The Influence of Slope and Surface Roughness on Trapezoidal Free Overfall Characteristics

by Robert J. Keller, Monash Univ, Clayton,
Daryl F. Walters, Monash Univ, Clayton,

Document Type: Proceeding Paper

Part of: Hydraulic Engineering


The brink depth-discharge relationship for trapezoidal free overfalls was investigated including the effects of slope and roughness. The theoretical relationship is based on the momentum equation for which the inclusion of slope and roughness necessitated the development of a generalized expression for the flow surface profile between the assumed location of critical depth and the brink. The resulting equation was solved using a Newton Raphson procedure. A large number of tests were carried out for each of three different slopes and four different roughnesses. For each test the brink depth, flow profile and flow rate were monitored. Very good agreement was noted between the theoretical predictions and the experimental results. Variations in slope were shown to have a negligible effect on the brink depth-discharge relationship. The effect of variations in roughness was significant.

Subject Headings: Slopes | Free surfaces | Hydraulic roughness | Fluid flow | Flow measurement | Flow profiles | Free flow | Water flow

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