A GEO-ECONOMIC MODEL TO EXPLORE COMMUNITY RESPONSES TO DOWNDRIFT GROIN-INDUCED EROSION

Coastal communities use hard and soft engineering to sustain beach recreation and to protect physical properties and infrastructure. Soft engineering involves external sand placement to widen beaches artificially; this placement is typically termed ‘nourishment’. Hard engineering involves the construction of immovable objects, such as shore-perpendicular groins, which slow alongshore currents and deposit sediments locally at and updrift of the objects. While groins accrete sediment updrift, they also limit downdrift sediment supply, exacerbating erosion and often forcing downdrift communities to respond with new engineering measures. We have developed a coupled geo-economic model to explore how communities make relevant management decisions. The model identifies a set of factors that could help explain the geo-economic condition and timing of a community’s responses to groin-induced erosion as observed in New Jersey. These include the community’s beachfront property value and its size (a proxy for its tax base), both of which determine its ability to finance groin construction or beach nourishment projects. Results of model simulations for future conditions, such as higher background erosion rates and higher rock material costs, suggest that management interventions will likely be economically infeasible, resulting in beachfront property loss and retreat from the coast. Depending on the balance between erosion rates and economic conditions, the model also highlights the possibility that the historical transition away from groins to beach nourishment as the main management response could be reversed in the future, and groins could again become the more commonplace intervention as communities adapt to sea-level rise.