Stratacells Revitalize Dubbo Streets

By Kristyn Levis

The Citygreen® modular Stratacell™ system has successfully been integrated in the beautification project for Brisbane Street in Dubbo, New South Wales. The Brisbane Street project initially started as a stormwater augmentation project by the Technical Services Division of Dubbo City Council to reduce the incidence and severity of flooding in Brisbane Street, which is a part of Dubbo’s Central Business District. After the stormwater project was completed, the Water and Sewerage Branch replaced the existing water main, which ran down the centre of the street, and moved it to the shoulder of the road on both sides of the street. After this, a budget was allotted for the purchase and installation of the Stratacells as well as the trees (Angophora floribunda or Rough-barked Apple). Because of the extent of the work, the Dubbo City Council had a tendering process for the supply of the structural cell system. Citygreen was picked for its outstanding product and competitive price point.

A project team, incorporating the skills and expertise of both horticulturalists and engineers, was established to implement the project that included Ian McAlister, Manager Horticultural Services, Manager Parks and Landcare Operations Mark Kelly, Manager Works Services Ian Bailey and Project Engineer Steve Howlett. David Moir from Moir Landscape Architecture was the lead landscape architect for the project. “The Parks and Landcare and the Technical Services Division worked collaboratively to undertake this project that was run extremely professionally and successfully. As a result, this project was completed significantly under budget,” Ian said. In June this year, the trees were planted over successive weekends to minimize disruptions to the general public. “Due to the large amount of existing underground services within the footpath and shoulder of the road, this left us a very small volume of space to plant reasonable sized trees. However, it opened up the opportunity to plant large, shade-producing trees down the centre of the street,” he added.

This was important to do as the Council wanted to match the scale of the street to the size of the trees. Ian said that the philosophy behind the design was in line with the City Wide Park concept that the Council adopted, which identifies the development of Park Streets. “Park Streets retain their functionality of providing vehicular movement but are embellished with values more closely aligned with parks, such as soft landscaping, footpaths, cycle ways, and more,” Ian said. They found that planting down the centre of the road also provided several benefits including improving the level of pedestrian lighting within the area by removing the conflict between the trees and the lights. Although this was the first time that any type of structural root cell system has been used in Dubbo, Operations Manager Mark Kelly said the whole operation went smoothly and that they found the system easy to install.

“It initially took us four to five hours longer for the first one as we had to figure out how to do it properly. But after that, it all went like clockwork,” Mark said. “One of the most important part of the installation process is to ensure that the base is flat and level. If this is done, the cells go together quickly,” Ian said. During the initial installation, the Council and Parks and Leisure Australia hosted a tree management day and invited surrounding Councils to learn about the system. At the workshop, a practice vault was constructed where they first identified the different module sizes. “Because of the position of the cells within the carriageway, we used a combination of Series 30 and Series 60 cells. Initially it was intended that a single row of Series 60 cells were to go on the perimeter of the pits and the 30 cells locked in the centre. However, it was discovered that even though both types of cells come out of the same mold due to different shrinkage rates, they were slightly different sizes that don’t connect properly,” Ian said. While the cells do connect individually, this was the first instance globally where innovative designers had sought to integrate both modules in a large soil cell matrix.

To overcome this, the Council changed the configuration of the cells slightly so that a double ring of Series 60 went around the perimeter with one or two cross connections providing additional rigidity to the structure. The Series 30 were then used to infill the internal spaces. Another issue was working around underground services. Fortunately, due to the modular format of the Stratacell system, the vault sizes were easy to modify around the services. “The Citygreen Stratacell system worked extremely well due to its modular format and the ability to work around, or incorporate underground services within the structural cell system,” Ian said. “This has resulted in the opportunity for the Council to undertake a long-term study of the trees and how they respond to different root space volumes.”

The trees have only been in the ground for four to six weeks so it’s too early to tell whether it’s growing healthily. But Mark said they are looking great after the completion of the project. The Council is going to do a cost and benefit analysis of using root vault systems in general. However, at the moment they intend to continue to use the root vaults to improve the quality of the trees in Dubbo’s urban forest. Ian said they are looking at using the Stratacell system again for the Darling Street beautification project in March 2014. The project is within the Central Business District of Dubbo and forms part of the City Wide Park.