Proposal of Universal Method for Runoff Calculation Using GIS

Abstract

 Large-scale flood damage caused by abnormal weather has occurred frequently in recent years. To mitigate such damage, some method is necessary to estimate the runoff and water level at any time and location. As a tool for doing so, the runoff calculation solver iRIC SRM, which is useful without complicated procedures, was developed. The SRM has a function for optimizing the model parameters for a given storage function method by inputting the rainfall and discharge. It also has a function for calculating the discharge by inputting the rainfall and model parameters. Regarding basins for which measured discharge data are not available, optimization of model parameters is not possible. Therefore, verification of the propriety of the calculated runoff is not possible. This study examined a method for estimating the necessary parameters by extracting the borders of drainage basins and the geological data of the land surface layer and by estimating the average rainfall for the basin, based on GIS data. The discharge calculated using the optimized parameters was compared to the discharge calculated using the geologically set parameters based on a multiple regression function in which the geological surface ratio was used as a variable. A comparison showed that runoff calculation with accuracy of the Nash coefficient of about 0.7 is possible using the geologically set parameters. Results show that runoff calculation can be accomplished easily at any location in Japan using the method presented in this report.