Construction of the O'Shannassy Aqueduct
O'Shannassy Aqueduct
The O'Shannassy aqueduct was a brilliant piece of engineering design and construction. It was to carry water from a 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 kilometers to supply clean, fresh drinking water to the eastern suburbs of Melbourne.
The open 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, accross 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 flowed.
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 levels.
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. Many 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 3 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) per day.
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).
The open 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, accross 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 flowed.
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 levels.
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. Many 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 3 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) per day.
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).
O'Shannassy Reservoir
O'Shannassy Reservoir
Construction of the Maroondah Dam commenced in October 1920 and was finally completed in 1927. However, during this protracted construction period, Melbourne's thirst for water and exposure to periods of drought continued.
Despite the success of the O'Shannassy aqueduct, it was felt that further measures were needed to "drought proof" Melbourne. It was decided additional storages were needed to overcome the problems of low streamflow in dry spells and construction began on the Silvan Reservoir near Mt Evelyn and on a small equalising reservoir on the O'Shannassy River, just upstream from the O'Shannassy Weir.
In 1918 preparatory work began on the 3,000 megalitre "equalising reservoir" on the O'Shannassy River to regulate flows to the weir (located downstream on the O'Shannassy River) and so provide a more regular water supply to the aqueduct, even in periods of drought. The reservoir was to be relatively small but was located in a very productive catchment (stream flow averaging 80,000 ML per annum). Water flow from the Reservoir could be controlled by a valve at the base of the dam wall, enabling the precise amount of water flowing into the aqueduct to be managed. In periods of particularly high streamflows, when the Reservoir became full, excess water would be discharged into the O'Shannassy River, via an open spillway.
Construction began in 1922 but not completed until 1928. The reservoir is an earthfill embankment with a reinforced concrete core wall, 226 metres wide and 34 metres high and has a surface area of 27 hectares (holding 930 million gallons) at full capacity. It was constructed by day labour involving in excess of 130 men and 30 horses. A tunnel 5 metres in diameter extends 250 metres through solid rock at the base of the wall and channels water to the O'Shannassy River to feed the weir. The flow of water through the tunnel is controlled by two large manually-operated valves (for each one full turn of the valve, 11 megalitres of water is released).
The reservoir cost 216,161 Pounds ($432,322) to construct and involved the purchase of 3 "Ruston" steam shovels, an air compressor, hydraulic stone crushers, concrete mixers, engines, boilers and a steam crane - all quite modern and innovative machinery at the time. The success of this approach was the foundation for the Board to adopt a similar strategy of construction for the larger Silvan Reservoir a number of years later.
Despite the success of the O'Shannassy aqueduct, it was felt that further measures were needed to "drought proof" Melbourne. It was decided additional storages were needed to overcome the problems of low streamflow in dry spells and construction began on the Silvan Reservoir near Mt Evelyn and on a small equalising reservoir on the O'Shannassy River, just upstream from the O'Shannassy Weir.
In 1918 preparatory work began on the 3,000 megalitre "equalising reservoir" on the O'Shannassy River to regulate flows to the weir (located downstream on the O'Shannassy River) and so provide a more regular water supply to the aqueduct, even in periods of drought. The reservoir was to be relatively small but was located in a very productive catchment (stream flow averaging 80,000 ML per annum). Water flow from the Reservoir could be controlled by a valve at the base of the dam wall, enabling the precise amount of water flowing into the aqueduct to be managed. In periods of particularly high streamflows, when the Reservoir became full, excess water would be discharged into the O'Shannassy River, via an open spillway.
Construction began in 1922 but not completed until 1928. The reservoir is an earthfill embankment with a reinforced concrete core wall, 226 metres wide and 34 metres high and has a surface area of 27 hectares (holding 930 million gallons) at full capacity. It was constructed by day labour involving in excess of 130 men and 30 horses. A tunnel 5 metres in diameter extends 250 metres through solid rock at the base of the wall and channels water to the O'Shannassy River to feed the weir. The flow of water through the tunnel is controlled by two large manually-operated valves (for each one full turn of the valve, 11 megalitres of water is released).
The reservoir cost 216,161 Pounds ($432,322) to construct and involved the purchase of 3 "Ruston" steam shovels, an air compressor, hydraulic stone crushers, concrete mixers, engines, boilers and a steam crane - all quite modern and innovative machinery at the time. The success of this approach was the foundation for the Board to adopt a similar strategy of construction for the larger Silvan Reservoir a number of years later.
