It has taken four years but finally Nepean River regulars have been vindicated – the new Penrith Weir constructed in 2009 is draining the river too quickly according to an independent report.
Works at Penrith Weir, including installing a new fishway, were completed in 2009. The weir was also modified next to the fishway to replace the culvert spillway and replicate pre-existing conditions under low river flows.
However, since the modifications too much water has been draining out of the river, creating chaos in dry spells.
“Ever since the new weir was built, in times of no rain, the river levels have just dropped like a rock,” explained Steve Defina of Nepean River Tours.
“People using the boat ramp have had troubles because they have driven their trailers off the end. And with the water level so low, rocks that haven’t been seen for 100 years suddenly emerge.”
Mr Defina said that his own cruise vessels are especially designed for shallow waters but that other boats such as the Nepean Belle have had issues when the water level has been low. Low water levels also make it more difficult for rowing crews to embark and disembark, and exposed rocks can damage their vessels.
After a meeting in November 2013 with concerned stakeholders, the Sydney Catchment Authority (SCA) commissioned an independent report on the weir by the University of NSW.
The independent report, released this week, found that the modifications to the weir had in fact changed the water flow.
“Modifications to the Weir allow more water to be discharged for any given water level. Water levels in the Penrith Weir Pool now fall faster than prior to the weir modification,” said the University report.
“Five of the 10 lowest water levels have occurred with the new weir in four years compared with 18 years analysed for the old weir.”
The report also found that river activities are quite sensitive to water level changes. Environmental flows from Warragamba Dam have also contributed to low water levels.
SCA is arranging a meeting with Fisheries NSW and NSW Office of Water to find a solution to the problem.
“We have also engaged Dr Martin Mallen-Cooper from Fishway Consulting Services to advise the SCA on what changes might be appropriate to address the depletion of weir pool levels whilst retaining the effectiveness of the fishway and the passage of environmental flows,” an SCA spokesperson said.
Mr Defina said changes need to be implemented as soon as possible.
“It’s great that we finally have the report, but we don’t want to be waiting another 12 months… we want to see changes as soon as possible,” he said.