inlet increases. (The past site of New Inlet (Figure 9), just north of 

 Rodanthe, also has experienced major erosion since 1850 (Figure 31).) The 

 sound shoreline has been affected to a lesser extent (Figures 34 and 36) , but 

 the net change has been one of progradation. This shoreline adjustment adja- 

 cent to Oregon Inlet is related to the normal alongshore sediment transport 

 (see paragraph 103) of beach sand. When this sand reaches the inlet throat, 

 some is carried landward by flood-tidal currents and deposited within the in- 

 let system. The large shoal area in Pamlico Sound west of the throat at Oregon 

 Inlet is evidence of that inlet's trapping capacity. The sand composing those 

 shoals is coarser than the sound sands upon which the shoal area rests. In- 

 lets such as Oregon Inlet probably trap sand until the sound shoals have grown 

 to attain a quasi-equilibrium condition, at which time the volume of beach 

 sand which enters the inlet on a flood tide is balanced by the volume carried 

 out on the subsequent ebb tide. The trapping rate of an inlet normally de- 

 creases with time after the inlet opens. However, when an inlet moves paral- 

 lel to shore as Oregon Inlet has done (29 m/year on the average, Figure 38) 

 the entrapment rate may not decrease very rapidly because the flood-tidal 

 shoals never attain a quasi-equilibrium state of development. 



112. An analysis of Oregon Inlet sand gains relative to adjacent ocean 

 shore sand losses provides an approximate means to illustrate that most of 

 the adjacent shoreline retreat is inlet-caused. Approximately 32,000 sq m/ 

 year (4.2 x 10 sq m, total) of barrier island surface area has been lost 

 since 1849 within 8 km of Oregon Inlet (Figure 40) (to some extent, these 

 values have also been influenced by previously open New Inlet (Figure 9)). 

 To calculate the volume of sand moved, the depth to which the shoreface 

 profile has been modified must be considered; a reasonable depth (Hallermeier 

 1977) is about 10 m. Using the surface area lost (Figure 40) and the assumed 

 10-m depth to which erosion occurred, approximately 4 x 10 cu m of sediment 

 was lost from the barrier islands adjacent to Oregon Inlet between 1852 and 

 1980. The ebb- and flood-tide shoals in Oregon Inlet cover an estimated 

 2.5 x 10 sq m of Pamlico Sound. At an average estimated thickness of 2 m, 

 these inlet deposits contain 5 x 10 cu m of sands transported from the ad- 

 jacent islands. Thus, according to this very crude analysis, the sands lost 

 from the beaches near Oregon Inlet can be accounted for within the inlet sys- 

 tem, primarily in Pamlico Sound flood-tide deposits. Of course, superimposed 

 on the inlet-caused ocean shoreline change, is the long-term 0.8-m/year 



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