DYNAMIC EQUILIBRIUM BEACH PROFILES: FORCES OF OFFSHORE SEDIMENT TRANSPORT IN MARYLAND’S CHESAPEAKE BAY

Abstract

To examine the impact of shoreline erosion on the near shore environment, it is necessary

to estimate the quantity and quality of yearly sediment mass that is likely to be added by

erosion. Data were collected in 2008 at ten sites along the Maryland shoreline of the

Chesapeake Bay and compared to both empirical and theoretical models of offshore

profiles. The data collected at each site included a series of three-dimensional

bathymetric profiles from offshore transects run at each site, as well as a series of

sediment core data that were acquired along each transect. Relationships between grain

size, beach type, sediment composition, and strength of eroding sediments were also

explored. The results showed that sands dominated offshore surficial sediments at most

locations, even though the source sediments were mixtures of sands and muds. The

observed offshore profiles were consistent with expectation from ocean beach profile

paradigms, with the exception that the steepness proportionality factor was not related to

sediment grain size. An adjusted form of the classic Bruun relationship for predicting

shoreline retreat was in approximate agreement with long-term observations.