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May 23, 2024In our latest blog, Atlantech Graduate Environmental Consultant Jonathan Kool explores the engineering concepts and environmental aspects of the Williams River and how it supplies drinking water for people in the Lower Hunter Valley region of New South Wales.
By Jonathan Kool
The Williams River is a beautiful tributary of the Hunter River. For those unfamiliar, a tributary is a stream that feeds into a larger stream or river. An estimated 50% of the primary drinking water for Newcastle and the Lower Hunter is harvested by Hunter Water from the Williams River and pumped into Grahamstown Dam.
The Williams River begins at the southern slopes of the Barrington Tops National Park, before passing through the townships of Dungog, Clarence Town, and Seaham where it meets historic engineered infrastructure. For example, the Seaham Weir, which protects the drinking water from salty tidal water, and the unique Balickera Canal, which channels and pumps water towards Grahamstown Dam.
Grahamstown Dam is significant for the Hunter Region as it is the largest drinking water supply dam in the region. It supplies 600,000 homes and businesses across the Lower Hunter and Newcastle, accounting for 40% of the water required for the region and meeting up to 75% of the daily water demand.
Engineering features of the Williams River
The Williams River has many engineered features to supply the drinking water of the Lower Hunter. These include Seaham Weir, Balickera Canal, and the Balickera Pumping Station.
Image source: https://www.hunterwater.com.au/documents/assets/src/uploads/documents/Plans--Strategies/CatchmentMangementPlan_FINAL_Mar2011_lowres.pdf
- Seaham Weir Pool
As Hunter Water describe, the Seaham Weir is used to separate the downstream tidal estuarine salt water from the upstream fresh water. About 45 kilometres from Newcastle, at Mill Dam Falls the Williams River changes from a river that is free flowing to a modified river weir pool spanning approximately 18 kilometres, called the Seaham Wier pool. This historic infrastructure was constructed in 1978 for the purpose of creating a pool free from tidal influence. The pool is essential for drinking water security but has led to environmental changes. The area is currently being managed and monitored due to the increased erosion risk.
- Uniqueness of Balickera Canal and Pumping Station
The engineering of the Balickera Canal and the pumping station is unique. This infrastructure screens the water of gross waste before pumping the water directly 15 metres upwards and then through a 1.2 kilometre long concrete tunnel before finally falling into Grahamstown dam.
After rainfall and when there are substantial flows of greater than 33 megalitres per day, the water can be harvested from the Williams River. In dry times most of the flow is sourced from the upper catchments of the Williams River and in wet times it is sourced mainly from the lower catchment. On average about 50% of inflow to Grahamstown Dam is pumped directly from the Williams River, according to Hunter Water.
Local Land Uses of the Williams River
Canoeing at Clarence Town, NSW. Image source: https://www.nsw.gov.au/visiting-and-exploring-nsw/locations-and-attractions/canoeing-at-clarence-town
The Williams River Catchment encompasses an area of 974 km2 with a variety of land uses estimated to be around 80% Agriculture, 14% National Parks and 6% owned directly by Hunter Water. Main townships and various residential areas are within the catchment namely Dungog, Clarence Town, and Seaham.
After the weir was constructed, the relatively static freshwater pool was valued by farmers as a secure freshwater source for agriculture and by the community for recreational purposes such as boating, kayaking and fishing. However, the clearing of vegetation on the riverbanks, cattle, and power-boating (which generates high energy waves impacting the narrow river bank), have been key factors that have contributed to ongoing erosion on the banks of the weir pool and declining water quality.
Threats to the health of the river
Clarence Town, NSW. Image source: https://www.aussietowns.com.au/town/clarence-town-nsw
- Water quality in decline
Hunter Water manages the drinking water supply system in line with the Australian Drinking Water Guidelines. Monitoring of the water in the Williams River during the past 30 years has shown that water quality is declining. One nutrient in particular, phosphate, has shown to be elevated in areas impacted by erosion. This is of significant concern as legally and safely harvesting water from the Williams River is dependent on water quality.
Natural processes that affect water quality include wind, waves, flood, fire and drought. These are sometimes exacerbated by man-made features. Land use activities including clearing, and run-off from agricultural and developed areas have also contributed to the declining water quality.
- Plans for restoration
Riverbank erosion can upset the water chemistry in the river and cause various ecological impacts. Increased water temperature, reduced light penetration and more negative micro-organisms in the water has had a negative impact on the water quality and lead to ecological and water security risks.
Through careful erosion management, and various other measures, water quality can be improved. The solution involves land and water-based management actions, including re-establishing vegetation along the river banks and reducing wave energy to protect the banks. Co-operation from all stakeholders who use the river and land will be required. On severely eroded sections, stock exclusion may be required or specifically engineered rock and/or log structures, weed removal, and revegetation.
Hunter Water and the NSW Government are funding a remediation program intended to resolve the erosion risk of Seaham Weir Pool. This will be a long-term strategy that is intended to work with Hunter Water, NSW Government, surrounding land holders and river users.
For more information and to have your say regarding the Seaham Weir Pool Erosion Management Plan visit https://www.hunterwater.com.au/haveyoursay/draft-seaham-weir-pool-erosion-management-plan.
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Sources and further reading
- Hunter Water Catchment Management Plan
- Hunter Water Grahamstown Dam
- Seaham Weir Pool Erosion Management Plan
Location of the Williams River catchment, New South Wales, Australia. Image source: https://www.researchgate.net/figure/Location-of-the-Williams-River-catchment-New-South-Wales-Australia-Topography-from_fig3_255603739