Improved rational hydrograph method

This paper presents an improved rational hydrograph method to compute the runoff at the outlet of a small urban catchment. The new formulation, based on the linear system theory, explicitly considers the contributions of pervious and impervious areas, the time variability of rainfall, the initial abstraction on impervious areas and the infiltration on pervious areas. Moreover, the rational method formula appears to be a special case of the proposed rational hydrograph method. A sensitivity analysis conducted on the improved rational hydrograph method has emphasized the most influent parameters. A sequential procedure is proposed to calibrate parameters of the improved rational hydrograph method on the basis of appropriate storm events. The improved rational hydrograph method was applied to 41 rainfall events gauged in 7 different North American and European urban catchments. Runoff computed with the improved rational hydrograph method was compared to measured runoff, as well as to the runoff derived from the nonlinear reservoir model. A good agreement was achieved between simulated and observed runoff hydrographs. Moreover, runoff hydrographs derived with the proposed method are equivalent to those computed with the nonlinear reservoir model.