Rethinking rain – our new ‘real time’ guidelines

The ‘wet’ is getting wetter and the ‘dry’ is getting drier. While not another climate change piece, this story is linked to our ever-increasing understanding of our natural environment.

In 2016, a significantly updated national guideline was re-released. ‘Australian Rainfall and Runoff (AR&R) 2016, rewrites the rules of how we will be designing, modelling, testing and building stormwater infrastructure. It is based on 30 years of research and replaces the 1987 version that is still widely used.

It was the general intent for this new revision of AR&R’ to be ‘live’ – to be able to be updated as needed, when needed, to capture the latest best practice and most current data available. Upholding that intent, as of just a few weeks ago, we have now seen the release of AR&R 2019.

So what’s changed? Surely rain is still rain? That’s true, but Australia is still a relatively young country and as such, the available data that informed the previous guideline was, in a word, limited.

Why re-invent the wheel?

  • 30 years of new rainfall data gathered by the Bureau of Meteorology considerably skews the rainfall data at different locations around the country that we plug into our designs
  • Quantum leaps in computing power now allow us to physically develop multiple higher fidelity simulations of real-world events.
  • We have an obligation to developers and our communities to achieve more efficient and safer designs. Yes, this includes considering climate change and the impact it will have to storm events 50 years from now.
  • We now have a feedback loop available where new data and best practice can be readily documented for the engineering and development community to consider; we don’t have to wait 30 years for the next revision.



What this means in practise.

In taking just one example we will now compare the ‘patterns’ of rain. What does this look like from the old to the new?

Under our new guidelines this means that yes, we now have to run 10 times the number of simulations for each individual pit and pipe in our network!

Looking forward, what do we anticipate?

There will be some changes to designs. For safety, some design elements may be increased in size at critical locations depending on the catchment layout and size however, on the whole, we generally anticipate design changes at a localised level to be minor.

The better data will help in optimisation and improving the efficiency of our designs. The data is simply more statistically grounded and reliable.

It is unclear how the new guidelines will impact the engineering approval process, yet. This will take time, working with council’s and certifiers alike until these new guidelines become second nature. In an ideal world this will remove differences in requirements across our numerous LGA’s. Communication between all stakeholders will be key to achieving this.

Our increase computing ability and new software will offset the increased amount of work required to adopt these new guidelines. The result is a better design, better safety for our communities and better long-term cost implications.

This will take time to be adopted in full!

In many cases the preceding planning controls, strategic master plans, trunk drainage and infrastructure designs – based on the old standard – will most likely prevail. This is especially true for the Sydney growth precinct, it’s simply not feasible to apply the new standards retrospectively to large scale planning controls already adopted retrospectively.

We are now seeing a significant uptake of these guidelines in new studies and reports, it’s not a matter of ‘if’ for these new guidelines, but ‘when’.

If you have any questions or would like to have a chat about how the implementation of AR&R might affect your development, please give Orion Consulting a call on (02)8660 0035.

Christopher Scholes | Civil Design Engineer | Orion Consulting


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