Date of Award
Doctor of Philosophy (PhD)
Charles S. Melching
Clifford J. Crandall
Hector R. Bravo, Neal O'Reilly
The primary hypothesis from the hydrological literature is that downstream moving storms with storm length (Ls) less than watershed length (Lc) magnify the peak discharges. This hypothesis was developed from the kinematic-wave modeling, and was evaluated in a plot between the dimensionless peak discharge and dimensionless storm velocity. Previously unpublished experimental data collected from the Watershed Experimentation System (WES), obtained from the late Professor Ben C. Yen at the University of Illinois at Urbana-Champaign, were used in comparison with the simulation results of the kinematic-wave model. It is found that downstream moving storms with Ls/Lc <1 increase the peak discharges to a limited extent compared to stationary storms, but the kinematic-wave model overstates the increase in the peak flows resulting from downstream moving storms with Ls/Lc <1. This difference between model projections and laboratory data was attributed to backwater effects in the experimental runoff.
To evaluate the importance of the backwater effects, the accuracy of kinematic-wave and dynamic-wave models for the simulation of surface runoff resulting from moving storms was evaluated utilizing the same experimental data. It is found that, the kinematic-wave model cannot deal with the backwater effects resulting from downstream moving storms in the V-shaped watershed in the WES. The kinematic-wave model simulates the upstream moving storms pretty well, whereas it totally overestimates the peak discharges for downstream moving storms.
To confirm the reliability of the nondimensional plots it was necessary to evaluate the kinematic-wave based equations for estimation of the time of concentration. Three methods, i.e., Ben-Zvi's method, the modified Ben-Zvi method, and Izzard's method were applied to determine the time of concentration from the experimental hydrographs of stationary rainstorms reaching the equilibrium state from the WES. The times of concentration determined by these three methods were compared to the mathematical equation proposed by Wong. It is found that a percentage of 89% can be a generally agreeable percentage to evaluate the experimental data from the WES. It is concluded that Wong's equation can predict the time of concentration acceptably well for the simplified watershed with mild overland and channel slopes and long durations.