Kinetic energy and momentum correction coefficients in compound open channels

Flood management is fundamentally unresolved in nature due to several sources of unreliability including parameter uncertainty. Applying inappropriate values for the kinetic energy and momentum correction coefficients (usually named alpha and beta, respectively) can lead to considerable error in the calculation of water surface profiles, critical depth and energy losses in rivers. Due to the strong variations in the streamwise velocity, the values of alpha and beta across compound open channels differ from those in a simple open channel. In this paper, the variations of alpha and beta coefficients are investigated across the main channel and floodplain of two different shapes of compound open channel (rectangular and trapezoidal). Also, variations of these coefficients against the relative flow depth (the ratio of floodplain to main channel flow depths) are discussed. The results show that the values of alpha and beta in the main channel are always lower than those over the floodplain. As flow relative depth increases, the hydraulic behavior of the compound channel tends to that of a simple channel.