Flow Measurement in Sloping Channels with Rectangular Free Overfall

Abstract

This technical note describes an experimental study of the free overfall from a rectangular channel with differing slopes and bed roughnesses. The relationship between the upstream critical depth and brink depth is explored and found to be influenced by both slope and channel-bed roughness, with roughness having a greater effect at steeper slopes. Two empirical equations are proposed for calculating this relationship, the first requiring only the channel slope to be known, and the second requiring a knowledge of channel slope and roughness. The accuracy of the two equations when used in a method for flow measurement are compared. The first relationship, in which the effects of slope and roughness are aggregated, provides a useful estimate of channel discharge if only the channel slope is known. If both bed roughness and slope are known then the second relationship can be used to calculate channel discharge with greater accuracy.