Authorities condemn old weir
WaterNSW is looking at replacing the century-old Gin Gin weir.
The Gin Gin weir is a rigid concrete wall built in the early 1900s which is severely damaged and no longer meets environmental requirements associated with fish habitat, or flow management.
With recent drought and predicted climate change risks, customers in the valley who rely on the river need a replacement, according to WaterNSW.
The proposed replacement structure is a low impact, gated design, which would allow high-flow events and floods to pass through and native fish to migrate, thereby freeing up 140km of river to native fish habitat.
The proposed weir would also have the capacity to hold small volumes of water that are released from Burrendong Dam, before releasing it downstream to meet demand for both environmental and irrigation purposes, thereby reducing the volume of water lost to evaporation, especially over summer.
“Some of the information circulating about this proposed replacement weir overlooks the fact that there is already a significant barrier in the river at Gin Gin, dating back to the earliest part of the previous century, which needs replacing,” says WaterNSW Executive Manager Assets, Ronan Magaharan.
“It probably met the standards of the early 1900s, but it certainly does not meet the environmental or operational expectations of water infrastructure in the 21st century. Add to that the damage and structural decline which has occurred over time and this crumbling relic represents all the worst features of an in-river obstacle.
“In contrast the proposed replacement weir is a modern, gated structure with the ability to let fish migrate upstream and downstream in that stretch of river for the first time in over a century.
“Its operating range is only a metre or so above and below the existing structure, thanks to gates that can let tributary flows and floods pass through or temporarily store water for delayed delivery. It can even maintain natural river flows several metres lower than the existing weir if needed.
“The ability to operate the gates flexibly means small volumes can be held and later released to the far reaches of the river system without that water always having to travel the huge distance from the Burrendong Dam, as is currently our only option.
“This means less water evaporates over the shorter journey from Gin Gin, rather than from the other side of Wellington.
“This will have long-term benefits of all users. WaterNSW will still be required to comply with the strict environmental regulations that oversee its operating conditions, and the legislated NSW Government water sharing plans which ensure equity and fairness among competing interests.”