From Coastal Retreat to Seaward Growth: Emergent Behaviors From Paired Community Beach Nourishment Choices

Coastal communities often address shoreline erosion through beach nourishment, adding externally sourced sand to widen beaches for recreation and property protection. While nourishment enhances beachfront property values, the need for periodic maintenance creates interdependencies where the actions of neighboring communities affect local shoreline dynamics. Using a coupled model of two neighboring communities, we examine the interplay between community nourishment decisions and the redistribution of nourishment sand. We find that the value a community places on wider beaches not only influences their propensity to nourish, but also their and their neighbors' nourishment efficiency and net benefits. Communities that nourish more frequently tend to have lower nourishment efficiency, as sand is redistributed alongshore, benefiting less-active neighbors at their expense. A 20-year New Jersey case study confirms that communities that nourish more have lower nourishment efficiencies, including instances where less wealthy communities nourish significantly more, enabling wealthier neighbors to enjoy higher efficiencies—suggesting that such dynamics may already be shaping real-world coastal outcomes. In future scenarios, we simulate the effects of rising sand costs and accelerated erosion due to sea-level rise under coordinated and non-coordinated planning methods, finding that less wealthy communities experience a higher risk of beachfront property loss under non-coordination, exacerbating disparities in coastal management. These findings underscore the importance of inter-community cooperation in optimizing economic and environmental outcomes in beach nourishment strategies.