Musings with Mario

Our on-going series of “Talks with Terry” has been so well received, that other members of the team want to get in on the action. That’s why we’re proudly presenting “Musings with Mario” – a series of insightful articles designed to give you more information on topics that relate to your water assets.

This particular “chat” builds on a previous article on using modelling software to study stormwater. You can find that here.

Mario here, folks. I’m one of the friendly engineers at Simmonds & Bristow (though Terry still remains our “friendliest”). Today I’m going to build on one of Terry’s previous talks with you, on stormwater modelling.

Cool. Okay, so Terry told us all about stormwater modelling and the benefits of using software for stormwater design.  However, something he said got me wondering…He mentioned that Australian Rainfall & Runoff (AR&R) published ways to estimate runoff discharges in storm events – so if those methods exist, why make the effort to do modelling ?

First of all, I should give some context about the method. Since 1958, AR&R has published the Rational Method for calculating peak runoff flows from a catchment. It has been tweaked a few times since, and smaller authorities (such as state government and councils) also put in their two cents about how the method should be used in their locality. For that reason, AR&R is actually considering ceasing endorsement of the Rational Method.

So, it sounds like it was useful… until quite recently. Should it still be used in 2016?

It really depends on what you’re looking to do. It’s definitely still handy to consider, especially for simple, initial investigations where a simple rational method calculation is likely to be far less time-consuming than going to full blown flood modelling.

The Rational Method, however, is a simple formula, originally designed to be processed by hand on paper, and it can’t really be used to provide an indicative result for a complicated catchment, such as a full water-sensitive urban design. With increasing catchment urbanisation, the effects of climate change and the frequency of extreme events, the Rational Method, while still useful, is not the be-all and end-all of catchment modelling it once was. The increase in general computer performance has also helped, with consultants now able to run relatively complicated 2-dimensional hydrological models from desktop computers, models which once required veritable super-computers and days of runtime to complete.

The method still gets updated because not all consultants have access to advanced modelling software suites yet, but there is an increasing trend for engineers to take advantage of modern software to improve prediction and model accuracy. Simmonds & Bristow have made the choice to be ahead of the curve, rather than behind it, in this aspect. Since then, we’ve used flood modelling software for a number of projects, and found that it provides exceptional value for clients.

Okay… so engineers are working in a period where paper based design methods are being phased out by computer-based methods? Is that what you’re getting at?

Exactly! It’s especially relevant for stormwater design, as the software we use has only been commercially available since the early 2000s. To give an idea of how fresh this software is, AutoCAD was released in 1982, and Microsoft Excel was released in 1985. Comparatively, computer-aided flood modelling is a new and exciting realm of engineering.

So, can you explain in more detail how this is beneficial for clients? In a practical sense, where does the value come from? I mean, what’s in it for me?

Flood modelling definitely provides great value for clients. Flood heights and flow volumes estimated from modelling suites can be highly accurate (provided that you’ve got quality input data), whereas the Rational Method gives approximations that really only suit very simple catchment areas or configurations. For the client, the extra accuracy means that they might not need to construct expensive flow control devices (in cases where the Rational Method overestimates flood impacts). On the other hand, the client has peace of mind that flood impacts haven’t been underestimated either. Risks can be much better defined with accurate models. There’s even the benefit that stormwater modelling holds much more authority when submitting a development application.

I never thought about it that way. Sounds like it could be super handy for developers.

Very true, but we aren’t just limited to using it for a residential setting, either. As a matter of fact, this is where flood modelling software really shines: it can be used for any type of environment that can store water. This includes rivers and creeks, quarries, dams, floodplains, arterial roads, or anything you could think of that could be affected by heavy rainfall.

What does the future look like for engineers and developers, in terms of stormwater management?

Increased flood hazards are expected in the future, with climate change, population growth, and urbanisation all leading to greater flooding. However, the trend for more engineers to use flood modelling will continue, and hopefully this will lead to a better understanding of flood events, and give us the power to manage these events wisely. Simmonds & Bristow will further our expertise in this field, and continue to provide value from modelling-based stormwater management.

So, Mario, do you suppose you’ll come back and talk to us again? Terry’s great, but it’s good to know there is an entire team at S&B that’s ready to tackle whatever problems I might end up with.

Absolutely. I’m not going to let Terry have all the fun. See you next time!