On 13 November 2006 the NSW Premier, Morris Iemma, announced the construction of a major new 450 billion litre dam at Tillegra on the Williams River, approximately 230 kms north of Sydney. The announcement was made without the prior knowledge of the local community or Dungog Council. The Premier’s announcement circumvents established urban water planning processes designed to protect consumers and the environment and allow public input.
At the Hunter Water Community Information Session at Dungog on the 16 December 2006 the Managing Director of Hunter Water, Mr Kevin Young, admitted that the Tillegra Dam was a political decision, NOT a decision initiated by Hunter Water. A representative from the Premiers’ Department made NO apology for the way the Tillegra decision was dumped on the affected families in the valley.
Vital Statistics relating to the proposed dam
- Storage capacity 450GL = approx. size of Sydney Harbour
- 80 metre high wall = approx size 25 storey building
- 700 metre length wall = approx 7 football fields long
- 19km length of inundation area
- 3,500 hectares total effected area
- 2,000 hectares farmland inundated
- $300 million estimated cost
- $10 million per annum economic losses in Dungog
- 90 farming families dislocated
Hunter Water Corporation’s estimated cost of the project is $300million for the dam plus associated pumping and hydro-power works costing a further $40million. The project, which has been scrapped several times over the last 50 years by both past Labor and Liberal governments, will wipe out about 90 family farms and, from a technical perspective, is likely to cost a much higher amount than the $340m due to geological instabilities in the surrounding rim zone.
Building a new dam at Tillegra would be far less cost effective than many demand management and water conservation initiatives. In environmental and social impact terms, progressive works to optimize the Grahamstown scheme are minor compared with a new dam in the upper catchment area. (Hunter Water Corporation, Integrated Water Resource Plan 2003).
Tripling the available surface storages in the name of ‘drought-proofing’ seems like gold-plating for a system that has performed well to date. In the longer term, the Central Coast has its own supply alternatives that it may choose to pursue. Building the dam (Tillegra) will simply entrench higher than necessary water usage in both industry and the community. Tillegra’s the dam we just don’t have to have. (Dr Simon Fane, Newcastle Herald, 17 Nov 2006).
Overview of sustainable water supplies for the Hunter and Central Coast regions, without the construction of a new dam at Tillegra, on the Upper Williams River – Dr Charles Essery, Sustainable Water Solutions
• A line of hills contains the “Tillegra Fault” and forms the east side of storage for nearly 3 km north
from the proposed dam wall.
• Landslips inside the proposed storage area already weaken rock strata forming the reservoir rim.
• As the water level rises with filling of the reservoir the groundwater table will rise and water will
soak through the fault, weakening the rock strata further.
• If the rim collapses the entire Williams River valley downstream would be inundated
Breaching of the rim of a storage in this manner is quoted in Fell, MacGregor, Stapledon & Bell, Geotechnical
Engineering of Dams (A.A. Balkema Publishers, 2005). Fell et al state ‘It is clear the possibility of landsliding is an important feasibility issue for storage projects.’
However, from an examination of 145 reservoir landslides case histories, the International Commission on Large Dams (Reservoir landslides – guidelines for investigation and management, Bulletin 120, 2002) has reported that:
• Only about 36% of the known reservoir landslides were recognized during the planning stage investigations;
• At least 75% of the known reservoir landslides were pre-existing dormant or occasionally active or active
• Such pre-existing slides caused the most problems for reservoir owners.”
Is the Tillegra Dam Storage Safe?– Mr Graham Holt, Geotechnical Report