Ana Manero, Australian National University; Anneliese Sytsma, University of California, Berkeley; Margaret Shanafield, Flinders University, and Sally Thompson, The University of Western Australia

Recent flooding in the Sydney Basin pushed thousands from their homes and left others facing enormous insurance costs.

These events show how traumatic and costly it can be to live in areas vulnerable to disaster. Too often, socio-economically disadvantaged populations are disproportionately affected.

Some flood dangers, however, can be far less visible – to planners, developers and home-buyers. Sometimes, the danger comes from groundwater beneath the surface.

Earlier this year, for example, residents of the New South Wales town of Stuarts Point were evacuated and decontaminated after sewage spilled into their streets, as septic tanks filled with shallow groundwater.

And across Perth’s Swan Coastal Plain, groundwater damage to buildings, parks, roads and piping has cost local residents millions of dollars in remedial works.

These problems are not inevitable. Our recent report shows how changes to urban planning, building design and construction practices could reduce groundwater risks. That means better outcomes for residents, developers, governments and the environment.

Urbanisation can cause the water table to rise

In many cities around the world, the water table is only a few metres or less below the ground. Groundwater levels tend to naturally rise and fall with winter rains and summer drying, as this UK video demonstrates:

However, urbanisation can cause the water table to rise above its “natural” level.

When we clear bush or farmland for housing, we reduce opportunities for plants to intercept and soak up rainwater. More rain then infiltrates through the soil and causes aquifers to fill up more quickly.

Balancing the short and long-term costs

The urban suburbs most affected by high groundwater are typically newer and cheaper. To attract buyers, developers must keep prices low, but mitigating the risk of groundwater flooding is expensive.

Developers sometimes import and install sand as “construction fill” to elevate the ground level. They may also install drainage to control groundwater levels. These sorts of measures can represent one-third of the price of developing a housing lot.

Such measures on their own, however, don’t solve the problem.

Our recent report for the Cooperative Research Centre for Water Sensitive Cities suggested ways to improve groundwater management on Perth’s Swan Coastal Plain. These findings may help people in other areas dealing with similar problems.