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Title: Hydraulics and dynamics of North Inlet, South Carolina, 1974-75
Authors: University of South Carolina
Finley, Robert J.
Keywords: Beach and inlet morphology
North Inlet, S.C.
Tidal hydraulics
Tidal inlets
Wave parameters
Publisher: Coastal Engineering Research Center (U.S.) General Investigation of Tidal Inlets Research Program
Engineer Research and Development Center (U.S.)
Description: General Investigation of Tidal Inlets Report
Abstract: Detailed quarterly studies at North Inlet, South Carolina, have shown variation in wave parameters, beach and inlet morphology, and tidal hydraulics which are related to seasonal climatic patterns. Wind magnitude and direction, occurrence of northeast storms, and brackish water influx from adjacent Winyah Bay are significant process variables. Over 800 unique visual wave observations indicate that annual resultant wave energy flux is directed to the south. However, an energy flux reversal due to ebb tidal delta morphology results in longshore transport of sediment toward the inlet, adding to swash bars, the channel-margin liner bars, and a northward recurving spit. An estimate of the volume of inlet-directed longshore sediment transport (3.5 * 10(5) cubic meters per year), based on observed energy fluxes, gives a value which is 83 percent of the annual longshore transport rate (4.43 * 10(5) cubic meters per year), based on 39 years of spit and shoal growth. Beach profiles at 11 locations shows that erosion is primarily due to northeast storms and that the shoreline is transgressive. A maximum of 7 meters of foredune retreat was observed during the winter of 1972-73, contributing abundant sediment to the ebb tidal delta, which has a present volume of over 35,700,000 cubic meters. The only beach not severely eroding lies immediately south of the inlet where the ebb tidal delta affords protection from northeast storm wave approach, and onshore migration of swash bars provides sediment to the longshore transport reversal. The southern channel-margin linear bar of the ebb tidal delta has increased in width and length during recovery from the February 1973 northeast storm. Reduction in the cross-sectional area of the inlet throat during the fall and winter months is related to sediment added to the northern channel-margin linear bar. The flood tidal delta is migrating westward under the influence of waves at high tide and is being dissected by ebb flow from a minor tidal creek. Hydrographic observations over complete spring, mean, and neap tidal cycles have been used to determine the volume of the tidal prism, examine current velocity distributions, and determine coefficients of friction and repletion. Prism volume varies from 7.43 * 10(6) to 25.52 * 10(6) cubic meters, depending on tidal phase and meteorological influences, with a mean of 14.96 * 10(6) cubic meters. Maximum tidal current velocities reach 120 centimeters per second, and time-velocity asymetry is present. Average Manning's n friction coefficients have been found to range from 0.032 to 0.041. Keulegan repletion coefficients are applicable to tidal flow at North Inlet, despite the complex nature of flow into a marsh-filled area and the hydraulic connection to adjacent Winyah Bay. The two major channels must be considered seperately, and extreme values of n which coincide with slack water must be excluded from any analysis. Note: Distinct numerals contained within brackets should be considered exponents for the purpose of scientific notation.
Rights: Approved for Public Release, Distribution is Unlimited
Appears in Collections:GITI Report

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