A common feature of ebb-tidal deltas is the segregation of ebb and flood 

 flow. Each inlet usually has a main channel oriented perpendicular to the 

 shoreline, which carries a large portion of the ebb flow. The flood flow, on 

 the other hand, tends to be distributed as a sheet, with several individual 

 flood channels developed in some cases. Usually the flood channels hug both 

 beaches, flanking the main ebb channel (Fig. 4-61). 



This segregation of flow is caused by the time-velocity asymmetry of the 

 tidal currents. Maximum flood velocities are usually late in the flood-tidal 

 phase of the tidal cycle, betvveen midtide and hightide. Similarly, maximum 

 ebb flow is between midtide and low tide, usually quite close to low tide. 

 Thus, the ebb flow tends to be more channelized than the flood, which is 

 evenly distributed across the inlet delta. 



The inner shoal-flood-tidal delta system of an inlet is typically more 

 difficult to categorize than the ebb-tidal delta because of the varied 

 physiographical system comprising the inlet landward of its ocean-shore 

 boundary. Just inside the landward end of the channel of many inlets, a large 

 shoal commonly termed the middle ground shoal develops. This shoal is 

 typically made up of finer material than are the beaches adjacent to the 

 inlet. The middle ground shoal is formed in the slow divergence area of the 

 flood tide. An example of a middle ground shoal is shown in Figure 4-63. 



A number of investigators (Bruun and Gerritsen, 1957; Bates, 1953; Galvin, 

 1971; Vincent and Corson, 1980) have studied the relationships among various 

 geometric properties of tidal inlets and noted various trends and correlations 

 among certain inlet parameters, such as inlet cross section minimum area, 

 channel length, maximum channel depth in minimum width cross section, ebb 

 delta area, and controlling depth over outer bar. Vincent and Corson (1980) 

 have systematically defined many of these inlet parameters, as shown in 

 Figures 4-64 and 4-65. They have also made statistical correlations of the 

 parameters to ascertain significant relationships for 67 inlets, most of which 

 did not have engineering structures (jetties, etc.) at the time of survey. 

 The more important of these correlations are provided in Figures 4-66 through 

 4-69. These correlations show a strong dependence of inlet geometry on 

 channel minimum width cross-sectional area, which has been found by O'Brien 

 (1969) and others to depend strongly on the tidal prism. 



O'Brien (1969) originally found a relationship between the minimum throat 

 cross-sectional area of an inlet below mean tide level and the tidal prism 

 (i.e., the volume of water entering or exiting the inlet on ebb and flood 

 tide) at spring tide. This relationship was predominantly for Pacific coast 

 tides, where a mixed tidal pattern is observed. A more recent correlation 

 between inlet minimum cross-sectional area at throat section and tidal prism 

 has been given in the work of Jarrett (1976) where regression analyses vere 

 made for various coastal areas with different tidal characteristics. Jarrett 

 (1976) has given a regression equation for each of the Atlantic, Pacific, and 

 gulf coasts. The equations, in metric (a) and English (b) units, are as 

 follows : 



4- 152 



