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Purpose of the Scheme
The Snowy Mountains Hydro-electric Scheme (SMHES) is very large, covering 7 780 square kilometres. The original purpose of the SMHES was to:

• collect, regulate, and use the waters of the southward flowing Snowy River and other streams in the Snowy Mountains for generating large quantities of peak load electricity for New South Wales, Victoria and the Australian Capital Territory
• supplement the westward flowing Murray and Murrumbidgee Rivers to enable expansion by irrigation of primary production on the dry but fertile plains of the Murray and Murrumbidgee region.

The Scheme operates entirely within the parameters of its enabling legislation, the Snowy Mountains Hydro-electric Power Act 1949 and the Schedule added in 1957.

(SMA, 1993: 8)

Building the Scheme
A massive construction program, above and below the ground, occupied workers for 25 years.

Australian and overseas contractors built:

• 16 dams
• 7 power stations
• 145 kilometres of tunnels
• 80 kilometres of aqueducts
  and access roads were cut through the mountainous country. There were many construction records set and broken on the Scheme.

Bridges Three types of bridge were built by the Snowy Mountains Hydro-electric Authority (SMA): reinforced concrete or steel girder Bailey, timber or composite timber span or suspension. Most bridges in use are concrete or steel girder. Bailey bridges were originally designed as portable and usually temporary bridges. One suspension footbridge has been retained at Geehi Outlet.

Suspension bridge (SMA, 1992)

Suspension bridge (SMA, 1992)

Dams
Dams are perhaps the most prominent above ground civil structures on the Scheme. There are sixteen dams spread over the Scheme with a total storage capacity estimated to be about thirteen times the volume of Sydney Harbour.

Satellite image of location of dams (SMA, 1993: 9)

Types of dams
There are five principal types of dam, these terms refer to the chief materials used in the construction of the dam wall:

Rockfill	an embankment dam dependent for its stability primarily on rock, usually containing selected impervious earth and filter zones, with more than 50% of its volume composed of compacted or dumped rockfill .	(SMA, 1993: 69)
Earthfill	an embankment dam consisting of less than 50% rock and mostly constructed of compacted impervious earth and filter materials in zones and protected by outer zones of rock.	(SMA, 1993: 17) View image of Eucumbene Dam
Concrete gravity	a concrete mass dam, which can be straight or curved in plan	(SMA, 1993: 51) View image of Tumut 2 Dam
Concrete arch	also a concrete mass dam. It is curved in plan with the convex (bulging) curvature on the upstream face. Designed so that most of the loads due to water pressure are carried to the abutments by arch action.	Section through Tumut pond dam (SMA, 1993: 40) View image of Tumut pond Dam
Slab and buttress	a concrete dam constructed with thin walls or buttresses perpendicular to the axis which support a flat slab of reinforced concrete that forms the water barrier. There is one slab and buttress dam on the Snowy Mountains Hydro-electric Scheme on Outstation Creek to divert water into the Tooma-Tumut tunnel.	(SMA)

Dams on the Scheme
The most common type of dam on the Scheme is the concrete gravity. Six dams are constructed in this way.

The highest dam on the Scheme is Talbingo, a rockfill dam, at 161 metres. The lowest is Khancoban, an earth- fill dam, at 18 metres. Eucumbene Dam has the largest reservoir capacity and Deep Creek the smallest.

Activity
Make labelled freehand sketches to explain the difference between the types of dam.

Eucumbene Dam
Lake Eucumbene is the largest reservoir in the Snowy Mountains Scheme. It holds approximately nine times the amount of water contained in Sydney Harbour and covers more than 14 500 hectares. Lake Eucumbene collects water from the Eucumbene, Upper Murrumbidgee and Snowy Rivers and its enormous capacity is central to the flexibility of the Scheme to generate electricity and provide irrigation waters.

An earthfill dam
Eucumbene Dam, one of only three earthfill dams on the Scheme, holds the water of Lake Eucumbene. The other earthfill dams are at Khancoban and Tooma. Eucumbene Dam stands 116 metres high and is 686 metres thick at its base. The outer walls of the dam are built of rock while the inner core is compacted, impervious clay.

Eucumbene Dam specifications

Section through Eucumbene Dam (SMA, 1993: 17)

Plan of Eucumbene Dam (SMA, 1993: 18)

Plan of Eucumbene Dam Spillway (SMA, 1993: 18)

