WaterNSW is continuing its works to investigate replacing the existing, century-old Gin Gin weir with a 21st century, more environmentally suitable structure.

The existing structure is a rigid concrete wall built in the early 1900s which is severely damaged and does not meet contemporary environmental requirements associated with fish habitat, or flow management.

The need to replace the old weir with a modern version to meet the long term needs of all customers in the valley is critical given the recent drought and predicted climate change risks that threaten the resilience of the environment and water supply to other customers in the valley who rely on the river.

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.

The existing weir is:

  • More than 100 years old, badly flood-damaged and structurally deteriorating
  • A barrier to native fish movement, and it has been for more than a century
  • An out-dated, ungated concrete wall, that restricts river flows and is entirely incapable of being operated to enhance river management.

The proposed new weir:

  • Features the most advanced design to minimise its environmental footprint
  • Is a gated structure which can temporarily capture smaller volumes of water that are released from Burrendong Dam and pass tributary flows and flood events through to the Macquarie Marshes
  • Is designed to withstand extreme floods events, with large piers to elevate critical operating components above the highest floodwaters

WaterNSW Executive Manager Assets, Ronan Magaharan, said replacing the existing, damaged structure 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.

“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.”