Saemangeum development project construction has begun on November 28. 1991, then problem of water pollution in accordance with the accelerated development has increased. A water pollution problem has emerged as a key social issue in water pollution. For the development of Saemangeum basin and Saemangeum reservoir which would be established after the dike construction, water management plan is important, especially vicinity of upstream and freshwater reservoir. Therefore, it is required to continuous monitoring and development of water quality simulation model that presents to response relations of water quality according to runoff for the watershed.
This study simulated water quality item and discharge of subbasin for Saemangeum watershed using SWAT(Soil and Water Assessment Tool) model and the results applied to EFDC(Environmental Fluid Dynamics Code) model which simulate hydraulic and water quality in three-dimensions. The SWAT model calibrated and verificated on a eight points of Saemangeum basin and discharge flow rate simulated with statistics such R2 0.54～0.90, RMSE 0.58～17.56, %diff. -32.56～21.01 and in case of water quality item, BOD ; RMSE 0.65～8.56, %diff. 4.88～20.12, T-N ; RMSE 0.64～4.51, %diff. 4.47～19.39 T-P ; RMSE 0.07～0.41, %diff. 5.30～27.5 and it is evaluated good in presenting the observed values.
The SWAT model results were applied to the EFDC model and the result statistics are water temperature ; RMSE 0.70～5.33, %diff. 1.41～11.72, DO ; RMSE 0.55～5.12, %diff. 1.61～15.22, Chl-a ; RMSE 0.21～13.36, %diff. 2.33～17.51, T-N ; RMSE 0.04～0.87, %diff. 1.19～18.66, T-P ; RMSE 0.01～0.06, %diff. 7.50～26.13, COD ; RMSE 0.53～3.62, %diff. 4.40～19.97 and it showed within error range. So simulated values can correspond observed value well.
The result of Gate operated simulation suggested that at the M3 and M5 points, it exceeds water quality standard and at the M3 and D3 points, a concentration change range is too wide, and upstream is sensitive to inflow flow rate. Compared to the annual average concentration for each point the discharge conditions, improvement of the upstream water quality was markedly compared to the downstream.
This study result demonstrated that Gate management has a big influence on Saemangeum water quality management and it needs to be considered in plans for Gate operation on Saemangeum reservoir.