Abstract
The storage-discharge relationship is an important property of many hydrological models, which are useful in the climate change adaptation strategies, for the flood risk reduction. Although the nonlinearity of river flow recession was proposed to be a power law function of the type S=kQp, a major problem still lies in the uncertainties of the coefficient k and exponent p for engineering applications. The most utilized model for the flood runoff analysis in Japan is based on the power law function of the storage-discharge relationship. However, a set of k and p in the power law function is different in each flood event, causing difficulty in estimating and forecasting the flood runoff hydrographs accurately.
The aim of this study is to identify the parameters in the storage-discharge relationship for floods. The hydrological model used in this study comprises the combination of the storage-discharge function and the Diskin-Nazimov rainfall infiltration model. The study basin is the Sameura Dam basin (472 km2) located in the mountains of Shikoku in western Japan. For the sensitivity analysis, 14 flood events of a single peak hydrograph are selected from hourly data for a period of 20 years. In order to optimize the set of k and p by maximizing the Nash-Sutcliffe efficiency, more than 30,000 simulations are carried out for each flood event by changing the values of k and p using a double-loop algorithm.
The results showed that the optimum values of the sets of p and k in the storage-discharge relationship fell on a linear line on the log-log graph, and thus can be represented by the power law function.
