GIS-based watershed management modeling for surface runoff calculation in Tatara River Basin, Japan

In the past few decades when Geographical Information System (GIS) technology was not fully developed in practical use, watershed delineation work used to be conducted manually by hydrologists based on topographic maps. The work was a tedious operation, since it had to be done repeatedly in similar manner for each basin or sub-basin of interest, and its process always left some unpredicted errors. Nowadays, GIS software is being upgraded regularly with powerful tools responding to the needs of users in different fields. In the present study, to find a simple hydrological solution for a basin (Tatara River basin), an extension tool (ArcHydro) of a well-known GIS software (ArcGIS) was essentially used for simulations of elevation, drainage line definition, watershed delineation, drainage feature characterization and geometric network generation. With sufficient resolution of DEM interpolated from point elevation data, all water bodies extracted from topographic maps in the basin were critically characterized-the depth and water volume of lakes, ponds, and rivers were numerically computed. The final goal of this paper is to calculate surface runoff of the study basin based on a GIS-based watershed management approach. The work was also processed under another extension called the ArcCN-Runoff model, which ran on the background of ArcGIS software. This extension tool was built based on a very popular model for surface runoff estimation known as the Soil Conservation Service-Curve Number (SCS-CN) model. A total discharge volume in the northern sub-watershed region of the basin was consequently computed on a monthly basis throughout one year. The computed discharges were totally consistent with those observed, and each of the discharges was also confirmed to be responsible for rainfall. These indicate that SCS-CN and ArcCN-Runoff models used in this paper are definitely valid and can be applied to other related projects of surface runoff calculation.