How Dams work

How Dams work

All dams operate differently, but most in Queensland are built for water supply.

When a dam fills to the maximum water storage level (also known as the full supply level) and starts spilling, excess water is safely diverted through a spillway to flow into the downstream river it’s built on.

While a dam may delay floodwaters simply by being there, it is unsafe to assume it can stop flooding in your area. By the same token, expecting flood waters to only pass through your local dam can mean you miss an important early warning relating to another creek, river or stream.

Find out more about Sunwater’s dams.

Dam types

Each type of dam is defined by its wall construction. Depending on the surrounding environment, Sunwater dams can be described as one or more of the following:

Embankment

Embankment

Constructed as an embankment of well compacted clay (earth fill), some with rock on the faces (rock fill).

Concrete Faced Rockfill

Concrete faced rockfill

Constructed as an embankment of compacted free-draining, granular earth, containing large particles of rock with concrete slabs on the upstream face.

Mass Concrete Gravity

Mass Concrete Gravity - Wuruma Dam

Constructed using a large volume of cast-in-place concrete.

Roller Compacted Concrete Gravity

Roller Compacted Concrete Gravity

Constructed in horizontal layers of dryer than normal concrete mix resulting in a gravity structure.

Multiple Arch Concrete Buttress

Multiple Arch Concrete Buttress

Constructed as concrete horizontal arches supported by small span buttresses (triangular concrete walls).


Dam operations

Spillways

Spillways are constructed to provide safe passage of excess inflows and/or flood waters as they occur from a dam into a downstream river. Depending on the location and capacity of a dam, the spillway specifications vary and can sometimes include spillway gates.

Gates

The spillway gates are designed to maximise a dam’s storage capacity, while increasing the spillway capacity for passing large flood flows, if required. They can also be used for environmental releases that are too large to be discharged from the outlet works.

Gates are usually raised or lowered by winch systems, hydraulic rams, or automatic float systems.

Dams also operate vertical-lift gates or radial gates.

Many Sunwater dams don’t have spillway gates. Callide, Leslie and Coolmunda Dams have radial gates, while Beardmore Dam has vertical lift gates.

Outlet works

Dam outlet works are not capable of large volume releases. They are designed to deliver customer water demand requirements. As a result, making outlet work releases to reduce dam levels would take months of continuous release and still only provide negligible downstream flooding benefits.

How we manage water levels

Flood events

All of Sunwater’s dams are designed principally for water supply purposes, with the exception of Peter Faust Dam in Proserpine which has been designed to provide both water supply and passive flood mitigation. No other Sunwater dams are currently designed or operated to provide downstream flood mitigation.

Sunwater dams are designed to store water to their intended capacity and then safely pass any excess water inflows through purpose built spillways, release gates or outlet works.

Purpose of releases

Sunwater releases water for two main reasons, including:

  • demand from downstream water entitlement holders, and
  • for the environment.

Most of Sunwater’s releases are made for customers, such as farmers, towns and industry.  These releases are based on customer demand and are regulated through Resource Operations Plans (ROP) for each particular water supply scheme.

The Department of Natural Resources and Mines manages the water through Water Resource Plans and ROPs in accordance with the Water Act 2000. The plans are developed through technical and scientific assessment, as well as extensive community consultation, to balance the economic, social and environmental demands on the state’s water resources.

Sunwater also makes scheduled water releases for environmental flow purposes. These are based on extensive environmental flow research and fall within each scheme’s ROP rules. Sometimes Sunwater makes small water releases through the dam’s outlet works based on minor inflows from rainfall across the dam’s catchment. Any additional ad-hoc releases from a dam would be in breach of ROP rules, established to protect water entitlement holders’ reliability of supply.

Ensuring our dams are safe

Sunwater’s experienced dam staff are trained to follow comprehensive and safety-focused operating procedures to ensure our dams pose minimal risk to the general public. All Sunwater dams undergo regular and comprehensive safety assessments to ensure they follow the National and State dam safety guidelines.

Get more information on playing safe at dams and weirs.