Title

Central Coast Highway 1 Climate Resiliency Study

Document Type

Article

Publication Date

Summer 7-2020

Abstract

Elkhorn Slough is a major estuary located in Monterey Bay, California that provides valuable habitat area for hundreds of aquatic bird, fish, marine mammal and invertebrate species. With nearly 2,700 acres of a suite of intact habitat types, the Slough is critical to regional biodiversity. Tidal estuarine habitats within the Slough and the ecosystem services they provide are at risk to substantial degradation and losses from sea level rise. With Central California already having lost over 90% of its historical estuarine marsh habitat area (Brophy et al. 2019), every effort is needed to maintain current marsh habitat area in the face of sea level rise. Presently, Elkhorn Slough holds the third largest extent of estuarine marsh in California and is well conserved. However, largely due to the surrounding steep topography, approximately 85% of this marsh is projected to be degraded or converted to tidal flats or open water with sea level rise without concerted restoration and conservation efforts. As sea levels rise, each acre of salt marsh now becomes that much more important to conserve or restore. Ensuring that Elkhorn Slough will perpetually host healthy salt marshes into the future is a high priority for the region (Fountain et al. 2020). Transportation assets in this region are also vulnerable to sea level rise impacts. The eight-mile stretch of Highway 1 through Elkhorn Slough is a critical transportation asset for the region and beyond. It provides local access to Moss Landing, is essential to freight movement and the economy, and is a major commuting route connecting two regionally important cities, Santa Cruz and Monterey. With 2 feet of sea level rise, major disruptions to Highway 1 transportation function are anticipated. The railway, which runs along the main stem of the Slough for five miles, is also critical to freight movement and envisioned to serve expanded passenger service to meet the needs of a growing population. Extreme tides, known as “King Tides” already cause periodic flooding and disruptions to the railway, which will increase in frequency and severity as sea levels rise. Maintaining or enhancing both transportation function and the extent of estuarine marsh in Elkhorn Slough are important priorities for the Central Coast and beyond. The Central Coast Highway 1 Climate Resiliency Study (Study) is a unique partnership between the Association of Monterey Bay Area Governments (AMBAG), California Department of Transportation (Caltrans), The Nature Conservancy (TNC), the Center for the Blue Economy (CBE) at the Middlebury Institute of International Studies, and Environmental Science Associates (ESA) to develop and evaluate adaptation strategies for Highway 1 and the railway to improve resilience of transportation infrastructure in a manner that most benefits the surrounding ecosystems throughout Elkhorn Slough.

Integrating regional development and adoption of natural infrastructure and transportation planning can provide better outcomes for both sectors (Marcucci & Jordan, 2013) and Federal Highway Administration guidance and California policy are encouraging this integrated approach (Safeguarding California Plan: 2018 Update, 2018). The project was funded by Caltrans via a Senate Bill (SB) 1 Adaptation Planning grant, a Sustainable Communities Planning grant, with additional funding provided by AMBAG, TNC and the CBE.

Comments

This study is a collaboration between the Center for the Blue Economy and the Association of Monterey Bay Area Governments (AMBAG) in partnership with with California Department of Transportation (Caltrans), The Nature Conservancy (TNC), and Environmental Science Associates (ESA) to develop and evaluate adaptation strategies for Highway 1 (and the adjacent railway) while protecting the surrounding ecosystems throughout Elkhorn Slough, California, a wetland system of national significance.

Elkhorn Slough is California’s third largest tract of tidal wetlands and hosts extraordinary biological diversity, providing critical habitat for more than 135 aquatic birds, 550 marine invertebrate species, and 102 fish species.1 Highway 1 runs directly through an eight-mile stretch of this important wetland, and it is threatened by flooding from increasingly common king tides and anticipated flooding by future sea level rise.

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