Middle Harbour Syphon NSOOS

Item details


Name of item:	Middle Harbour Syphon NSOOS
Other name/s:	The Spit Syphon
Type of item:	Built
Group/Collection:	Utilities - Sewerage
Category:	Other - Utilities - Sewerage
Location:	Lat: -33.8071977118 Long: 151.2519700590
Primary address:	Monash Crescent (East Side), Clontarf, NSW 2093
Local govt. area:	Northern Beaches
Local Aboriginal Land Council:	Metropolitan

Property description

Lot/Volume Code	Lot/Volume Number	Section Number	Plan/Folio Code	Plan/Folio Number
LOT	B		DP	434649
PART LOT	263		DP	752067

All addresses

Street Address	Suburb/town	LGA	Parish	County	Type
Monash Crescent (East Side)	Clontarf	Northern Beaches			Primary Address
Parriwi Road (West Side)	Mosman	Mosman			Alternate Address

Owner/s

Organisation Name	Owner Category	Date Ownership Updated
Sydney Water	State Government

Statement of significance:


	The Middle Harbour Syphon is a rare item of considerable cultural heritage significance. The syphon is a key component of the Northern Suburbs Ocean Outfall Sewer (NSOOS), the third major sewerage system to be built to service Sydney's growing wastewater needs. The syphon is one of three syphons associated with this sewerage system, the others being the Lane Cove Syphon and the Queenscliff Syphon located at Manly. The Lance Cove Syphon and The Middle Harbour Syphon are similar in size while the Manly Syphon is much smaller. It was built between 1922 and 1925 and provides an excellent example of the skills of engineers of the time in constructing major public works. It is also possibly the best example in the state of an inverted syphon on such a scale. The syphon remains a vital part of Sydney's sewerage system, it is still in first rate condition and has been in constant use since its completion. The two access houses are well known foreshore landmarks and are of architectural interest because of their Art Deco style which displays influence of Egyptian architecture. The northern side of the syphon also consists of an aqueduct which runs along Clontarf Reserve.
	Date significance updated: 15 Nov 01
	Note: The State Heritage Inventory provides information about heritage items listed by local and State government agencies. The State Heritage Inventory is continually being updated by local and State agencies as new information becomes available. Read the Department of Premier and Cabinet copyright and disclaimer.

Description


Designer/Maker:	E.M. de Burgh - Public Works Department
Builder/Maker:	Public Works Department
Construction years:	1922-1925
Physical 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 1.8m diameter concrete pipes laid on the Harbour bed. The total length of piping is 358m, and the greatest depth below water level is 22m. 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 comprise of 20 reinforced concrete pipes, made in sections of 30.5m long and weighing 150 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.
	Date condition updated:04 Jan 01
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.
Further information:	Refer to Northern Ocean Outfall Sewer listing card number 4570286.


Current use:	sewerage syphon
Former use:	sewerage syphon

History

Historical notes:

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 Public Works Department 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 PWD from 1916 to 1928, then transferred to the Board, along with many staff memebers, 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.

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.

Historic themes

Australian theme (abbrev)	New South Wales theme	Local theme
3. Economy-Developing local, regional and national economies	Environment - cultural landscape-Activities associated with the interactions between humans, human societies and the shaping of their physical surroundings	(none)-
3. Economy-Developing local, regional and national economies	Health-Activities associated with preparing and providing medical assistance and/or promoting or maintaining the well being of humans	(none)-
3. Economy-Developing local, regional and national economies	Technology-Activities and processes associated with the knowledge or use of mechanical arts and applied sciences	(none)-
4. Settlement-Building settlements, towns and cities	Utilities-Activities associated with the provision of services, especially on a communal basis	(none)-

Assessment of significance


SHR Criteria a) [Historical significance]	The Middle Harbour Syphon is one of the three syphons associated with NSOOS and one of two syphgons of its size, the other being the Lane Cove Syphon. Both are significant as major components of NSOOS, which provides sewerage services to a considerable portion of Sydney.
SHR Criteria c) [Aesthetic significance]	Notable for the two imposing accesshouse structures which are prominent and well known foreshore landmarks. The two structures are also of architectural interest as early examples of the Art Deco style, displaying influence of Egyptian architecture. In addition the accesshouse on the east side has an imposing flight of stairs facing the water, its platform provides an excellent view of much of the Harbour, and has been used as a command post by the Army during water transport exercises.
SHR Criteria d) [Social significance]	The system is a vital part of Sydney's sewage system and is listed with the National Trust of Australia (NSW). The Middle Harbour Syphon is a key component of the Northern Suburbs Ocean Outfall Sewer (NSOOS), providing for the crossing of Middle Harbour at The Spit. The NSOOS, including the syphon, is a further example of the community's hidden heritage associated with public health and the quality of life.
SHR Criteria e) [Research potential]	Possibly the best example in the state of an inverted syphon on such a scale. Also an excellent example of major engineering public works techniques of the 1920's. Innovative engineering techniques were required so that the sewer line was able to cross Middle Harbour. The Navy crane TITAN was used to carry out the work on the syphon.
SHR Criteria f) [Rarity]	The Middle Harbour Syphon is one of two large syphons associated with the NSOOS. The associated superstructures are of architectural significance displaying Art Deco style which is quite rare within the current Sydney Water sytem.
SHR Criteria g) [Representativeness]	Uses a syphon method which is typical of resolving particular gully, valley or river crossings.
Integrity/Intactness:	Substantially intact
Assessment criteria:	Items are assessed against the State Heritage Register (SHR) Criteria to determine the level of significance. Refer to the Listings below for the level of statutory protection.

