Conference Agenda

To address regulatory commitments, Seattle Public Utilities (SPU) launched the Natural Drainage Systems (NDS) Partnering program in 2017 by developing retrofits in the three major creek watersheds within the City. Due to topography, historical development, and economic factors, much of this area lacks formal drainage infrastructure.

Working with sister agencies, concurrent SPU programs, and community partners, the purpose of the NDS Partnering program is to deliver high-value improvements to over 60 blocks of neighborhood streets in Seattle’s urban creek watersheds. The purpose of the partnering in the NDS program is to develop shared projects within SPU programs and between SPU and other City agencies to offer multiple benefits to neighborhoods and the natural environment, including greener neighborhoods, reduced flooding risk, improved natural habitat for native plants and animals, healthier creek ecosystems, and calmer traffic patterns. This presentation will highlight the program goals and site selection process and share lessons learned in addressing the challenges and opportunities of partnering to retrofit underdeveloped urban right-of-way.

The current NDS program consisting of the Longfellow Basin (under construction), South Thornton Basin (construction starting summer 2023), and North Thornton and Pipers Basins (under development and design). This program leverages innovations developed under recently constructed retrofit projects to enhance the viability of green infrastructure in challenging site constraints and soils. These innovations include the use of weirs, underdrains, structural soil cells, and underground injection control wells.

The program’s innovative green infrastructure improvements are an example of how to successfully balance the needs of the right-of-way while improving quality of stormwater runoff. SPU strives for continual program improvement through delivery community-centered projects that economically improve service.

Oftentimes long term localized drainage issues require a root cause, basin-wide analysis to identify the truest source of the issues. Leaving no rock unturned leads to developing sustainable solutions. Issues from frequent roadway flooding, localized ponded water, high groundwater, poor water quality, and lack of conveyance systems can all be addressed through taking a big picture look at the existing systems and focusing on aligning solutions with current and future community needs and funding sources. A comprehensive plan can then be developed, breaking down the basin approach into bite-sized solutions that can be implemented over time.

Josh and Ronnie will discuss how they work with the full suite of stakeholders to get to resolution on sticky long-term drainage issues. They will examine four case studies to understand key lessons learned associated with creatively addressing multiple issues in route to developing an actionable basin plan. The resulting action plans are focused on optimizing and retrofitting existing regional facilities and existing conveyance systems to manage stormwater from current and future developments, in order to drive and maintain economic growth and meet environmental requirements. Aiming to steer conversations with the community through the implementation of innovate stormwater concepts, these case studies offer valuable methods for problem solving on a larger scale.

The root cause analysis performed by the team includes in-depth data reviews, field walks with O&M staff, review of maintenance records, on-site conversations with impacted community members, collection of detailed field information (geotechnical and flow monitoring data) and ultimately performing detailed hydraulic modeling to identify drainage areas of concern. All feasible alternatives to improve water quality and reduce flows to surface water by increasing stormwater infiltration, retention, and detention are considered and analyzed in terms of cost-effectiveness. Alternatives that are developed include a variety of projects from new storm drain systems, groundwater collection drains, hydraulic connections for disconnected areas, and new/retrofitted regional facilities. We will discuss our teams approaches to engaging with the community to assist in developing practical and creative solutions that minimize disruption to citizens lives, reduce the risk of flooding on private property, and provide sustainable solutions.