New runoff simulation model for small urban catchments

This note presents a new runoff simulation model based on the improvement of the rational hydrograph method. This improved rational hydrograph method explicitly considers the contribution of pervious and impervious areas, the time variability of rainfall, the initial abstraction on impervious areas, and the infiltration on pervious areas. Moreover, the traditional rational method appears to be a special case of the proposed rational hydrograph method. A structured procedure is proposed to calibrate parameters of the improved rational hydrograph method on the basis of appropriate storm events. The proposed method was applied to ten rainfall events gauged in two different 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, runoffs derived with the proposed method are equivalent to those computed with the nonlinear reservoir model.