Why don’t our cities cope with heavy rain?

By Amy Edwards

1 December 2017

4 minute read

Updated 12 February 2020

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Torrential rain has fallen over New South Wales, with evacuation orders in place for several areas around Sydney, and thousands of homes without power across the state.

Although this deluge of rain is welcome after a summer of droughts and bushfires, extreme rainfall events can cause major flooding, car accidents, property damage and loss of life. We also know we’ll see more severe storms and rain events as our climate changes.

Our research can’t prevent extreme events from happening, but it can help protect people from the effects. We’re working on better city planning for heavy rains and extreme events.

Our cities in full flood

“Planning cities to cope with extreme rainfall events is critically important to minimise property loss and reduce danger to lives,” said Dr Simon Toze, from our Liveable, Sustainable and Resilient Cities team. “It can also reduce any negative effects on the natural environment, especially waterways.”

Our research, based on water and future resilient cities, includes finding environmental-friendly solutions for long-term sustainability and water supply. It focuses on preventing contaminants, and reducing discharge of water and wastewater, while protecting human health.

Our cities are predominantly covered in artificial surfaces such as roofs, roads and pavements. This stops natural rainfall from penetrating into the soil and groundwater recharge. These surfaces increase runoff, which can result in pollution of waterways with urban contaminants, and increased risk of flash flooding. Water Sensitive Urban Design approaches are designed to increase natural infiltration of rainfall, which can help reduce runoff and pollution of waterways, particularly from regular rainfall events.

a paved surface with rain falling

Urban landscapes tend to have lots of impenetrable surfaces which can cause flooding

Waterways in our cities

Using public open spaces and naturalising our water ways is important in slowing water flows. This helps to reduce peak floods, and remove sediment and other contaminants out of the storm water.

Our research is exploring how to significantly reduce disposal of our excess water and wastewater by looking at storage mechanism, improving sanitation and decreasing contamination of waterways. But there are also things residents can do individually to help.

Rainwater tanks have the potential to reduce the impact of urban flooding, especially if tanks have available capacity to capture some of the rainfall. It is helpful to ensure the tank is empty prior to a large rainfall event. Our previous research has shown that many people neglect regular maintenance of rainwater tanks systems, so make sure you keep it clean.

“An intense storm has the potential to fill a rainwater very quickly (e.g. 20 mm rainfall on 100 m2 roof can fill a 2,000 litre tank),” said Dr Magnus Moglia, one of our senior research scientists.

“To ensure rainwater tanks operate as designed it is important to check before the storm that gutters and downpipes are clear of leaf litter and other debris.”

Melbourne: Raingarden at the Federation Square carpark.

Five things we can do to prepare for storms

  1. Ensure roads and parks are as clean as possible to reduce contaminants being washed into our waterways.
  2. Encourage the growth of native grasses and bushes on the edges of our creeks and streams. This helps slow down water flowing into the streams and clean the water.
  3. Naturalise our creeks and streams, including creating floodable pond areas, to slow down water flows.
  4. Design more ways to capture and store water for later use, for example storing underground in aquifers.
  5. Understand that some areas in our cities will always flood and redesign them to deal with those floods.
people crossing the road as it rains

As heavy rain hits, how do our cities deal with it?