Enlarging the Aqueduct
Joint line where the extra wall height was added
During the 1920's Melbourne's need for water seemed insatiable and as the construction of Maroondah and O'Shannassy storages fell behind schedule, other options to rapidly augment supplies to Melbourne were pursued.
In 1924 works commenced to increase the height of the walls of the O'Shannassy aqueduct so it could carry a greater volume of water. The inverted siphons were also duplicated to provide for the inceased flow. By increasing the height of the channel walls by a relatively small amount - top width was increased from 9 feet 3 inches to 12 feet 11 inches and depth increased from 3 feet 4 inches to 5 feet 2 inches - the capacity of the aqueduct was effectively tripled from 90.7 megalitres (20 million gallons) per day to 272 megalitres (60 million gallons) per day (although, in practical terms, the aqueduct ran "full" at 50 million gallons per day). The color difference and the join in the cement walls of the aqueduct are still clearly visible. A number of other aqueducts serving Melbourne were also enlarged at the same time.
In 1924 works commenced to increase the height of the walls of the O'Shannassy aqueduct so it could carry a greater volume of water. The inverted siphons were also duplicated to provide for the inceased flow. By increasing the height of the channel walls by a relatively small amount - top width was increased from 9 feet 3 inches to 12 feet 11 inches and depth increased from 3 feet 4 inches to 5 feet 2 inches - the capacity of the aqueduct was effectively tripled from 90.7 megalitres (20 million gallons) per day to 272 megalitres (60 million gallons) per day (although, in practical terms, the aqueduct ran "full" at 50 million gallons per day). The color difference and the join in the cement walls of the aqueduct are still clearly visible. A number of other aqueducts serving Melbourne were also enlarged at the same time.
Silvan Dam
Steam shovel working at Silvan
The next major phase in the O'Shannassy project was to be the construction of Silvan Dam, near Mt Evelyn. The Silvan Reservoir had been planned from 1916 as a storage reservoir for the O'Shannassy system, particularly to hold water from the aqueduct and provide a back up storage in times of extreme drought, such as that in 1914. It would also act as a settling basin to further ensure the quality of Melbourne's drinking water.
The site was selected in 1919 and the 442 hectares of Crown Land plus 449 hectares of freehold land was vested in the MMBW. The site was conveniently close to the O'Shannassy aqueduct so that both inlet and outlet channels would be as short as possible. Pipelines from Silvan would carry water to Surrey Hills reservoir and from there be distributed to the higher eastern suburbs of Melbourne.
It was decided to construct Silvan using day-labour and "modern" machinery, building on the success of this approach used at the earlier O'Shannassy Dam construction. Works began in 1927 and the project was finally completed in 1930 at a total cost of just over 500,000 Pounds ($1 million). The dam was officially opened on 7 July 1931 (by which time it was almost three-quarters full). Total capacity was 40,000 megalitres. The main dam wall was was 644 metres long at its crest, 219 metres wide at its base and 43 metres high. The wall required 46,000 cubic metres of concrete and 1.3 million cubic metres of earthfill. The cellular core wall principle was almost entirely new and represented a notable advance in the construction of large earthen dams. The foundations of the core wall extended up to 140 feet (42 metres) below natural ground level.
A number of innovations were used on the project, including:
- electric power was brought 11 kilometres from Lilydale to provide power for the works (including lighting to enable operations to continue at night)
- a 5 kilometre long aerial ropeway (using an electric powered motor) was built from Mt Evelyn station to carry sand, cement and other materials to the construction site: there were 200 buckets on the line, carrying an equivalent of 5 bags of cement each and each bucket took about 52 minutes to reach the site - providing around 16 tons of cement per hour - and skips dumped their loads directly into the formwork on the dam wall
- an aerial cableway carried material from the crushing plant to the dam wall
- a nearby quarry provided rock for the dam wall
- compressed air crushers were used to crush the rock
- a 3 foot 6 inch rail transport line was built and steam locomotives carried rock from the quarry to the on-site crushing plant
- use of the largest steam shovel in Australia at the time
- use of steam powered excavators, locomotives, rollers and cranes
- workers were accommodated for free in huts on site (all quarters were provided with water, sewerage and garbage services)
- the camp and works had its own telephone exchange with 30 lines
All of this was absolutely "best practice" at the time.
