٨Research Trends and Results

Management of Sewers
YOKOTA Toshihiro, HeadFUKATANI Wataru, Researcher
MIYAMOTO Toyohisa, Researcher
Wastewater System Division, Water Quality Control Department

2. Predicting Survival Ratio of sewers
To predict future works volume in the medium tolong term, it is necessary to have a survival ratio
prediction formula to predict change over years of thepercentage of pipes which are reconstructed. Survival
ratio is a value obtained by dividing total length ateach deterioration rank by total surveyed length ofpipes surveyed after any number of years of service.
The survival ratio prediction formula indicates thiswith an approximate line.
The NILIM improves the precision of the survival
ratio prediction formula by conducting a nationwide
survey of pipe length by year of installation. And theNILIM updates the soundness prediction formulaannually (Fig. 1).
Emergency level II – no deterioration
Emergency level III – no deterioration
No deterioration

Survival Ratio

1. Introduction
At the end of 2009, the sewerage coverage ratio
reached about 73%, and the vast stock of pipes
providing this coverage reached approximately
420,000km. It is predicted that sewerage facilities will
deteriorate, pushing up the cost of their maintenancein the future, resulting in the need for systematic andefficient facility management to ensure that thesefacilities continuously provide their specified
functions. One way to achieve this is stock
management (SM).
To develop and implement the SM method, rational
operation plans must be drawn up based on theprediction of the medium to long term quantity ofwork considering the soundness of the facilities. This
will permit maintenance of good quality sewerage
services under harsh financial restraints.
And a sewerage service contributes to improving
the living environment and conserving water quality inpublic bodies of water. At the same time, theconsumption of energy resources and emission ofgreen house gases by the construction and operation of
its facilities create a variety of environmental loads.
Therefore, to operate a service, it is necessary toevaluate its environmental load from the medium tolong term perspectives.
The NILIM is contributing to the promotion anddevelopment of the SM by carrying out research on avariety of basic technologies such as facility
soundness (survival) evaluation and prediction,
standardization of future works volume, and theevaluation of the impact of sewerage system operationon the global environment as Life Cycle Assessment(LCA).

Ages of Sewer Pipes

Figure 1.Survival ratio prediction formula
3. Application of LCA to sewers
To establish concepts to guide cases where LCA isapplied to calculate the environmental load of sewers,
we collected information about environmental load
basic units by pipe material and by work method, etc.
at each stage—pipe manufacture and installation,
operation, and disposal—to prepare an environmentalload calculation function (Fig. 2). This simplifies
environmental load calculations, permitting its use as
material to select work methods when installing newpipes or reconstructing existing pipes.
4. Conclusion
Initiatives to develop SM in the sewerage field havebarely begun, and even local governments are at thetrial and error stage. Under such circumstances, wehope that the SM method established by the NILIM
will further promote the introduction of SM.
Centrifugal reinforced concrete pipe (JSWASA-1 external pressure pipe, class 1)

Quantity of CO2 produced per unit length(kg-CO2/m)

Research Trends and Results(Key words) Sewers, stock management, Survival Ratio, LCACompany ACompany B
Company C

Nominal diameter (mm)Figure 2. Environmental Load Calculation Function Graph(Example)