Construction on Stage 2A of the $24 million Ewen Maddock Dam upgrade on the Sunshine Coast will get underway by the end of this month (March) and will bring the dam in line with modern engineering design standards. Seqwater CEO Neil Brennan said the project was part of an ongoing dam improvement program to ensure all Seqwater dams continued to perform safely well into the future.
The project need was realised following a risk assessment of all Seqwater dams across
the SEQ region, including Ewen Maddock Dam, against the relevant dam
safety guidelines and latest engineering standards. Our assessments and ongoing
investigations have allowed Seqwater to prioritise dam upgrades.
The Dam Safety and Acceptable Flood Capacity Review for Ewen Maddock Dam recommended that dam safety upgrade works be completed in two stages. Stage 1, which was completed in 2012, consisted of installing pressure relief wells and constructing a partial height filter buttress to reduce the risk of internal erosion or heave failure in the foundation.
The second stage, Stage 2 upgrade works, are designed to reduce the remaining dam safety risks to a tolerable level. This second stage will be delivered in two sequential components, Stage 2A Embankment Works and Stage 2B Spillway Works.
The scope of the Stage 2A Embankment Works includes:
|Description of Required Upgrade|
|Lake Lowering||· Temporary works to lower the lake level to 60% Restricted Full Supply Level by installing 6 x DN710 HDPE siphons and associated infrastructure. The siphons inlet is located upstream of the spillway, lay on the left spillway abutment and discharge into the existing stilling basin. The estimated maximum flow rate of the siphons is 10m3/s.|
|Main Embankment||· Installation of an internal chimney filter to existing dam crest level and reinstatement of the outer earthfill zone to buttress the new filter.
· Construction of a reinforced concrete parapet wall along the crest of the dam, keyed into the new filter zone to raise the crest and provide the required additional flood capacity.
· Relocating or reinstatement of existing dam instrumentation.
· Recreation Facilities Improvements
The Stage 2A project has been awarded to Sunshine Coast-owned and operated construction company Hall Contracting and it is estimated to create up to 70 local jobs.
“This is a great outcome with a local contractor being awarded the work for the first stage,” Seqwater’s CEO Mr Brennan said.
Construction on the 18-month first stage (Stage 2A) is planned to begin at the end of March.
The dam’s water level will have to be lowered to about 60 per cent of its full supply to allow the works to proceed. Currently, both the Ewen Maddock Water Treatment Plant and Environmental Outlet Valve are being maximised to assist in the reservoir lowering needs.
Mr Brennan said “Seqwater has staged construction to reduce the amount of time water levels have to remain lowered.”
The second stage, Stage 2B, will involve strengthening the existing spillway and will be subject to a separate tender process. The timing of Stage 2B works is expected to be finalised by end of the year.
Author: Chris Owen, Seqwater