Middle Harbour Syphon
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| Middle Harbour Syphon | |
|---|---|
  Location of Middle Harbour Syphon in Sydney | |
| Location | Monash Crescent (East Side), Clontarf, Northern Beaches Council, New South Wales, Australia |
| Coordinates | 33°48′26″S 151°15′07″E / 33.8072°S 151.2520°E |
| Built | 1922–1925 |
| Architect | E. M. de Burgh, NSW Public Works Department |
| Owner | Sydney Water |
| Official name | Middle Harbour Syphon NSOOS; The Spit Syphon |
| Type | State heritage (built) |
| Designated | 15 November 2002 |
| Reference no. | 1628 |
| Type | Other - Utilities - Sewerage |
| Category | Utilities - Sewerage |
| Builders | Public Works Department |
The Middle Harbour Syphon is a heritage-listed sewerage syphon located at Monash Crescent (East Side), Clontarf, Northern Beaches Council, New South Wales, Australia. It was designed by E. M. de Burgh, an engineer in the NSW Public Works Department and was built from 1922 to 1925 by the Department. The sewerage syphon is also known as the Middle Harbour Syphon NSOOS and The Spit Syphon. The property is owned by Sydney Water, an agency of the Government of New South Wales. The property was added to the New South Wales State Heritage Register on 15 November 2002.[1]
The Middle Harbour or Spit Syphon is a key component of the Northern Suburbs Ocean Outfall Sewer (NSOOS), which was the third major sewerage system to be built to service Sydney's rapidly growing wastewater needs. It is one of two large syphons located on the NSOOS being built between 1922 and 1925, the other being the Lane Cove Syphon (built 1916 to 1930). A third and much smaller syphon is located at Manly. The history of NSOOS is intricately linked to the earlier smaller council systems it replaced. In 1916 a scheme proposed by the NSW Public Works Department (PWD) was approved by Parliament. The scheme involved replacement of all sewage treatment plants on the North Shore (with the exception of Hornsby) by a large main sewer with several branches. It also involved an Ocean Outfall System for suburbs along the Milsons Point - Hornsby railway line. Construction of the sewer was carried out by the PWD from 1916 to 1928, then transferred to the Board, along with many staff members, to complete the remainder by 1930. Today, the system as a whole services areas as far west as Blacktown and bounded to the north by Narrabeen Lagoon, St Ives and Hornsby and to the south by Sydney Harbour, Lidcombe, Yagoona and Guildford.[1]
In constructing the NSOOS the engineers were faced with the problem of taking the line across Middle Harbour. The need to maintain a clear passage for navigation ruled out bridging, and the depth to solid sandstone beneath the harbour bed made tunnelling impracticable. It was therefore decided to carry the sewer across in two parallel pipelines laid on the bed of the harbour where it was sufficiently deep not to interfere with shipping, and to operate it as an inverted syphon. Major syphons had already been completed on the SWSOOS, near the present Kingsford-Smith Airport.[1]
Description
The Middle Harbour Syphon crosses Middle Harbour at The Spit, between Parriwi Point and Clontarf Flat. The syphon consists of two large concrete towers (accesshouses) carefully designed with an Egyptian architectural influence, and an above-ground concrete aqueduct on the Clontarf Flat. The accesshouses are linked by two parallel 1.8-metre (5 ft 11 in) diameter concrete pipes laid on the harbour bed. The total length of piping is 358 metres (1,175 ft), and the greatest depth below water level is 22 metres (72 ft). The system operates as a pressure tunnel or inverted syphon, with the east end being slightly lower on the opposing shore than the western end. The syphon carries the entire flow of NSOOS from suburbs west of Middle Harbour. The twin pipelines encompass 20 reinforced concrete pipes, made in sections of 30.5m long and weighing 140 tonnes (150 short tons). Groups of concrete piles were driven into the sand of the harbour bed to support these pipes. The valve chambers contain apparatus for handling the sewage flow via either or both of the pipelines. For many years these "legs" were used alternatively, but in recent years the flow has increased so as to require the continuous use of both pipes.[1]
Substantially intact.[1]
Modifications and dates
A renovation program is presently underway at the accesshouses, principally to renew corroded metal fittings and to fit steel hatches over the inlet and outlets to prevent the escape of offensive odours.[1]
