LATERAL MOMENTUM TRANSFER EFFECTS IN THE MODELING OF UNSTEADY FLOWS IN COMPOUND CHANNELS

The impact of lateral momentum transfer (LMT) on channel conveyance is examined through applications of a new mathematical model for routing unsteady flows in compound channels. The model accounts for LMT through three parameters that relate: (i) 'actual' to 'isolated' sub-section discharge, (ii) main channel to flood plain lengths between stations, and (iii) flood plain to main channel depths. The model was applied to route a series of flood events in a hypothetical compound channel consisting of a deep smooth main channel between two wide and rough flood plain zones. The routing exercise was repeated with and without LMT in the analysis. Three empirical methods to account for LMT were investigated by comparing their corresponding simulated stage and discharge hydrographs. In general, LMT was found to have little impact on simulated stage hydrographs, however, for the case of small flood plain flows, LMT was responsible for some attenuation in the discharge hydrographs.