A GIS-based distributed parameter model for rainfall runoff calculation using arc hydro tool and curve number method for Chikugo River basin in Japan

Determination of peak and total runoff due to rainfall is the most important for watershed management and designing hydraulic structures. The measurement of runoff is always the best way but it is not possible at desired time and location. A rainfall runoff modeling, which uses geographical information system (GIS) data based, is a convenient and powerful tool to solve the above mentioned complexities. This technology was applied in this study in order to simulate the runoff discharge in the Chikugo River basin in Kyushu Island, Japan. First, an extension tool (Arc Hydro) of a GIS software was used for simulations of elevation, drainage line definition, watershed delineation, drainage feature characterization, and geometric network generation. Second, the spatial distribution of land-cover, soil classification, and rainfall were analyzed for calculating the rainfall excess distribution in the basin. An important point of this approach is that the spatially distributed rainfall excess volume was computed by the Natural Resources Conservation Service Curve Number (NRCS-CN) method. The final goal of this study is a total discharge volume in the sub-watershed region of the basin was consequently computed on a monthly basis throughout one year (from April 2005 to March 2006) by using NRCS-CN model. The results show that the simulated stream network was totally consistent with its existing one. Additionally, the observed and simulated runoff discharges were in good agreement, indicating that the proposed model is applicable for rainfall runoff analyses in this river basin. For further, this model will be able to provide managers and operators a useful tool that is to optimize the water surface management in the Chikugo River basin.