Recommended management:

Manage the place and its significant components in accordance with the Heritage Council State Owned Heritage Asset Management Guidelines and the Minimum Standards of Maintenance and Repair in the NSW Heritage Regulations. Manage significant site elements in accordance with a Conservation Management Plan (CMP). If no CMP exists, consult with Asset Management Commercial Services with respect to commissioning a CMP. When commissioning a CMP, do so in accordance with the Model Brief for CMPs available on ConnectNet. Seek endorsement of the CMP from the Heritage Council of NSW. Works undertaken in accordance with a Heritage Council-endorsed CMP do not require further approval under the NSW Heritage Act. Involve heritage professionals as required under the terms of the CMP, or as otherwise determined necessary. Review CMP every 5 years or in a major change of circumstances, whichever is sooner. Review of a CMP should only be undertaken following consultation with Asset Management Commercial Services . When commissioning a CMP review, do so in accordance with the Model Brief for CMPs available on ConnectNet. Where no CMP is in place, or where works are outside the scope of the existing CMP, assess heritage impacts of proposed works in accordance with Sydney Water Environment Impact Assessment guidelines (e.g. undertake a Heritage Assessment and/or Statement of Heritage Impact as required, obtain Heritage Council approval as required). Consult with the Heritage Manager, Environment and Innovation, when major works are planned which affect items of State heritage significance. Undertake archival and photographic recording before major changes, in accordance with Heritage Council guidelines. Lodge copies of the archival record with the Sydney Water Archives and the NSW Heritage Office. Where the item is listed in a Local Environmental Plan Schedule of Heritage items, determine if works are exempt from approval under the LEP provisions. Where works are not exempt, obtain necessary approvals from the local council, in accordance with SWC EIA Guidelines.

Procedures /Exemptions

Section of act	Description	Title	Comments	Action date
57(2)	Exemption to allow work	Standard Exemptions	HERITAGE ACT 1977 ORDER UNDER SECTION 57(2) TO GRANT STANDARD EXEMPTIONS FROM APPROVAL I, Penny Sharpe, the Minister for Heritage, on the recommendation of the Heritage Council of New South Wales and under section 57(2) of the Heritage Act 1977: revoke the order made on 2 June 2022 and published in the Government Gazette Number 262 of 17 June 2022; and grant an exemption from section 57(1) of the Act in respect of the engaging in or carrying out the class of activities described in clause 2 Schedule A in such circumstances specified by the relevant standards in clause 2 Schedule A and General Conditions in clause 3 Schedule A. This Order takes effect on the date it is published in the NSW Government Gazette. Dated this 29th day of October 2025 The Hon Penny Sharpe MLC Minister for Heritage For more information on standard exemptions click on the link below.	Nov 7 2025

Standard exemptions for engaging in or carrying out activities / works otherwise prohibited by section 57(1) of the Heritage Act 1977

Listings

Heritage Listing	Listing Title	Listing Number	Gazette Date	Gazette Number	Gazette Page
Heritage Act - State Heritage Register		01628	15 Nov 02	220	9709
Heritage Act - s.170 NSW State agency heritage register

Study details

Title	Year	Author	Guidelines used
Sydney Water Heritage Study	1996	Graham Brooks and Associates Pty Ltd	Yes
Heritage Study of the Upper Nepean Scheme	1992	Edward Higginbotham & Associates Pty Ltd	No
Conservation Plan for WS 19 at Wiley Park and WS 87 & 88 at Penshurst	1993	Edward Higginbotham & Associates Pty Ltd	No
Conservation Plan Sewage Pumping Station No. 41	1997	AWT EnSight	No
Conservation Plan Sewage Pumping Station No. 41	1997	AWT EnSight	No
Conservation Plan Sewage Pumping Station No. 41	1997	AWT EnSight	No
Conservation Plan Sewage Pumping Station No. 41	1997	AWT EnSight	No
Conservation Plan Sewage Pumping Station No. 41	1997	AWT EnSight	No
Quakers Hat Aqueduct	1999	Godden Mackay Logan	Yes
Quakers Hat Aqueduct	1999	Godden Mackay Logan	Yes
Alexandra Canal Conservation Management Plan	2004	NSW Department of Commenrce, Heritage Design Services	Yes

References, internet links & images

None

Note: internet links may be to web pages, documents or images.

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Data source


The information for this entry comes from the following source:
Name:	Heritage NSW
Database number:	5053866
File number:	H07/00070

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