Determination of discharge coefficient in ogee weirs and investigation the effects of submergence, upstream slope and apron elevation on its variations

Discharge over the ogee weir is related to the length of crest, upstream total head and discharge coefficient. Also discharge coefficient is influenced by several factors. In this study, some parameters that are affecting the discharge coefficient in ogee weir are investigated. These are: ogee weir upstream slope, apron elevation and downstream submergence. In this regard, some ogee weir physical models were fabricated. These models include: (1) ogee weir with vertical upstream face; (2) ogee weir with inclined upstream face (18, 33, and 45 degrees); (3) ogee weirs with downstream apron elevations (3, 5, 7, and 10 cm thickness) in free flow; and (4) ogee weir with vertical upstream slope in submerged flow condition. Results show that in all the ogee weirs, the discharge coefficient (C) increases with increasing (P/He), and then remain constant. The value of discharge coefficient decreases from 2.25 (in free flow) to 2.15 (in submerged flow). For a constant value of head over ogee weirs (He), the discharge coefficient decreases with increasing in downstream apron elevation and submergence. The relative discharge coefficient has constant trend at beginning with parameter (hd/He), then has decreasing trend. The threshold value for submergence (hd/He), is 0.75 in ogee weir in this study. With increasing relative submergence (hd/He) from 0.75 to 1, the relative discharge coefficient (Cs/C0) decreases from 0.88 to 0.24.