Godfrey Street greening

The Donkey Wheel House is a large building that occupies approximately half of the eastern street frontage along Godfrey Street. Rainwater is captured on the roof of the building and flows into five downpipes, spaced along the façade. The irrigation system redirects rainwater from these existing downpipes to trees and gardens in the street.

An underground trench

We have redirected three of the downpipes into an underground channel of structural soil and structural cells beneath the pavement. Runoff from the footpath is also directed into the channel via a grill in the pavement.

We have planted trees along the channel. When the water soaks into the structural soil it passively irrigates the trees. The roots of these trees are able to grow freely along the channel, giving the tree a stable base and encouraging vigorous canopy growth.

Garden bed

At the southern end of Godfrey Street, stormwater is diverted from two downpipes on Donkey Wheel House into a roadside gutter that flows into a garden bed. This provides passive irrigation to the shrubs and trees in the garden bed. It also removes pollution from the water. In heavy rain, excess water is able to flow out from the garden bed and into the stormwater drain. This prevents flooding.

Planning and research: 2011 to 2013

Detailed designs: May 2013

Construction: May 2013 to September 2013

Monitoring and maintenance: ongoing

This project was completed by City of Melbourne staff and contractors. The State Government of Victoria was our funding partner.

This greening project cost a total of $650,000.

Traffic study         

We carried out a traffic study in 2011 that showed that Godfrey Street had low levels of traffic. In 2012 we studied the impact of different options on traffic in surrounding streets. This analysis showed that complete closure of the street would have too great an impact on surrounding traffic flow. However, it was feasible to close one lane.

Concept designs

We developed concept designs to help engage local resident and business owners about the proposed changes.

Community engagement   

We held a number of consultation sessions where local residents and businesses were invited to participate in developing the designs.

Services

Melbourne’s central city is a densely developed area and there are many underground services providing electricity, gas and telecommunications. We worked around these existing services when designing the size and location of the structural cell channel in Godfrey Street.

Traffic

Our study of traffic in surrounding streets influenced our designs. We were considering completely closing Godfrey Street, but the impact on traffic would have been too great.

Our study showed that trucks require a wide turning space due to a centre median tram stop on Bourke Street. This meant that we had to incorporate a turning arc for long vehicles into the open space at the end of Godfrey Street.

Parking

Because a large number of trucks use Godfrey Street to unload goods, our designs had to include loading zone parking. This meant that we could only widen the pedestrian area at the northern end of the street.

As part of the concept design process, we worked closely with building owners, businesses and owners corporations’ representatives. We held a consultation session for community members to share their visions and concerns, and received largely positive feedback.

We also asked every property owner, resident and business in the street for feedback on our concept plans. It was overwhelmingly positive, so we didn’t make any design changes. We also provided all stakeholders with final plans before construction began.

The most important part of this process was ensuring that local residents were aware of the changes and our desired outcomes.

Under the Melbourne Planning Scheme, we are responsible for public open space and streetscapes. As the works cost less than $1 million, we did not need to apply for a planning permit.

We removed one lane of the two-way street to double the amount of pedestrian space and plant new trees. We also excavated a channel beneath the new pedestrian area. This was lined with geotextile fabric and filled with structural cells and soil.We planted street trees at intervals along the channel and diverted downpipes from the nearby building roof into the channel. The area was then paved with bluestone and street furniture was installed.

The system makes use of the existing downpipes from the adjacent building.

• 3 downpipes connect to the underground structural cell channel
• 2 downpipes connect to the gutter and irrigate the garden bed at the southern end

A channel is dug for pipes that will collects water from the downpipes and divert it into the system.

Purpose

To retain rainwater around the tree roots and allow healthy root growth

Size

25 metres long, 1 metre deep and 1.5 metres wide

Location

Runs parallel to Godfrey Street, 0.5 metres from the kerb with a slight angle down to the south.

We planted the trees in a long, underground trench rather than in individual pits because the increased soil volume allows for better root growth. Water is able to flow along the channel through, ensuring that all of the trees are passively irrigated by the rainwater.

Purpose

The structural cells retain water in the soil, making it available for the tree root systems and providing prolonged water after a rain event.

Location

Two layers of structural cells fill the channel and structural soil was used to fill any voids

Type

Stratacell plastic modules.

Purpose

To ensure that fine particulate matter does not move from the channel and to ensure the tree roots stay within the channel

Type

Geonet heavy grade non-woven filter fabric

Location

Lining the base and walls of the channel, and covering the top of the structural cells

Purpose

The compacted soil gives the structural cell modules stability and increases the load-bearing capacity of the matrix.

Type

Sandy loam

Location

The soil is used to fill the space around and between the structural cell modules in the channel.

We compacted the soil into the channel, in and around the structural cells. The structural cells were then vibrated to shake the sandy loam into any gaps, and more soil was added. This was repeated until there were no spaces and the trench was completely stable.

Purpose

Water from the downpipes flows into the two drainage pipe lengths that run horizontally under the footpath and is evenly distributed throughout the channel. Slots in the bottom of the drainage pipe allow water to be dispersed into the strata cell matrix below as it flows down the length of the pipe.

Type

90mm sleeved UPVC water infiltration spreader pipe with slots facing down.

Location

Two lengths of drainage pipe sit on top of the structural cells, running the length of the channel.

Purpose

To provide an ideal growing environment for the new trees. The moist soil encourages healthy root growth, which in turn encourages healthy canopy growth.

Species

Japanese Zelkova

Detail

Trees were planted in compacted sandy loam soil, covered with porous pavement (40 mm thick layer of 7 mm aggregate)

Location

Four tree plots were sunk into the channel at even intervals

Dimensions

60 cm deep and 120 cm along each edge.

Purpose

To prevent the tree roots from growing into the drainage pipe and blocking the flow of water into the soil.

Type

Geonet heavy grade woven filter fabric

Location

Vertical root barriers separate the soil in the tree plot from the drainage pipe drains

Type

Sawn bluestone pavers

Location

Bluestone pavers are set down on a reinforced concrete slab, covering the channel and the entire open space area.

Porous bluestone paving was not necessary here because the pavers drain to a grill that allows the water to flow to the channel below. This feature turns regular pavement into a permeable surface.

The grill allows water runoff from the bluestone pavers to flow down into the trench.

Purpose

To grow plants that will climb up the wall of the Donkey Wheel House building, creating a green façade. The bed is also used to grow herbs for the café next door.

Size

4 metres by 0.5 metres and 0.5 deep.

Details

Filled with sandy loam soil and various plants. A drain pipe allows excess irrigation water to flow back into the channel.

Location

The planter bed sits flush against the wall of the Donkey Wheel House, level with the pavement.

The Godfrey Street Greening project requires very little maintenance. We monitor the downpipes to ensure there are no blockages. During times of drought we may have to manually irrigate the trees to ensure they continue to grow healthy and cool the surrounding area.

This regular maintenance is carried out as part of the existing open space management contract at the City of Melbourne.

We will use the health of the new trees in Godfrey Street as an indicator of the project’s success. All rainwater falling on the roof of the Donkey Wheel House building will be directed to the trees. They should grow healthy and strong in the moist soil.

We will monitor the success of the project by considering the following questions:

• Have the streetscape changes improved amenity in the area?
• Does the greening provide workers and visitors at Southern Cross Station a better entrance to the central city?
• Is Godfrey Street more pedestrian friendly?