APPLICATION OF PORTLAND'S EXPLICIT COMBINED SEWER SYSTEM MODELS

In recent years, the Bureau of Environmental Services (BES) of the City of Portland, Oregon, developed a detailed technique for modeling its sewer facilities called Explicit Modeling. This technique combines off-the-shelf modeling engines with database, GIS, and automation tools. BES first applied Explicit Modeling to a large basement flooding relief project named the Holladay/Stark/Sullivan Predesign Project. The goals of the project were to characterize basement flooding problems, identify relief alternatives, and incorporate inflow controls to reduce stormwater flows into the combined system. Because of the success in using the explicit model on this first project, BES built and calibrated explicit models for all twenty-nine Willamette River Combined Sewer Basins and is currently using the explicit models for Predesign and Design projects.BES' experience shows the disadvantages in run times and data management for large, 4000 to 5000 node and conduit, models are overcome with automation tools. The disadvantages of large models are also offset by more accurate characterization of basement flooding problems and cost effective designs.Two former publications by the BES modeling group discuss the foundation and application of explicit models for large-scale CSO facilities and one basement flooding relief project. This paper describes the application of explicit modeling for basement flooding problem characterization, supporting sewer design, and using a model to justify funding an expensive sewer inspection and maintenance project.