What is significant?
The Main Outfall Sewer was constructed in 1892-4 and was a vital link in the sewerage system of Melbourne which, when it was constructed in the 1890s, was the largest civil engineering project ever undertaken in Victoria. The Main Outfall Sewer consists of a semicircular brick or concrete lined channel (in places arched over to form a circular tunnel with an earth covering) and three brick arched aqueducts. The sewer was constructed by seven contractors employing 1300 workers and cost £240,748. During the 1880s the phenomenal growth of Melbourne led to a crisis in sanitation. The situation was exacerbated by the existence within the metropolitan area of many municipalities which would have to agree on any sewerage system. A Royal Commission recommended the formation of a Metropolitan Board of Works, comprised of commissioners from each of the local government authorities, with responsibility for both water supply and sewerage. Eminent British engineer James Mansergh was appointed to advise on a suitable system. At a time when most cities dumped their untreated wastes directly into rivers and the sea, Mansergh advised treatment of Melbourne?s sewage by broad irrigation with a capacity large enough able to deal with the expansion in population expected over 50 years. The system he conceived and which was implemented in only slightly modified form began with a water closet at every property which delivered the sewage by gravity through a network of underground sewers of increasing diameter to a steam pumping station at Spotswood (VHR 1555) where it was forced up wrought iron rising mains to Brooklyn to begin its 25 kilometre journey along the Main Outfall Sewer to the sewage farm at Werribee. As could be expected, the Main Outfall Sewer has had much repair and replacement of fabric over the last century and its function has now been entirely replaced by the Western Trunk Sewer. Nonetheless, there is still extensive original fabric remaining within its easement.
How is it significant?
The Main Outfall Sewer is of historical and scientific (engineering) significance to the State of Victoria.
Why is it significant?
The Main Outfall Sewer is historically important as an artefact of the process of development of Melbourne into a modern metropolis. The decision in 1890 to build a sewerage system with a capacity well in excess of the contemporary population was far sighted. The project not only addressed an existing sanitary crisis, but also enabled expansion of the city into new areas because the ?downstream? sewerage infrastructure was of sufficient capacity. Unlike the rest of the system which is underground and out of sight, the Main Outfall Sewer is a visible manifestation of the entire system. The Main Outfall Sewer is also a tangible link with the formation of the Melbourne Metropolitan Board of Works whose role as the unifying force for major infrastructure projects in Melbourne over the last century is of enormous historical importance. The construction of the system is all the more remarkable because, although conceived during the years of the 1880s Boom, its completion was achieved during the years of the catastrophic 1890s Depression.
The Main Outfall Sewer is of scientific (engineering) importance as a major link in the most extensive engineering project undertaken in Victoria to that date. The concrete and brick open and covered sewer is a fine example of the technology of the period, exhibiting a high level of integrity. The three major red brick aqueducts over Kororoit Creek, Skeleton Creek and the Werribee River are excellent examples of multi-spanned, arched masonry bridges.