Project background

Paradise Dam is located 80 kilometres southwest of Bundaberg, Queensland, Australia on the Burnett River. 

The dam is owned and operated by Queensland government-owned corporation, Sunwater and is part of the Bundaberg Water Supply Scheme which supplies water for irrigation and urban use in the Bundaberg Region and was not designed for flood mitigation. 

Paradise Dam is a 52-metre-high compacted concrete (RCC) gravity dam designed and constructed by the Burnett Dam Alliance from 2003-2005. It was completed in November 2005 at a cost of $266 million (AUD) with a storage capacity of 300,000 megalitres (ML). In December 2006, Sunwater acquired operations and ownership of Burnett Water Pty Ltd and its assets, including Paradise Dam. 

Following the unexpectedly severe damage to the dam and erosion of the riverbed immediately downstream of the dam apron after the January 2013 flood, a series of investigations began. These investigations, along with the development of subsequent technical reports between 2013 and 2019, revealed issues with the dam’s structural condition. This process culminated in 2019 with the discovery of concerns about the stability of the dam wall under extreme weather conditions. 

In April 2020, an independent Commission of Inquiry report confirmed structural and stability issues with the dam and outlined the design failure and poor concrete mix in the initial construction.  

During 2020 and early 2021 Sunwater lowered the dam (to EL 61.8m AHD) and completed essential works to improve the safety of the dam for people living downstream. These works reduced the risk of dam failure to a 1 in 5000-year event. Prior to the works, the dam failure risk was a 1 in 200-year event, such as the community experienced in 2013. The dam remains safe at the current lower supply level and will be so for the life of the project. However, it is still not within the acceptable level of risk for the long-term. 

As part of the essential works project, extensive testing identified further concerns about long-term strength and quality of the dam’s concrete, compounded by the low cement content in the concrete mix design in the existing dam. These issues are: 

• Swelling clay: due to the porous nature of the concrete, low cement content, and high clay content including swelling clays, moisture causes repeated swelling and contracting over time. 

• Cement leaching: due to the porous nature of the concrete, key ingredients that bond the cement leach out leading to deterioration and strength loss. 

• Carbonation: the mix of carbon dioxide, moisture and cement results in low pH (increased acidity) and increases the effects of the swelling clay, resulting in lower overall concrete strength.  

A previously planned improvement project was expected to restore Paradise Dam to its full 300 gigalitre capacity by re-raising, strengthening and stabilising the existing dam wall, however a wide range of international and Australian experts verified these issues as unprecedented and unique to Paradise Dam, advising that repairing the existing dam wall is not feasible. 

Sunwater is now progressing a detailed business case for a new Paradise Dam wall, with project costs and timeframes to be confirmed as part of this process. Sunwater has appointed CPB Contractors and Georgiou as construction partner and GHD as the ongoing design partner for the project, which will ensure design and construction challenges are considered and addressed early.

Separate to planning for a new dam wall, Sunwater will also commence a detailed business case to expand the irrigation network within the Bundaberg Water Supply Scheme. This will build upon previous investigations to understand distribution constraints. Therefore, Sunwater will combine the two focuses into one detailed business case.

While determining details for the new wall at Paradise Dam and irrigation network capacity upgrades takes time, Sunwater is working as quickly as possible and will provide regular progress updates to the community.