9 August 2023
In early 2022, many regions across eastern Australia experienced high rainfall, storms, and floods. Sadly, these events devastated many communities and more than 20 people lost their lives.
In early 2022, many regions across eastern Australia experienced high rainfall, storms, and floods. Sadly, these events devastated many communities and more than 20 people lost their lives.
As the flood waters flowed downstream over the coming months through the Murray-Darling basin, communities towards the end of the river system faced the inevitable consequences. Eventually the water from the many rivers across southern Queensland and New South Wales would converge into the one channel at Wentworth and a deluge of water would flow down the Murray into South Australia’s Riverland communities.
It wasn’t a matter of ‘if’, but ‘when’.
Thankfully, the downstream communities had time on their side, and many councils, residents and businesses started preparing early to manage the situation as best they could. Generally, councils took on much of the preparation work to protect as much community infrastructure as possible, with state government authorities becoming more involved as the emergency progressed.
Civil and structural engineers, and asset management specialists from Tonkin’s Adelaide, Mildura and Berri offices worked closely with a number of councils in the affected areas. Below are some of our key takeaways on how government and the private sector can work together to prepare for and recover from flood events.
Preparation works
Ahead of floodwaters arriving, one advantage downstream communities had was time to prepare. While there was uncertainty around peak flood levels and exact timing, the downstream communities knew months ahead of time that the flood was coming. We noticed some councils moved much faster than others and were generally much more proactive. Some councils had the best of intentions, identified issues and were proactive – but didn’t have the resources available to them, as is often the case for regional councils.
As part of their preparation, the most proactive councils investigated the history, actions and outcomes of past floods their communities had experienced – particularly the 1956 flood.
One of the Riverland councils used this knowledge to implement a solution that had been used previously; they sent divers into the river to physically plug stormwater outlets. This stopped river flows going up the stormwater outlets and into the township areas that were being protected. It was fortunate that this solution had been documented after the 1956 floods and the engineering layouts were available to refer to. In some other areas where such solutions had not been implemented, we saw flooding of areas inside levees as as a result of ingress through service networks.
Rapid construction of temporary earth-filled levee structures to hold back flood waters was another key element of flood preparation. While on the surface levees may look like simple mounds of dirt, levees that are not planned and constructed well, often fail.
The placement, materials, and construction of emergency levees should be planned in consultation with experienced civil engineers, well ahead of the waters arriving in order maximise the effectiveness and stability of the structure. Typically, the design and documentation of levee banks takes weeks or months and is underpinned by a range of site investigations including survey and geotechnical investigations.
While there was a long warning time that flooding would occur, the predictions of peak water levels grew as the event neared. With support from a range of stakeholders including local contractors and government bodies we were able to facilitate the rapid construction of a number of temporary levees that protected critical infrastructure from the flood waters.
In regard to existing, permanent levees, we became aware of quite a few instances where the ownership of levee structures was unclear, or the integrity of the levee was not prioritised by the owner. With levee structures potentially being owned by local governments, state governments and private landowners, our advice is this: if there is any uncertainty about who is responsible for the upkeep and integrity of a flood structure in your community, get that sorted out well before the next flood arrives.
Councils that were on the front foot undertook pre-flood inspections, or engaged engineering consultants such as Tonkin, to identify levee banks which were potentially not able to withstand the effects of the predicated flood levels. This allowed councils to action works quickly to resolve potential issues before flood waters arrived.
Responsiveness and collaboration
One of Tonkin’s key contributions during the unfolding flood emergency was our ability to facilitate a cohesive cross-council and cross-agency response regarding engineering solutions. Our team worked with every Riverland council from the Victorian border, acting as an information conduit between organisations, and facilitating cohesive cross-council solutions.
In some areas, levees were still being designed and constructed with the flood waters only two weeks away from arriving. While it was a busy and high-pressure period, we’re extremely proud of our team’s agility and responsiveness in assisting as many of our clients as possible, in a relatively short amount of time.
