The Future of Developed Barrier Systems - Part II: Alongshore Complexities and Emergent Climate Change Dynamics

Abstract

Developed barrier systems (barrier islands and spits) are lowering and narrowing with sea-level rise (SLR) such that habitation will eventually become infeasible or prohibitively expensive in its current form. Before reaching this state, communities and other entities will make choices, in the face of changing climate conditions, to modify the natural and built environment to reduce relatively short-term risk. These choices will likely vary substantially even along the same developed barrier system as these landscapes are rarely uniformly managed alongshore. Building on the results from a companion paper, here we use a new modeling framework to investigate the complexities in barrier system dynamics that emerge as a function of alongshore variability in management strategies, accelerations in SLR, and changes in storm intensity and frequency. Model results suggest that when connected through alongshore sediment transport, barriers with alongshore variable management strategies – here, the construction of dunes and wide beaches to protect either roadways or communities – evolve differently than they would in the absence of alongshore connections. Shoreline stabilization by communities in one location influences neighboring areas managed solely for roadways, inducing long-term system-wide lags in shoreline retreat, even decades after nourishment ceases. Conversely, when barrier segments managed for roadways are allowed to overwash, this induces shoreline curvature system-wide, thus enhancing erosion on nearby stabilized segments. Feedbacks between dunes, storms, overwash flux, and alongshore sediment transport also affect the long-term outcome of climate adaptation measures. In the case of partial, early abandonment of roadway management (i.e., decades before the road is deemed untenable), we find that system-wide transitions to less vulnerable landscape states are possible, even under accelerated SLR and increased storminess.

The Future of Developed Barrier Systems: 1. Pathways Toward Uninhabitability, Drowning, and Rebound

“…Cross sections illustrating how the management strategies are implemented in each module through time are shown in Figure 1b. We refer interested readers to the CASCADE GitHub (Anarde, Reeves, et al, 2024) where management module rules and dynamics are thoroughly described (including pseudo code within the model documentation) are thoroughly documented for ease of reproducibility and use within other model frameworks. For ease of model coupling, both modules modify the post‐storm Barrier3D domain at the end of each model year (instead of after individual storms).…”