Commissioning of the Thames Water ring main Phase 2 tunnels in the spring of 1994 signalled an important milestone for major investment on London's watertreatment and trunk distribution systems. This included not only the ring main itself, but also the progressive installation of advanced water treatment processes in the water-treatment works supplying the city, due for completion at the end of 1998. This paper reviews the benefits of the ring main and looks at future developments, focused largely in local distribution rehabilitation and leakage control. The objectives and benefits of future possible extensions of the ring main are discussed, and a configuration is put forward as potential for development in the long term.
It was the Thames Water Authority's predecessor, the Metropolitan Water Board, who had the enlightened concept of going underground with the Thames-Lee Tunnel, and later with the southern main ring. The project for the ring main is much larger. The historical section of the Paper shows the development of the current distribution system from the utilization of rivers, springs and the abstraction of water from the underlying strata. The per capita requirement for water within London has doubled this century. This is surprising as the expected rise could have been larger, bearing in mind how the world has developed over that period. However, probably more importantly 50% of that rise has been during the past 20 years.73. It is noted that the daily loss of water is approximately 200 Mlitres a day, which is a large figure but is only about 10% of the total water flow. Figures much higher than that have been quoted in the past. A major part of the proposed scheme and programme is to tighten leakage control. With 50 major failures a year, which is one a week, this must be a major maintenance problem.74. Did Thames Water consider restriction of the amount of water rather than an increase in the supply by installing metering? It would indeed attract a major cost. What proportion of the use of water at present in the area is monitored by meters? If people were using meters and had to pay by the amount of water supplied the amount of water used would decrease considerably. When I was on a drainage system which was pumped out once a month, there was used about a third of the amount of water which would normally have been used, mainly because the removal of the water had to be paid for.75. The first major tunnelling project was the Thames-Lee Tunnel and the initial 300 m experimental length, was in Stoke Newington in 1950-51 with the first expanded lining. This was the Don-seg lining. It was probably the last major development in tunnel linings, where the linings were not bolted and there was no grouting and therefore the rate of progress could be increased considerably. However, this type of lining is used mainly in clay. The second experimental tunnel was constructed with the wedge block lining which has been used subsequently for most of the small diameter expanded linings. The 30 km Thames-Lee Tunnel was constructed with the Don-seg lining. In the first section of this tunnel a steel lining was installed, and for the main length a spun mortar lining was installed because it was felt that a pressure lining was not required.76. It is noted in the Paper that special consideration is being paid to the frequency of inspection of tunnels, which is about every five years, because of minor damage which has occurred during the dewatering process, particularly as ~ ~~ Paper published: Proc. Instn Civ. Engrs, Part 1,1988,84, June, 445-474 ~~~~ ~~~ 133 Downloaded by [] on [12/09/16].
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