As the waters continued to rise, engineers from our Mildura, Berri and Adelaide offices worked together to conduct in-field inspections and develop solutions in real-time, to help protect communities and infrastructure. We provided ongoing monitoring of levees to identify potential leaks and failures and provide advice on how to best reinforce and strengthen levee structures where possible.
As the waters continued to rise, engineers from our Mildura, Berri and Adelaide offices worked together to conduct in-field inspections and develop solutions in real-time, to help protect communities and infrastructure. We provided ongoing monitoring of levees to identify potential leaks and failures and provide advice on how to best reinforce and strengthen levee structures where possible.
The role of asset management
Prior to the peak of the flood Tonkin worked with one of the Riverland councils to create a levee inspection tool which helped to understand the existing level conditions and flagged areas of repair work to improve the integrity of the levees. The tool also stored levee levels in relationship to various flood events to help understand the criticality of levees. A team of Tonkin engineers was mobilised on short notice to do these inspections.
During the event the same council wanted to expand the cloud-based solution to undertake daily inspections and to record any actions or areas of concern for potential breaches as an early warning mechanism. This solution once implemented with one council was then rolled out to others. Tonkin provided on-the-ground geotechnical engineering support to councils where areas of concern began to be noticed during the flood.
Tonkin then adapted this solution for the State Emergency Service, drawing on the Department for Environment and Water’s GIS system. The outcome was a state-wide GIS tool for recording various defects and raising early warning red flags to enable the SES to prepare.
After the flood receded the GIS tools were further adapted to log damage to public infrastructure and fast-track potential funding claims for repair/replacement.
Planning for the future
Tonkin’s hydrology and flooding teams were particularly interested in the flood behaviour in the river, as the water levels appeared to defy modelling predictions. In many places the water levels peaked at a higher-than-expected level – both based on historical flow/water level relationships and model predictions. It is theorised that this was in part due to modifications and development within the floodplains along the river which limited the volumes of water and associated flow attenuations provided by the flood plain. It highlighted the need to better understand the impact of development on our river systems, and the benefits that an updated model of the river would have provided.
Planning for developments along the South Australian sections of the River Murray typically requires development to be above the 1956 flood levels, which in some instances seems ‘excessive’ when compared with the surrounding natural land. Review of the peak 2022/23 flood levels has highlighted that using the 1956 flood levels , which have become the standard design level for development along the South Australian section of the river, are not ‘excessive’. It highlights the role that engineering design can play in not only mitigating the financial impacts of future floods, but also in mitigating the social impacts that floods cause.
Recovery efforts and lessons learned
Natural disasters will eventually fade into the history book, however it is imperative that we continue to learn from these events to better prepare for the next event. The importance of ongoing maintenance, record keeping and contingency planning cannot be understated. Similarly, there have been some positive lessons learned in collaborative partnering between a range of stakeholders to deliver real world outcomes faster than anyone could have ever imagined.
The floods have also driven innovation, as a need was identified by one of our council clients to capture asset condition data for the purpose of recovery funding. There was no off the shelf solution to cover the requirements of the council, so a customised solution needed to be developed that was fit for purpose. To do that, Tonkin needed to innovate in both developing the content for the solution as well as the selection of the various platforms to use and we had to be adaptable to the change in requirements.
Unfortunately, climate change means we are likely to see an increase in the frequency and severity of extreme weather events in the future. With this in mind, it’s more important than ever for governments to prioritise disaster resilience funding, including funding for the upgrade and replacement of aging flood mitigation infrastructure.
While flood infrastructure may not be as exciting and high-profile as other infrastructure projects, it is an imperative investment to protect communities and save lives. At Tonkin we are proud of the role we played in working collaboratively with our clients and other stakeholders to help mitigate the impacts of the floods on our Riverland communities.
Many Tonkin team members were mobilised to assist with the Murray River flood response.
Some of the key team members are below.