Australians love beach living, but we’re pushing our coastline to the point of no return

The recently released hazard assessment for Port Phillip Bay highlights two critical facts: first, large areas of the bay are at risk of flooding, and second, this is going to get a lot worse as climate change accelerates.

Like most Australians, Melburnians live on or near the coast. The things we love, especially beaches, are nature’s way of absorbing the impact of the sea, with the coast acting as a buffer between the water and the land.

Port Phillip Bay on Wednesday, after rains across the state.Credit: Jason South

But this buffer zone is the same place where we’ve built houses, roads and the critical infrastructure of our modern lives. All of which now is at risk of being damaged by or lost to coastal flooding and erosion.

What’s more, the impact of the structures introduced to combat these issues, like seawalls and channels, is felt much further than a singular beach or stretch of coast. A seawall, for example, can actually double the rate of erosion further down the coastline. This then leads to a cascade of further structures, worsening erosion and the problem progressively shifting further and further along the shore.

The fundamental issue we face is the scale of the things we love is a lot larger than we can see. When we walk on a beach, we’re standing on only a small part of the entire landform. In Port Phillip Bay, the active beach extends to between seven and 10 metres’ water depth.

Recent research shows sand in the bay moves along kilometre-stretches on a seasonal basis, with the movement dependent on where you are. Sandringham acts differently to St Leonards, for example, and both are different to Dromana.

But all share the same fundamental character: that is, the area you walk on – scientifically known as the subaerial profile – is a store of sand for the beach to use when it responds to storms. It is a moveable buffer, and it includes the dunes found at the back of the beach.

Generally, the sand will move offshore during a storm and return during calm periods. This is commonly observed in the Frankston region, where wide flat terraces with ridges are found hundreds of meters from the waterline. In other areas like Sandringham, the sand also moves along the beach during storms.

This ability to constantly move is why we have beaches, and why they are the perfect buffer against the sea. But the shoreline of Port Phillip Bay has progressively become urbanised and less natural since the 1830s.

For over 100 years there was little interest in protecting our beaches, with management prioritising “reclaiming” the sea, or fixing the land boundary to a specific place. This loss of natural features ensued with the shoreline becoming “harder” and dominated by concrete and brick walls.

Over time, the bay, seawalls, groynes and harbours have all worked to disrupt the natural functions of the landform because the needs of a city, and the planning boundaries created with this, override the natural system.

Today, we recognise beaches as great places worthy of protection, maintenance and saving. Research shows renourishment programs can reverse human-induced erosion trends of the past in many places, including Sandringham Beach. But the bay is complex, large and energetic and the sea level is rising. There is no magic solution; difficult decisions need to be made.

Through next-generation computer modelling, advanced data collection and a new wave buoy network, we have the scientific basis from which decisions can be made. What is needed now is the legislative frameworks to be put in place.

To begin with, we need to learn from mistakes of the past and move beyond localism. Though councils have the passion and desire, they do not have the resources. And as has been proven time and again around the world, when it comes to coastal planning, private and industry pressure often wins out over public good. But sand ignores government boundaries, meaning we must have an approach that recognises the scale of this natural movement.

Ideally, we need a federal approach to the problem that is backed by legislation and policies that provide firm and precise planning, and that will guide us in sustainably managing our coastlines for future generations. At a minimum, we need a statewide approach to this problem.

To manage our inevitable retreat as sea levels rise, as well as to sustainably develop our communities outside of current and future hazard zones, these things are needed. Without it, local authorities will be forced to continue with a band-aid approach to the problem, with the result ending in a beachless Port Phillip Bay, surrounded by seawalls.

David Kennedy is an award-winning coastal geomorphologist, who received the 2020 Eureka Prize for Innovation in Citizen Science.

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