2006 – Ross River Dam Spillway Gate Reliability and the Impact on the Design

Malcolm Barker, Barry Vivian and David S. Bowles

Ross River Dam is located approximately 15 km upstream of Townsville and provides a dual role of water supply and flood mitigation. The dam comprises a 39.6m long concrete overflow spillway flanked by a central core rockfill embankment of 300 m in length with a 7,620 m long left bank earth fill embankment, which has inadequate internal filter zones for piping protection. Since completion, design rainfall predictions for the area have doubled, technical data has changed and so, too, have dam safety standards. Dam safety evaluations during 2000-2002 showed that the dam required upgrading in order to bring it up to international standards. As an interim measure, the spillway was cut down by 3.6m.

Upgrade design works were then completed using risk-based design criteria to validate the design, and construction is in progress. The upgrade works comprise spillway anchoring, installation of three radial gates on the spillway, stilling basin modifications, embankment filter protection, and dam crest raising.

This paper presents the options considered, the method of reliability analysis, and how the results influenced the spillway system design and overall risk evaluation for the upgrade design.