A methodology to examine a depth-discharge constitutive equation for rainfall-runoff modelling

A number of rainfall-runoff models have been developed for hydraulic and hydrological engineering with an empha‐ sis on reproducing river discharge time series. Physicallybased rainfall-runoff models have recently reached a certain level of achievement following the advancement of com‐ puters and the development of various geographical and meteorological datasets. However, it has been pointed out that the current physically-based models do not properly reflect observed hillslope water dynamics. The present paper proposes a methodology to examine the capability of a depth-discharge constitutive equation for physicallybased rainfall-runoff modelling to simulate hillslope water dynamics. An application of the methodology suggested that 1) the targeted constitutive equation was capable of representing the depth-discharge relationship on hillslopes under the assumed conditions, 2) the runoff simulations with the constitutive equation described hillslope water flows, at least in the downward direction, and 3) there was a possibility that the parameters in the constitutive equation was determined from the internal structure of hillslope water dynamics.