THE USE OF DIFFERENT CONVEYANCE CALCULATIONS FOR MODELING FLOWS IN A COMPACT COMPOUND CHANNEL

Flow measurements have been taken for steady and unsteady flows on a r each of a river having a compact compound channel. The 'single channel ', 'divided channel' and 'lateral' distribution methods have been used to calculate conveyances for use in a one-dimensional unsteady flow m odel of the reach. Comparisons with measured flows show that the divid ed channel method and the lateral distribution method both underestima te floodplain flow depths. The lateral distribution method gives the c losest accuracy in the relative depth range 0.15 less than or equal to Yr < 0.40. For large flow depths the single channel method becomes mo re accurate and slightly over-estimates flow depths. The accuracy of u nit width discharge distributions, calculated from the lateral distrib ution method are assessed by comparison with observed distributions fo r overbank flows.