Coastal sediment transport, Popponesset Beach, MA

Abstract

Pathways and rates of near-bed sediment transport near Popponesset Beach, MA ., were calculated using several distinct techniques. For the nearshore platform, sand transport in the form of sand waves was determined from vertical aerial photography spanning periods of four decades. In addition, calculations based on theoretical and empirical equations for near-bed sediment transport were made using field measurements of wind waves and tidal currents. Net sediment transport to the southwest inferred from these two techniques differed by about a factor of five. The higher net transport rate predicted in the aerial photographic method is a result of lack of wave measurements during storm conditions. Storm waves increase the net transport through a local increase in bed shear stress. Net transport to the southwest across the platform is between 700 and 3300 m3/yr. Littoral sand transport along Popponesset Beach was calculated from one month of directional wave measurements, extrapolated to a yearly value using long-term meteorological observations. Littoral transport from these calculations is 10,000 m3/yr to the northeast, opposite the sense of alongshore transport in the shallow nearshore. Patterns of shoreline change are discussed from a historical perspective, and using the transport calculations discussed above. Several management alternatives for coping with predicted shoreline change are presented for consideration by the Town of Mashpee.