A raingarden is a garden bed that is specially designed to improve the health of our waterways. That is, it mimics the pre-urbanisation water cycle, to filter and treat stormwater flows.
Why do we need raingardens?
When it rains, water is washed off our roofs, driveways and roads, and runs to our rivers and creeks. We call this water ‘stormwater’.
On its way to our rivers and creeks, the stormwater picks up lots of litter and harmful pollutants like oil, chemicals and animal droppings. After heavy rainfall, the volume and speed of the stormwater can also erode river beds and banks.
This is a problem for the fauna and flora that live in our waterways, as it damages the quality and structure of their habitat.
How do raingardens work?
When it rains, water is directed into the raingarden from a nearby hard or sealed surface, such as a road, driveway or roof.
As water collects in the raingarden, the first step is to slow down its flow rate. This allows litter and coarse sediment to be filtered and left behind on the surface.
As the water begins to soak into the ground, the second step is to treat it. This is done by the soil and plant roots, which work together to naturally filter the water to remove finer sediment, toxins and pollutants. The water then enters the stormwater drain system through a pipe below the soil.
This video by Melbourne Water briefly explains what raingardens do and how they work.