FLOOD ROUTING IN CHANNELS WITH FLOOD PLAINS

Experimental data on unsteady flows in a channel with flood plains obt ained in a laboratory test facility are presented. Flood flow at the u pstream end of the channel was produced by an electrically actuated bu tterfly valve in the supply pipe. Water level variations were recorded at nine stations along the channel using capacitance probes and a com puterized data acquisition system. Tests were conducted for various in itial conditions, and duration and peak of the flood wave. Complete da ta for two tests are presented which may be used to verify numerical m odels. A one-dimensional numerical model was developed to simulate flo od flow. The model solves the St. Venant equations by using the Preiss mann four-point implicit finite-difference scheme. The suitability of two procedures for approximating the channel cross-section is investig ated: (1) the flow velocity over the flood plains is negligible, the f lood plain acts as storage only and does not contribute to the momentu m (the flood plains and the main channel are separated by a vertical l ine at their interface and the division line is not included in the we tted perimeter); (2) the entire channel section contributes to momentu m flux, the entire channel section has uniform average flow velocity a nd the non-uniform velocity is taken into consideration by a momentum coefficient, Although comparisons between the computed and experimenta l results are satisfactory in both cases, Approximation (1) gives bett er results than Approximation (2).