THE EFFECTS OF WEALTH INEQUALITIES IN NEIGHBORING COASTAL COMMUNITIES ON THE POTENTIAL ECONOMIC BENEFITS OF COORDINATED BEACH NOURISHMENT

Coastal communities facing erosion maintain their beaches for both recreation and property protection. One form of beach maintenance is nourishment, the placement of externally sourced sand to increase its cross-shore width, forming a seaward protrusion. Over time, these protrusions diffuse along-shore, requiring periodic re-nourishment. Beach nourishment adds value to a community’s nearshore properties, thereby affecting future nourishment decisions. Examining this feedback in one community ignores any behavioral interdependencies between coastal neighbors, however. Economic studies suggest that coordinated nourishment between neighbors can be optimal, but whether communities actually behave as such is unknown. To address these issues, we developed a coupled geomorphic-economic model for two neighbors, where communities that act alone choose nourishment frequencies that maximize myopic net benefits, and communities that coordinate choose frequencies to maximize their joint net benefits. We define the economic benefit of coordination as the difference between the benefits of coordination and non-coordination, and examine how community-scale wealth (property values) could affect these economic benefits of coordination.

The model produces four primary behaviors based on nourishment frequency: 1) seaward growth; 2) hold position; 3) slow retreat; 4) maximum retreat. Results indicate that coordination is strongly beneficial for wealth asymmetric systems, weakly beneficial for low wealth systems, and of no benefit to wealthy/symmetric systems. In addition, wealthy systems grow beaches seaward over time, moderately wealthy systems hold shoreline position, less wealthy systems retreat slowly by nourishing infrequently, and the poorest systems retreat rapidly by doing nothing. Under future increases in sand costs and background erosion due to sea-level rise, however, coordinated systems might experience a sharper transition from seaward growth to slow retreat, whereas uncoordinated systems might either over-nourish or abandon more properties than would be optimal. These results suggest at least two contradictory policy responses: (i) encourage more coastal development to amplify geo-economic feedbacks or (ii) abandon coastal properties that coordination might have preserved.