52 MARINE FISHERIES OF NORTH CAROLINA 



Chief of Engineers of the U. S. Army, dated February 21, 1876, which con- 

 tains a table stating the condition of the inlets at various dates according to 

 old maps or other available source data. Table 8 is essentially a condensed 

 and up-to-date version of Abert's table as supplied by the Corps of Engineers 

 in recent correspondence. Figure 24 will orient the reader as to the location 

 of the existing and past inlets as far south as Beaufort. 



Through the years inlet changes due to natural forces have been rather 

 great. Because of the obvious importance of these passages for navigation and 

 from the standpoint of modifying the sounds for fisheries development, there 

 have been many proposals for artificially developing inlets, reopening old 

 ones, etc. The Division of Water Resources of the North Carolina Depart- 

 ment of Conservation and Development and the Corps of Engineers, U. S. 

 Army have conducted surveys that bear wholly or in part on such questions. 

 A background in theory is indispensable for comprehending the problem 

 involved and, since Johnson (1919, 1938) not only offers such theory but 

 discusses its application to North Carolina, I will quote from him at length: ^^ 



"It is commonly assumed that the amplitude of the tide is the only factor 

 involved in determining the number and width of tidal inlets through offshore 

 bars. Both theoretical considerations and field observations negative this 

 assumption. In addition to the varying strength of longshore action (mainly 

 beach drifting), the volume of land water, the extent to which the lagoon is 

 filled with sediment or marsh deposits, the abundance and rapidity with 

 which debris is supplied, and the strength of storm-wave attack, are all 

 factors of importance. With the same tidal range along two offshore bars, it 

 may happen that longshore current action is weak on one, but vigorous on 

 the other. Under such conditions the one with the weaker longshore currents 

 will have more or wider inlets. Where large rivers empty into a lagoon, the 

 ebb current of the tide is greatly reinforced by the land waters, and will keep 

 open inlets which would otherwise be narrowed or closed. As sedimentation 

 and marsh growth decrease the water space of the lagoon, the volume of tidal 

 waters admitted and the strength of the tidal currents is reduced, in con- 

 sequence of which longshore currents may be able to narrow or even close 

 some of the inlets. If an abundance of debris is supplied to longshore currents 

 with great rapidity, the closing of inlets will be more readily accomplished 

 than if a smaller amount of debris is supplied very slowly. An inlet, once 

 closed, might never be re-opened were it not for breaches made in the bar by 

 storm-wave attack. Tidal action tends to keep inlets open; but, except in the 

 case of an unusually high tide overflowing a low point on a bar, does not tend 

 to produce inlets. Impounded land water may in rare instances open an inlet 



23. Reprinted by permission from Shore Processes and Shoreline Development by D. W. John- 

 son, published by John Wiley & Sons, Inc., 1919. A similar discussion but in a more tecl^nical 

 vein is offered by Brown (1928). 



