Stormwater pollution is a concern for all urban areas. It consists of visible pollution, such as litter and rubbish, and less seen pollution such as sediments, and nutrients including Nitrogen and Phosphorus. These unseen pollutants can cause algae blooms, disrupt natural ecological processes, and reduce water quality therefore reducing amenity for water users.
Raingardens work by filling with water during rain events, filtering this water through specific types of media which treat the water with the water flowing off back into the stormwater system. They are not designed to remain filled with water, as opposed to a pond, and are typically much smaller than wetlands systems.
From the top they look like a planting bed but underneath they are engineered structures with various filter media of various sizes placed in layers to filter out nutrients. These filter materials create a home for biofilms, groups of bacteria, which process the Nitrogen and Phosphorus pollutants in the water.
The raingarden at Wanniassa consists of three separate pods and will remove over 20,000kg of nitrogen, phosphorus, and suspended sediment every year. This area was previous used as an informal car park, which resulted in erosion and sediments. The site now contains rocks and seating which can be used as an outdoor classroom area.