South Park Green Stormwater Infrastructure Modeling

The King County Wastewater Management Division uses green stormwater infrastructure retrofits in some urban Seattle neighborhoods to reduce the frequency and volume of combined sewer overflows into local waterways. In the South Park neighborhood, green stormwater options were evaluated as a method of reducing sewer overflows and encouraging community redevelopment. Principal, Tony Dubin, led the SWMM hydraulic modeling effort that included simulating runoff and routing on a block-by-block basis and evaluating how the configuration, sizing and location of green stormwater retrofits (e.g., bioretention, permeable pavement, and soil cells) affected their performance. The model was calibrated to available flow monitoring data. The results identified two common weaknesses of retrofit projects: a) locating facilities where they cannot recruit enough flow and b) undersizing facilities so that they fill too quickly when the storm of interest for regulation occurs. The initial modeling effort was used to establish preferred locations and minimum sizing criteria for green stormwater infrastructure. Follow-up modeling was used to develop metrics relating a) the facility type, b) facility configuration, c) construction cost and d) flow reduction and to assist King County staff with facility planning.

Services: Modeling, LID/GSI