37. Four clusters of closely spaced ridges trend oblique to the shore- 

 line and tie to the shoreface between Cape Henry and Cape Hatteras. They are, 

 from north to south, False Cape Shoals, Oregon Shoals, Wimble Shoals, and 

 Kinakeet Shoals. Swift et al. (1978b, p 270-271) note these characteristics 

 of shoref ace-connected ridges: (a) the ridges rest on surfaces exposed as 

 the shoreface retreats to the west, (b) shoref ace-connected ridges form angles 

 with the coast opening into the direction of prevailing flow (i.e., from north 

 to south), (c) sand on the seaward (downcurrent) flanks is finer than sand on 

 the landward (upcurrent) flanks, (d) ridges tend to be steeper on the seaward 

 side except next to their shoreface connection, and (e) ridges tend to migrate 

 downcoast and offshore. These ridges are emphasized because they appear to 

 have an influence on adjacent shoreline retreat rates. 



Tides, Winds, and Waves 



38. The data in paragraphs 39-46 are presented for reference only and 

 are not used in the analysis section; they provide background on the dynamic 

 conditions which have existed in recent times. 



Tides and other sea level fluctuations 



39. An astronomical tide is the periodic rising and falling of the 

 water surface resulting from the gravitational attraction of the moon and sun 

 on the rotating earth. The period of a complete tidal cycle in the study 

 area is 12.4 hours; the mean and spring tide ranges from NOS Tide Tables for 

 1981 are shown in Figure 14. 



40. Sometimes superimposed on the astronomical tides is storm surge; 

 i.e., wind and wave setup and water surface differences caused by barometric 

 variations. Wind setup is the vertical rise in water level at a lee shore 

 caused by wind shear stresses on the water surface. Wave setup is another 

 superelevation of the water surface, caused by the onshore mass transport of 

 water by waves. In the sounds 20 km or more away from Oregon Inlet, the 

 astronomical tide range is less than 0.3 m, but the wind setup may raise the 

 water surface a meter or more for a 1-year wind event. Return periods for 

 storm surge along the ocean shore at Kitty Hawk are shown in Figure 15 (Ho 

 and Tracey 1975). 



41. A changing sea level occurring over a period of years may have a 

 profound effect on shoreline position. Changes on the order of years in sea 



29 



