The first update of the Australian Rainfall & Runoff guidelines since 1987 will address climate change for the first time.

By Giles Parkinson

The first complete book from a wholesale update of Australian Rainfall & Runoff (AR&R) – the de-facto bible for stormwater design – is due for release within a few months.

The overall revision, involving more than 100 people, a budget of more than $20 million, and more than a decade of painstaking research, thought and revision, will affect the standards for the design and management of all infrastructure that conveys water – from household stormwater drainage through to major dams, bridges, and flood mitigation systems – as well as land-use decisions and planning by emergency services.

It is the first update of this document since 1987. Editor James Ball, an Associate Professor at the University of Technology Sydney, has been working on the project since 2003, so the publication of the first of a series of nine books will be a notable occasion. It will also be keenly awaited by local government and other engineers, and all those whose projects are impacted by water.

It has been and still is a massive task. When the last edition was published in 1987, PCs were only just becoming available, so many of the techniques were designed for hand calculations and have since become computerised. The new edition will be considerably longer – 45 chapters instead of 14 – because many of the models will be re-thought and re-formulated, as well as expanded. “It is quite a substantial expansion,” Ball says.

As an example, there is, for the first time, a key focus on pluvial flooding, which is from rainfall as opposed to rivers (fluvial). Changes in local government processes mean that pluvial flooding is now taken into account. This recognises that houses can be flooded by rain as well as streams and rivers.

Ball says the new document also recognises that there is greater variation in rainfall across the country. The updated AR&R will have more short-duration rainfall data and guidance on how to account for the impact of climate change. From a rainfall perspective, the team is getting assistance from the Bureau of Meteorology and the CSIRO to add what is known to the document and provide guidance on what is unknown and how to incorporate that into flood estimations.

The update will include key components that cover climate change – an issue that has been thrust to the fore of policy and planning decisions since the guidelines were first published. Climate change was mentioned in previous editions, but then completely discounted for lack of data.

“We are now in the situation where we have got to give more definite guidance on the issue,” Ball says. “We are staying out of the argument of human-caused climate change versus natural causes. But we recognise that the climate is changing, and that people need to take these changes into account.”

Some of its studies have already had an impact. One that focused on the safety of people in flood events took children into account. Previously, information was available only for adults. This was used in a discussion on land use and a proposed childcare facility adjacent to a creek. In the end, the facility was not allowed.

On the other hand, one government body refused to adopt updates included in a draft chapter on flood-frequency analysis because it was just that – a draft. Yet, Ball points out, even the 1987 edition recommended that someone undertaking flood design should use the latest information, even if it is not in the AR&R.

The first book is close to release and is just waiting for a few final changes on methodology. The second book is at the stage of ‘advanced draft’, while a number of others have significant sections drafted but are not yet ready to go into either an internal or external review. Uncertainty about funding for the remaining work was resolved recently when Geoscience Australia agreed to pay Engineers Australia $5.15 million over three years to complete the third and final stage of the revision. Ball estimates it will be another two or three years of writing and review prior to full publication.
 
“It’s extremely detailed,” Ball says. “One of the things we found out is the number of regions in the world that look to AR&R to provide guidance, with local information inserted. It is an example of where Australia is leading the world in many aspects.”

For Ball, this has been a massive project. “For the last five years, I have been spending 50 per cent of my time on this,” he says. “It will be very satisfying to complete the task. You don’t get many opportunities to put all your thoughts together in one form like this.”

He says his biggest concern when accepting the challenge was how to get the profession to follow in behind. But he need not have worried. It’s been a $20 million project, but only half has come from the government; the rest has come in kind. “I have been delighted by how much support I’ve been given by my colleagues.”

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