arches, and a lattice bridge. This scheme was subsequently abandoned in favour of using a carrier and supporting arches of reinforced concrete construction, the contract for which was let in mid 1896. The engineer credited with the design is W. J. Baltzer, an engineer in the Sewerage Branch of the Department of Public Works. Baltzer, a graduate of a German university, worked for the firm Carter Gummow & Co. which held the patent rights for the Monier system of reinforcing concrete. Carter Gummow & Co were instrumental in bringing reinforced construction into widespread use. The design provided for a sewer carrier internally U shaped in section 3-ft. 6-in (1m.) by 4 ft. 6-in (1.37 m) constructed in reinforced concrete. The sewer carrier is supported by a series of arches: there are 9 large spans, each of 81-ft 10-in (25 m.) centre to centre with a clear span of 75-ft (23 m.), and a number of smaller subsidiary arches at the western edge. The total length is 990-ft. (301.7 m.). Each of the arches is seated on mass concrete piers. The aqueduct has required only minor repairs in the first 90 years of its existence. The first major renovation of the Monier arch aqueducts was necessary in 1986, when it was fitted with a new liner. Since 1990 the aqueduct has been listed on the NSW State Heritage Register, Register of the National Estate, Leichhardt Local Environmental Plan, Sydney Water Corporation's section 170 Heritage & Conservation Register and classified by the National Trust of Australia (NSW) in recognition of its significant technical accomplishment and as a major element of the historic built environment. The western section of the original site (21 & 1/2 perches) was transferred to the Municipality of Leichhardt in 1926 for widening of Edna Street. The remaining area (2 roods & 6 3/4 perches) accommodates the underground section of the structure and has been used for Sydney Water operations as a maintenance depot. The aqueduct has required only minor repairs in the first 90 years of its existence. It was repaired 1986, consisting of the insertion of a plastic liner in the flume. The arches are in a stable condition. Description The White's Creek Aqueduct is an original key component of the upstream extension of the BOOS (then called the Main Northern Sewer). It presently carries the sewage derived from the Balmain/Annandale areas across Whites Creek on its