In this paper, the free overfall in rectangular channel with a different slopes and bed rough distribution was studied. Bed roughness was made of wood allocated in three different cases: two, three and zigzag rows. The aim of this study is to obtain discharge equations for free overfall depending on brink depth and slope. Three empirical equations proposed for calculating discharge. These equations influenced by slope, channel bed roughness as well as method of roughness distribution. Three rows bed roughness having grater effect on these relationships at steeper slopes. the average values of hc/he at smooth bed is greater by (4%) with respect to that for bed rough at two rows, by (19%) with respect to that for bed rough at zigzag rows and by (24%) with respect to that for bed rough at three rows, so that values for three rows rough and horizontal channel is greater by (4%) with respect to that for channel slope at (1/200) and by (14%) with respect to that for channel slope at (1/100).

A free overfall at the end of the channel is used as a flow measuring device. In this paper, theoretical end depth ratio (EDR) and end depth discharge (EDD) relationships have been studied and obtained for subcritical flow in a rectangular channel with a free overfall and with different end lip shapes; i.e., triangular and skewed lip. For all models, Froude number at the brink section Fb, EDR and EDD are predicted using the theoretical relationship and compared with the values computed experimentally. The mean absolute error varies from 0.5% to 8.5% and the standard deviation varies from 0.824% to 7.35%.

In this paper the effect of the lower gate edge on the water surface profile (W.S.P) have been studied in a rectangular flume with four gate openings (2, 3, 4 and 4.5) cm, five upstream of water heads (18.9,21,24,26 and 28.9) cm and five gate cases (vertical and inclined vertically by angle (45)o with and opposite to flow direction )with horizontal and sharp lower edge ( inclined by angle (45)o ) Were adopted in the experiments. The results show that the convergence length for inclined gate with flow direction and horizontal edge increases by (28.7)"%" with respect to vertical, while decreases by (21.4)"%" when gate inclined opposite to flow direction and horizontal edge. The convergence angle decreases by (38.7)"%" when gate inclined with flow direction and horizontal edge, while increase by (22.4)"%" when gate inclined opposite flow direction and horizontal edge. The horizontal lip for the inclined gate with flow direction reduced the (W.S.P) convergence angle and then reduced the scour downstream sluice gate.

In the present work the alternative concept of an elementary discharge coefficient along the longitudinal side weir was studied using an oblique weir. Five different angles (30o, 45o, 60o, 75o, and 90o) in the flow direction (inclined to the left) with respect to the branch channel wall were examined. A numerical solution of two ordinary differential equations was proposed for discharge and flow depth conducted with program using Euler’s method and compared with experimental values. Results referred to the possibility of correlating water surface profile (W.S.P), water depth, and flow discharge numerically as well as the possibility of increasing flow discharge passing through the branch channel by an oblique side weir installation. Thus flow discharge can be increased with side weir angle. Maximum discharge occurred at an angle of 30o where the percent increase compared with that at 90o was 70%.