2007 – Calculating spillway crest pressures for high-head operation

Paul Hurst, Tom Ewing, Steven Fox and Bob Wark

For an ogee-shaped spillway crest, it is well recognised that sub-atmospheric pressures will develop on the lower-nappe profile for operating heads greater than design head. This effect is useful in providing an increase in efficiency of the spillway discharge for small increases in operating head. However, there is limited data on the formation of sub-atmospheric crest pressures for high-head operation above 1.3 times greater than the design head

This paper reports on modelling work done by GHD and the Water Corporation for the Wellington Dam Remedial Works Project in Western Australia where the current design flood has increased to more than twice the original design head. Two-dimensional physical scale modelling and 3-D Computational Fluid Dynamics (CFD) modelling of the existing Wellington Dam spillway profile was carried out to determine the discharge coefficient and uplift force generated by the formation of sub-atmospheric crest pressures under high-head operation.

The paper compares the results of the physical scale model and the CFD model and earlier published data by Cassidy (1970) and concludes that there exists a good correlation between the three data sets.

Keywords: Ogee, sub-atmospheric, crest pressures, Wellington Dam