Purpose and Background

The Watershed Approach for Stormwater Task Committee that is part of the Sustainable Stormwater Infrastructure Standing Committee in association with the Water, Wastewater, and Stormwater Council presents a 3-part webinar series.

Low impact development (LID) and green infrastructure (GI) approaches that infiltrate, evapotranspire and/or reuse stormwater to reduce the rate and volume of stormwater runoff are quickly becoming the national standard of practice for how stormwater is managed in urban areas. The EPA Stormwater Management Model (SWMM) has many capabilities for modeling LID and GI at the watershed and site levels; however, in many cases detailed guidance and criteria for applying SWMM to model effects of LID and GI are lacking. This webinar short course will teach SWMM modeling techniques applicable to suburban and highly urbanized settings through the use of two case studies:

• A greenfield development in Parker, Colorado is a new development in the Cherry Creek watershed consisting primarily of residential development. SWMM analysis for this project included event-based and continuous simulation from the lot scale to the watershed scale. This case study will provide examples of applying SWMM at varying scales and will discuss some of the challenges with representing hydrologic processes in continuous simulation mode.
• An ultra-urban redevelopment project in downtown Denver will transform the South Platte riverfront. This case study will illustrate application of SWMM to evaluate LID and GI approaches in an ultra-urban environment.

This is the second webinar in a series of three webinars on this topic. This webinar provides an overview of basics of SWMM to prepare participants for the second and third webinars in the series, which address event-based and continuous simulation techniques, respectively.

Primary Discussion Topics

• Basics of the four-cover model for impervious and pervious surfaces
• Representation of LID and GI at the watershed scale
• Modeling of LID and GI at the site scale
• Representation of permeable conveyances in SWMM – infiltration and surface roughness
• Modeling distributed detention and water quality facilities
• Comparison of modeling at varying scales and surrogate techniques for representing small-scale processes in larger-scale models

Learning Outcomes

• Understand the four-cover impervious/pervious model and the importance of disconnecting impervious area
• Learn about the hydrologic and hydraulic analysis capabilities of SWMM for representing LID and GI
• Gain skills for representing “treatment trains” of hydrologic processes in SWMM
• Understand how the scale of the model dictates explicit versus implicit representation of processes in SWMM

Webinar Benefits

• Improve SWMM application capabilities for event-based modeling
• Learn new techniques for representing LID and GI in SWMM
• Understand differences in approaches for modeling suburban versus ultra-urban sites
• Reinforce understanding of importance of “treatment train” approaches to stormwater management
• Expand knowledge of SWMM capabilities for hydrologic and hydraulic representation of stormwater control measures
• Share experiences with troubleshooting SWMM

Intended Audience

• Civil engineers (water, environmental, civil)
• Public agency engineers (development reviewers)
• Hydrologists
• Hydraulic engineers
• Development engineers

Webinar Outline

• Suburban development
• Site stormwater management objectives
• Treatment train approaches in suburban setting
• Representation of impervious area connectivity
• Site-level lid
• Permeable conveyances
• Distributed detention
• Calibration methods and challenges
• Urban development
• Site stormwater management objectives
• Treatment train approaches in ultra-urban setting
• Roof treatment alternatives
• Permeable pavements
• Infiltration beds
• Underdrains
• Comparisons with end of pipe approaches – pros and cons

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