An Experimental Study for Radial-Gated Ogee Spillway Discharge and Comparison with Other Model Studies

Abstract

The book "Design of Small Dams" is a renowned reference publication used for the design of dams in America and it is commonly used in Turkey as well. Flood spillways of many dams are ogee profile radial-gated weirs, and accurate calculation of discharges passing over a partially open radial-gated ogee spillway is important in flood routing computations. Because each spillway and its appurtenant structures have geometrical and hydraulic properties peculiar to their own, a generalizable method for calculating the discharge over a partially open radial-gated spillway should not be realistic. Therefore, many laboratory experimental studies are done both in America and in Turkey for more accurate calculation of spillway discharge of dams individually. With the objective of comparing the results of these studies and the method given in that book another experimental study is performed as summarized in this paper. For this purpose, experiments for the partially open radial gate in a laboratory setup having a 95 mm high, 10 cm wide ogee spillway model with an adjustable radial gate of proportionate dimensions both placed in a 5 meter long, 10 cm wide and 30 cm high channel are done with many combinations of flow rates and gate openings as allowed by the physical dimensions of the open channel setup available in our laboratory and the maximum flow rate its pump can generate. Taking a scale ratio of 1/100, the relative differences of the discharge coefficients given in the above-mentioned book from the experimental discharge coefficients measured in this study for the same configurations are found to be between +3% and +34%. Although the discharge coefficients determined by this experimental study are not too deviant from those obtained from 15 laboratory model studies done by the United States Bureau of Reclamation and the United States Army Corps of Engineers in America and seven such studies done by the State Water Works in Turkey, it is concluded that the discharge – head relationship of a radial-gated spillway of a dam should be determined by a laboratory experiment on a model of not too small a scale, and a generalized method cannot be applicable to all spillways in the world as a whole.