Canberrra faces threat of flooding
Researchers reveal chance of 'mini tsunami'
By Julian Lee Canberrans are safe from the type of tidal wave that last month devastated Papua New Guinea but two ANU-based researchers claim many of the city's residents may be in the path of "mini-tsunamis". Dr Stephen Roberts of the School of Mathematical Sciences (SMS) and Dr Christopher Zoppou of ACT Electricity and Water and a visiting research fellow at SMS, have developed a computer model which simulates the flooding caused by the sudden collapse of residential water supply reservoirs. "Around the world this century there have been more than 200 failures of reservoirs greater than 15 metres high. This has caused millions of dollars worth of damage and the loss of more than 8000 lives," Dr Roberts said. In Canberra alone there are over 50 reservoirs located in elevated positions around residential areas, some containing up to 45 million litres of water - the equivalent of 10­15 Olympic-sized swimming pools, he said. The major concern is over reinforced concrete reservoirs which, unlike newer steel reservoirs, collapse completely when they rupture releasing their contents in a matter of seconds. "Some of these concrete reservoirs are over 50 years old and there is no doubt they will eventually fail," Dr Zoppou said. To accurately model the effects of failure, Drs Roberts and Zoppou had to ensure the model could handle real life conditions such as shock waves, complex landscapes, buildings and water flow over dry river beds. In each of the three case studies - Narrabundah, Lower Hackett and Karralika - chosen for their different terrain, the computer model was able to simulate the results of a sudden collapse of the reservoir. "If the Narrabundah reservoir were to collapse, a wall of water 1.5 metres high travelling at 60 kilometres per hour would travel down Hindmarsh Drive - a major arterial road with a speed limit of 100 kilometres per hour," Dr Zoppou said. The simulation showed that at Karralika the walls of the quarry in which the reservoir is held directs the water so that it just misses a nearby child-care centre. Not so fortunate however are residents of Lower Hackett and Karralika, where the terrain directs the deluge directly into their homes. "A flood warning system will be useless as it all occurs within 15 seconds of collapse," Dr Zoppou said. Part of the problem is that residential areas have crept up on these once-distant reservoirs presenting new risks for engineers to consider, he said. "The model we have developed uses commercially available software to animate the progress of flood waters. This will allow engineers to do risk analyses on their own computers without the need for expensive supercomputers," Dr Zoppou said. "Engineers will be able to use this model to find ways of redirecting flood water before the collapse occurs and to find the best location for future reservoirs," he said. The model is not limited to residential reservoirs however, "it can be extended to help plan for large dams, irrigation channels and the sort of flooding we have seen in Wollongong and the Hunter Valley," Drs Roberts and Zoppou said.