Today London is building a huge new trunk sewage main 30 metres under the bed of the River Thames, following it for some 20km through London to an expanded sewage treatment works near the mouth of the River. The tunnel is being cut by giant boring machines. It will be the size of a London underground railway (Tube) tunnel. It is costing £5 billion (approx. $A10 billion). Disruption is minimised by tunnelling under the river, not the city, and barging spoil down river, not trucking it through the city streets.
London needs the new sewage system capacity because the overflow of raw, untreated sewage into the Thames occasionally during storms became more of a constant discharge as the population grew towards its present 8m. The population may continue to grow slowly. The problem was deferred. It cannot go on. (SBS TV, March 2019)
The Melbourne and Sydney sewage systems built for about 3m, with extra capacity which has accommodated the 5m today, are unlikely to cope with 8-10-12m. They may become very strained at 6m. New enlarged systems will be required, unless the extra raw sewage for millions more people were permitted to flow into the Yarra and the Parramatta Rivers, which is unlikely and unacceptable.
Sydney presently discharges most of its raw sewage well out to sea at Bondi and North Head. When the population was about 3m, swimmers on Bondi Beach began to object, so the pipeline was extended further out. Melbourne city and the western suburbs sewage is treated at Werribee Sewage Farm on the city outskirts. Treated water is discharged into Port Philip Bay. The suburbs are now beginning to encroach on the location. The eastern treatment works serves the eastern suburbs. It is located at Bangholme on the Mornington Peninsular. Treated water is discharged into the ocean. Some is recycled.
London is located upstream from the mouth of the Thames, so sewage will flow downstream in the tunnel to the treatment works near the mouth of the river and be discharge as treated water into the sea. Unlike London, Melbourne and Sydney are located around the mouth of their rivers. There is no land suitable for sewage treatment works. Discharging raw sewage to sea for 8-12m people is not desirable. A new trunk line could be built under the rivers like London. Sewage would have to be pumped long distances from the end of the trunk lines to treatment works beyond city fringes which keep on expanding outwards. Rapid population growth of Melbourne and Sydney would require renewal of old sewage mains and many new sewage mains connected to the enlarged new trunk lines, large-scale pumping facilities and long pipelines to the treatment works for +8m people at great extra expense.
The cost of providing very much larger, widespread sewage systems for Melbourne and Sydney than London for the same populations is enormous now. If deferred until later, it will be breath-taking. London’s $10 billion today becomes about $350 billion in 5 decades time, allowing for wage and inflation increases doubling the cost every 10 years. That is for one city. It is $700 billion for two. Of course, prices may not double every 10 years as in the past. It cannot be left for 5 decades and growth to 8m people without sewage facilities expansion. Never-the-less, it may cost $100-200 billion each in total; depending on delay, inflation and scale needed for the size of population for which it is planned. ($100 billion would be double Melbourne’s proposed underground railway to cost $50 billion and built over 35 years.)
In terms of sewage cost alone, it is worth considering the building of new cities designed for 1m, 2m, and 3m in the country on the coastal HSR line built to connect them rapidly to major city CBDs. Construction costs of greenfield housing and utilities in the regions are much lower, maybe half major city costs, and there is plenty of space for the cities and their peripheral sewage treatment works. This would relieve Melbourne and Sydney of overcrowding, mass congestion and huge sewage costs of growing to 8-10-12 million. It would cater for Australian population growth by gradually distributing people to lower cost locations rather than concentrating them in the eastern capital cities.