Dynamic characteristics of west Florida Gulf Coast beaches

Abstract

During 1962 fifteen beach stations were established along the Florida coast and monitored at monthly intervals. Observations of beach profiles, sediments, wave conditions, water characteristics and wind speed and direction were recorded. Techniques closely followed those of a nearly contemporaneous study on California beaches ( Ingle, 1966). This made possible a comparison of beach conditions in a low- and medium-energy environment (Florida) with a high-energy environment (California). Average wave conditions in Florida range from low ripples in the low-energy eastern segment near Keaton Beach, to over 30 cm wave height along the broad arc from Cape San Blas to the Alabama-Mississippi peri-delta region. Maximum wave heights reach 100 cm and more along the Pensacola shore and approach the average condition for high-energy beaches. Longshore current velocities, however, are surprisingly constant and range from 30 to 150 cm/sec in the general area. The much larger waves of the California coast produce essentially the same range of current velocities. This is a function of the increase in dimensions of a surf zone as larger waves necessarily break farther offshore, thus the larger amount of water moved in translation is balanced by the increased area. Statistical studies of the sediment textural parameters confirm the observations of Schiffman (1965) regarding the greater variation in texture occurring in the swash zone than in other parts of the beach system. Some evidence suggests that sediment composition differences east and west of Cape San Blas reflect different sources. Magnitudes of profile changes are approximately a direct function of wave height up to average heights of 30 cm and more. Thereafter, increasing wave height apparently does not markedly increase the rate of sand level variation. Volumes of sand transported in longshore drift, however, are directly related to wave height, but show considerable variation from month to month and day to day. Net sand transport is to the west and apparently is actively prograding the large spits of the area from Mobile Bay to Pensacola. Wave energy decreases west of Mississippi Sound and transport diminishes.