Deterioration of water quality is a serious problem in the EDO castle outer moats due to CSO (Combined Sewer Overflows). People who live in the area are suffered from stench and landscape destruction. In this study, to calculate a more accurate CSO loads and to construct a model which is water and material movement based on OHAM. Furthermore effect of water quality improvement measures (rainwater storage facilities and moveable weir) was evaluated quantitatively. As a result, the new model has higher reproductivity than the previous one. It was confirmed by the model that pollution loads has been to be 35????40 % reduced by moveable weir.