Case study: Infiltration understanding improves urban stormwater management

Improving the health of waterways in Australia’s urban centres is the aim of a new research collaboration that aims to better understand how stormwater flows through the soil in urban environments and mobilises surface and soil pollutants.

Of particular concern are urban karsts – highly porous subsurface networks created by the ubiquitous gravel-filled trenches used for laying pipes and utility services beneath our streets.

Significant volumes of stormwater can infiltrate these karsts and move as quickly underground as they do over land and into local waterways, carrying pollutants with it into local waterways.

The University of Melbourne’s Department of Infrastructure Engineering and Faculty of Science are collaborating with Melbourne Water on the three-year project to quantify these impacts and develop improved mitigation strategies.

Dr Meenakshi Arora, at the Department of Infrastructure Engineering, says the initial solution has been to build stormwater infiltration basins to hold flows. This allows time for pollutants to settle out, as the water slowly filters into deeper groundwater aquifers and streams.

But the current understanding of how these basins work is based on rural catchments. In contrast, urban catchments are littered with pockets of polluted soil and karsts.

Dr Arora says when stormwater falls into one of the gravel trenches it quickly follows the urban karst into streams, bringing many pollutants with it; it doesn’t get filtered through the soil at all. “When we understand the hydrology and pathways of urban stormwater, we can make better recommendations on where to put infiltration basins to get the best outcomes.”

Working with Dr Arora are Professor Tim Fletcher, Professor Andrew Western, Dr Justin Costelloe and Dr Matt Burns, combining expertise in water quality, hydrology and integrated urban water management. Melbourne Water is assisting with access to extensive field test sites and monitoring equipment. The project is funded through Australian Research Council Discovery Projects grant.

More information: Dr Meenakshi Arora, +61 3 8344 6644, marora@unimelb.edu.au