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From Coastal Retreat to Seaward Growth: Emergent Behaviors from Paired Community Beach Nourishment Choices
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  • Arye Janoff,
  • Jorge Lorenzo-Trueba,
  • Porter Hoagland,
  • Di Jin,
  • Andrew Dale Ashton
Arye Janoff
Montclair State University

Corresponding Author:[email protected]

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Jorge Lorenzo-Trueba
Montclair State University
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Porter Hoagland
Woods Hole Oceanographic Institution
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Di Jin
Woods Hole Oceanographic Institution
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Andrew Dale Ashton
Woods Hole Oceanographic Institution
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Abstract

Coastal communities facing shoreline erosion preserve their beaches both for recreation and for property protection. One approach is nourishment, the placement of externally-sourced sand to increase the beach’s width, forming an ephemeral protrusion that requires periodic re-nourishment. Nourishments add value to beachfront properties, thereby affecting re-nourishment choices for an individual community. However, the shoreline represents an alongshore-connected system, such that morphodynamics in one community are influenced by actions in neighboring communities. Prior research suggests coordinated nourishment decisions between neighbors were economically optimal, though many real-world communities have failed to coordinate, and the geomorphic consequences of which are unknown. Toward understanding this geomorphic-economic relationship, we develop a coupled model representing two neighboring communities and an adjacent non-managed shoreline. Within this framework, we examine scenarios where communities coordinate nourishment choices to maximize their joint net benefit versus scenarios where decision-making is uncoordinated such that communities aim to maximize their independent net benefits. We examine how community-scale property values affect choices produced by each management scheme and the economic importance of coordinating. The geo-economic model produces four behaviors based on nourishment frequency: seaward growth, hold the line, slow retreat, and full retreat. Under current conditions, coordination is strongly beneficial for wealth-asymmetric systems, where less wealthy communities acting alone risk nourishing more than necessary relative to their optimal frequency under coordination. For a future scenario, with increased material costs and background erosion due to sea-level rise, less wealthy communities might be unable to afford nourishing their beach independently and thus lose their beachfront properties.