Flow over side weirs

A literature survey has been carried out to assess the merits of the diverse methods of analysis of side weir flow previously available. Two of these appeared to have potential as practical methods of analysis and they were tested against the data obtained during this investigation.
A momentum analysis of the flow in the main channel yielded a general differential equation which, for supercritical now, included terms to allow for the effect of curvature on the vertical pressure distribution. The discharge over the side weir, per unit length, was obtained using the transverse weir equation. These two simultaneous equations formed the basis of a mathematical model incorporating standard integration techniques.
Preliminary tests were conducted in a large rectangular channel which tapered uniformly so as-to produce a constant head along the weir, This enabled values of the coefficient of discharge to be obtained for use in the transverse weir equation, and values were found to lie within 2% of those given by the Rehbock equation. Velocity distributions were measured to establish values of the momentum flux correction factor, and these were found to correspond to normal values.
In the main experimental investigations five side weirs were tested in a prismatic rectangular channel. The most significant parameters that affected the discharge over the weir were the settings of the channel controls and the crest height. Substantial variations in the weir length were required to affect the side spill discharge significantly, whilst the effect of the channel slope was almost negligible.
A comprehensive set of experimental data was obtained and this was used to test the accuracy of the mathematical model. It was found to give extremely good simulation of the flow with both mean and standard deviation of errors in the computed discharge less than 5% in all cases.