The National Capital Authority (NCA) today announced that major engineering works at Scrivener Dam have required them to lower lake levels. It is anticipated the work will be completed within 1 to 1.5 years.

Lake Burley Griffin was lowered 200mm on the evening of Friday 25 November 2011 in anticipation of increased water inflows over the following days. This enabled safe completion of inspection and testing works below the flap gates.
Today (1 December 2011), it will be lowered by another 300mm. This will reduce it to approximately the same level reached in February 2003 under drought conditions. Lowering the lake to this level will assist in managing risks associated with both the day-to-day operation of the dam and the completion of these engineering works.
The NCA expect that the lake will remain at this lower level throughout the work. There may be occasions where the lake needs to be lowered even further. Lake users will be given advance notice of expected changes in the lake level whenever possible.

The works involve progressively replacing 120 anchor bolts, which are part of the flap gate mechanism. The flap gates are opened in flood events to regulate the water level of Lake Burley Griffin.

NCA Chief Executive said the works were identified during an annual safety audit and surveillance inspection of Scrivener Dam.

“As part of our management of Scrivener Dam, the NCA commissions an annual, independent, safety and surveillance inspection report. The 2011 report, received three weeks ago, advised that some of the anchor bolts on the dam were showing signs of corrosion,” Mr Rake said

“The NCA immediately commissioned further inspections and tests to assess the extent of the corrosion.

The majority of the anchor bolts are encased in steel structures or concrete. These anchor bolts were not visible to previous safety audits and surveillance inspectors.

The non-destructive testing involved either cutting away small sections of non-structural concrete, or drilling small holes through the steel structures and using an endoscopic camera to inspect the previously hidden bolts.

“Yesterday we received advice that all the hinge bolt anchors will need to be replaced within one to two years. It is anticipated this work will take 50 to 80 weeks to complete, so work needs to commence shortly,” he said.

The anchor bolt system will be redesigned as part of these engineering works to ensure that future inspections can be conducted easily. We will also install cathodic protection to minimise future corrosion.