Response Characteristics of an Ebb-Dominated Tidal Inlet Channel

Abstract

ABSTRACT A three-year study (July 1974 to July 1977) of Price Inlet, South Carolina, monitored inlet hydraulics and channel morphology. The inlet is strongly ebb-dominant. Both the peak and mean current velocities during ebb exceed the corresponding velocities during flood. The velocity asymmetry is caused by changes in inlet efficiency during the tidal cycle. The intertidal marsh of the Price Inlet drainage area experiences a change in open water surface area of about 670 percent during an average tidal cycle. At high tide, the large water surface of the marsh is responsible for inefficient exchange of water through the inlet. This causes a long time lag between ocean and bay tides. The small surface area of open water in the marsh at low tide, on the other hand, yields nearly no time lag. These differential time lags cause longer flood durations than ebb durations in the inlet throat and, consequently, stronger ebb elocities. Monitoring of the cross-sectional flow area of the inlet throat demonstrates rapid adjustment to changing flow conditions. The 1159 m2 cross sectional area of the inlet throat varied as much as 8.3 percent during one tidal cycle. The cross sectional area varied in phase with the tidal range. Long-term changes in the dimensions of the channel appear to be a direct result of changes in the size of ebb-tidal delta shoals. During the study period, the growth of the linear bars in the channel margin gradually reduced wave energy along the inlet shoreline and on the inner ebb-tidal delta platform. This in turn reduced sediment transport into the inlet, which resulted in a gradual increase in the cross-sectional area of the channel. Seasonal fluctuations in mean sea level appear t have little effect on the inlet channel.