Determination of Discharge Coefficient in Ogee Spillways and Investigation the Effects of Submergence, Upstream Slope and Apron Elevation on Its Variations

Abstract

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