QLD – Upgrade work progressing well at Ewen Maddock Dam

Upgrade work progressing well at Ewen Maddock Dam

Ewen Maddock Dam is one of a number of dams in South East Queensland (SEQ) being upgraded as part of Seqwater’s Dam Improvement Program.

In March 2020, Seqwater started work on Stage 2A to strengthen the existing embankment and raise the dam wall to increase its floodwater capacity. The original project schedule was expected to take 18 months to complete, subject to weather conditions and other unexpected delays. The project is currently ahead of schedule with expected completion by mid-2021.

For work on Ewen Maddock Dam to be delivered safely, the lake was lowered to less than 60% of the total capacity using five siphons in July this year. Operational releases to lower the lake to 60% were necessary to undertake the embankment strengthening work safely, as per the Dam Safety Management Plan (Construction), thus mitigating dam safety failure risk during construction works.

An innovative approach was used to lower the dam level which reduced carbon emissions and minimised the time that recreation around the lake will be closed. Together with Sunshine Coast-based local contractor Hall Contracting, Seqwater safely released water via the siphons at the spillway into the natural waterway along Addlington Creek and into the Mooloolah River Catchment. This mirrored the flow of water out of the dam when it is full and spilling excess water. Typically, Ewen Maddock Dam spills a few times a year from rainfall.

By using gravity and siphons in place of more traditional systems like diesel-fuelled pumps, this helped reduce carbon emissions. This approach, which was decided during the planning stages, also helped to reduce the length of the project and enabled much of the embankment strengthening work to be completed within the dry season. The lake will return to full supply capacity on completion of the project and following natural rain events. ​

To ensure a ‘no surprises’ method, Seqwater gave advance notice of work to directly impacted residents and businesses from lake lowering activities. A letter was sent to downstream residents and included the option for Seqwater to send text messages to keep them informed of the work and rises in Addlington Creek in the coming months. Subscribers to Ewen Maddock Dam on Seqwater’s Dam Alert Service also received the text messages to ensure as many users of the catchment were aware of the releases and able to plan accordingly.

The scope of the Stage 2A Embankment Works includes:

Upgrade Component

 

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

Seqwater have monitored the environmental impacts throughout the lake lowering using historical survey data and a UAV (unmanned aerial vehicle, usually a drone). Riparian vegetation has remained in good health and water quality is being monitored for any impact on the health of foraging bird and aquatic species. Flora and fauna monitoring will continue during the construction lowering phase of this project.

Ewen Maddock Dam represents 0.7% of the total water storage in the SEQ Water Grid, and the reduced dam level has not impacted on the long-term water supply security for the region.

The upgrade will raise and strengthen the existing embankment and make improvements to the recreation area.

For more information visit www.seqwater.com.au/project/ewen-maddock-dam-upgrade

Author: Chris Owen