Fayoumi Standard Weirs have been modified by adding one, two or three pipes, to convey
much water to downstream direction. Measurements of discharge with these structures are
complicated due to existence of the openings. In this research, an experimental study is
carried out to investigate the effect of installing pipes through a piped clear over fall weir
and bottom-pipes. Twelve weir models with different heights are tested in horizontal
laboratory flume of 17 m length, 0.3 m width, and 0.5 m depth. Weir height is changed two
times. Contraction of weirs is changed two times. For each one, the diameter of opening is
changed three times. The downstream depth is changed to cover all the concerned flow
regimes of flow rate for a submerged pipe and a free weir. The downstream water depth
begins with the upper tangent of the pipe and ends with the crest level of the weir. The
contraction and the un-contraction of the weir are discussed. The effect of downstream
water depth is taken into consideration. The results of flow over weir with opening are
compared with those of weir without opening having the same dimensions. It is found that
there is a large difference between them. Multiple regression equations based on energy
principal and dimensional analysis theory are developed for computing discharge over
clear over fall weir with bottom pipes. 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