First of all, what do we mean by ‘Green’ and ‘Blue’? In this context, we’re talking about best practice for growing healthy trees (Green), and best practice for treating and managing stormwater (Blue).

For decades it has puzzled me that there is a major disconnect between the fields of urban forestry and stormwater engineering. Think about it – we plant trees into paved areas (car parks, malls, plazas, streetscapes) and partly paved areas (narrow road verges, centre medians, planter beds etc), and now we’re also paying attention to soil specifications, soil volumes for life needs of the trees, and so on. But one of the really key requirements for plant growth (H2O) is very efficiently sent away from our trees as soon as it falls on the large expanses of surrounding pavement! This doesn’t make sense whichever way you look at it.

A number of forward-thinking people around the globe have done some pioneering work in this – primarily to divert and capture water for tree health. However, how can the costs and benefits be quantified from all aspects? We need to carry the confidence of all stakeholders in the green building space, besides the developers and investors.

So, a few of us have been working with design engineers to try and clarify this issue, and bring some visibility to the discussion. Let’s break this up a little:

storm water management

  1. Passive Watering: this relates to the basic interception of rainwater, to enhance or replace manual or automatic watering of trees. Whilst there’s not a huge amount of science available publicly, there is definitely a growing interest. Based on regional climatic data, catchment areas per tree, soil type, and tree species, it is possible to optimise this and address each of these needs.
  2. Stormwater Management: this relates to flows, and is a really crucial component of many development approval mechanisms globally. We are trying to restore pre-development flows for the health of waterways and improve safety of the broader populace in presence of flooding events induced by changes in land uses and climatic events. The volume of soil within our treepits can definitely be used as part of a stormwater management plan, and incorporated into numbers of different modelling programs. Note: we also have to balance the other factors (tree health, soil volumes etc) along with the stormwater flows, using a Water Balance tool.
  3. Stormwater Treatment: this relates to pollutant removal from stormwater, and is absolutely integral to the suite of benefits that are brought to the table by combining treepits with stormwater treatment and management. The statutory targets for a given region can be achieved, and in many cases surpassed, when properly sized and specified treepits are used as part of a Green plus Blue initiative.

To wrap up: ideally, none of the above should be viewed in isolation, or else one or more of the design components will be compromised. For success, and all that this means (massive benefits to society, developers, the environment, and so on) a cross-functional approach is needed – one that combines the latest science for stormwater management and treatment with current best practice in treepit designs. When this is accomplished, there are significant savings to be achieved – and this makes sense to me. Because, after all, we are just re-connecting an environmental cycle that has been broken in our cities and urban spaces.

treating and managing stormwater

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