Stormwater issues

Stormwater system

The stormwater system is designed to take rainwater from our streets and guttering into the closest waterway. Unlike sewage, stormwater is not treated before it enters our waterways. In some cases it is filtered by traps or wetlands, usually located at the end of the pipe system, but in most cases it flows directly from our streets and gutters into our creeks, rivers, bays and the ocean.

Maintaining our water quality is a challenge that we all should strive to meet. As our population grows and urban development continues, we must be mindful of the direct link between the stormwater system and our rivers, creeks and bays. All Victorians have a role to play in maintaining the quality of our waterways now and for future generations.

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Urban stormwater quality

Urban areas have expanses of constructed hard and impervious surfaces like roads, driveways, car parks, roofs and paving. When stormwater runoff flows over these hard surfaces, it readily accumulates pollutants. Stormwater pollutants originate from many different sources ranging from fuel and oil from our roads, excess fertilisers and soaps for cleaning, to litter dropped on our streets and sediment from building sites. Improving stormwater quality in the long term will require effective prevention and management of these pollutants at their source as well as treatment of stormwater before it enters our waterways.

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Urban stormwater quantity

In urban areas, the increase in the number and size of impervious areas has reduced the amount of rain that infiltrates the ground or is retained by vegetation. Consequently, increased quantities of stormwater runoff enter the drainage system and the receiving waterways. Urbanisation has also changed the timing for stormwater discharged into water environments. Traditionally, stormwater drainage systems have been constructed to remove stormwater from urban areas as quickly as possible in order to minimise the risk of flooding and to prevent water from becoming stagnant. The increased volume entering waterways causes scouring (in stream erosion) of waterways. In less modified catchments the runoff water is released over a longer period of time, which maintains healthier water environments.

Reducing stormwater runoff can be more difficult in well-established urban areas that have high density of buildings and infrastructure. However, new developments and the re-development of some urban areas are moving to incorporate measures that increase infiltration and reduce adverse impacts on our waterways. For example, we can increase the amount of stormwater infiltrating the ground by using grass swale drains, vegetated filter strips and porous pavements. We can also protect stream habitats and restore creeks that were previously modified (channelled), by incorporating meanders, pools and in-stream vegetation.

Measures designed to improve stormwater quality and quantity can compliment objectives of public safety and local flood protection.

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