Massive storms are pumping pollution into our oceans: time to clean up our cities

The storms that have lashed Australia’s east coast are not just a threat to lives and property, but also to our marine wildlife, write Katherine Dafforn and Emma Johnston.

The storms that have lashed Australia’s east coast over the past few weeks are not just a threat to lives and property, but also to our marine wildlife, write GWI's Dr Katherine Dafforn and Professor Emma Johnston. The increasing urbanisation of our coastlines, and proliferation of impervious surfaces, has meant that up to 80% of stormwater now runs rapidly into a dense underground network of drains. These drains act like an expressway for pollution and debris in our cities, roads, gutters and gardens, sending a cocktail of contaminants directly into the aquatic ecosystems that lie at the end of the pipe.

Earlier this year, Newcastle recorded its wettest January day since 1862. In 2015, New South Wales experienced a “once in a century” storm event. These storms along Australia’s east coast originated mainly from naturally occurring low-pressure systems, which may become less frequent but more severe in the future. Worldwide extreme weather events are becoming more common, with about 18% of heavy precipitation events attributed to global warming.

More than two-thirds of the pollutants entering Sydney Harbour have been estimated to do so via stormwater drains, creating hotspots of pollution with concentrations 20 times higher than natural levels. More than 80% of the city’s catchment is covered by concrete, increasing the volumes of stormwater run-off, a mixture of rain and any dissolved or solid pollutants carried along with it - litter, oil and grease, metals, fertilisers, pathogens, pesticides and soil. When stormwater reaches a waterway it represents a significant ecological risk. Mobile animals such as fish and crustaceans may be able to avoid pollution by temporarily moving. But other aquatic organisms such as seaweeds and animals that anchor to rocks are more vulnerable. If they don’t die from the exposure, they may accumulate significant concentrations of pollutants within their bodies.

More than two-thirds of the pollutants entering Sydney Harbour have been estimated to do so via stormwater drains, creating hotspots of pollution with concentrations 20 times higher than natural levels.

Kathrine Dafforn and Emma Johnston

The solution to stormwater run-off is to build better cities: to design and construct cities to protect waterways such as rivers, manage stormwater and also make them livable for people too. This approach is known as water-sensitive urban design. One example is the large underground water tanks that collect stormwater to be reused for irrigation at Sydney’s Barangaroo Reserve. Homeowners can help by retaining vegetation, installing rainwater tanks, clearing excess leaf litter and debris from guttering and driveways, and reducing the use of pesticides and fertilisers on gardens.

While we need to clean up our waterways, we also need to make sure that enough water and organic matter are flowing through our rivers and into the oceans. Getting the balance right will make for better cities and healthier oceans.

Katherine Dafforn is a Senior Research Associate in Marine Ecology, UNSW.
Emma Johnston is Professor and Pro Vice-Chancellor (Research), UNSW.

This opinion piece was first published in the Conversation