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Dams of the Hunter Valley, New South Wales

4 March 2012 UPDATE: Some of the information below is now out of date (some of the links given below no longer work). In particular, the drought in eastern Australia has ended to be replaced by floods and the Tillegra Dam project as been scrapped (Tillegra Dam Project)

The Prime Minister of Australia, John Howard has announced major changes in the way water is managed and conserved in Australia; Howard's $10bn Water Plan

In making the announcement of the new Water Plan, John Howard criticised Australian State Governments for the lack of dam building programs over the last 20 years; Beattie welcomes water reform dam push

In New South Wales, shrinking dam levels due to the drought have put building new dams back on the political agenda, e.g. Tillegra Dam

The Tillegra Dam, north of the New South Wales city of Newcastle, is proposed to ease the current water shortage on the N.S.W. Central Coast and the Lower Hunter Valley. The Hunter Valley is an area known for horse studs, vineyards, coal mining and coal fired power stations; Tillegra Dam Project Information

With the prospect of a new dam to be built at Tillegra it is interesting to compare this dam site with several other existing dams in the Hunter Valley, especially with regard to the geology of the different dam sites.

Geology of the Hunter River Valley, New South Wales

The above figure shows the geology of the Hunter River Valley from the town of Scone in the north-west to the city of Newcastle in the south-east. The Hunter River rises north of Scone and flows in a south-east direction until it enters the ocean at Newcastle.

The geology of the area is as follows;

Map Colour Rock Types Geological Age
Orange Basalt and Dolerite Tertiary
Green Sandstone Triassic
Blue Sandstone, Shale and Coal Permian
Grey Sandstone, Mudstone and Volcanic Ash-Flow Tuff Lower Carboniferous

Topographically the blue Permian coal-bearing sedimentary rocks occupy the relatively flat, central portion of the Hunter Valley through which the Hunter River flows. The New England Highway (route 15) which is the main inland highway between Sydney and Brisbane also runs along this flat, central area of the river valley.

On the southern side of the valley, the green Triassic sandstones form hilly country that marks the northern edge of the Sydney Basin which has the city of Sydney at its centre.

On the northern side the valley rises into hilly country formed by the grey Carboniferous sedimentary and volcanic rocks and further north continues to rise to the mountains of the Barrington Tops that are capped by orange Tertiary basalt.

Several major dams have been built on the northern side of the Hunter River valley as shown below.

The dams shown in the above figure are, from west to east:

Glenbawn Dam on the Hunter River itself, located east of Scone

Glennies Creek Dam on Glennies Creek (shown on the map as Lake St. Clair)

Lostock Dam on the Paterson River, one of the northern tributaries of the Hunter River (not named on the map)

The site of the proposed Tillegra Dam is shown by the large green arrow. Directly north of the Tillegra Dam Site is Chichester Dam (not named on the map). Chichester Dam is located on the southern edge of the large green coloured area that marks the Barrington Tops National Park. This is an undeveloped area of very steep, rugged terrain that is heavily timbered.

A more detailed view of the eastern half of this area is provided by the map below which covers the area from Lake St. Clair (Glennies Creek Dam) in the west to Chichester Dam (not named but directly north of Dusodie) and Tillegra Dam Site in the east;

In this map the large green arrow identifies Lostock Dam. All the dams mentioned (Glenbawn, Glennies Creek, Lostock, and Chichester) are located in the same Carboniferous sequence of sedimentary and volcanic rocks in which Tillegra Dam Site is located.

Although all these dams are located in the same broad sequence of geological strata, there are significant differences in the details of the geology from dam site to dam site. Nevertheless, experience at the existing Glenbawn, Glennies Creek, Lostock and Chichester Dams should provide important clues regarding potential geological problems that may be encountered at the site of the proposed Tillegra Dam.

I was Project Geologist for both the Glennies Creek and Lostock Dams and was also involved in the geological investigations for the Glenbawn Dam Enlargement project. In my experience, geological problems are most likely to be encountered where volcanic rocks such as ash-flow tuffs occur in the dam foundations (e.g. Glennies Creek Dam) or where sandstones in the dam foundations contain clays derived from volcanic glass (e.g. Lostock Dam).


Singh, S.K., Geology of Tillegra Dam Site

Journal and Proceedings of The Royal Society of New South Wales
Volume 121 Part 4 pp. 179-184 [Issued July, 1989]

Abstract. Geological investigation of the proposed dam site at Tillegra indicates that the site is suitable for construction of a concrete-faced rock fill dam. Arenites of variable composition are the predominant lithological constituents of the site. The beds are conformable, strike NNW, and dip upstream into the pondage (westerly) with an average angle of 42 degrees. Weathered horizons are present and sometimes may need excavation of more than 10 m during foundation work for the dam. Rock mechanics and petrographic analysis favour the chosen construction mode. Unconfined uniaxial compressive strengths of up to 85 MPa for the arenites, indicates that the foundation is very strong. Most importantly the site does not exhibit any structural anomaly.

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