Seattle Center's Broad Street and Theater Commons Stormwater Infiltration and Low Impact Development (LID)

Owner: City of Seattle Location: Seattle, WA Contact us for more information.

Project Background & Challenges

The Broad Street Redevelopment project was designed to increase the usability of the site to pedestrians while also reducing the load on the City’s stormwater handling systems through infiltration of stormwater. Specific elements of the project included rerouting underground utilities, new pedestrian walkways, retaining walls and seating walls, grass lawns and planter, and a rain garden to accommodate onsite infiltration of stormwater. The Theater Commons project included transformation of a parking area and underutilized landscaping into a landscaped north entry between the Seattle Repertory and Intiman Theatres. The project was designed to maximize sustainable land-use by incorporating native plantings, raingardens, and permeable pavers for on-site infiltration of stormwater.

Both sites were underlain by relatively impermeable soils and one of the challenges for Aspect was to maximize infiltration within the physical constraints of the projects. In addition, buried utilities and abandoned trolley lines complicated investigations and construction and all work at Theatre Commons needed to be scheduled to occur in between events.

Solution

Providing infiltration assessment and geotechnical support for both projects, Aspect conducted exploration programs with drilled borings and exploration pits to characterize subsurface soils for their infiltration characteristics, address geotechnical considerations, and evaluate re-use of on-site soils as structural fill. All field work was conducted to minimize site disturbance and the impacts to events and operations. The explorations were able to identify areas with better infiltration characteristics and the designs were modified to locate infiltration facilities in these areas. Aspect worked with the civil engineer, landscape architect, and the City of Seattle to design pervious pavement sections and infiltration facilities that maximized the infiltration potential of the sites within the physical constraints of the site. Aspect provided construction monitoring during construction to observe and document soil conditions and provide rapid engineer judgments on an as-needed basis. This approach facilitated quick turnaround on design changes and allowed construction to proceed with minimal impact on events during the busy theater season.