Stormwater is a term used to describe rainwater runoff in urban areas. Stormwater generally starts as rain falling on roofs, driveways, roads, car parks, pavements, gardens and other open spaces in urban areas. Some of this water soaks into the ground, evaporates or is captured by rainwater tanks but most of it ends up in stormwater drains which flow directly into our natural waterways.
These waterways include rivers, creeks, lakes, wetlands, estuaries and marine waters which are home to fish, frogs and other sensitive aquatic organisms (e.g. aquatic animals and plants). These waterways are also often areas we like to spend time ourselves for swimming, fishing, etc.
Unlike wastewater from kitchens, laundries, toilets and bathrooms; stormwater is generally NOT treated before it enters these waterways. That’s why only clean rainwater runoff should enter the stormwater system.
Stormwater runoff is mostly untreated, transporting pollutants collected as it flows through urban areas directly into natural waterways. Such pollutants can be harmful to aquatic organisms and ourselves, and can generally impact on the health and natural beauty of Tasmania’s waterways.
Stormwater pollutants such as oil, grease, fuels, fertilisers, herbicides, pesticides, detergents, chemicals, litter and heavy metals which aren’t naturally found in our waterways can be toxic and dangerous even in small amounts. Other pollutants like soils, nutrients from organic wastes (lawn clippings, leaves) and bacteria (animal droppings) are naturally found in waterways, but are now there in such large amounts that they too can be harmful.
Stormwater pollution in urban waterways today has a bit to do with changes in Tasmania’s landscape and some of our own activities over past years.
Before the development of urban areas Tasmania was covered with dense vegetation which helped to slow the flow of stormwater. This allowed more time for stormwater to soak into the ground, which reduced the amount of stormwater runoff. This vegetation also helped by soaking up some of the stormwater and nutrients it may have been carrying, with root systems that acted as anchors to trap sediment and prevent erosion.
As our population has grown and urban areas have expanded, much of this vegetation has been cleared and replaced with sealed surfaces like roofs, driveways, roads, car parks and pavements. These surfaces prevent rainwater from soaking into the ground which increases the amount of stormwater, and commonly collect pollutants deposited by vehicles we drive, pollutants from our gardens and stray pieces of litter which end up in stormwater. This stormwater then flows into gutters and drains before ultimately discharging to our natural waterways.
Before urban development - a vegetated area which allows rainwater to soak in, and is free from pollution generating activities
After development - vegetation replaced with sealed surfaces (roofs, driveways, roads, car parks, pavements) which collect pollutants and prevent rainwater from soaking into the ground
Through new approaches to stormwater management like Water Sensitive Urban Design, and improvements in Sediment and Erosion Control on building and construction sites, we’re getting much better at reducing the impacts associated with stormwater pollution these days.
The Northern Tasmanian Stormwater Program and Regional Stormwater Quality Management Strategy are here to help this process, but there’s still plenty we can all do to improve the way we manage stormwater at home.