Natural Shoreline Infrastructure in Humboldt Bay for Intertidal Coastal Marsh Restoration and Transportation Corridor Protection
Publication Date
9-29-2021
Publisher
GHD
Abstract
This report evaluates the feasibility of a project to develop natural shoreline infrastructure, also known as naturebased adaptation strategies or nature-based solutions, along a vulnerable segment of Humboldt Bay shoreline adjacent to the Highway 101 transportation corridor between Eureka and Arcata. Transportation infrastructure, utilities, businesses, low-income residential areas, and wildlife areas are protected by this shoreline segment and a recently completed adaptation plan (Humboldt County 2021) identified the substantial risks to critical resources from continued shoreline erosion and coastal flooding. The California Natural Resources Agency defines natural shoreline infrastructure (NSI) as “using natural ecological systems or processes to reduce vulnerability to climate change related hazards while increasing the long-term adaptive capacity of coastal areas by perpetuating or restoring ecosystem services” (Newkirk, 2018). The California Coastal Commission defines nature-based adaptation strategies (NBAS) as a resilient approach to climate adaptation that “incorporate ecological principles into shore protection strategies to support multiple benefits, including hazard adaptation and mitigation, natural resource resilience and enhancement, and recreation and scenic resource preservation (Vu, 2021). The Federal Highway Administration (2018) encourages naturebased solutions to prevent coastal highway flood damage and/or disruption by implementing approaches that mimic characteristics of natural features and protect or improve the build environment while maximizing the habitat value associated with the natural system. Similar terms include green infrastructure and living shorelines. For the purpose of this report the term NSI will be used to represent this broad suite of terms and definitions. Although highly compelling as a concept and encouraged by public agencies, NSI projects are still considered innovative and relatively few projects have been implemented in California. The NSI approach face challenges, limitations, and tradeoffs which must be addressed in order to identify feasible projects. Feasibility encompasses multiple dimensions including technical feasibility (effectiveness at achieving goals and objectives), economic feasibility (capable of being funded), legal and regulatory feasibility (capable of receiving permits and approvals), and social feasibility (consistent with core community values). Each NSI project will have a unique design based on the geomorphic conditions, physical processes, and habitat types at a given site. One of the technical challenges is to understand the dynamics of natural systems at a specific location and how they have been disturbed by human intervention over time. Other challenges include the need to demonstrate an overall net ecological benefit to the intertidal habitats affected; the need to develop site-specific designs with interdisciplinary teams; and aligning the innovative approach with existing permitting paradigms. This feasibility study was developed specifically to address these challenges. The overall goals of the study are to: ➢ Integrate the natural flood risk reduction properties of salt marsh into the shoreline management strategy for the Eureka-Arcata Highway 101 transportation corridor. ➢ Perform site characterization and prepare preliminary designs for a project utilizing tidal benches or similar NSI techniques. ➢ Lay the groundwork for an innovative approach to restore and perpetuate intertidal coastal marsh, increase community resilience to flooding and demonstrate the use of natural ecological systems for sea level rise adaptation.