- Design and Construction
The major initial design components and years of construction of the O’Shannassy System were:
The Aqueduct 1911-1914
O’Shannassy Weir 1911-1914
The O’Shannassy Reservoir 1922-1927
The Silvan Dam 1927-1931
The O'Shannassy Aqueduct System carried water some 82 km to the Surrey Hills Reservoir.
In 1931, the large Silvan Holding Reservoir was completed.
The System was a key component
in Melbourne's water supply system (especially supplying the fast-growing eastern suburbs of Melbourne) and was managed first
by the Melbourne and Metropolitan Board of Works (MMBW) and later by Melbourne Water. Whilst most of the Aqueduct remains
physically in place today (in a much deteriorated condition), it has been disused for some time and has fallen into considerable
disrepair (some parts of it have disappeared altogether.
The O'Shannassy River, and subsequently
the Aqueduct, was named after Sir John O'Shannassy, three times Premier of Victoria. The O'Shannassy River rises
in the slopes of Mounts Strickland, Arnold
and Grant in the ranges east of Melbourne.
O'Shannassy Aqueduct was a brilliant piece of engineering design and construction. It was to carry water from a diversion
weir on the O'Shannassy River via an open concrete channel along the slopes of Mount Donna Buang and several other steep mountainsides
for over 80 km to supply clean, fresh drinking water to the eastern suburbs of Melbourne.
The Aqueduct was designed
to have a constant gradient of 2 feet to the mile (1:2500) and was to operate completely by gravity, without the
need for any pumps or other mechanical devices.
Water would be carried up and down steep slopes, across roads,
creeks and rivers and through both farmland and residential areas by means of siphons, pipes and weirs. Some of the
pipes were timber and some steel.
Water flow into and out of the Aqueduct (both from the weir at its source and from
numerous creeks and rivulets along its course) was to be carefully controlled via a series of manually operated locks and
gates. Caretakers would be stationed along the route to maintain the aqueduct, keep it clean and ensure the water always
Plans were drawn up and construction work commenced in the
second half of 1911. Defining the route and clearing the forest trees was the first step. A series of wooden marker posts
were then built along the full length of the aqueduct to help workers locate particular points and maintain prescribed
Where the aqueduct crossed the lower lying areas around Wandin and approaching Mount Evelyn, it was in steel or wood-stave
piping, converting to open concrete-lined channel when the higher levels were reached. It went through the township of Mount
Evelyn in open channel (except for a short distance adjacent to the railway line) winding around the local contours to just
above what is now Johns Crescent, then part of the ‘Pine Mont Estate.’
From this point, the aqueduct was again transferred to steel pipes to go under the Olinda Creek and Swansea Road to
feed the Olinda Reservoir, in the Edinburgh Road area. This reservoir, now roofed over, was open to the skies.
The pipes crossing the Olinda Creek valley cut across the Lilydale Water Race, so water was fed from the Aqueduct to
the Race, the pipe creating the Race at the Cascades was cut away, and the section of the Race upstream fell into disuse.
The part of the Race downstream to the small reservoir on Birmingham Road was lined with concrete.
Mount Evelyn residents adjacent to the open channel were permitted to syphon water out of the channel for their own
use. Those on the high side of the channel were only allowed to pump water where there was no possibility of drainage back
into the open channel. One was the Pine Mont Guest House, where a windmill pumped water up to the house on top of a small
hill, and the drainage went down the other side. This first aqueduct system, before later enlargement, had a capacity of 20,000,000
gallons (75 megalitres) per day.
The Aqueduct channel was principally dug by
hand (aided by horse-drawn scoops). It comprised an open channel 9 feet 3 inches (2.81 metres) wide at the top and
3 feet 4 inches (1.026 metres) deep and was founded on a solid clay base.
Next to the channel, a flat access track
was constructed from the excavated material and fitted with rail lines to enable workers access to the site and to facilitate
the delivery of heavy construction materials including timber, stone, pipes, steel and cement.
of these were delivered by horse-drawn or manual trolley. Stones and crushed rock came from Blacks Quarry in Coldstream.
Horse-drawn flat-top wagons carried a mortar board on which to mix cement and this was hinged to enable the cement
to be tipped into the channel to be hand-troweled into place by the men standing in the channel below. It was important
that the cement was mixed at exactly the right consistency so that it would "stand" in place on the slope and not slump
to the bottom. If it was too dry, it would crumble and break up. Cement mixers were used in some locations to keep
up a steady flow of concrete to the workers.
Construction was hard work and labour-intensive and continued for
just over three years (39 months) in sweltering hot summers and freezing cold, wet winters. Falling trees and limbs, landslips
and wild storms were constant hazards. Construction took a relatively short time however, considering the degree of difficulty
and the exacting nature of the work and the fact that it involved hundreds of workers and almost 100 horses. The aqueduct
consisted of 23 miles (37km) of open or covered channels, three tunnels totalling just over half a mile, over 25 miles
(40km) of steel pipes (up to 36 inches in diameter) and a water supply capacity of 20 million gallons (75.7 million litres)
The new system was completed in October 1914, just in time to help Melbourne avert a major drought which
affected most of Australia.
The total cost of construction (as at 30 April 1915) was 426,890 Pounds ($853,780).
1928, the weir was replaced by the new larger O’Shannassy Reservoir, upstream.