David Gribble is a committee member of the Planning Institute of Australia and is the principal at Gribble Engineers.
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TT: We hear a lot about rising sea levels, hotter summers, longer droughts but little about heavier rainfalls during storms. Can you give a layman's explanation?
DG: Rising air temperatures associated with global warming will bring extreme heat events, increased bushfire risks and extended dry periods. And when the rain does fall, it is likely to involve more intense storms and heavier rainfalls. As the atmosphere gets warmer it is able to hold more moisture than when it is cool. Think about the tropics and the build up to the monsoon. When there finally is a trigger for rainfall, it comes down in a torrent. A similar thing occurs with summer storms in Canberra. But in the future there will be more moisture in the atmosphere to drop on us.
TT: And the problem is?
DG: Most of our drainage systems were designed as much as 50 years ago when few had even heard of climate change. They were sized to get rid of the flows that were expected with the knowledge of the late-1950s. That was stormwater management in the '60s and '70s. Under a changed climate they are unlikely to contain the flash floods of the future.
TT: So will we need to build bigger drains?
DG: Canberra was planned with extensive linear parks along most of our waterways. These give us wriggle room for more sustainable waterways infrastructure involving less concrete and more vegetation. With more of the parks being flooded when the banks are over-topped however some reaches will need to stay as concrete drains.
TT: Are we heading for a crunch?
DG: Despite the media-hype, climate changes don't happen overnight. I had previously thought that it would be many years before we start seeing the effects of climate change in Canberra. But after studying local weather records dating back to 1940, I now think that long-term trends are emerging more rapidly than we thought.
TT: Longer dry periods then flash-floods. How worried should we be?
DG: The ACT should probably get a bouquet rather than a brickbat in this regard. And as long as planning for our waterways systems keeps pace with our understanding of climate change, we are OK. The ACT government is modelling our main waterways for more than 'the 100-year event' that most people would be familiar with. The new models have a big focus on what is known as the 'Probable Maximum Flood'. For the past decade there has been a government-driven push towards Water Sensitive Urban Design, which can reduce the runoff from local storms. Less focus on getting stormwater away as quickly as possible, more focus on reducing the amount of stormwater in the first place.
Tony Trobe is director of the local practice TT Architecture. Is there a planning or design issue in Canberra you'd like to discuss? Email tonytrobe@ttarchitecture.com.au.
