With our changing climate and rapid urbanisation, the number of people affected by disasters is set to increase. Solutions for the built environment must be holistic, informed by industry-leading technical expertise and include the critical voice of communities, via consultation and participation in future planning.

BG&E’s Integrated Approach

BG&E have evolved to respond with an integrated approach which comprises helping clients and communities to develop flood management plans, hydrology, drainage, civil and structural design, as well as risk and durability assessments of existing infrastructure.

Insights from Laura Baxter

Addressing the Risk of Natural Disasters

Laura Baxter, Flooding and Water Lead at BG&E says, “In my experience, the risk associated with flooding and natural disasters can too often be considered a low priority; a simple tick box exercise for approvals. This is often because people have not experienced for themselves the effect of natural disasters. I believe that it is our responsibility as an industry to make our clients, and the community affected by the projects we work on, aware of the risks of natural events such as flooding and how we can live and work with them.”

Laura is an experienced hydrologist and hydraulic modeller with over fifteen years’ experience in the area of river and surface water flooding, and floodplain risk management. She says, “As hydrologists and engineers, it is important that we use accurate terminology but also ensure the meaning is clearly understood by not only our clients but also the community that may be affected. The media can often present misleading phrases to create more dramatic stories. The danger of the lack of understanding around flooding is ultimately additional risk to life and property.”

Misleading Terminology in Media

The Hawkesbury River Flooding

In March 2021, some media reported the Hawkesbury River flooding as a one in 100-year event. Not only is this terminology misleading as two “one in 100” floods can happen in succession, the peak river levels at Windsor in March 2021 had a probability of between one in 15 to a one in 20 chance of flooding in any one year. The area and the new Windsor Bridge will flood again and more than once in our lifetimes. In fact, flooding in 2022 also inundated the bridge deck.

The True Frequency of Flooding

Average Exceedance Probability (AEP)

In June 2022, the Insurance Council of Australia released data which indicated the destructive flood that swept through South-East Queensland (QLD) and Northern New South Wales (NSW) in late February and early March caused $4.8 billion in insured damages and was the third costliest extreme weather event in Australia’s history.

Flooding is more common than people think and the “100-year” terminology can be misleading, and a better term is Average Exceedance Probability (AEP). A one per cent AEP flood has a one in 100 chance of being equalled or exceeded in any one year. To put the frequency of a one per cent AEP flood into perspective, if you lived for 70 years in a house located in a one per cent AEP floodplain, the chance of that house being flooded is 50 per cent (a one in two chance).

BG&E’s Contributions to Flood Management

Diverse Project Involvements

In Australia, Laura and the Flooding and Water group assist their clients to understand the real risk of flooding, and to develop suitable risk mitigation solutions. The team use hydrodynamic models to assist with flood risk mapping and analysis, overland flow path analysis, bridge design, flood mitigation and management, emergency response, flood damages assessments, dam break analysis, channel diversion and restoration, coupled with a robust understanding of the Australian Rainfall and Runoff Guidelines, to deliver a broad range of solutions for the Transport, Property and Resources sectors, as well as local and state government.

Laura adds, “It’s reasonable to assume every infrastructure and property project, and precinct or land development, needs a flood assessment conducted whether to confirm low risk or input to complex mitigation and risk management. We are continually communicating with clients about the evolving issues of climate, rising water levels and extreme weather events. The key is explaining how the risk of flooding could be mitigated and striking a balance between that, the development objectives and community needs.”

BG&E’s Recent Projects

Queensland

• In QLD, our engineers and designers have been supporting the QLD Department of Transport and Main Roads – South Coast District, since 2020, through a series of sustained Disaster Activations for Events 21C, 21J, 22A and 22F. The team’s work has helped communities reconnect and recover from disasters.

Western Australia

• Northlink WA Stage 3, Forrestfield Airport Link, Kwinana Freeway Project, Kumina Mine and Haul Road Waterways Assessment, Bunbury Outer Ring Road, Nyindighu Transport Options Baseline Hydrological Study and Roy Hill Iron Ore Rail Bridge and Infrastructure.

New South Wales

• Sydney Metro Tunnels and Station Excavation, Horsley Drive Upgrade, M12 Motorway Central, Country Rail Network Washaway Assessments, Bonalbo Flood Study and Risk Management Plan, Urbenville and Woodenbong Flood Studies, Parramatta Square Flood Assessment and Evacuation Plan, WestConnex 3B Temporary Works and Murray Irrigation Hydraulic Investigation.

Queensland (Continued)

• Fortitude Valley State Secondary College, Brisbane City Council Footbridge Replacement, Nebo Rail Maintenance Facility.

Victoria

New Avon River Bridge, Hallam North and Heatherton Road Upgrade and Hoppers Road Upgrade.

Sources: Insurance Council of Australia – Media Release, 2022 Flood Now Third Costliest Natural Disaster Eve, June 2022 and World Metrological Organisation – Climate Change Leads To More Extreme Weather, August 2021.