Leakage Prevention Guidebook - Bureau of Waterworks Tokyo ...

In 23 wards, we have long addressed leakage preventions. We handle leakage investigation works with 6 branches (14offices) and majority of repair works are subcontracted.In Tama area (excluding some cities and villages) administration of waterworks used to be consigned to respective citiesand towns, but sequentially been shifted to direct administration under Tokyo Metropolitan Government. Leakinvestigation works are currently conducted by administrative bodies (,which are the stock companies invested by TokyoMetropolitan Government at the rate of 25% or more in total capital), and repair works are constructed by subcontractors.aPatrol work (Circulating checking)In the patrol works are individual investigation work that determines leakage with acoustic rod attached to meter onevery home, acoustic investigation work that is conducted during the night when there is less traffic to identify point ofleakage with electric leakage detector from the road surface etc.To determine the blocks to patrol, we take previous work history, leakage occurrence in the previous year, and residualnumber of lead supply pipes into consideration.In addition to that, we consign administrative bodies to conduct such individual investigation with time integral type leakdetector (please refer the page 19) replacing acoustic rod on some blocks since FY2003.bLeakage volume measurement workTo estimate total leakage volume within Tokyo municipal and understand the leakage trend, we conduct leakage volumemeasurement works. To gain an understanding of more accurate leakage volume in urban areas where operate 24 hours aday, we measure minimum flow at night (leak volume) limited to around 400 valves which is the marginal idle volume atnight. (Refer to P15 Minimum night flow measurement method) By estimating leakage volume within a certain block, weare able to make total assumption of leakage volume within municipal Tokyo. Together with leakage investigation andmeasurement work that has been put into practice since FY2010, we will put such works to improve our leakageprevention plan.For the leakage volume measurement work, we subcontract to external management bodies since FY2005 for someblocks.cLeakage investigation and measurement workTo minimize water outage during the earthquake disaster and fast react on to recover the facilities, it is important toensure the water flow from distribution main to small distribution pipes. To do so it is essential to secure the exhaust valvefunction at distribution main. And then it is necessary to avoid damaged channel and secure the available water routes assoon as possible and recover the service area.This leakage investigation and measurement work is a practical series of works that conduct functional measurement ofwater valves required to secure water route after securing the safety of exhaust valve on distribution main, assuming thechannel where leakage volume are high as damaged points, then recover/expand the service area sequentially. We conductinvestigation on the whole water flow area based on the volume of leakage, and then operate repair works on leakagepoints one by one when found. Such data will also be partially facilitated to leakage volume measurement work.- 8 -