INLET DYNAMICS FROM SEMI-ANNUAL SURVEYS

Owen W. Callard, William R. Dally, Kathy FitzPatrick

Abstract


Field surveys, carefully conducted with state-of-the-art equipment, remain the best source of information for studying tidal inlets. Data from an ambitious hydrographic surveying program that is ongoing at Sebastian Inlet, Florida (see Figure 1), are being analyzed to examine the morphologic dynamics of the inlet, to maintain a sediment budget, and to identify any ongoing impacts of the inlet to the adjacent beaches. Historically, the presence of Sebastian Inlet caused the formation of both ebb and flood shoals, and accretion and erosion along the beaches to the north and south, respectively. However, because 1) the inlet is relatively small, 2) its jetties were originally constructed in 1923-24, and 3) a sediment trap in the inlet's throat is periodically dredged and the material placed on the downdrift beaches, any persistent, long-term erosion/accretion trends have abated. Modern-day changes are limited to variation about a quasi-equilibrium state (Dally and FitzPatrick, 1997). The predominant wave energy along the east central Florida coast during the winter months emanates from the north and northeast sectors due primarily to extratropical storms commonly referred to as 'northeasters'. It is thus expected during the winter months sand will accrete at the north side of the inlet, and erode from the south. During the summer months, the direction of predominant wave energy switches to the southeast quadrant. Low-energy 'recovery' swell is caused by persistent winds from an entrenched system of high pressure (Bermuda High) which dominates the summer weather in the central North Atlantic. Higher energy swell from this sector also occurs as a result of occasional hurricanes. Consequently during the summer, erosion of the north fillet is expected, with accretion on the south. The purpose of the study described below is to identify and quantify this seasonal behavior, and any other patterns or trends present.

Keywords


inlet dynamics; semiannual surveys

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