By Rebecca Dargie
The extraordinary pictures of subsumed gardens and a swimming pool wrenched from the ground by the giant waves that battered Sydney’s northern beaches last month have revived debate about seawalls and the impact of human attempts to keep the rising ocean from our doors.
Given their spectacular locations, the homes in the frontline of raging waves are usually valuable property. Attempts to fortify them are met with resistance from ecologists and other beach users, who say the houses should not have been built there in the first place.
They object to seawalls because they stop the beach from being a dynamic system, in which wind and waves continually reshape the shore. Natural processes will usually redeposit much of the lost sand back on to beaches in the weeks after a storm. But where there is a seawall, heightened waves run up the shore and slam against it. The beach can’t move backwards, so the sand disappears.
But seawalls, like dykes, levees and berms, have been used across the world for centuries to protect homes and other assets. From Sydney to São Paulo to New York, a sea-level rise of even a few centimetres can threaten to swallow homes and highways, inundate sewage treatment plants, and contaminate water supplies. Whether faced with king tides or swelling rivers and lakes, planners in coastal and estuarine urban settings must find a way to brace against the impacts of climate change.