Sediment transport in a dynamic, tidally-influenced coastal embayment exemplified by Pleasant Bay and Chatham Harbor, Cape Cod, Massachusetts

Mark Borrelli, University of Rhode Island


Sediment transport in a coastal embayment was documented on multiple spatial and temporal scales. An inlet formed in Chatham Harbor in 1987 and as a result the primary flood-tidal delta began to migrate. The relationship between the evolution of the tidal inlet and the flood-tidal delta was documented using field studies and spatial analyses of georeferenced aerial photographs. A feedback mechanism was documented such that the migrating flood-tidal delta increases in surface area, which causes the ebb-tidal flow to become more channelized, which in turn allows more intertidal area to be created by flood-tidal currents and further channelizing ebb-tidal flow. As a result of this cycle two outcomes can be reached. First, the flood-tidal delta restricts ebb-tidal flow to such an extent that a new inlet is formed through the barrier during a storm event. Second, ebb-tidal flow creates channels in the flood-tidal delta, decreasing the surface area of the flood-tidal delta and restarts the cycle. ^ In April 2007 a new inlet formed through Nauset Beach, a barrier spit within the boundaries of Cape Cod National Seashore. This inlet formed during an extratropical storm as did the 1987 inlet. However, the 2007 inlet did not form as a result of increasing hydraulic inefficiency due to spit elongation. The restriction and redirection of the main tidal channel in the central part of the harbor gave rise to conditions that led to the 2007 inlet formation. The placement of dredged material within Chatham Harbor also contributed to that restriction and redirection. ^ A new shoreline proxy for calculating shoreline change in the Pleasant Bay-Chatham Harbor coastal lagoon was developed and tested. Shoreline change not discernible using a traditional shoreline proxy was documented using this new proxy along shorelines with fringing salt marsh. This method can track low-energy sediment transport that over time can have dramatic impacts to, and implications for shoreline change, water quality issues, predator-prey relationships and overall ecosystem health. Salt marshes are among the world's most biologically productive ecosystems and these findings will improve our understanding and management of these areas. ^

Subject Area

Geology|Physical Oceanography

Recommended Citation

Mark Borrelli, "Sediment transport in a dynamic, tidally-influenced coastal embayment exemplified by Pleasant Bay and Chatham Harbor, Cape Cod, Massachusetts" (2008). Dissertations and Master's Theses (Campus Access). Paper AAI3328718.