Detention basins across Australia are intended to prevent or reduce flooding, but one hydrological expert says some could be managed better by incorporating design concepts that have been utilised in China for hundreds of years.
Presenting at the Australian Water Association TAS Stormwater Symposium this week, Pitt&Sherry Senior Principal Engineer Dr Haydn Betts said there are potential issues with the way detention basins have been designed in Australia, issues that require reconsidering the current design paradigm.
“Many basins around Australia aren’t designed efficiently and don’t take into account the design tools or data now available, particularly regarding antecedent wetness or pre-burst rainfall,” Betts said.
“Some detention basins actually receive a lot of water before the design flood arrives and produces ineffective flood management consequences. Designs sometime consider peak inflow rates only, and on many occasions the peak flood volume is not taken into account.”
Betts said that with the flood data provided by the Bureau of Meteorology, Australia must consider its detention basin designs more carefully.
“When you start looking at data available now and consider the its implications, we potentially have made mistakes and current design practices need to be thought through,” Betts said.
“With the new data and using current design approaches, basins are likely to become larger than previously considered. The implications are increased cost of construction and maintenance and inefficient utilisation of land. There are also safety issues.
“How can we make our basins smaller? The solution might be to go to the Chinese practice, downscale the concept and think about how it might be applied here. I think detention basins could be smaller, less costly and provide a better utilisation of available resources.”
Betts said Chinese practices are useful for Australia to consider because they have very large detention basins, but approach water level management differently.
“They have large inhabited and intensely utilised detention basins. These basins can contain anywhere between 10,000 and 250,000 people that would be evacuated if there was a major flood along the Yangtze River,” Betts said.
“These are sacrificial detention basins, an approach they have used for at least 100 years, are operated when a large flood arrives. Parts of the surrounding dykes are breached to divert flood water to flow into the basin from the river.
“It’s done in a strategic and targeted manner, so they can progressively transfer the top off the flood into a selection of 35 polders, and reduce the total flood wave passing at two or three key locations along the river.”
Betts said an adaptation of this design concept could help Australian detention basins become smaller as Australia moves into an uncertain water future.
Register for the Australian Water Association TAS Stormwater Symposium to hear more from Haydn Betts about the possible design applications for sacrificial detention basins in Australia.