A log suspected to have jammed up part of the Hospital Creek Stormwater System during the October 2024 flooding in Balclutha. Photo: Supplied / Clutha District Council
A jammed log may have been a factor behind flooding in an industrial area of the Clutha District earlier in the year, a new independent report has found.
In October Balclutha's industrial area in Balclutha was left badly flooded after heavy rain.
Clutha District Council deputy chief executive Jules Witt said they sought an independent report into the performance of the Hospital Creek Stormwater System and the flooding in the industrial area due to the extent of flooding, given the amount of rain.
He said in previous years they have had more rain, but less flooding in that area.
"It was unusual in that this event was smaller than previous events where we hadn't experienced flooding," Witt said.
"Particularly in the industrial part of Balclutha.
"There was also some questions about how our infrastructure was operated. So in order to give the public confidence we wanted someone independent to look at what actually happened and then what recommendations to improve our procedures and things going forward."
Witt said the amount of rain that fell during the October event was only about two thirds of the amount that fell during a February 2020 rain event, which did not cause flooding in that area of Balclutha.
He said a key finding was that the pump station did not respond as effectively as it had during previous rain events.
The exact reason for that could not be determined, but a potential cause is a large log which was found on the outfall pipe after the flood.
"We suspect it held a (stormwater) flap gate open, which usually closes when the river gets high. It could be that or a number of other reasons."
Witt said the log appeared to have been deposited by the river during the flood, and sat on a chain which held the flap gate open.
As part of the report recommendations, in future the council will ensure the chain is completely slack before any rain event.
Witt said there are also a number of checks in the pump station, and changes to procedures which will be undertaken in the future as part of the recommendations.
