Modelling responses of a foredune barrier complex to climate change and sea-level rise impacts: insights from Humboldt Bay, northern California

The shores of the Eureka Littoral Cell (ELC), which extends from Trinidad to Cape Mendocino, CA, are comprised of extensive sandy beach-dune systems and a foredune barrier complex that formed from interactions between littoral, fluvial, and aeolian processes. This barrier complex creates the lagoon systems of Humboldt Bay and protects the communities of Arcata and Eureka from storm surge flooding, coastal erosion and sea-level rise (SLR). The region experiences among the highest rates of relative SLR in California, partly due to contributions from tectonic subsidence (relative SLR of 4.81 mm/yr based on a regional vertical land motion of -2.33 mm/yr). The barrier system provides a wide range of ecosystem services, however, little is known about how it might evolve with future SLR and increasing storminess scenarios. Here, we employ the Windsurf model to examine plausible future evolution states of the barrier from 2D cross-shore profiles in response to both marine and aeolian forcings. The Windsurf platform integrates three modeling cores for subaqueous processes, aeolian sand transport and subaerial eco-morphodynamics. To validate the model, we calibrate and apply it to existing vegetation characteristics and elevation data obtained from interannual cross-shore surveys along the ELC shoreline over three years. Next, we evaluate system morphodynamic and sediment budget responses to SLR and extreme event scenarios. Simulated results on depositional and erosional dynamics between surf and swash zones and beach and foredune zones are used to investigate the vulnerability and resiliency of barrier foredune systems to future environmental change.