In 2012-13, we commissioned an independent review of our 26 referable dams, which found improvements are needed at a number of our dams to meet the Queensland Dam Safety Guidelines into the future.

Dam improvements are prioritised across the region in a staged program that is scoped and scheduled to maintain water supply security, while delivering best value for money.

Leslie Harrison Dam is one of a number of dams in South East Queensland to be upgraded within the next six years, as part of Seqwater's Dam Improvement Program.

Leslie Harrison Dam upgrade

In 2014-15, the water level at Leslie Harrison Dam was lowered and the gates were removed for the ongoing safety of the dam. Since then, detailed investigations were conducted to identify a preferred option to address the dam's safety issues and meet Queensland guidelines. 

Following an assessment of all the dam safety options, the decision has been made to upgrade Leslie Harrison Dam in 2018-19 and maintain its current full supply level once work is complete.

We take public safety very seriously and while we appreciate the strong community interest in how we manage Leslie Harrison Dam, upgrading the dam is what we must do to keep it operating safely.

Construction is expected to start in mid-2018 and will take about 12 months to complete, subject to weather conditions and material availability.

A number of tools have been developed to help you learn more about Leslie Harrison Dam, it's history, how the dam operates and plans for the future. We have also created an animation to help explain a gated and ungated Leslie Harrison Dam works during heavy rainfall events.

Find out more

Frequently asked questions

Why does the dam need upgrading?

Dams are long-life assets and require continual assessment, monitoring and maintenance. In 2012-13, Seqwater commissioned an independent review of its 26 referable (regulated) dams, which found improvements are needed at a number of them, including Leslie Harrison Dam, to meet the Queensland Dam Safety Guidelines into the future.

Just like cars, dams need regular checks and maintenance to keep them in good working order. We regularly monitor and assess our 26 referable dams throughout the year. Through this work, dams may be identified for upgrades to meet changes to the safety guidelines.

Leslie Harrison is one of a number of dams in South East Queensland to be upgraded over the next six years as part of Seqwater’s Dam Improvement Program. Following an assessment of all the dam safety options, we have made a decision to upgrade Leslie Harrison Dam in 2018-19 and maintain its current full supply level once work is complete.

Does an upgrade mean the dam is unsafe?

Queensland has a good dam safety record, but just like cars, dams need regular checks and maintenance to keep them in good working order. There are some key changes since Leslie Harrison Dam was originally built in 1968, which have resulted in increased dam safety standards, including data from past flood events and updated modelling, and advances in dam design. In 2014, a safety review of Leslie Harrison Dam identified a number of issues needing further investigation and as a result, the water level at the dam was lowered and in 2015, its spillway gates were removed to reduce water pressure and loads on the dam wall.

In Queensland, dam owners are responsible for the safety of dams in accordance with the Water Supply (Safety and Reliability) Act 2008. Seqwater’s Dam Improvement Program is about upgrading our dams in line with the latest engineering standards and meeting the current Queensland Dam Safety Guidelines.

What will the upgrade involve?

The aim of the upgrade is to strengthen the dam’s main structures including its embankment and spillway to better withstand earthquakes and extreme floods. Construction is expected to start in mid-2018 and will involve a number of works including:

  • building a weighting berm with rocks and fill along the main embankment to provide greater stability (to widen the structure)
  • placing a specially design sand layer across the downstream face of the embankment and stabilising the sand layer with additional fill material
  • anchoring the top (crest) of the concrete spillway for stability
  • modifying the intake tower to increase its flood immunity.

Will the water level be restored?

No. Seqwater has made a decision to keep the dam at its current lowered full supply level and the gates will not be reinstated for the foreseeable future. Since lowering Leslie Harrison Dam’s water level, we have investigated a number of options to safely restore the original full supply level and reinstate the spillway gates at Leslie Harrison Dam. To restore the dam’s original full supply level, we would have to raise the dam embankment and undertake major works to the spillway at a significant additional cost.

We found we would need to spend about $42 million in total (a further $18 million investment) to address all the safety issues reinstating the spillway gates present. We then did the modelling and found there would be minimal benefit to the security of the region’s drinking water supply if the dam’s full supply level was restored. After carefully considering the costs and benefits, we have decided not to reinstate the spillway gates and will keep the dam at its current full supply level.

Will the gates be reinstated?

No. Seqwater has made a decision to keep the dam at its current lowered full supply level and the gates will not be reinstated for the foreseeable future. In 1984, four vertical gates were installed on the spillway crest to increase the drinking water storage available in Leslie Harrison Dam. To put the gates back on, we would have to raise the dam embankment and undertake major works to the spillway at a significant additional cost.

We found we would need to spend about $42 million in total (a further $18 million investment) to address all the safety issues reinstating the spillway gates present. We then did the modelling and found there would be minimal benefit to the security of the region’s drinking water supply if the dam’s full supply level was restored. After carefully considering the costs and benefits, we have decided not to return the spillway gates and will keep the dam at its current full supply level.

Does this mean there will be more flooding downstream?

No. In fact, Leslie Harrison Dam provides more flood mitigation un-gated than it does as a gated dam. In 1984, four vertical gates were installed on the spillway crest to increase the drinking water storage available in Leslie Harrison Dam without raising the dam embankment.

All un-gated dams help mitigate flooding to some extent. At its most basic level, flood mitigation is capturing and temporarily storing flood water and releasing it at a slower rate with the aim of reducing river levels downstream of the dam. When rainfall in the catchment results in water flowing into (inflows) an un-gated dam and it fills up beyond the dam’s full supply level (FSL), water will begin to flow out (outflows) over the dam’s spillway. The peak outflow from an un-gated dam during a flood event is less than the peak inflow that would have occurred had the dam not been built, because some water is held in the dam to be released over a longer time period while it is spilling.

Will recreation be permitted on the lake?

There are no plans to introduce recreation at Leslie Harrison Dam in the foreseeable future. In 2014, Seqwater engaged experts to conduct a water quality study and develop a screening tool to help us better understand the impact recreation has on water quality in our drinking water lakes. The landmark study was one of the most complex and comprehensive of its kind ever undertaken in Australia. In 2016, a water quality assessment was conducted at Leslie Harrison Dam using this screening tool. The assessment found, given the dam’s role as a drinking water source for the Redlands, recreation cannot be considered because of unacceptable risks to water quality.

Will the upgrade affect water security?

Under normal operating conditions, most of the Redlands’ drinking water is sourced from North Stradbroke Island, with the rest coming from Leslie Harrison Dam and the SEQ Water Grid via the Eastern Pipeline Interconnector (EPI). Seqwater is charged with delivering safe, secure and cost-effective water to South East Queensland. The Water Security Program 2016 – 2046 is our long-term water plan for the region. Under this plan, keeping Leslie Harrison Dam at a reduced water level will have minimal impact to water security in Redlands.

What is the SEQ Water Grid?

The SEQ Water Grid is our connected network of dams, water treatment plants, reservoirs, pump stations and pipelines. The grid means we can move water around the region and in both directions, from the Sunshine Coast to Greater Brisbane, to Redlands and south to the Gold Coast.

How will the upgrade affect my water bill?

It won't. The cost of the Dam Improvement Program has been built into the current bulk water price path and will not impact the bulk water component of your water bill.

What will happen to the exposed land around the lake?

As a result of our decision to permanently lower the full supply level at Leslie Harrison Dam, we will need to update our plans for managing the catchment land around the lake. We recognise there is strong community interest in what happens around the lake and protecting the natural environment. We want to work with our neighbours to better understand their land management issues and improve the way it’s managed in the future. This planning process is expected to get underway within the coming months.