Abstract
Adoption of area-wide sewerage system has brought about long-term planning problems such as uncertainty of the planning parameters and increasing investment at the initial stage of the project. Time phased construction becomes a present problem of sewerage planning.
This paper discusses the case that the multiple sewers are adopted as the main sewer system. Multiple sewer system has an advantage of sizing flexibility at the intermediate stage, comparing to the case of full-scale construction at the initial stage.
Optional sizing at the initial stage is examined with the present value of expected total project cost calculated by serial demand patterns and its occurrence probability. Case study reveals the advantage of multiple sewer system and necessary conditions to perform the time-phased construction of main sewer system.
