FLOW MEASUREMENT IN SLOPING CHANNELS WITH RECTANGULAR FREE OVERFALL

This technical note describes an experimental study of the free overfa ll from a rectangular channel with differing slopes and bed roughnesse s. The relationship between the upstream critical depth and brink dept h 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 seco nd requiring a knowledge of channel slope and roughness. The accuracy of the two equations when used in a method for flow measurement are co mpared. The first relationship, in which the effects of slope and roug hness are aggregated, provides a useful estimate of channel discharge if only the channel slope is known. If both bed roughness and slope ar e known then the second relationship can be used to calculate channel discharge with greater accuracy.