2011 – Awoonga Dam Acceptable Flood Capacity design – the anguish of erosion risk and implications for design

Malcolm Barker, Toby Loxton

The Gladstone Area Water Board (GAWB) owns and operates Awoonga Dam, which is a concrete-faced rock fill embankment with a fixed crest concrete spillway on the left bank impounding a storage volume of 770,000 ML.

The current arrangement can accommodate the Probable Maximum Flood, allowing for flow over Saddles 3, 4 and 6 on the left abutment. A comprehensive study was carried out to evaluate the erosion potential downstream from Saddles 3 and 6 as well as other spillway options adjacent to the existing dam. One option was a radical approach including the removal of the Saddle Dam 3 and provision of downstream erosion protection works. This reduced the PAR and improved the overall dam flood capacity; however concerns were expressed about the environmental impact of possible erosion downstream from Saddle 3 for relatively frequent events.

A risk assessment showed that the erosion protection works downstream from the Saddle 3 or 6 were not cost effective and the preferred option for the upgrade was the closure of the Saddle Dam 3 with an auxiliary spillway created in Saddle 6,

This paper summarises the methods used and the outcomes from this study.

2011 – Awoonga Dam Acceptable Flood Capacity design – the anguish of erosion risk and implications for design

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