Since 1862 Queen’s Park in Ipswich has been a landmark park of cultural significance and a popular destination for families for recreation. There are many magnificent, heritage trees growing in the park providing wonderful habitat for many varieties of native wildlife to use and creating shade for human visitors from the hot, Queensland sun. The responsibility and conservation of these significant trees and upkeep and care of the park belongs to Ipswich City Council.
Unfortunately, some significant Poinciana trees in the park were failing to thrive. These trees are situated on a hillside on a nature strip close to the popular nature reserve, with a road on one side and a concrete footpath on the other. Heavily compacted soil (penetrometer readings of past 950 PSI) was preventing rainwater from infiltrating into the ground and therefore not providing the underground network of tree roots with much needed hydration. This hydrophobic soil caused the knock-on effect of flooding of the footpath during major wet weather events and caused erosion of the footpath. Another troublesome problem that regularly occurred was the washing away of surface mulch from the ground onto the nearby footpath and road which was subsequently washed into the stormwater drain.
The Urban Soil Science Research team at Heritage Tree Care were tasked with coming up with a long term practical solution that would allow rainwater to easily infiltrate into the soils, preserve the footpath from erosion and be financially prudent. Senior Arborist at Heritage Tree Care Daniel Oaten formulated a plan which involved the Heritage Plant Health team, the Porous Paving team, the Vacuum Excavation team and of course the Arboriculture team working together to achieve a successful result.
The main aims of this project was to stop overland water flow erosion and to improve the health of the trees and to do this effectively and financially viably, the soil needed to be decompacted using an innovative VOGT geo injector. Using the injector, the ground was given a much-needed boost of soil amendments and inoculums this in turn gave the trees a health boost. This soil decompaction and health injection was completed several times throughout the project due to the extreme compaction issues.
Vacuum excavation was utilized to safely install a trench alongside the pavement as well as lateral drainage trenches to individual trees without damaging any tree roots systems. The vacuum excavation team also dug out a water outlet baffle bed to soak up any access water in an extreme wet weather event. Once the ground was prepared and the trenches dug, a variety of geotextile materials, Aggi pipe and gravels were placed in the trenches to stabilize the soil 30mm versi cell was also installed over the drainage. To complete the project a layer of Arbor Flex Porous Rubber was installed and then a layer of PermaMulch porous paving.
Porous permeable paving allows air and water to flow through the porous material at a rate of over 300 litres per minute per square metre, enabling the water to soak into the soil below. It was decided that Porous PermaMulch would be the most suitable material to use as the top layer over the rubber base not only for its fantastic absorption abilities (1000 litres per metre per minute) but also for its aesthetic qualities as looking like normal Aged Forest Mulch, it would naturally blend into the park landscape.
The project was an overwhelming success and the months of planning and preparation paid off. A demonstration for the Ipswich City Council was completed where 2000 litres was released onto the site over two minutes. This highlighted how the water is now easily and quickly absorbed into the ground, watering the trees as opposed to running down the path to the storm water drain, taking debris with it. Fundamentally the Permamulch slows down and baffles the overland water flow,the the ArborFlex Rubber disperses the water across nearly a two metre wide area. This allows percolation of water into the profile and to re-hydrate and recharge the soils deep into the ground.
Watch the video below to see the development of the project in pictures and also the overwhelmingly excellent result of 2000 litres of water being released onto the area.