Runoff Simulation Using SWAT Model In The Three Gorges Reservoir

Simulation of surface runoff is widely used in many research fields, such as soil erosion, agricultural pollution, and surface water balance. Water cycle plays an important role in the process of soil erosion and non-point source pollution. Therefore, hydrological process is of critical importance in soil erosion and non-point source pollution at watershed scale.The current study conducted a simulation of runoff in Tangxihe watershed, which is located in the Three Gorges areas, using SWAT model and a geographic information system (GIS). According to the model, soil and land use types of the study area were re-classified and coded. A meteorological simulation generator was created using long-term observed weather data. The model was calibrated and validated using rainfall data from June to October of 2005.The distributed hydrological model was constructed on the basis of the results. The main contents and results were as follows:(1)With the help of GIS,spatial database of TangXihe basin were built. A digital elevation model (DEM) with a resolution of 83×83m was created using the original topographic map. Hydrology information was extracted from the DEM. The research area was divided into 21 sub-basins using the hydrology information. Spatial database of soil and land use were constructed using soil map of the national second soil survey and land use map of 2005 at a scale of 1:500000. Thirty-eight hydrologic response units were extracted by overlaying the sub-watershed, soil, and land use map.(2) Construction of attribute database. On the basis of the national second soil survey, thirteen parameters including soil layer, soil bulk density, and soil effective moisture content were collected and converted according to the model requirement. Land use type codes were transformed to that of the American system which were available to the SWAT model. Observed meteorological data from 1956 to 2000 of Wanzhou and Fengjie were used to construct the meteorological simulation generator of the study area.(3)Calibration of parameters. Seven main parameters, namely, SCS(Runoff Curve Number Method), SOL_AWC(Available water capacity of the soil layer), SOL_K(Saturated hydraulic conductivity), GW_DALAY(Gesidence time of groundwater recharge), ALPHA_BF(Base flow recession coefficient), and ESCO(Evaperation compensation facor in soil), were calibrated after numberous repetitions of experiemnts.(4) Development of the distributed hydrological model.The model was calibrated and validated using the daily runoff data from June to October in 2005.The attendant errors of the model calibration using the daily runoff data from June to August were repressively-12%,-19% and-17% and correlation coefficients were repressively 0.85,0.87 and 0.88.The determination coefficients were 0.56,0.89 and 0.68 repressively. All the results from calibration and validation were acceptable and satisfied with the application of SWAT hydrological model in TangXihe River Basin.(5)The results suggested that SWAT model could be applied to simulate the runoff of Tangxihe watershed in the Three Gorges areas with the help of GIS, soil, land use, DEM, and rainfall data. The outcome of this research showed that the SWAT model can be used to simulate the process of rainfall-runoff in conditions of limited observed hydrological information.