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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. 

Abstract. We investigate the controls upon the shape of freely extending spits using a one-contour-line model of shoreline evolution. In contrast to existing frameworks that suggest that spits are oriented in the direction of alongshore sediment transport and that wave refraction around the spit end is the primary cause of recurving, our results suggest that spit shoreline shapes are perhaps best understood as graded features arising from a complex interplay between distinct morphodynamic elements: the headland updrift of the spit, the erosive "neck" (which may be overwashing), and the depositional "hook". Between the neck and the hook lies a downdrift-migrating "fulcrum point" which tends towards a steady-state trajectory set by the angle of maximum alongshore sediment transport. Model results demonstrate that wave climate characteristics affect spit growth; however, we find that the rate of headland retreat exerts a dominant control on spit shape, orientation, and progradation rate. Interestingly, as a spit forms off of a headland, the rate of sediment input to the spit itself emerges through feedbacks with the downdrift spit end, and in many cases faster spit progradation may coincide with reduced sediment input to the spit itself. Furthermore, as the depositional hook rests entirely beyond the maximum in alongshore sediment transport, this shoreline reach is susceptible to high-angle wave instability throughout and, as a result, spit depositional signals may be highly autogenic.