High Street Northcote Tree Pits

The High Street, Northcote tree pits are designed with the following three special features:

• Pit size is large, allowing each tree to continue to grow without restriction over a long period of time.
• Pit shape and size slows down and spreads out the flow of stormwater, helping to reduce erosion and giving tree roots the opportunity to take up more water.
• Water Sensitive Urban Design (WSUD) features such as bioretention layers (eg layers of crushed rock, sand and gravel to help filter oils, detergents, litter, organic matter (anything that was once living) and other contaminants out of the stormwater before it reaches the nearby Merri Creek.

Each tree pit is made up of important levels. The top level is flush with the kerb and is a polished steel lid (lintel) with many holes in it to allow stormwater to pass through easily. The lintel protects the pit and prevents large pieces of litter from getting into it.

Beneath the lintel is a layer of stone mulch, and beneath this are layers of gravel and bioretention media (special soil mixes that are able to trap or absorb contaminants from water). As stormwater filters through the layers of the tree pits, contaminants are slowly trapped. Larger particles are trapped in the top layers and smaller particles are eventually trapped in the lower levels.

The tree takes up excess water and some nutrients from the soil through its root system. A deep drainage layer of crushed rock sits at the bottom of the pit where the treated water seeps into drains that take it to the Merri Creek.

Technical drawing of tree pit system

Tree species:
The trees planted in the tree pits are a type called bella pink (Brachychiton populneus x acerfolis), which are native to Victoria and Tasmania. These trees tend to grow outwards rather than upwards, which creates excellent shade, as well as requiring less maintenance.

Base of Tree:
A lintel, or steel lid, sits flush with the kerb and footpath.

Below the surface:
Layers of stone mulch, gravel and soil help trap contaminants and slow stormwater. A final layer of crushed rock sits at the bottom of the pit, to aid drainage to the Merri Creek.

2012
Darebin City Council inspected existing street trees and planter boxes along High Street, Northcote and decided to replace and upgrade them with water sensitive tree pits. The tree pits were designed in consultation with the community and were constructed. Tree-planting was started.

2013
The final construction of 27 tree pits and planting of trees was completed.

$300,000 was spent on the design, construction and planting of the 27 High Street, Northcote tree pits.

Maintenance includes pruning trees and removing litter and smaller particles trapped in the lower levels of the pits.

Consultation with retailers and the community was carried out during the design and construction phases of the High Street, Northcote tree pit project.

The High Street, Northcote tree pits have helped to upgrade the streetscape of this area, improving the amenity of the shopping precinct and providing shade for pedestrians. The native bella pink trees blossom in summer, providing a beautiful example of an attractive, flowering native tree that is also a good environmental option for local gardens.

Business owners and community members now have a sense of ownership over the trees, and pride in their streetscape.

The stormwater that flows into tree pits irrigates (waters) the trees, meaning less potable (drinking) water is needed for irrigation. This saves Darebin City Council and rate-payers money and helps preserve the community’s drinking water supply.

Many animals and insects, such as the platypus, rakali (native water rat), water bugs, frogs, fish and birds (including the sacred kingfisher) call the Merri Creek and other Darebin waterways home. When it rains, stormwater picks up contaminants from roofs, streets, carparks and other hard surfaces, and these end up in the Merri Creek. The contaminants include litter such as plastics and cigarette butts that we can see, as well as ones we can’t easily see, such as oils, detergents, bacteria and pesticides. Contaminants pollute our waterways and harm the wildlife use them for food and habitat (homes).

The High Street, Northcote tree pits help to clean and filter contaminants out of local stormwater from contaminants, before it enters the Merri Creek and flows on into the Yarra River and Port Phillip Bay. Tree pits also help to slow down the speed that stormwater enters the Merri Creek, reducing erosion of creek banks. Slowing the speed that water enters our waterways and removing contaminants helps to improve stream water quality.

Darebin City Council acknowledges the Wurundjeri people as the traditional owners and custodians of this land and pays respect to their Elders past and present.