Australian utility WaterNSW is planning to replace an existing century-old weir on the Macquarie River with a more environmentally suitable structure, with plans to be unveiled to the public at a round of community information sessions this week.
The existing Gin Gin Weir is a rigid concrete wall built in the early 1900s which is severely damaged and does not meet contemporary environmental requirements associated with allowing fish to migrate and mimicking natural flow variability.
The need to replace the old weir with a modern version to meet long term needs in the valley is critical, given the recent drought and predicated climate change risks that threaten the resilience of the environment and other customers in the valley who rely on the river.
The proposed replacement structure is a low impact, gated design, which would allow native fish to migrate - thereby freeing up 140km of river to native fish habitat – and let water for the environment pass through in line with strict environmental laws and the water sharing plan.
The proposed weir would also have the capacity to hold and manage small volumes of water released for customers out of Burrendong Dam, before releasing it on downstream to meet demand for both irrigation and environmental purposes, thereby reducing the volume of water lost to evaporation, especially over summer.
WaterNSW Executive Manager Assets, Ronan Magaharan, said replacing the existing weir with a fit-for-purpose design will benefit all water users. “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,” he said.
“In contrast the proposed replacement weir is a modern, gated structure, designed to benefit all customers, including the environment. The gates can be lifted so tributary flows and floods can pass through, or lowered to temporarily store water for delayed delivery and even maintain natural river flows several metres lower than the existing weir if needed.
“Additionally the structure will have the ability to let fish migrate upstream and downstream in that stretch of river for the first time in over a century.
“This upgraded infrastructure helps WaterNSW regulate the river for the long-term benefit of all users and must 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.”