Regional Stormwater Solutions for Western Washington: Building Resilient Basins

Author: Jackie Corley

Western Washington faces a unique stormwater challenge: heavy soaking, seasonal rains, steep slopes, and older neighborhoods built without water quality controls. These factors make managing runoff more than a site-by-site issue—it’s a regional priority. For more than two decades, AHBL has helped shape regional strategies with cities and counties to turn these challenges into opportunities for cleaner water, safer streets, and stronger communities.

Why Regional Solutions Matter

Stormwater doesn’t stop at property lines. When older neighborhoods lack treatment, downstream basins bear the burden. That’s why Stormwater Management Action Plans (SMAPs) have become a game-changer. They help cities identify where investments will make the biggest impact, whether that means reducing flooding, improving water quality, or restoring habitat.

From Parking Lots to Parks: Real-World Examples

For example, at the South Hill Apartments in Puyallup, AHBL replaced a single oversized stormwater facility with a network of rain gardens in parking areas, earning LID credits and reducing traditional infrastructure footprint. At the same time, Pierce County expanded a regional pond downstream, creating capacity where it mattered most. This approach wasn’t just environmentally sound, it was financially smart. By leveraging the regional pond and distributing bioretention on-site, AHBL avoided the cost of a massive vault, while excavated soils were reused to meet sewer grades, eliminating hauling and trucking expenses. This resulted in lower construction costs, minimized disruption, and a solution that balanced site needs with regional priorities.

Flooding isn’t just inconvenient; it can disrupt entire sites. At an AHBL project at Naval Base Kitsap, a frequently flooded parking lot demanded a comprehensive solution. AHBL raised grades, diverted upstream runoff, and installed a fish-passable culvert. The team restored 900 feet of stream, adding flood capacity and ecological value. These improvements didn’t just solve a problem; they created long-term resilience.

Green Streets and Community Benefits

Stormwater solutions can also enhance public spaces. AHBL’s Pacific Avenue Green Street project introduced rain gardens and bioretention along the corridor, improving water quality while calming traffic and creating a more inviting streetscape. As Wayne Carlson, FAICP, and AHBL Planning Principal, explains, “Green infrastructure works best when it’s integrated into street and park designs, where maintenance and multiple community benefits reinforce each other.”

That same logic underpins 132nd Square Park, a SMAP-driven stormwater retrofit in Kirkland that went beyond stormwater treatment. The project captures runoff from upstream neighborhoods built decades ago without modern stormwater controls, then treats and slows it before it reaches sensitive waterways. Beneath the park, an underground stormwater storage facility manages flows, enabling the construction of turf fields above. These fields not only provide recreational opportunities but also generate revenue for the city through additional field rentals and events. At the same time, the park was redesigned to include new trails, play areas, and accessible open space, creating a hub for recreation and equity while solving a regional water quality challenge. By pairing regional storage and treatment upgrades with community amenities, 132nd Square Park demonstrates how stormwater investments can deliver multiple benefits in one project.

Planning for the Future

Looking ahead, assumptions must keep pace with intensifying storms and legacy constraints. As Todd Sawin, PE, and AHBL Civil Engineering Principal, cautions, “We are likely underestimating storm events, and that has real consequences for communities. The storms we’re seeing today are stronger and more frequent than what many systems were designed for decades ago. If we don’t plan for larger flows and build in redundancy, we risk flooding, infrastructure failures, and costly emergency fixes. Regional planning isn’t optional, it’s essential.”

Expect more basin-scale planning: optimizing regional facilities, increasing conveyance capacity, removing downstream barriers, and aligning city-level infrastructure programs with SMAP priorities. The most effective delivery will deepen synergy between parks, streets, and utilities, supported by sharper modeling, asset management, and multi-agency coordination. When planning, engineering, and community priorities pull in the same direction, regional solutions deliver cleaner water, reduced flood risk, and lasting public value.

The Path Forward

Washington’s stormwater challenges are inherent, but coordinated regional solutions can transform them into opportunities. By linking planning, engineering, and community priorities, we can deliver cleaner water, reduce flood risk, and create public spaces that people value for generations.