Monroe Avenue Infiltration Facility Renton, Washington

To manage stormwater runoff from 260-acres of a highly-urbanized area of Renton, Washington, the Monroe Avenue Infiltration Facility delivers a comprehensive approach that reduces flooding and enhances water quality for the surrounding community. As one of the largest water treatment facilities in Washington, the project allowed the city to avoid extensive trunkline options that would directly discharge and impact the local river system. In designing this regional stormwater facility, Otak utilized detailed surveying as well as hydrologic and hydraulic modeling of the subbasin to estimate peak flows during up to 100-year storm events, optimizing its capacity and improvements.

Green Stormwater Infrastructure to Reduce Flooding and Enhance Water Quality

Persistent flooding along Monroe Avenue in the City of Renton was addressed through a comprehensive green stormwater infrastructure (GSI) solution centered around an infiltration facility. An alternatives analysis led to the selection of a treatment train approach that begins with a hydrodynamic separator and a flow splitter, which diverts water quality treatment flows to a Filterra Bioscape treatment system. From there, treated runoff is conveyed to three isolator rows, allowing for additional settling and fine sediment removal before infiltration into the ground. High stormwater flows that bypass the bioscape unit are also directed to the isolator rows, ensuring full use of the facility’s infiltration capacity. This system not only eliminates localized flooding but also recharges cool, clean groundwater that feeds into the Cedar River. The improved stormwater conveyance system manages flows from a 25-year storm through existing infrastructure. Hydrologic and hydraulic modeling also account for a 100-year event, minimizing the risk of roadway overtopping during extreme flood events. Overall, the facility delivers both flow control and enhanced water quality treatment tailored to the Renton Highlands subbasin.