Upper Strangers Pond Rain Garden is in the parkland adjacent to Upper Stranger Pond. It will treat about 1800 litres of stormwater a second with a treatment area of 5200m2. Water from this rain garden is a first step of treatment for water entering Lake Tuggeranong via Isabella Pond.
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.
Rain gardens 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 rain garden at Upper Strangers Pond will remove over 80,000kg of nitrogen, phosphorus, and suspended sediment every year.