Protrusions on Stepped Spillways to Improve Energy Dissipation

[摘要] Stepped spillways constructed of roller compacted concrete (RCC) is a hydraulicand cost effective measure to dissipate energy of large water flows over thespillway of a dam. Stepped spillways, like other spillway types, have its limitationsand a measure to improve the energy dissipation effectiveness is proposed.Two hydraulic models were constructed at the hydraulics laboratory of theDepartment of Water Affairs and Forestry (DWAF) in Pretoria, South Africa. Thescales of the models were 1:20 and 1:30.The study proposes the use of triangular protrusions applied over the spillwaysurface. The protrusions have the same height as the steps, with the width of theprotrusions varying. The triangular protrusions deflect the water sideways resultingin higher energy losses.The results indicate that the protrusions reduce scouring at the toe of the dam, thusincreasing the roughness of the steps. It also indicate that aeration occur earlierthan with normal stepped spillways. An optimal spacing, lateral and across thesteps, are proposed. The construction of the protrusions is also discussed, as wellas the cost implications.It is concluded that the protrusions are effective at a unit discharge up to 35m3/s.m. This value is however dependent on the configuration of the aprondownstream of the toe of the dam. It is proposed that protrusions be added on thedownstream face of the dam on every second step, with one protrusion and thenno protrusion alternating in the flow path. It is recommended that the protrusions becast in situ.

[发布机构] Stellenbosch University