3.4 Time integral type leakage detector 143.5 Transmission-type leakage detector 153.6 Other methods 164 Problems and the future <strong>of</strong> leakage prevention 185 Annex 19Table-1Distribution volume analysis in FY2010 20Table-2Trends in total distribution volume, 21leakage volume and rate from FY2000 to FY2010Table-3Trends in number <strong>of</strong> each kind <strong>of</strong> repair works 21from FY2000 to FY2010Table-4Specifications <strong>of</strong> leakage cases in FY2010 22Table-5Organization <strong>of</strong> water leakage prevention 23Table-6Technical developments in leakage prevention 24by <strong>Tokyo</strong> Metropolitan GovernmentTable-7Trends in percentages <strong>of</strong> ductile cast iron pipes 25in distribution pipes, stainless steel pipes inservice pipes, leakage repair cases, leakageratefrom FY2000 to FY2010
1 Outline <strong>of</strong> leakage prevention1.1 Present situationThe rivers flowing in this area, namely Tone, Ara,Tama and Sagami rivers are the main source <strong>of</strong> waterused in the <strong>Tokyo</strong> Metropolitan area.<strong>Leakage</strong> vol.42million m3 2.7%We collect raw water from these rivers, processpurification at water plants such as coagulation,sedimentation and filtration, convey into undergroundwater pipes with pressure, then supply as tap water tocustomers. In the process <strong>of</strong> supplying tap water, somewater leaks from the pipes into the ground. This is the“leakage <strong>of</strong> water”.Water leakage in FY2010 decreased to 42 million m 3 ,2.7% to total distribution <strong>of</strong> 1.569 billion m 3 , comparedfrom 6.4% <strong>of</strong> water leakage rate (107 million m 3 ) inFY 2001,which is ten years ago. (Fig.1, Table-1 and 2)Most <strong>of</strong> the leakage is caused by cracked or corrodedservice pipes and distribution pipes due to aging. Thetotal cases <strong>of</strong> leakage repair work in FY 2010 recordedaround 14,500, and 97% <strong>of</strong> which were at supply pipes,and the remaining 3% were at distribution pipes.(Table-3 and 4)Distribution vol.1,569 million m3Fig.1 Annual distribution volumeand leakage volume in FY2010Mobile work13,777 cases94.5%Planned work801 cases5.5%<strong>Leakage</strong> is classified into two types by its form;“surface leakage” flows out on the ground and“underground leakage” leaks out underground withoutappearing on the surface.Surface leakage is handled by mobile work andunderground leakage by planned work. The ratio <strong>of</strong>two types <strong>of</strong> work is shown in Fig. 2-1.Basically we conduct repair works <strong>of</strong> groundleakage within a day <strong>of</strong> occurrence. Total number <strong>of</strong>repair cases (mobile work) in FY2010 was 13,777. Onthe other hand, the underground leakage (planned work)forms about 70% <strong>of</strong> total leakage volume because theseare kept unnoticed for a long time without publicexposure. (Fig.2-2). Therefore, unless we identify andrepair leakages systematically, valuable water willcontinue to leak and large accidents may occur. Thenumber <strong>of</strong> repair cases (planned work) in FY 2010 was801.Fig.2-1 Comparison betweenMobile work and Planned workMobile workPlanned work3,387 m 3 /D3.971 m 3 /D46.0%54.0%There always is a danger <strong>of</strong> water leakage on waterpipes from corrosion, affected by heavy traffic loadings,various construction works, not to mention earthquakesand unequal ground subsidence/settlings.Although water leakages are repaired as soon as they are- 1 -Fig.2-2Breakdown <strong>of</strong> leakage repair works(<strong>Prevention</strong> Volume )
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