Policy Approaches to Stormwater Facility Sizing and Sustainable Site Design

Author(s): Overbey, E.; Gallo, W.

A difficult challenge in implementing sustainable stormwater facilities is navigating stormwater policies designed to use complex stormwater models to size large detention basins. The presentation explores unique stormwater facility sizing approaches that have been used and modified for over ten years by landscape architects, architects and civil engineers in Portland, Oregon. Through a survey of design professionals, the research highlights the opportunities for policy to influence where and how stormwater facilities are incorporated into the design process.

The Portland Stormwater Management Manual (SWMM) primarily utilizes two approaches to meet the city's stormwater requirements. The Simplified Approach uses simple sizing factors accompanied by standard design details and specifications to streamline the process. Alternatively, the Presumptive Approach utilizes a unique sizing calculator that allows for maximum design flexibility and control of an array of best management practices. Both of these approaches promote multiple, small-scaled facilities that infiltrate and manage stormwater as close to where it falls as possible.

Results of the survey indicate that design professionals differ on how they utilize sizing tools in the design process. Art based disciplines lean toward the Simplified Approach that allows exploration of multiple solutions early in the design process, while engineers tend to lean toward the more robust Presumptive Approach, allowing refinement of the facility design.

The new and evolving paradigm of sustainable stormwater management can be shaped by policies that are designed specifically for implementation of small-scaled infiltration facilities. By simplifying the sizing process, these tools allow designers to use facilities as an integral part of overall site design. However, simplifying the sizing methodology is not a shortcut for simplifying design of the individual facility which requires careful consideration and refinement to meet specific needs of the site.
Download the presentation

Go back


Technical Sessions

1 Best Management Practices #1
2 Delta Water Assessment
3 Flood Assessment & Mgmt.
4 Wetlands
5 Watershed Mgmt. #1
6 Non-Point Source Assessment
7 Modeling
8 Water Quality
9 Best Mgt. Practices #2
10 Delta Water Conservation
11 Sedimentation
12 Storm Water
13 Watershed Mgt. #2
14 Public Water Systems
15 Surface Water Assessment & Evaluation

Click here to view the entire agenda