Protrusions on Stepped Spillways to Improve Energy Dissipation
Date
2006-12
Authors
Wright, Henry-John
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : University of Stellenbosch
Abstract
Stepped spillways constructed of roller compacted concrete (RCC) is a hydraulic
and cost effective measure to dissipate energy of large water flows over the
spillway of a dam. Stepped spillways, like other spillway types, have its limitations
and a measure to improve the energy dissipation effectiveness is proposed.
Two hydraulic models were constructed at the hydraulics laboratory of the
Department of Water Affairs and Forestry (DWAF) in Pretoria, South Africa. The
scales of the models were 1:20 and 1:30.
The study proposes the use of triangular protrusions applied over the spillway
surface. The protrusions have the same height as the steps, with the width of the
protrusions varying. The triangular protrusions deflect the water sideways resulting
in higher energy losses.
The results indicate that the protrusions reduce scouring at the toe of the dam, thus
increasing the roughness of the steps. It also indicate that aeration occur earlier
than with normal stepped spillways. An optimal spacing, lateral and across the
steps, are proposed. The construction of the protrusions is also discussed, as well
as the cost implications.
It is concluded that the protrusions are effective at a unit discharge up to 35
m3/s.m. This value is however dependent on the configuration of the apron
downstream of the toe of the dam. It is proposed that protrusions be added on the
downstream face of the dam on every second step, with one protrusion and then
no protrusion alternating in the flow path. It is recommended that the protrusions be
cast in situ.
Description
Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2006.
Keywords
Spillway, Hydraulic roughness, Stepped spillway, Protrusions, Theses -- Civil engineering, Dissertations -- Civil engineering