Abstract

The Storm Water Management Model (SWMM) was originally developed in 1971 as a computer-based tool for simulating storm water runoff quantity and quality from primarily urban areas. Since then, it has undergone several major updates, the last of these being Version 4.4. Throughout each of these updates, the block nature of the program, as well as the basic structure of its Fortran source code, have remained intact.

In 2002, EPA’s Water Supply and Water Resources Division partnered with the consulting firm CDM to develop a completely rewritten version of SWMM. The goal of this project was to apply modern software engineering techniques to produce a maintainable, extensible, and easier-to-use model. The result of this effort, SWMM 5, consists of a platform-independent computational engine written in C, as well as a graphical user interface for the Microsoft Windows operating system written in Delphi.

A rigorous quality assurance program was developed to ensure that the numerical results produced from the new SWMM 5 model would be compatible with those obtained from SWMM 4.4. The new SWMM 5 software was released to the public in October of 2004.

The sub-model that was the most numerically challenging to implement within SWMM 5 was the dynamic wave flow routing routine known as Extran (short for extended transport). It routes nonsteady flows through a general network of open channels, closed conduits, storage facilities, pumps, orifices, and weirs. In contrast to simpler routing methods, this procedure can model such phenomena as backwater effects, flow reversals, pressurized flow, and entrance/exit energy losses.

Rather than simply encode a line-for-line copy of Extran, SWMM 5 restructured the code in a more readable and maintainable fashion. It also employed a slightly modified computational scheme with the intent of producing more numerically stable solutions in less time.

This report documents the quality assurance testing program that was used to compare the dynamic wave flow routing procedures of SWMM 4.4 with SWMM 5. Before describing the tests made and the results obtained, it will be useful to contrast the way in which each version of the model implements dynamic wave flow routing.

Contact

Lewis Rossman (513) 569-7603

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