Beach and Nearshore Processes in Southeastern Florida

Allan E. DeWall · Joseph J. Richter

1977年1月 · Coastal Engineering Research Center

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A 4.5-year series of daily and week littoral environment observations and beach profile surveys was made at 3 localities in southeastern Florida. As a result of varying protection by the Bahamas Banks, the amount of wave energy reaching the shoreline decreases from north to south. Mean annual breaker height decreases from a maximum of 2.8 ft at Jupiter on the north to a minimum of 1.6 ft at Hollywood on south. A pronounced seasonal variation is evident with waves and currents from the northeasterly sector dominating during October through March from the southeasterly sector dominating during April through September. Monthly averages of breaker height and period data were the same for a 4.5-year set of daily observations and a subset of weekly observations. Potential gross longshore transport rates, estimated using this wave data, ranged from 2,300,000 yd3/yr at Jupiter to 400,000 yd3/yr at Hollywood. The magnitude beach changes decrease from north to south and was low compared to changes on more exposed beaches on the U.S. east coast. Contributing factors include the sheltering effect of the Bahamas Banks, the lack of significant storms, and the underlying coquina limestone which characteristically crops out just below the MSL shoreline at the two sites with the highest waves, forming a protective reef that effectively retards beach erosion. Beach width and sand volume were the highest during the summer months at two of the localities (Jupiter and Hollywood), but were highest during the winter months at one locality (Boca Raton). Seasonal beach changes were two to three times greater than year-to-year changes. The average unit volume change above MSL was -0.71 yd3/ft/yr at Jupiter, + 0.89 yd3/ft/yr at Boca Raton, and -0.04 yd3/ft/yr at Hollywood. Corresponding MS-shoreline migration rates were -0.4 ft/yr at Jupiter, +1.5 ft/yr at Boca Raton, and -2.9 ft/yr at Hollywood.