DISCHARGE RATIOS IN SMOOTH AND ROUGH COMPOUND CHANNELS

No entirely satisfactory method of estimating discharge capacity in co mpound channels and rivers has been developed. However, a large body o f experimental data has now been acquired covering small-scale and lar ge-scale laboratory compound channels as well as full-sized rivers. Tw o key ratios, namely total to bank-full discharge and main channel to floodplain discharge, have been shown by theoretical analysis to be si gnificant and the available data have been analyzed to illustrate thei r behavior for smooth and homogeneously roughened compound shapes at v arious scales. The ratio of total compound section to bank-full discha rge has been shown to be independent of bed slope and scale and to be a function of cross-sectional geometry only. The ratio of main channel to floodplain discharge is independent of bed dope and scale, but is influenced by lateral floodplain bed slope. The coefficients and expon ents in equations relating the ratios to depth have been evaluated. It has been suggested that the use of these ratios may provide a compara tively simple method of discharge estimation in compact homogeneously roughened compound channels, and may be extended to other cases when m ore data are available.