Designing Sanitary Sewers with Microcomputers

Abstract

A program titled Sanitary Sewer Design (SSD) has been developed for the Apple II microcomputer. SSD is a heuristic program that attempts to find the least costly design of a sanitary sewer network or pipeline. The program computes velocities, water depths, pipe slopes, and inverts corresponding to inputted diameters, flows, pipe lengths, ground elevations, and design criteria. SSD was used to find the least costly design of a 3.25 mile sewer trunk line in Chapel Hill, N.C., for the Orange Water and Sewer Authority (OWASA). It was also used to perform a sensitivity analysis, which evaluated the effect that design criteria, uncertainty in flows, and alteration of pipe diameters have on the cost of a sewer system. The sensitivity analysis indicated that: (1) Costs can be reduced 20‐25% by relaxing the pipe size progression criterion; and (2) sewer design was relatively sensitive to flow uncertainty.