Shoreline Resilience and Inlet Management

Summary

We are investigating the resilience of sandy shorelines, and in particular the evolution and subsequent recovery of beaches after inlet breaching. Many coastal ponds on Cape Cod, Martha’s Vineyard, Nantucket, and mainland Massachusetts shorelines are drained intentionally (“breached”) to lower pond water levels that threaten homes, to promote healthy habitats, and to facilitate migration of marine species. However, often breaches close before tidal flushing has had sufficient time for nutrient goals to be reached. For example, the breach of Sesachacha Pond, Nantucket (Fig. 1, and this video) can close in as little as 24 hours after it is opened, preventing significant exchange with the ocean and frustrating local efforts to improve habitat.

Although numerical models accurately simulate storm-induced erosion, allowing coastal engineers and managers to make predictions and plan accordingly, the slower recovery of the shoreline is not well understood. The several-times yearly breachings of Sesachacha Pond (Fig. 1) and Tisbury Great Pond (Fig. 2) provide a unique opportunity to observe and develop models for the recovery of beaches and the corresponding closing of ponds after inlet breaching. We are using existing observations and new model simulations to (1) determine the causes of beach recovery after storms or inlet openings and (2) develop breaching strategies that optimize exchange between coastal ponds and the ocean for a range of ponds and barrier beaches, as well as a range of wind, tidal, and wave conditions. Our objective is to explore the recovery of beaches after they have been disturbed to determine the best approaches (e.g., inlet geometry, tide stage, wave and wind conditions) for machine-made breaches at different locations. Additionally, we aim to improve understanding of sediment transport mechanisms so that numerical modeling systems can be developed to simulate the evolution of complex sandy shorelines.