It was very interesting to attend the TREENET 16th National Street Tree Symposium 2015, on the 3rd and 4th of September, with some of Australia’s leading tree scientists, arboricultural consultants, Local Government arborists and engineers.
The theme was around engineering issues, which included how to grow healthier trees and root systems in increasingly tighter spaces and how to direct storm water into the soil through, using water sensitive urban design methods, such as permeable pavements and rain gardens. See videos of the presentations.
The idea is to capture rain in the soil (‘bio-retention‘), rather than allowing it to just run off roads and carparks directly into drains and straight into lakes or out to sea. We can’t afford to lose water, our soils are drying rapidly and this is affecting the health of our street trees and reducing our ground water reserves.
When you see tree roots bucking pavement like this, it is often because the tree is trying to find water. By using permeable pavements and rain gardens, trees are less likely to die and need replacing and expensive on going road and pavement repairs can be avoided. Healthy trees with full canopies provide more benefits.
Creating rain gardens and wells around existing trees or new trees, allows run off from rain to be directed into gardens and tree root systems. Excessive rain, over flows into a drainage backup system to avoid flooding.
Trees and plants also act as filters, they remove pollutants from water before it seeps down into the ground water system or into rivers and lakes. This process is called bio-filtration.
Permeable pavement and pavers are a logical alternative to impervious paving or concrete.
The City of Stirling council voted last week (on the 1st of September, 2015), to continue to allow residents to pave up to 1/3 of their verge with impervious paving, artificial turf or In-situ concrete. Where verge areas are less than 10 square metres and/or verge widths less than 1.5 meters they may be fully paved. See the new policy from the 1st of September minutes.
What a shame they didn’t require people to use permeable paving on their verges? Being such a large council, the square meters add up. This means more valuable water down the drain in stead of into soil where it is needed.
At the same meeting the City of Stirling council voted to cease their Verge Makeover Program which wasn’t very popular and staff are currently investigating alternative programs to encourage residents to look after their verges, such as a rate rebate? Councilor Terry Tyzack vehemently rejected this idea saying that the last thing the city needed was more costly programs and a rebate system would reward wealthier residents who look after their verges anyway.
Perhaps they could offer grants to install rain gardens on verges to help keep street trees healthy?
