A few years back a developer chummy with the planning authority convinced the council that modern water resource management meant the floods were no longer a threat, and that the prime real estate in the middle of town was suitable for residential development.
You know where this is going.
So the developer manages to win the bidding for this land (funny that he managed to guess one dollar over the highest bid in a blind auction) and developed it to medium density housing. They were typical cheap crappy houses: four walls and a roof erected as quickly and cheaply as possible while still complying with building code. Prices were set high because they were riverfront properties, best location ever!
Anyhow at about this time there was some work going on upstream to remove willow trees from the river corridor. Willows are considered an invasive species here, especially since they can sprout from broken off roots that float downstream. The catchment area where these willows were being removed from was rugged country: out of town, in a steep valley, so hauling the logs out on truck was not an option, it all had to be done by helicopter.
The catch with hauling lumber out with helicopters is that helicopters only fly in good weather. So the forestry folks headed in, cutting trees in whatever weather they deemed safe because they were on a fixed price contract. Forests of willow massacred with logs and detritus everywhere, waiting for better weather to allow it all the be lifted out by helicopter.
Only the better weather didn’t come. The rain settled in and stayed. The dam upstream flowed over the top, so the effective size of the catchment for the town’s flood plain was now tripled.
So when the 100 year flood arrived, there were people living in these houses by the river, the developer had long since taken the money and moved on to greener pastures, and the flood was accompanied by hundreds of tons of willow logs, loose branches, leaves and mud.
The 100 year flood level in town was 5 metres. At that level these houses would have had wet floors, and some would have lost doors or windows. With the logjam from the forestry work and the extra water from the flooded dam, the water rose over 8m.
It was not a pretty sight.
So government approves some developer’s crazy idea of building on a flood plain, and years later the government has to cover the cost of emergency services coping with houses being flooded and people displaced from their homes.
Some facts have been enhanced for dramatic effect, but the essentials of the story are true.
TLDR: Queanbeyan River peaked at 8.4m December 2010, partly aided by logjams due to forestry works upstream. 100 homes were evacuated due to flooding.