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Inlets exchange water between the sea and the bay during each tidal cycle. 

 Therefore, currents in tidal inlets are typically unidirectional, changing 

 direction diurnally or semidiurnally, depending upon the tides along the 

 adjacent open coast. Flow through the inlets can be complicated by the 

 hydrodynamics of the inland bay, especially if there are other openings to the 

 sea. 



Various numerical and conceptual models have been developed to describe 

 flow through inlets and allow researchers to predict the effects of changing 

 inlet dimensions, lengths, and orientations (Aubrey and Weishar 1988; 

 Escoffier 1977; Seelig, Harris, and Herchenroder 1977; Shore Protection 

 Manual 1984). Most models, however, benefit from or require calibration 

 with physical measurements made within the inlet and the general vicinity. 

 The required field measurements are usually either tidal elevations from the 

 open sea and within the adjacent bay or actual current velocities from within 

 the inlet's throat. 



Display of tidal elevation data is relatively straightforward, usually 

 consisting of date or time on the x-axis and elevation on the y-axis. Examples 

 of tidal elevations from a bay and an inlet in the Florida Panhandle are 

 presented in Figure 17. Although the overall envelope of the curves is 

 similar, each one is unique with respect to the heights of the peaks and the 

 time lags. The curves could be superimposed to allow direct comparison, but, 

 at least at this 1 -month-long time scale, the result would be too complicated to 

 be useful. 



Display of current meter measurements is more difficult because of the 

 large quantity of data usually collected. An added difficulty is posed by the 

 changing currents within an inlet, which require a three-dimensional repre- 

 sentation of the flow, which varies with time. Current measurements from 

 East Pass, Florida, collected during three field experiments in the mid-1980's, 

 are presented as examples. Currents were measured with manual Price-type 

 A A meters deployed from boats and with tethered Endeco 174 current meters. 

 The manual measurements were made hourly for 24 hr in order to observe a 

 complete tidal cycle. The measurements were made across the inlet at 

 four stations, each one consisting of a near-surface, a mid-depth, and a near- 

 bottom observation (Figure 38). Therefore, 12 direction and velocity data 

 values were obtained at each hour (Figure 39). One way to graphically 

 display these values is to plot the velocities on a plan view of the physical 

 setting, as shown in Figure 38. This type of image clearly shows the direc- 

 tions and relative magnitudes of the currents. In this example, the data reveal 

 that the currents flow in opposite directions in the opposite halves of the inlet. 

 The disadvantage of the plan view is that it is an instantaneous snapshot of the 

 currents, and the viewer cannot follow the changes in current directions and 

 magnitudes over time unless the figure is redrawn for each time increment. 

 Temporal changes of the currents can be shown on dual plots of magnitude 

 and direction (Figure 40). Unfortunately, to avoid complexity, it is not 

 reasonable to plot the data from all 12 measurement locations on a single 

 page. Therefore, measurements from the same depth are plotted together, as 



Chapter 5 Analysis and Interpretation of Coastal Data 



