Between March 2009 and May 2011 Auckland Transport undertook a major project widening Lake Road between Napier Avenue and Jutland Road. The Lake Road runs from Devonport to Takapuna and is one of New Zealand’s busiest thoroughfares, with more than 39,000 vehicle movements on it a day. Lake Road is effectively the only road in and out of Devonport and carries buses and cycles as well as cars.
Lake Road has long been regarded as one of Auckland’s worst roads however efforts to improve it have proved contentious for a range of reasons including efforts to save a stand of Pohutukawa trees (2002), followed by the discovery of a large Maori midden(2007) and opposition to cycle paths.
The widening of this section of Lake Road was approved by the North Shore Council in 2008 with the objective of improving safety for the many users of the road – car drivers, buses, cycles and pedestrians – and improving its appearance.
Work commenced in 2009, with the relocation of underground services and improvements to stormwater infrastructure. In 2010 Fulton Hogan was awarded the main works contract to undertake boundary relocations, relocation and undergrounding of the many services running down Lake Road, widening the roadway and installation of new kerbs, stormwater drainage systems, footpaths and tree pits. A small ‘pocket park’ was also created at one of the main intersections, which involved extensive paved areas and the planting of eight trees.
Auckland Transport project managed this development, LA4 was the landscape architect and Fulton Hogan, the contractor.
When completed the project was to provide:
- Two lanes in both directions
- A continuous flush median to prevent queues and make it safer for turning vehicles
- New footpaths and a signalised crossing making it safer for pedestrians
- A dedicated on-road cycle lane in each direction
- Indented bus bays to avoid holding up traffic
- A pleasant landscaped plaza (pocket park) on the corner of Lake and Hauraki roads.
The design also included an avenue of trees along either side of Lake Road, replacing those which had been removed earlier to enable the widening. ‘Maori Princess’, a cultivar of the Pohutukawa tree or New Zealand Christmas Tree, was chosen being a native NZ coastal variety bred to be a street tree with an upright single stem and able to be grown effectively in a confined area.
And a confined area it was. Space was at a premium on the footpath. Services including water mains, gas and telephone had been laid directly under the footpath, leaving a margin of about one meter up to the boundary fence post footings. The cost of moving these services was exorbitant so a way had to be found to plant the trees without disrupting the cables and services.
Citygreen® Stratacell™ modules, supplied by Arborgreen NZ, were used in this project. They were placed in six by one meter tree pits dug in a narrow area between the fence post footings and the services under the footpath. Citygreen Stratacell modules are patented, load-bearing engineered plastic modules with vertical and lateral interlocks which create void space beneath pavements. After a suitably sized tree pit had been dug, taking into account the mature root size of the selected trees, multiple layers of Stratacell modules were placed in the pit and snapped together to form a matrix. An opening for the tree root ball (as detailed and dimensioned on the tree pit plans) was provided within the matrix.
The cells provide structural support for the footpath while creating a void for filling with soil for the trees. The cells prevent the soil becoming compacted, ensuring the tree roots can obtain essential oxygen, water and other nutrients.
The Stratacell modules provided much-needed flexibility in working around the underground services.
“Using Arborgreen cells gave us the flexibility to work around services. We could whip out the odd cell here and there to make room for the cable and pass other services actually through the matrix. We managed to get around moving the services which would have cost about half a million dollars’, commented the Council Project Manager.
Had the traditional concrete containers been used to hold the trees, relocation of services would have been unavoidable.
Citygreen root barriers, supplied by Arborgreen NZ, were also used to line the tree pit, preventing tree roots invading services or accumulating directly under the footpath, causing heaving in times to come. Finally permeable paving was placed over the rootcell area to enable stormwater to seep in, providing water for the trees.
All parties are very pleased with the final result.
As stated by the Landscape architect:
“The avenue of trees looks good and the trees are healthy. Planting the trees in Autumn will give them a very good start and the use of best-method urban tree technologies will assure long-term health and vigour”.
– Rosalind King