The Hyde Park Obelisk is a heritage-listed obelisk that served as a sewer vent and is now a monument located in Hyde Park at the intersection of Elizabeth Street and Bathurst Street, in the Sydney central business district, New South Wales, Australia. It was designed and built by the NSW Department of Public Works. It is also known as The Obelisk and Obelisk Sewer Vent. It is also jokingly referred to as Thornton's Scent Bottle after mayor George Thornton. The obelisk is owned by Sydney Water, an agency of the Government of New South Wales. It was added to the New South Wales State Heritage Register on 15 November 2002. Completed in the Victorian Egyptian style, it was modelled on Cleopatra's Needle on the banks of London's River Thames. The overall structure is 22 metres (72 ft) high, including the square sandstone base which is 6.5 metres (21 ft) high. The vent at the top is a filigreed bronze pyramidion.
History There are two types of sewer vents within the Sydney Water system: educt and induct. Induct vents draw air into a sewerage system to aerate the pipelines. Educt vents allow gases to escape when the gas is lighter than air. The shape of the cowling on the older types of vents were set to produce either eduction or induction whenever there is a natural breeze. This is an educt shaft, a simple masonry shaft modelled on Cleopatra's Needle (now situated on the Thames Embankment, London) and erected in 1857 during the period of George Thornton as Mayor of Sydney. Vents are for the safety of personnel as well as to prevent corrosion by chemical decay. The ventilation of sewers is a very important facet of continued operation of a sewerage system; poor ventilation can result in serious odour problems and breakdown in fabric. Unveiled in 1857 by Mayor Thornton, it served as a sewerage duct vent to allow the escape of noxious gases from the sewer (although it now ventilates the stormwater system, following works to separate Sydney's sewerage and stormwater systems). The Hyde Park Obelisk was the first special sewer ventilation shaft built in Sydney and New South Wales, and is the only example of a sewer ventshaft constructed of sandstone within the Sydney Water system. On 7 November 2014, the Hyde Park Obelisk was covered with a giant pink condom as a temporary installation to raise awareness about HIV, primarily in Sydney's LGBTIQ community.
Description Completed in 1857, the obelisk is a simple masonry shaft consisting of a sandstone base and decorative bronze ventilator apex. It was built to ventilate Sydney's first planned sewerage system which was constructed by the Municipal Council. Sydney's first planned sewerage system consisted of five harbour outfalls. The only means of ventilating this system was a sandstone ventshaft, which was erected at Hyde Park (corner of Bathurst and Elizabeth St) in 1857. As the sewerage system developed, it became obvious that ventilation of the system was inadequate and some form of ventilation was necessary. In 1875, the Sydney City and Suburban Health Board recommended in its Sixth Progress Report, that two sewerage schemes be constructed to deal with the health problems being faced due to the pollution within Sydney Harbour. From that period, several methods of ventilating the sewers were investigated to deal with the disease, odour, pressure and chemical problems being experienced within the sewers. Of the methods investigated and adopted, including street vents, house vents (cast iron traps and water traps) and flues, the tall ventshafts were determined by J. M. Smails in several reports to the government of the day, to be the most efficient way of dispersing the pressure and gases found within the sewers. Initially, after the Obelisk, ventshafts were constructed using bricks, were ornate and fairly major features in the city landscape. This technology was replaced with smaller, steel tube vents, which were used at intervals of approximately every 350 metres (1,150 ft) of sewer. The Oberlisk remains considerably intact apart from alterations to its base.
Further information See inventories for the Main Northern Ocean Outfall Sewer, Lewisham Sewer Ventshaft, Marrickville Sewer Ventshaft, Glebe and Bellevue Hill Sewer Ventshafts for other details relating to sewer vents.
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