Author(s): Christopher. I. Thornton; Faisal A. Alsultan; Robert Ettema; Jeff Ellis; David K. Hughes; Yongqiang Lan; Michael Zusi
Linked Author(s): Robert Ettema
Keywords: Dam; Spillway; Ogee; Vortex; Flow Distribution
Abstract: In civil-engineering hydraulics there are times when aspects of flow fields commonly considered undesirable become desirable. This statement especially holds when hydraulic structures must be designed to form flow fields that address local needs, which often are prescribed by the terrain in which a spillway is set and presence of existing structures along the spillway's alignment. This paper uses the example of a spillway design for a heightened dam whose spillway-entrance abutments caused flow to contract and separate from the abutments, thereby forming a large region separation inducing flow non-uniformity and vortex formation just upstream of the spillway's ogee crest. Two studies were conducted: Study 1 (physical and numerical models) concerned the spillway's overall performance. Study 2 (physical model) addressed the following two questions that arose during Study 1: When spillway abutments are upstream of the spillway's ogee weir, and the depth of approach flow is important, where should the spillway's ogee weir be positioned relative to the spillway's entrance? What criterion should be used for acceptable performance of an ogee weir? The answer to the first question is given in terms of weir position (and weir width) relative to length of a flow-separation zone created by the abutment. The answer to the second question is given in terms of lateral distribution of unit discharge at the weir.