WATER-SURFACE SLOPE AT CRITICAL CONTROLS IN OPEN-CHANNEL FLOW

A general equation is proposed for the determination of water-surface slope of a steady, gradually varied open-channel flow at a critical se ction. Thereupon the different types of singular points and water-surf ace slopes are given at such a section caused by changes in (1) bed sl ope, (2) channel width, (3) surface roughness of the channel, and (4) discharge, or their combinations. Although these factors are very diff erent they have similar hydraulic effects on the occurrence of a certa in type of singular point and water-surface slope. It is shown that a saddle type singular point is the only one which can become a control. The water-surface slopes at a critical control are evaluated using th e proposed equation and are verified by the experimental results of Wi lkinson (1974) for cases (1) and (2).