The scheme provided a model for future Board projects involving the use of the latest technology (replacing much manual labour and horse-power), efficient use of day labour and the purchase of its own plant and equipment. The project actually came in several hundred thousand Pounds under budget and was hailed a great success!
Silvan was fed from both the O'Shannassy and Maroondah aqueducts (from O'Shannassy Weir and Graceburn Weir respectively).
In 1933 parts of the Mt Evelyn section of the O'Shannassy aqueduct were widened to increase its capacity. One side of the concrete channel was removed, the channel was deepened and widened, then re-concreted. Piped sections of the aqueduct were also duplicated to further increase flows and to maximise the benefits now available from Silvan.
With the completion and commissioning of Silvan, all three principal components of the O'Shannassy aqueduct system were now complete: O'Shannassy Reservoir, the aqueduct and Silvan Dam.
The system was later supplemented by the construction of the Upper Yarra aqueduct, which was commenced in 1929.
In 1936, after more drought conditions, the Board reported that Silvan "has been a tower of strength in maintaining the supply of water under these unusual conditions" and without it Melbourne would have been almost without a water supply.
The site was selected in 1919 and the 442 hectares of Crown Land plus 449 hectares of freehold land was vested in the MMBW. The site was conveniently close to the O'Shannassy aqueduct so that both inlet and outlet channels would be as short as possible. Pipelines from Silvan would carry water to Surrey Hills reservoir and from there be distributed to the higher eastern suburbs of Melbourne.
It was decided to construct Silvan using day-labour and "modern" machinery, building on the success of this approach used at the earlier O'Shannassy Dam construction. Works began in 1927 and the project was finally completed in 1930 at a total cost of just over 500,000 Pounds ($1 million). The dam was officially opened on 7 July 1931 (by which time it was almost three-quarters full). Total capacity was 40,000 megalitres. The main dam wall was was 644 metres long at its crest, 219 metres wide at its base and 43 metres high. The wall required 46,000 cubic metres of concrete and 1.3 million cubic metres of earthfill. The cellular core wall principle was almost entirely new and represented a notable advance in the construction of large earthen dams. The foundations of the core wall extended up to 140 feet (42 metres) below natural ground level.
A number of innovations were used on the project, including:
- electric power was brought 11 kilometres from Lilydale to provide power for the works (including lighting to enable operations to continue at night)
- a 5 kilometre long aerial ropeway (using an electric powered motor) was built from Mt Evelyn station to carry sand, cement and other materials to the construction site: there were 200 buckets on the line, carrying an equivalent of 5 bags of cement each and each bucket took about 52 minutes to reach the site - providing around 16 tons of cement per hour - and skips dumped their loads directly into the formwork on the dam wall
- an aerial cableway carried material from the crushing plant to the dam wall
- a nearby quarry provided rock for the dam wall
- compressed air crushers were used to crush the rock
- a 3 foot 6 inch rail transport line was built and steam locomotives carried rock from the quarry to the on-site crushing plant
- use of the largest steam shovel in Australia at the time
- use of steam powered excavators, locomotives, rollers and cranes
- workers were accommodated for free in huts on site (all quarters were provided with water, sewerage and garbage services)
- the camp and works had its own telephone exchange with 30 lines
All of this was absolutely "best practice" at the time.
The scheme provided a model for future Board projects involving the use of the latest technology (replacing much manual labour and horse-power), efficient use of day labour and the purchase of its own plant and equipment. The project actually came in several hundred thousand Pounds under budget and was hailed a great success!
Silvan was fed from both the O'Shannassy and Maroondah aqueducts (from O'Shannassy Weir and Graceburn Weir respectively).
In 1933 parts of the Mt Evelyn section of the O'Shannassy aqueduct were widened to increase its capacity. One side of the concrete channel was removed, the channel was deepened and widened, then re-concreted. Piped sections of the aqueduct were also duplicated to further increase flows and to maximise the benefits now available from Silvan.
With the completion and commissioning of Silvan, all three principal components of the O'Shannassy aqueduct system were now complete: O'Shannassy Reservoir, the aqueduct and Silvan Dam.
The system was later supplemented by the construction of the Upper Yarra aqueduct, which was commenced in 1929.
In 1936, after more drought conditions, the Board reported that Silvan "has been a tower of strength in maintaining the supply of water under these unusual conditions" and without it Melbourne would have been almost without a water supply.