Overland Flow Hydrographs for SCS Type II Rainfall

Abstract

A mathematical model, which is founded on the kinematic‐wave and Green‐Ampt equations, is presented for the conjunctive overland flow‐infiltration process. Within the context of this model, it is shown that overland flow resulting from a specified time distribution of rainfall intensity can be described in terms of only three physically‐based nondimensional parameters. In cases where a less precise geometric shape is adequate, overland flow hydrographs for the 24‐hr SCS‐Type II rainfall can be approximated by triangular hydrographs. It is possible to evaluate the elements of such a triangular hydrograph in terms of the three governing physically‐based parameters of the overland flow‐infiltration process without using a computer. A dimensionless standardized triangular hydrograph is proposed that predicts the peak discharge, the time of occurrence of the peak discharge, and the volume of runoff before and after the hydrograph peak.