Chatham, Massachusetts Coastal Sediment Transport Study

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As a result of natural and man-induced evolution of the Chatham South Shore, the beach system fronting much of the shoreline has eroded significantly over the past 50+ years, primarily due to a deficit of littoral sediments.  For the past 10 years, the Town of Chatham has been performing periodic beach nourishment in the vicinity of Cockle Cove, with lesser amounts placed at Forest Beach and Pleasant Street Beach, to provide sediments to the overall beach system.  Despite these efforts, shoreline erosion has continued and the Town decided that a better understanding of the South Shore coastal dynamics would provide beneficial information for future shore protection decisions.  To this end, a more comprehensive evaluation of coastal processes governing the beach system, as well as an assessment of corrective actions that can be taken to stabilize the shoreline, was performed.

To determine the local sediment transport pathways associated with the observed shoreline change, an in-depth scientific analysis was performed to quantitatively evaluate wave and longshore sediment transport processes that influence sand movement along the Town’s south shoreline.  The main purpose of this analysis was to assist in the development of a practical management plan for the Town’s southern shoreline.

In this study, the 2-dimensional wave model swan was used to compute average wave conditions using an available 23-year wind record from the area.  The computed wave conditions were then used to develop shoreline change models for three separate segments of the Chatham shoreline.  The shoreline models were calibrated using historical shorelines taken from a GIS analysis of the coast.  The models were used to simulate different beach fill scenarios, ranging between 10,000 and 50,000 cubic yards. 

The models developed in this study will be used in a follow-on study by the USACE New England District.  This purpose of this new study is to look at beneficial use scenarios for sediment dredged from the federally authorized channel at Stage Harbor.