Longfellow Creek Floodplain Restoration Opportunities

Seattle Public Utilities (SPU) is proposing the use of floodplain reconnection and natural flood storage in the Longfellow Creek Watershed as an alternative to using traditional stormwater detention vaults to meet the flow control requirements triggered by two multimodal transit improvement projects in the basin. Located in the Delridge Neighborhood of West Seattle, Longfellow Creek has severely altered flow and sediment regimes, degraded water quality and habitat conditions, a confined floodplain, and a history of residential flooding problems. Herrera is leading a multidisciplinary consultant team that is collaborating with SPU in completing an Options Analysis to evaluate whether, where, and how best floodplain reconnection and restoration can be used within the project corridor to achieve alternative compliance with the City’s stormwater code while simultaneously reversing some of the negative trends that have affected the creek’s ecology and adjacent residential communities by also improving habitat, flooding, erosion, and water quality conditions. Herrera has completed a field investigation, documented existing conditions in the project corridor, developed preliminary flood storage concepts for 5 sites within the project corridor, led the development of a community engagement plan and a modeling plan for evaluating and documenting alternative compliance, and is currently embarking on a more detailed evaluation of specific alternatives for maximizing flood storage potential at two of the sites.