Hawkesbury-Nepean environmental flows and weirs project

Healthy rivers and catchments are important for the ecosystems, communities and economies that rely on them. Dams and weirs affect the natural flow of water in rivers, affect water quality, restrict the migration of fish through the river and limit their habitat.

An environmental flow is water released from a dam or weir for the health of the river downstream. Environmental flows are important to improve water quality, fish passage and habitat conditions for native flora and fauna. They help native fish to breed, reduce the growth of weeds and improve water quality for recreation.

The NSW Government recognised the need to improve environmental flows and make better provision for fish passage in the Nepean River in the NSW Metropolitan Water Plan 2006. The plan committed to the release of new variable environmental flows from the water supply dams and weirs in the upper Nepean River. The new environmental flows began in July 2010 after a series of upgrades to the dams and weirs along the river.

The new variable environmental flows from the water supply dams and weirs in the upper Nepean River mimic natural conditions as closely as possible. This will contribute to reducing the adverse effects that dams and weirs have on river health and ecological values.

Works at water supply dams and weirs in the Upper Nepean catchment

The Upper Nepean catchment consists of four water supply dams (Avon, Cataract, Cordeaux and Nepean) and two major water supply weirs (Broughtons Pass and Pheasants Nest).

To release the environmental flows for the Nepean River, particularly when the water supply dams and weirs are not spilling, modifications have been made to the dams and the water supply weirs. At Avon Dam new environmental release outlets have been installed and new environmental releases started in March 2008. Construction works at the other dams and supply weirs commenced in January 2009 and is now complete. The first of the new environmental releases started in July 2010.

Works at weirs on the Nepean River

The Nepean River also contains a number of weirs from Maldon, south-west of Sydney, to Penrith. These weirs can act as barriers to the environmental flows and fish passage along the river.  To ensure the environmental flows can make it all the way downstream, modifications have been made to most of these weirs. These works included the installation of environmental release outlets and the construction of new fishways.

The NSW Department of Water and Energy, in consultation with the various weir owners, identified the best options to allow for the environmental flows and improved fish passage. The SCA commissioned the design and assessment of the new works and project managed their construction.

The modifications ensure the weirs continue to provide water for local irrigation while also allowing the environmental flows and fish to move through the Nepean River.

Works undertaken at Nepean River weirs

The following works were commissioned as part of the Hawkesbury-Nepean environmental flows and weirs project.

Hawkesbury-Nepean environmental flows and weirs works

Community consultation

As part of the Hawkesbury-Nepean environmental flows and weirs project, a community engagement process was undertaken that included information meetings with landholders, residents, Councils, other stakeholders (in particular irrigators) and recreational groups (including fishing groups and commercial operators). Additional meetings were held with individual property owners on properties which were directly affected by the weir construction program.

The broader community was informed about the project through advertisements in local newspapers and information signs. 

Download

Map of weirs on Nepean River (398.2 KB PDF File)
Hawkesbury-Nepean River Environmental Flows and Weirs Project brochure (308.9 KB PDF File)