Prospect Reservoir
The Prospect Reservoir is a heritage-listed potable water supply and storage reservoir created by the Prospect Dam, across the Prospect Creek located in the Western Sydney suburb of Prospect, in New South Wales, Australia. The eastern bounds of the reservoir are a recreational area and the western periphery are within the bounds of Western Sydney Parklands. It was added to the New South Wales State Heritage Register on 18 November 1999.
Prospect Reservoir is Sydney's largest reservoir and stores water conveyed from Warragamba Dam, the Upper Nepean Dams and if necessary, from the Shoalhaven Scheme, for supplying the larger component of the water distribution system of the Sydney metropolis. Located approximately 34 km west of Sydney, the reservoir is a zoned earth embankment dam that is 26m high and approximately 2.2 km long, with a storage capacity of 50,200 megalitres and an open capacity of 8,870 megalitres.
History
Shortly after 1808, William Lawson was appointed aide-de-camp to George Johnston and was granted at Prospect. He built a large house there in the 1820s, which he named Veteran Hall. He died on the property on 16 June 1850 and the property was eventually acquired by the Metropolitan Water Board. The house was demolished in 1929 and most of the low lying surrounding property is submerged.In 1867, the Governor of NSW appointed a Commission to recommend a scheme for Sydney's water supply, and by 1869 it was recommended that construction commence on the Upper Nepean Scheme. This consisted of two diversion weirs, located at Pheasant's Nest and Broughton's Pass, in the Upper Nepean River catchment, with water feeding into a series of tunnels, canals and aqueducts known as the Upper Canal. It was intended that water be fed by gravity from the catchment into a reservoir at Prospect. This scheme was to be Sydney's fourth water supply system, following the Tank Stream, Busby's Bore and the Botany Swamps.
Prospect Reservoir was the first earthfill embankment dam in Australia and was completed in 1888. At the time it was intended to deliver water from the Upper Nepean Scheme via the Upper Canal to the reservoir. The quintessential feature of the scheme was the diversion of the Nepean River below its junction with the Avon and Cordeaux Rivers. The Pheasant's Nest weir, near the township of Wilton, diverts the water through a 7 km long tunnel to the Cataract River at Broughton's Pass, near the township of Appin, where a similar weir diverts the flow of the four rivers through a 58 km system of tunnels, aqueducts and open channels to Prospect Creek upon which the earthen dam wall is located. When it was completed in 1888, Prospect reservoir provided the storage component of the scheme, as the weirs did not have the capacity to store water. Prior to the completion of the Lower Canal, the water shortage still needed to be dealt with. Hudson Brothers of Clyde built a temporary raised pipe structure to deliver water from Prospect direct to the Botany Swamps.
In 1895 a painting of the Prospect Reservoir was created by Arthur Streeton which was owned by the Metropolitan Water and Sewerage Board before being donated to the Art Gallery of New South Wales in 1937.
Between 1893 and 1916, extensive remedial works were carried out in order to correct slumps in the upstream face.
With completion of Warragamba Dam in 1960, Prospect Reservoir continued to play an important role in storing Sydney's water. A second pipeline linking Warragamba and Prospect was completed in 1966, significantly increasing the volume of water that could be transferred during peak demand periods. In 1979–80, a major strengthening programme on the reservoir wall was completed by increasing the volume of its downstream side. The upstream face was strengthened in 1997.
With the commissioning of the Prospect Water Filtration Plant in 1996, raw water transferred from Warragamba and the Upper Nepean Dams was sent directly to the treatment facility, by-passing the Reservoir. However, the filtration plant can draw water directly from the Reservoir if needed. This is one of the largest such facilities in the world and it has changed the role of the Reservoir to that of a service reservoir and large off-line settling basin for the Warragamba and Upper Canal systems in the event of a water quality problem, covering daily fluctuations of demand in the distribution system. Since its construction, parts of the area surrounding the reservoir have formerly been used for passive community recreation, and consequently the Water Board provided numerous parks and picnic facilities, primarily on its eastern side.
From 2006 a new raw water pumping station and associated infrastructure were built on the reservoir's south-eastern side, including pipeline, power supply and access road.
It was formerly the major distribution reservoir for Sydney's main water supply system until the commissioning of the Prospect Water Filtration Plant in 1996. The reservoir's role has since been changed to that of an off-line storage service reservoir, which covers daily fluctuations of demand in the distribution system. The reservoir can now be drawn on when needed to supplement the Warragamba Pipeline and Upper Canal inflows into the Filtration Plant. It remains an essential component of Sydney's water supply system and therefore is critical Government infrastructure.
Scour/outlet system
Prior to construction of the Prospect Water Filtration Plant, the water supply was delivered to the Lower Canal via the scour/outlet system, which consists of a number of components (including submerged inlet pipelines, outlet tower with access walkway, lower valve house with outlet to the Lower Canal, scour pipelines, various control and guard valves, brick-lined interconnecting tunnel between outlet valve and lower valve house, with ventilation shaft and access shaft/manhole, discharge pipelines under the Sydney Water Corporation-owned picnic area and an outlet structure.The Outlet Tower is a small octagonal brick structure standing in the Reservoir waters with access by a small riveted iron footbridge. The tower extends below water with three main platforms accessed by ladders. The interconnecting tunnel is routed in a large U running from the Outlet Tower, into the hillside, then curving back to skirt the end of the Reservoir wall.
The Lower Valve House is similar in style to the Outlet Tower and originally controlled water entering the Lower Canal. The Lower Canal was decommissioned in the 1980s, but the original equipment in the Lower Valve House remains largely intact. The tunnel extends a short distance beyond the Lower Valve House.
The scour/outlet system originally terminated at the end of the tunnel, with a simple brick headwall with wing-walls and iron grill gate. In the late 1970s the scour system was extended with twin concrete pipes and a new outlet structure constructed closer to Prospect Creek. At that time the area downstream and east of the Reservoir wall was re-shaped to form a public picnic area, burying the end of the tunnel and new concrete pipes.
Since decommissioning the Lower Canal, the sole purpose of the scour/outlet system is to allow scouring or draining of the Reservoir. This is critical to ensure dam safety and consequently the system must be adequately maintained. The primary control valves were imported from England in 1887 and are believed to be the last remaining examples of their type in the world. They are in poor condition and at high risk of failure if operated to drain the Reservoir. They are beyond their operational life and cannot be refurbished. Consequently, SCA can no longer test the system as required or safely dewater the Reservoir under emergency conditions.
Description
With the completion of the main storage dams, the reservoir's function has changed from largely being a storage apparatus to the main service reservoir and sedimentation basin for the metropolitan system. Prospect is an earth dam 2210 metres long and consists essentially of a puddle clay core with shoulders of selected earth placed in layers 300mm thick. During construction these were compacted by rolling. It was completed in 1888, and in 1898 the crest level was raised by 0.5 metres. The upstream slope of the wall is pitched with locally quarried diorite blocks 450 mm thick. The curtilage includes the boundary of the grounds owned by Sydney Water Corporation and the components within it, namely;- the reservoir itself;
- side spillway and channel at the southern end of the wall;
- drainage and monitoring installations at the toe on the downstream face of the wall;
- the access road along the toe of the downstream face of the wall; and
- the outlet works which connect the stored water to the Lower Canal – consisting of outlet tower, pipelines, valve house and valve, scour lines and valves, and the other metering, screening and control installations.