Flood Reduction at South 180th Street SeaTac, Washington

The flood reduction at South 180th aimed to address longstanding flooding issues in the area caused by a ditch with inadequate capacity. A critical areas assessment developed solutions focused on the goal of reducing flooding through flow control and additional conveyance capacity.

A Critical Area Assessment to Solve Persistent Flooding

Flooding at 180th would happen several times a year. An evaluation of flood risk to adjacent properties as well as capacity for the ditch and downstream drainage system delivered alternatives using both conventional or natural drainage systems. These alternatives considered factors such as construction cost, right-of-way availability, property acquisition, erosion in downstream ditches, and permitting requirements. Otak played a critical role in this project, providing project management, topographic survey, hydraulic and hydrologic modeling, and stakeholder engagement. The evaluation has the South 180th Flood Reduction project well-positioned to succeed in its mission to reduce flooding and protect the surrounding properties and community.