largest change in the peak elevations occurs at the North Ocean Entrance, a 

 site at the ends of tha jetties. The constricting effects of the structure 

 raise the peak surge <»"jout 2 ft in the middle cf the inlet, while little 

 difference is noted on the bay side of thf opening. Velocities on the bay 

 '"ide are actvaliy reduced by the jetties (i.e. Bonner Bridge) until the flood 

 flow reaches the iii-ddJe of the inlet. Figure 14 shows a comparison of eleva- 

 tion contours around the inlet for the peak of the storm for this structural 

 alternative. 



58. Plate 48 shows the flow patterns at the inlet for the 5,000-ft 

 structure. The shoal in tlie channel acts to move the fastest velocities near 

 the two jetties. Plates 49 and 50 compare water elevations for this case with 

 existing conditions, while Plates 51-54 co;T;pare velocities for the stem. The 

 influence of the jetties on either the surge or the velocities is negligible, 

 even in the channel. Figure 15 shows a comparison of computed su'-ges at the 

 peak of the storm, and clearly indicates that the effects of the 5,000-ft 

 spacing jetties are limited to small variances within the inlet, and no 

 impa<:t on Pamlico Sound, as represented by the nearshore model. 



59. A tabular comparison of computed peak surge results for Hurricane 

 Donna at selected Outer Bank locations with the various inlet configurations 

 is presented in Table 4. Results in this comparison also indicate no impact 

 of the structures on peak surge levels within the Albemare/Pamlico Sound 

 systems as recorded along the Outer Banks. 



Tidal Tests 



60. Tidal simulations with the jetties were conducted with the near- 

 shore and shore process models. A mean tide was simulated with the 2,500-, 

 3,500-, and 5,000-ft jetties. Structure effects at the inlet vicinity were 

 evaluated with the shore process model, and effects at more distant locations 

 along the Outer Banks were determined with the nearshore model. The jetty 

 configurations were simulated with natural bathymetry features including the 

 offshore shoal and no specific dredging. In general, structure effects were 

 limited to the immediate inlet vicinity with no changes observed at Outer Bank 

 locations. 



61. Plates 55-59 present comparisons of natural conditions versus the 

 2,500-ft jetty alternative for both nearshore and shore nrocess models. Local 



39 



