The Raingarden tree pits in Bellair Street, Kensington were one of the first projects delivered during my time at City of Melbourne. They where co-funded by Melbourne Water’s Living Rivers program.
The project came about because most of the existing London Plane Trees where in decline and/or had been significantly damaged by repeated knocks from parking cars. The replacement trees get passive irrigation from stormwater flowing past. Treated excess water, drains out of the sand filter media into the underdrain. As with most inner city WSUD projects, exiting services such as, in this case, a redundant water main and gas pipes placed challenges and constraints on the project. This required on-site discussion with the contractor and a change in tree pit dimensions.
The project was also aiming to develop a replicable and affordable design to be used in the future. For this we chose spike down kerbs to surround the pits and to prevent cars backing into the tree trunks.
These soon proved not up to the task as they where frequently hit and coming loose.
A cast in-situ exposed concrete kerb with a stiffening metal brace at the gutter side was developed to match the urban design style of the area. These have performed well with the design used in many other locations.
The tree pits in Bellair St are now 10 years old and the trees are looking healthy. Over the years there have been many house renovations in the street and I suspect fine sediment has washed into is clogging the filter media. However, with the tree maturing, council is unlikely to replace the filter media as this would damage the tree roots. This is one of the compromises of combining canopy cover/cooling with stormwater treatment.