Moshier Park Stormwater Project Yields Benefits to Community and Fish Habitat

July, 2021

King County, in Washington, is situated within a natural watershed, home to various native fish species, including Coho Salmon. Restoration and preservation have become a priority focus across the region with salmon runs declining due to loss of habitat, barriers to fish passage, and poor water quality. For cities like Burien, with sensitive Coho salmon-bearing creeks running directly through them, there is an urgency to address water quality and pollution from stormwater run-off.

Public works projects need to balance multiple priorities against available funding and budget restrictions. So, when Otak was hired by the City of Burien (City) to do the final design of a stormwater retrofit at Moshier Park along Miller Creek, the team took a multi-disciplinary approach. The goal was to resolve a complex set of issues and provide maximum benefit in conjunction with other planned park improvements.

Addressing Untreated Stormwater Runoff, Flooding

Miller Creek, a natural waterway for spawning Coho Salmon, crosses through urbanized areas and ultimately discharges into the Puget Sound. Due to the amount of untreated stormwater runoff draining from the creek basin, the health of the creek is greatly degraded and conditions are poor for supporting the aquatic habitat. In addition, localized flooding and erosion along the creek’s banks have resulted from existing vegetation being converted to impervious or less pervious surfaces.

Moshier Park is a 15.2-acre public park that features lighted athletic fields, a community arts center building, and a large parking lot that is also used by Highline High School for events at Highline Stadium. The park was identified as an area for a stormwater retrofit project, funded in part by the Washington Department of Ecology, which would have the highest benefit value to Miller Creek.

Balancing Priorities, Maximizing Opportunities

While the project’s primary objective was to retrofit Moshier Park to provide stormwater flow control and runoff treatment, Otak saw the greater opportunity to incorporate other park improvements the City wanted to complete. Otak project engineer, Tyson Hounsel, explains that “by packaging some of the other park improvements into the design and construction timeline, we were able to save the city both time and costs. Plus, through all of our teams—survey, architecture, landscape architecture, water and natural resources, and engineering—we could develop a comprehensive design that includes the stormwater facilities, as well as a synthetic sports field, and a new restroom and concessions building at the park.” Otak also aided in obtaining the necessary environmental permitting and will act as the construction manager to oversee the retrofit and park improvements through completion.

One of these key improvements will be converting the large asphalt parking lot to less-impervious surfaces and installing an underground water detention tank and treatment facility that will capture stormwater runoff. Interpretive signs will also be installed in the park, which will be used by the neighboring high school as well. The project will break ground later this summer and is slated for completion in 2022

In the end, the City will have a newly designed and updated multi-purpose park that, as Tyson states, “will be a real community center.” Miller Creek will also benefit from improved water quality and will provide a more hospitable environment for spawning Coho Salmon.