The Overlooked Key to Extreme Weather Resilience

Laura Baxter

Water Lead
BG&E Sydney
Around the world a disaster related to a weather, climate or water hazard has occurred on average every day during the past 50 years, killing up to 115 people daily and causing up to $277.7 million in daily losses.

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 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.

Laura Baxter, 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 and local politicians can often present misleading phrases to create more dramatic stories, or to win votes. The danger of the lack of understanding around flooding is ultimately additional risk to life and property.”

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.

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). Over the life of the average 30-year home mortgage, there is about a 25 per cent chance (one in four chance) that house will be flooded.

In Australia, Laura and the Water team 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.”

Some of BG&E’s Water projects include:

• 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, in Western Australia;

• 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 in New South Wales;

• Fortitude Valley State Secondary College, Brisbane City Council Footbridge Replacement, Nebo Rail Maintenance Facility in Queensland; and

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

Source: World Metrological Organisation – Climate Change Leads To More Extreme Weather, August 2021.

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