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Plunge Pool Rock Scour Experiences and Analysis Techniques

Author(s): Eric J. Lesleighter; Colleen S. Stratford; Erik F. R. Bollaert

Linked Author(s): Erik Bollaert, Eric J Lesleighter

Keywords: Rock erosion; Plunge pool; Spillway; Scour; Plunging jets; Pressure transients

Abstract: Experiences of rock scour in plunge pools at spillways which has occurred in many countries and situations, including the Wivenhoe Dam spillway in Australia, the subject of this paper, highlight the extreme hydraulic conditions which occur due to highly-aerated plunging jets. Most are aware of the Kariba dam experience, which has scoured the base of the plunge pool to a depth of around 90m below the tailwater level. Our paper presents a description of dramatic scour for a much lower dam. In 2011, Wivenhoe dam in Australia experienced floods which eroded boulders the size of a bus and weighing up to 1200 tonne from the plunge pool during spillway operation. For many engaged in spillway design, the extent of erosion at Wivenhoe was viewed to be almost ‘unbelievable’. The rock scour which has occurred at Wivenhoe and many other dams provides a timely reminder of the need to be able to predict rock scour to ensure that when the spillway needs to be operated, there is no concern regarding the development of a scour hole compromising the integrity of the dam. The question is asked, “Can we accurately predict rock scour, and if so, what level of confidence can we have in the results?” Thepaper describes the sequence of discharges that caused the damage over a few days, the hydraulic behaviour in the plunge pool, and presents guidelines to dam owners and designers on what considerations need to be given when selecting an analysis method, gives insight to the latest modelling techniques. It also provides information on the limitations on rock scour studies, with application of the details of the depth, lateral and longitudinal extent of erosion at the Wivenhoe dam.


Year: 2013

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