BARDEN INLET, N.C. A CASE STUDY OF INLET MIGRATION

Abstract

The migratory pattern of a small coastal inlet was examined in terms of the factors generally acknowledged to control inlet behavior. That is, the tidal discharge which acts to flush the inlet and, on the other hand, the intrusive littoral materials depositing in the inlet environment. Specifically, a "flow conveyance index" was computed and compared to shoreline movements. The "flow conveyance index" was defined as the ratio of the mean distribution of the overall planform area of the throat of the inlet to the mean distribution of the planform areas of shoals within the throat of the inlet. High and low "flow conveyance index" values would correspond, respectively, to periods of relatively high and low inlet flushing conditions. A consistent pattern obtained from this analysis, wherein high and low index values corresponded with high and low shoreline movements. Additionally, the plot of rates of shore movements against rates of change of "flow conveyance index" was fitted with a simple linear regression line having a positive correlation coefficient of 0.85. Further analyses of the mean distribution of the shoals within the throat of the inlet demonstrated the cause of timevarying rates of movement of points along the spiriferous east shoreline of the inlet. Shoreline movement rates were plotted on a time-space plane and isolines of shore movement rates contoured. The result was a three-dimensional image of shore movement rates over time and distance. The position of the centroid of the inlet shoal distribution at different times was superimposed upon the three-dimensional image. This revealed that variations of shoreline movement rates along the shore at any point in time are dependent on the mean position of the inlet shoal distribution. Also, the direction of movement of the mean position of the inlet shoal distribution appeared to indicate the predominant direction of flushing action, that is, flood or ebb tides.