Constructing the dam Before the dam could be built, the waters of the Eucumbene River had to be diverted around the site of the dam wall. The diversion tunnel was constructed through the side of the valley by the Australian company Allied Constructions. This mid-1950s photograph shows the river flowing through the end of the diversion tunnel on the left while the dam wall takes shape in the background.	Photo: Bayram Ali (Powerhouse Museum Collection)
The water intake tower, shown partially completed in the photograph below, stood at the beginning of the diversion tunnel. With the completion of the dam, the tunnel still permits the release of small amounts of water down the Eucumbene River.	Photo: Bayram Ali (Powerhouse Museum Collection)
While work on the wall and intake tower proceeded, the hillside that would form the reservoir basin was cleared of trees. This was necessary to prevent damage to the intake tower from plant material. This photograph shows a bulldozer clearing the forest that covered the Eucumbene River valley.	Photo: Bayram Ali (Powerhouse Museum Collection)
To minimise seepage and maximise dam strength, the ground at the edge and base of the dam wall was reinforced by grouting. Holes were drilled with machines such as the one below and filled with concrete.	Photo: Bayram Ali (Powerhouse Museum Collection)
The core of the dam wall was built up slowly with compacted clay to prevent seepage. This was carried out primarily by the sheep's foot rollers shown in this photograph. They are being pulled by International TD-24 bulldozers, which were used throughout the Scheme. The clay was excavated from a soil quarry downstream of the dam wall and carted to the site in trucks and earthmovers.	Photo: Bayram Ali (Powerhouse Museum Collection)

Tunnels
Approximately 98% of the Scheme's engineering features are underground. Tunnels and pipelines, dug deep under the Snowy Mountains, measure 145 kilometres, and with 80 kilometres of aqueducts, collect and divert the inflows of the Snowy Mountains area.

Overview of tunnel features (shown in order of length)

Summary of principal features (in SI Units) - tunnels (SMA, 1993: 172)

Specifications of Eucumbene-Tumut tunnel (SMA, 1993: 25)

Plan of Eucumbene-Tumut tunnel (SMA, 1993: 25)

Profile of Eucumbene-Tumut tunnel (SMA, 1993: 25)

Tunnel cross-sections (SMA, 1993: 55)

Tunnelling
The longest tunnel is the Eucumbene-Snowy at 23.5 kilometres. This tunnel diverts the water of the Snowy River from Island Bend Pondage to storage in Lake Eucumbene, and when required returns the water to the Snowy-Geehi Tunnel at Island Bend. It took four years to build the tunnel, a remarkable achievement when it is realised that the geology of the Snowy Mountains is predominantly granite and the diameter of the tunnel at maximum is 6.30 metres.

World tunnelling records were established on the Scheme. In 1961, the Australian firm Thiess Bros, were contracted for the Geehi section of the Snowy-Geehi tunnel. In 1963, the firm established the world record for hard rock tunnelling when 165 metres of tunnel was formed in a week.

Swift progress in tunnelling was the result of many factors, but two deserve a special mention:

• the sliding tunnel floor and
• rock bolting.

Sliding tunnel floor The sliding tunnel floor comprises a large sectionalised steel working floor platform, which carried rail tracks, points and crossings, drilling gantry and other tunnelling equipment. A hydraulic jacking system moves each of the three floor units forward in six stages.

(Raymond, 1999)

Rock bolting
Rock bolts were used to support the roof and walls of major structures such as tunnels and power stations. Steel bolts, of different length and spacing, were inserted into the rock where they were found to be an excellent anchorage for the rock.

Rock bolts were tension bolts, that when placed, compressed broken or jointed rock surrounding the tunnel and converted the rock into a self-supporting arch structure. The technique of grouting, between the bolt and the rock, was developed for upward sloping bolts. It is claimed that the Snowy engineers developed the world's first successful method of grouting the holes between rock and bolt.

Expansion shell bolt. Adapted from (SMA, 1959: 2) Click to enlarge

Sliding wedge bolt. Adapted from (SMA, 1959: 2) Click to enlarge

Slot and wedge bolt. Adapted from (SMA, 1959: 2) Diagrams re-drawn by Yvette Hayes. Click to enlarge

Activity
1. List a range of hardware items that can be used to join masonry or support loads in rock. State the advantages and disadvantages of each support mechanism.
2. Make labelled freehand sketches to illustrate how these support mechanisms work.

Power stations The seven power stations (two of which are underground) house the large generators and turbines that produce the electricity from water that is stored in the Scheme's ponds and reservoirs. Power from the Snowy Mountains Scheme is transmitted at 330kV to the electricity systems of NSW, Victoria, the ACT, SA and Queensland. The Scheme can generate 3 756 megawatts, representing about 17% of the generating capacity of South Eastern Australia.

Lower Tumut Switching Station at Talbingo in the final stages of construction. Since 1973 this facility has redistributed the power generated at nearby Tumut 3 Power Station to Victoria and NSW along 330 000 volt transmission lines. Photo: Bayram Ali (Powerhouse Museum Collection)

Towns
Towns like Eaglehawk, Sue City, Happy Jacks and Bella Vista were purpose-built to service specific projects. Home to hundreds or even thousands of people for several years, they were dismantled after work was completed. There were eight major townships.

This photograph depicts a street of houses for workers' families at Eaglehawk near the Eucumbene Dam site in winter in the mid-1950s. The town was built by the NSW Public Works Department, which began the Eucumbene Dam project. These buildings were prefabricated in Sydney by Frank R. Wolstoneholme Pty Ltd and transported to the Snowy by semi-trailer. Unfortunately they were not specifically designed for use in the freezing climate of the Snowy Mountains. External water pipes froze in winter and the lack of insulation and double-glazing added to the discomfort in cold weather.

Photo: Bayram Ali (Powerhouse Museum Collection)