Woods Hole Group performed a reconnaissance survey and analysis of two offshore sand borrow sites for a proposed beach nourishment project at Siasconset, MA located on the southeast side of Nantucket Island.  The Town of Nantucket required that both of the selected borrow sites must be able to provide enough sand to nourish up to 14,000 linear feet of the eastern shore of Nantucket with approximately 1.4 million cubic yards of sand.  The purpose of selecting two potential borrow sites was to maximize flexibility and dredging alternatives, and to reduce adverse environmental impacts such as wave focusing and benthic habitat disturbance.

The extensive survey was completed during the summer of 1992 and included the collection of detailed and regional bathymetry, coring, beach sediment sampling, side-scan sonar, sub-bottom profiling, and magnetometer surveys.  The bathymetric data were acquired using a high-precision fathometer linked to a computer-integrated microwave navigation system.  The survey covered 30,000 linear feet of the Eastern Shore of Nantucket.  Survey lines for the detailed bathymetry at each borrow site were spaced at 100 foot intervals.  Bathymetry for the regional survey was collected along transects spaced at 500-foot intervals and extended from a distance of 5 miles offshore to within approximately 250 feet of the shoreline.

The side-scan and sub-bottom data at each of the borrow sites were collected simultaneously with the bathymetry.  Grain size and chemical analyses were conducted on the core samples collected from the borrow sites.  These were compared with grain size data from the beach samples for size compatibility.  A combination of the regional and detailed bathymetric data was used to model teh wave climatology at the site.  The objective of the wave modeling was to determine the potential effects of dredging from the proposed borrow sites on the shoreline.  The average annual wave climatology was determined using hindcast wave data, and the waves were transformed across the potential borrow sites using the numerical model.  The results were used to calculate sediment transport potentials and gradients in sediment transport.