Obtaining Overland Flow Resistance by Optimization

A mathematical model simulates and predicts overland flow hydrographs. The kinematic form of the nonlinear partial differential equations of unsteady, spatially varied, shallow-water flow are solved simultaneously by numerical integration. The mathematical model is verified by laboratory data obtained from a rainfall generator and a physical model. Parameter optimization provides a set of representative, synthetic, resistance-parameter values. The synthetic data and a dimensional analysis yield predictive resistance-parameter relationships. Power equations relate the resistance parameter to the precipitation number (precipitation rate divided by the product of unit discharge and downstream depth) during rainfall and to the Weber number after rainfall. Satisfactory results are obtained using a constant resistance-parameter value during rainfall and another smaller constant value during recession. This suggests that the hydrographs are fairly insensitive to changes in the precipitation number and the Weber number.