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