1D/2D integrated PCSWMM modeling for storm sewer capacity improvements

Alex Partridge


In recent years, stormwater planners and engineers have begun to face a daunting task: designing and maintaining drainage systems that can keep up with ever-intensifying storms. In many cases, stormwater infrastructure implemented decades ago is no longer capable of meeting local design requirements nor preventing costly flood damage to homes and other structures. For example, in July 2019, several watersheds in Northern Virginia experienced significant flooding as a result of a storm that exceeded a 1000-year return period during its most intense hour. To mitigate future residential flood damage, GKY & Associates, Inc. was tasked with evaluating the existing storm sewer systems, identifying their weak points, and suggesting various retrofit improvement ideas. One particular watershed study is the subject of this presentation.

From the start, it was determined that PCSWMM 1D/2D integrated models were the best means to these ends. Over the course of the four-month effort, three improvement scenarios were developed, each with its own set of goals, requirements, challenges, and results throughout the 80-acre watershed. Scenario “A” aimed to eliminate structural flooding during the 10-year storm event by increasing underground drainage capacity; Scenario “B” aimed to eliminate structural flooding and minimize yard and roadway flooding during the 100-year storm, all while containing proposed construction within existing easements; and Scenario “C” aimed to eliminate structural flooding during the 100-year storm while containing proposed construction within the County’s right-of-way. After numerous calculations and trial-and-error models, the three designs were finalized and presented back to the client. As of January 2023, the project is poised to move into concept planning and community outreach.

This presentation will discuss what made PCSWMM 1D/2D the right tool for the job, what made the project challenging, interesting, and unique, and how similar modeling work can impact stormwater infrastructure design to meet increasing resiliency needs.

 Click here to watch recorded presentation on YouTube.

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