Evaluation of Water Surface Elevation in Non-Prismatic Compound Channels

Predicting the water level in non-prismatic compound channels is necessary to determine the boundaries of floodplains in the range of converging or diverging and also to determine the stage-discharge curves of river flow during floods. In this study, using laboratory data taken from three compound channels with divergent and convergent floodplains at different angles of divergence and convergence, depth ratios and different roughness ratios, the relationships for estimating the water level in such sections have been investigated. The maximum relative error of the proposed relationships for depth ratios is less than 0.4 in divergence and convergence conditions is 13.29% and in depth ratios is greater than 0.4 and in divergence and convergence floodplains is about 1.98%. The results show that the water surface level along a diverging and converging range in non-prismatic compound channel with different divergence angles respectively increases and decreases with increasing depth ratios. Also, in this experimental conditions, the water level in the divergence (convergence) range of floodplain is affected by factors such as depth ratio and relative distance and follows less than relative roughness and divergence (convergence) angle.