HYDRAULICS OF CLEAR OVERFALL WEIRS WITH BOTTOM-OPENINGS

Abstract

Many Fayoum Standard Weirs have been perforated by one, two or three pipes, to convey much water in downstream direction. Measurements of discharge with these structures are complicated due existence of the opening. In this research, an experimental study was carried out to investigate the flow over clear over fall weir with bottom opening. Nine weir models with different heights were tested in horizontal laboratory flume of 17 m length, 0.3 m width, and 0.5 m depth. Weir height is changed three times. For each one, the diameter of opening is changed three times. The downstream depth was changed to cover all the expected flow regimes of the pipe and the weir. These flow regimes are; free pipe-free weir, submerged pipe-free weir and submerged pipe-submerged weir. The results of flow over weir with opening were compared with those of weir without opening having the same dimensions. It was found that there is a large deviation between them. Multiple regression equations based on energy principal and dimensional analysis theory were developed for computing discharge over clear over fall weir with bottom opening. Also, values of discharge coefficients were estimated for combined flow over the weir and through the pipe. Then the total discharge can be computed by multiplying the discharge coefficient by the summation of theoretical weir discharge plus theoretical orifice discharge. Equations for computing the discharge of combination are awarded.