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 we all play a role in. As our population grows and urban development continues, we must be aware of the direct link between the stormwater system and our rivers, creeks and bays.
Urban stormwater quality
Urban areas have expanses of constructed hard and impervious surfaces like roads, driveways, car parks, roofs and paving. When stormwater run-off flows over these hard surfaces, it readily accumulates pollutants. Stormwater pollutants originate from many different sources including fuel and oil on our roads, excess fertilisers and soaps from cleaning, 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 sources, as well as treatment of stormwater before it enters our waterways.
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, more stormwater run-off enters the drains system and receiving waterways.
Urbanisation has also changed the rate of stormwater discharge into water environments. Stormwater drainage systems have usually been built to remove stormwater from urban areas as quickly as possible, to minimise the risk of flooding and prevent water stagnating. The increased volume entering waterways causes scouring (in-stream erosion) of waterways. In less modified catchments the run-off water is released over a longer period of time, which maintains healthier water environments.
Reducing stormwater run-off can be more difficult in well-established urban areas that have a high density of buildings and infrastructure. However, new developments and the redevelopment of some urban areas are moving to incorporate measures that increase stormwater infiltration and reduce adverse impacts on our waterways. For example, grass swale drains, vegetated filter strips and porous pavements allow more stormwater to soak into the ground. We can also protect stream habitats and restore creeks that were previously modified (by channelling), by incorporating meanders, pools and in-stream vegetation.
Measures designed to improve stormwater quality and quantity can complement objectives of public safety and local flood protection.