Leakage Prevention Guidebook - Bureau of Waterworks Tokyo ...

1 Outline of leakage prevention1.1 Present situationThe rivers flowing in this area, namely Tone, Ara,Tama and Sagami rivers are the main source of waterused in the Tokyo Metropolitan area.Leakage 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 of supplying tap water, somewater leaks from the pipes into the ground. This is the“leakage of water”.Water leakage in FY2010 decreased to 42 million m 3 ,2.7% to total distribution of 1.569 billion m 3 , comparedfrom 6.4% of water leakage rate (107 million m 3 ) inFY 2001,which is ten years ago. (Fig.1, Table-1 and 2)Most of the leakage is caused by cracked or corrodedservice pipes and distribution pipes due to aging. Thetotal cases of leakage repair work in FY 2010 recordedaround 14,500, and 97% of 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%Leakage 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 oftwo types of work is shown in Fig. 2-1.Basically we conduct repair works of groundleakage within a day of occurrence. Total number ofrepair cases (mobile work) in FY2010 was 13,777. Onthe other hand, the underground leakage (planned work)forms about 70% of 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 of 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 of 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 of leakage repair works(Prevention Volume )