Hansen Creek Alluvial Fan and Reach 5 Restoration at Minkler Road Bridge

Hansen Creek, a tributary to the Skagit River, is located approximately one mile east of Sedro Woolley in Skagit County. To reduce the frequency of flooding of nearby properties and homes, the Hansen Creek channel was historically realigned and straightened, levees were built up along both banks, and until recently, the channel was also dredged. These historical hydromodifications simplified habitat conditions, cut off the hydrologic connection between Hansen Creek and its adjacent floodplain, alluvial fan, and wetlands, and limited salmonid use to the main channel.

Between 2007 and 2016, Herrera collaborated with Skagit County, the Upper Skagit Indian Tribe, and the Skagit River System Cooperative to improve channel and floodplain connectivity and restore aquatic habitat within Hansen Creek, while also addressing flooding and sedimentation problems for nearby properties and roadways. Herrera completed reach- and watershed-scale analysis, design, construction oversight, environmental assessment, and permitting support for multiple phases of channel, wetland, alluvial fan, and floodplain restoration within Reaches 3, 4, 5, and 6 in the Hansen Creek Watershed. By employing a holistic and process-based approach, Herrera helped its clients prioritize and phase projects given limited funding and opportunities for construction access. Taking a phased approach to restoration garnered broad support from the local community; enabling the flood- and sediment-reduction benefits of keystone projects to be experienced first, and paving the way for ongoing and future habitat restoration efforts.

Technical analyses completed by Herrera included hydrologic, hydraulic, geomorphic, and biological assessments to support levee and fish passage barrier removal and preparation of a phased habitat restoration and flood mitigation master plan. Herrera developed a comprehensive 2D hydraulic model covering the Hansen Creek floodplain to the confluence with the Skagit River to understand existing and potential future flooding risks. Herrera conducted geomorphic analyses to understand the processes that influence salmonid habitat, to develop a basis for a stable channel design, and to anticipate the potential lifespan of a reactivated alluvial fan. Herrera presented findings and draft design plans at several workshops with the County, tribes, regulatory agencies, fisheries enhancement groups, the local agricultural community, and regional utility companies and incorporated feedback from the workshops into the designs. Herrera led final design and provided construction support for five separate restoration projects that included three fish passage designs, large scale alluvial fan and floodplain reconnection, log structure design, geomorphic change and sediment evaluation, and drainage and flooding improvements. The completed projects have successfully connected tens of acres of floodplain rearing habitat, significantly improved habitat complexity, and improved fish passage to upstream reaches. Additional project phases are currently undergoing construction planning.