Laboratory Experiments with Surface Runoff

Kinematic wave and instantaneous unit hydrograph concepts are used to predict overland flow hydrographs. Laboratory conditions satisfied idealized assumptions of the tested mathematical models that the hydrographs correspond to direct runoff resulting from rainfall distributed uniformly in time and space over a runoff plane with a constant slope. Time to peak, peak value, and total time base of the instantaneous unit hydrograph is found to be dependent on the rainfall intensity. Predicting runoff by means of a convolution integral leads to erroneous results. Satisfactory results are obtained by analytical solution of the kinematic wave formulation of overland flow equations. Time to equilibrium predicted by the kinematic wave model as a function of rainfall intensity is in good correlation with empirically determined apparent time to equilibrium. Nonlinearity of the rainfall-runoff relationship is not affected by the slope or roughness of the runoff surface.