) and annual losses equivalent to 3% of total precipitation. The share of 15.3 percent of the total sub surface flow and groundwater from total precipitation is valuable for planners to implement management plans in study area.