We are carrying out a project to upgrade dam safety at Cressbrook and Cooby Dams.

Cressbrook and Cooby Dams, along with Perseverance Dam, are key suppliers of drinking water for Toowoomba and surrounding towns.

The safety upgrades will meet the Dam Safety Condition Schedule issued by the Department of Regional Development, Manufacturing and Water. This schedule required Council, as the owner of the dams, to undertake appropriate works to meet the requirements of the Queensland Dam Safety Management Guidelines 2020.

The project aims to deliver the upgrades without impacting the security of the drinking water supply.

Due to the significant cost of the project and the complex nature of the works for Cressbrook Dam, Council will invite Expressions of Interest before inviting selected construction and design partners into an alliance to finalise design and undertake construction works for the delivery of the project.

Council will make an announcement when the proponent is engaged, which is expected to be in the fourth quarter of 2023.

Upgrade works are expected to begin in the 2023/24 financial year.

For further information please contact damsafetyupgrades@tr.qld.gov.au.

Drone image courtesy GHD

Cressbrook Dam is located on Cressbrook Creek, approximately 15km downstream of Perseverance Dam and 35km north, north-east of Toowoomba. The dam was designed by Farr Evrat & Associates between the early 1970s and 1980, with construction completed in 1983. The reservoir first reached full supply level in May 1989. The full storage capacity of Cressbrook Dam is 81,900 ML.

The structure is a central core zoned earth-fill embankment with a concrete-lined spillway and chute on the left abutment.

Cooby Dam is located on Cooby Creek, approximately 20km north of Toowoomba. The dam was designed by the Department of Irrigation and Water Supply in the 1930s with construction completed in 1941. The dam is a zoned earth concrete faced upstream and roc-fill downstream embankment dam. A steel-reinforced concrete wave wall of 1.1 metres in height was constructed in 1997 as part of a minor safety upgrade requirement for the dam.

The embankment is 207 metres long with a maximum height of 32 metres. An open cut unlined rock chute is located on the right abutment and controlled by a low-level curvature Ogee crest spillway. The full storage capacity of Cooby Dam is 23,100 ML.

Dams are long-life assets which require continual assessment, monitoring and maintenance to ensure they can provide water security for years to come. Council’s dam upgrade projects include upgrades to our referrable dams to ensure their long-term viability so that they can continue to 

  • safely pass excess volumes of water during periods of extreme rainfall
  • meet modern engineering design standards
  • comply with the safety requirements set out in the Water Supply (Safety and Reliability) Act 2008 (Qld).

Dam safety is regulated by the Queensland Government's Queensland Dam Safety Management Guideline 2020 which outlines the processes and procedures dam owners need to follow.  

The Dam Upgrade Project will ensure Council’s dams meet all requirements under these legislative guidelines for continued safe operation.

Of the three referrable dams (Cooby, Cressbrook and Perseverance), dam safety assessments found that upgrade works are required to Cressbrook Dam to meet the Queensland Dam Safety Management Guideline 2020 requirements.

Cressbrook Dam safety upgrade works include widening of the existing spillway, raising the dam crest level and associated ancillary works.

While Cooby Dam does not require any spillway widening or crest raising, safety upgrade works include pipe replacement, structure replacement and various ancillary works.

All dams are regularly monitored and inspected, with some additional scope being assessed at Cooby Dam as part of these inspections.

Preliminary investigation work will include geotechnical investigations including geological mapping to investigate ground conditions; hydraulics, hydrology risk assessment; and constructability.

The project scope also includes:

  • investigation of options for access to Cressbrook Dam, including upgrade of access roads for all-weather 2WD access and any impact on buildings
  • development and confirmation of project delivery model and staging
  • all legislative and statutory approvals
  • other technical and project delivery elements
  • environmental and cultural heritage investigations.

Construction work on the project includes:

  • upgrades to access roads
  • establishment of site facilities, construction plant, laydown areas
  • excavation of rock for spillway widening
  • excavation and stockpiling of dam wall materials
  • importation of new dam wall filter soils from offsite
  • reconstruction of dam wall
  • construction of concrete spillway
  • construction of concrete parapet wall along the new dam crest
  • restoration of areas affected by construction activities.

Some access roads will be repaired and/or upgraded as part of the project to improve accessibility to the construction site at Cressbrook Dam. Landowners or residents affected by these works will be notified prior to commencement of any construction activities.

Construction planning and delivery will consider seasonal weather patterns and long-range forecasts.

Early works will include construction or upgrading of access roads, water treatment and batch plant facilities.

There will be some impacts on dam access roads during construction. Early notification and appropriate traffic management will be implemented on affected roads during construction.

Further details will be provided once the construction program has been confirmed.

Environmental controls on the project will include control of dust.

The dam safety must not be compromised during construction. Council will engage with experienced contractors to undertake the work, with demonstrated techniques to ensure a flood can safely pass over the spillway even during construction.

Some access roads will be repaired and/or upgraded as part of the project to improve accessibility to the construction site at Cressbrook Dam. Landowners or residents affected by these works will be notified prior to commencement of any construction activities.

Contractors undertaking the upgrade works will be required to maintain the water quality at Cressbrook Dam. Water is drawn from the dam some 1000 metres away from the construction area.

The dams will be able to meet the current water supply demand requirements during the construction phase.

Raw water from both dams is pumped to Council’s Mt Kynoch water treatment plant. This will not change as part of the project.

The current timeline to meet the date for completion of the work set by the Dam Regulator is 1 October 2025. Some ancillary works may be required to the end of 2026.