Date of Award
Master of Science in Oceanography
R. L. McMaster
Wave characteristics, longshore drift velocities and beach elevation changes were monitored at Weekapaug, East, and Green Hill beaches on southwestern Rhode Island’s moderate energy shoreline. Results showed that erosion was generally the consequence of southeast waves while accretion was usually associated with southwest waves. Also, measured longshore velocities were fastest at Green Hall, slower at Weekapaug and slowest at East Beach. Stronger littoral currents at Weekapaug and Green Hill beaches probably resulted from the closer proximity of potentially steeper longshore hydraulic gradients associated with adjacent.
As no field observations were available regarding nearshore circulation, the longshore component of wave power curves and generated breaker heights from a mathematical model (May and Tanner, 1973) were used to suggest circulation patterns. For oblique wave approaches, both sets of data indicated that small circulation cells tended to stack on the windward sides of headlands with longer cells to leeward.
Field data were compared with the computer model output for three cases of beach erosion-deposition response. In each case the model provided the correct simple response but did not indicate a compound response of erosion on the foreshore and deposition on the backshore. Furthermore the model failed to successfully predict the representative field example for non-uniform response; i.e., erosion at Weekapaug and Green Hill and deposition at East. However the theory related to the model was used to demonstrate that refraction in a beach re-entrant is responsible not only for the magnitude of the cutting and filling response but also for the uniform and non-uniform erosional and accretional responses.
An evaluation of the model revealed that initial grid size and ray spacing were responsible for the predicted longshore energy distribution and drift direction. Moreover rapid bathymetric changes, shoals, and surf zones caused the model to breakdown due to mathematical limitations. Further longshore speed forecasts were greater than measured because the model was incapable of considering reformed smaller waves. Finally no positive correlation between storm and fair-weather seasonal ΔPL curves and their corresponding seasonal elevation changes were found because a sufficient wave spectrum was not available to be considered.
Donovan, Nancy Susan, "Wave Energy and Beach Response for Three Southern Rhode Island Beaches" (1977). Open Access Master's Theses. Paper 2039.
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