A STUDY OF WATER MAIN REPLACEMENT PLANNING WITHIN A CONTEXT OF DEPOPULATION —QUANTITATIVE ANALYSIS OF REDUNDANCY THROUGH TRUNK WATER MAIN DUPLICATION AND WATER SUPPLY INTERCONNECTION BY USING PIPE IN PIPE METHOD—

Abstract

 Many waterworks in Japan are making their own pipeline systems more redundant because they have experienced massive water supply outages associated with pipe failure due to earthquake, deterioration etc. On the other hand, the Pipe In Pipe (PIP) method, which can retrofit and downsize pipe diameter without traffic interference, is becoming popular. However, no one has quantified the effectiveness of trunk water main replacement to eventually increase system redundancy by using PIP method while accounting for the effect of depopulation. Therefore, this study implemented cost benefit analysis for three pipe replacement plans: main duplication, main interconnection with another water supply system, and simple pipe replacement. It was found that (1) the main benefit of redundant pipeline systems is water supply outage prevention, (2) by lowering the discount rate to reflect current Japanese government bond yields, redundant pipe replacement plans would be more feasible than simple, not redundant pipe replacement plan, based on cost-benefit analysis. (3) When purification plants with large capacity surpluses are located nearby, it is possible for main interconnection to be the most feasible redundancy plan.