Hydraulics of flow over side weirs

This thesis reviews the present state of knowledge of the hydraulics of flow over side weirs, and describes an experimental investigation into the flow of water over side weirs using a laboratory flume. A detailed exeimination is made of the assumption conventionally used by many investigators that the total energy of the flow remaining in the channel does not vary along the length of the side weir (excluding friction loss). Some new conclusions are suggested concerning the weir coefficient, the variation of the velocity sind pressure distribution coefficients and the end controls. The secondary flow observed along the side weirs in the experimental work and the changes it underwent on progressing along the side weir are described in detail. Some degree of confirmation of the analysis was achieved for the exact way in which the flow moves along the side weir as it leaves the channel section and enters the side weir section. The background of the side weir theory is given in detail, preceding an examination of the predictions of this theory in terms of the results of the present and other experimental investigations. It has been found that even when the energy of the secondary flow and the non-uniform velocity distribution are allowed for, the observed Total Energy Line along the weir length falls considerably below the horizontal. From observations it could be seen that the longitudinal component of velocity of water flowing over the side weir is usually considerably higher than the average velocity of the water remaining in the channel. In this situation it was found necessary to use a momentum approach, taking into account the momentum of the water flowing over the side weir. The derived equation for the water surface profile along the side weir based on the momentum principle has been discussed in detail, some relationships for different cases are derived depending on the ratio between the spill flow over the side weir to the flow in the main channel upstream of the side weir, and also on the type of flow along the side weir. A computer programme based on the derived momentum equation predicted water surface profiles which compared well with the observed profiles. Also, a satisfactory comparison was made between the observed water surface profiles obtained by some earlier researchers and the computed water surface profile based on the technique developed in this thesis.