Spencer Street Raingardens

Raingardens are special types of garden beds that are designed to collect and filter stormwater run-off from hard surfaces such as streets, driveways, paving and gutters.

The Spencer Street raingardens are low-lying with high edges surrounding them, letting stormwater pool on the surface before slowly soaking through to the plant roots and soil layers.

Each raingarden is planted with native plants and grasses that are able to survive long periods of time without rain, and inundations (floods) at other times. These plants have deep, fibrous (hairy) and spreading root systems, that are good at taking up water and nutrients that pass through the soil.

A layer of large pebbles on the surface of each garden and pit helps to trap litter and sediment (small particles of soil and pollutants).

Below the raingarden surfaces, layers of soil, sand and bioretention media (a special soil mix designed to filter out pollutants) work to clean stormwater. Layers of sand and gravel also help drain water to the lower levels. Larger particles are generally trapped in the top layers, with smaller particles trapped in the lower levels. At the lowest level is a layer of crushed rock laying over a slotted pipe, where the cleaned, filtered water can exit the raingarden and drain to the Merri Creek.

Each of the Spencer Street raingardens contains a combination of the following plant species. These plants are all good at filtering out pollutants, each in a slightly different way:

• Amber velvet kangaroo paw (Anigozanthos)
• Gold velvet kangaroo paw (Anigozanthos)
• Roundleaf correa (Correa reflexa var. nummularifolia)
• Knobby club-rush (Ficinia nodisa)
• Cushion bush (Leucophyta brown)
• Tall sedge (Carex appressa)
• Purple flag (Patersonia occidentalis)

The top layer amongst the plants is a Tuscan stone mulch layer, 10cm deep, that helps hold in water. Beneath it is a sandy loam layer, 25cm deep, followed by a 10cm transition layer of coarse sand. At the bottom is a drainage layer of aggregate sitting over a slotted PVC pipe that collects the filtered water and connects it to the stormwater system.

How a raingarden works

The Spencer St raingarden consists of the following layers:

Top layer: Deep-rooted plants consisting of kangaroo paw, sedges, club rush, hollow rush, mat rush and cushion bush for raingardens.

Middle layers: Boulders, gravel mulch, bioretention media.

Bottom layer: Crushed rock laying over a slotted drain connected to stormwater system.

June 2011 – January 2012
Design phase

August 2012 – October 2012
Construction phase

May 2013
Rectification works

Total cost of six raingardens: $78,000

Total cost of Spencer Street redevelopment: $380,000

The Spencer Street redevelopment included: the reconstruction works between Woolton Avenue and Beaconsfield Parade included the replacement of bluestone open channels, footpath construction, traffic management works, pavement repairs and resurfacing, and drainage works – including six raingardens.

Maintenance tasks include:

• Weeding and replacement of plants.
• Monitoring how long it takes for water to filter through the raingarden to ensure the system is working.
• Replacing the substrate (layers of gravel and soil) when required.

The Spencer Street raingardens provide an attractive, green streetscape for residents and visitors, with the added advantage of slowing traffic and creating a safer walkway for pedestrians and cyclists.

The raingardens improve the streetscape and increase biodiversity (the range of plants and animals) in the area as well as reducing the risk of flooding, by re-routing some of the stormwater that would normally flow into the stormwater system. The raingardens provide a smart and sustainable environment to be enjoyed by residents and visitors.

Signs near the raingardens also help educate the community about stormwater management. They help us understand how litter, silt, oils, chemicals and other pollutants can be filtered out of stormwater to improve water quality in our waterways. This helps us to see the connection between our community and natural environment.

Many animals and insects call our local creeks and waterways home. The platypus, rakali (native water rat), water bugs, frogs, fish and birds (such as the sacred kingfisher) are all found in Darebin waterways.

When it rains, pollutants washed from our streets end up in the waterways. These pollutants include those we can see (such as plastics and cigarette butts) and those we can’t see (such as oils, detergents, bacteria and pesticides). Pollution of our waterways has a negative health impact on our local aquatic wildlife and plants.

Raingardens clean, filter and separate pollutants from water, before it enters our creeks, rivers and ultimately the ocean. Raingardens also help to slow down the speed that stormwater enters our waterways, reducing problems of erosion (loosening of soil) on creek banks. Slowing the speed at which water enters our waterways also helps to improve creek water quality. Protecting our local waterways is an important environmental benefit. Raingardens create healthier and cleaner waterways for all.

Raingardens also improve the streetscape of an urban environment. They introduce plants and birds to areas that are mainly concrete, roads and buildings. Increasing plants, trees and soil in an area can also help to absorb excess heat and provide shade (improving the microclimate).

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.

Artwork infographics developed and supplied by the City of Melbourne. For other examples of WSUD Urban stormwater treatment projects visit the City of Melbourne Urban Water Interactive Map here.

Council has been working closely with Melbourne Water to integrate sustainable measures into our capital works program.