Birkenhead Raingardens
Construction
Raingardens are expensive to build. Usually there is a civil component involving connecting concrete entry and overflow pits to the street stormwater network. Typically raingardens are excavated to 900-1400mm depending on whether they have trees included in the design.
Integration
Raingardens are good at integrating with the street landscape and infrastructure. This photo shows where the gutter has a break to form the inlet and the SEP (Side Entry Pit) is reversed so only when the bed is flooded does the water go into the pit - as opposed to whenever there is water flowing along the kerb.
Functions
Raingardens mitigate floods by infiltrating water into the soil and drainage layer, and providing a detention of water on the surface during high flows - usually 100-150mm deep. Water that exceeds the underdrainage storage re-enters the stormwater network cleaned by biofiltration.
Greening and Cooling
These gardens installed at City of Port Adelaide Enfield include evergreen trees which will provide cooling and the understory will aid greening and biodiversity.
No More Floods?
The client in the home on the left in this picture reported to me that he used to have to carry his wife to their car parked on the street as it flooded often. Now he says the new gardens have solved that problem
Heath Street
In a neighbouring street, raingardens with the same planting plan have been installed. In the background is a Memorial Naval Reserve which now functions as a detention basin. The Lefevre Peninsula has a mounting issue with rising sea levels, storm surges, subsiding land and higher less predictable run-off volumes
Maintenance
One of the most important maintenance item is to clear the inlets of rubbish / debris or sediment which can prevent water from entering or infiltrating to the raingarden special soil and drainage layers.
Overflows
This garden has inlets at each end and a large overflow weir / pit to take water once it reaches 100mm above surface height. These overflow devices are important to protect surrounding areas and infrastructure from floods
