PART V: Nin-IERICAL MODEL VERIFICATION 



38. After calibration, the ability of the models to simulate the 

 hydrodynamics of storm surges was verified with the two historical storms. 

 Hurricane Donna and the March 1962 northeaster produced some ot the highest 

 surges recorded along the Outer Banks, and they had severe effects on Oregon 

 Inlet. These storms were considered rigorous tests for the models of the 

 North Carolina coast. 



39. The eye of Hurricane Donna passed just west of Pamlico Sound 

 during the storm's movement north (Figure 9), with the highest winds concen- 

 trated over the Sound. During the peak of the storm, 60- to 80-knot winds 

 Meu across Pimlico Sound from the sou.tli and southwest", causing a large surge 

 to pile up along the bay side of the barrier islanas near Oregon Inlet. The 

 elevation difference between the surge in the bay and the level of the Atlantic 

 Ocean created a 10-ft head across the inlet, which caused an enormous flow 

 through the inlet. The surge in the bay also caused extensive flooding at the 

 barrier islands, Roanoke Island, and the nearby mainland. 



'0. The March 1962 storm derived its force not from high peak winds but 

 from sustained gales over several days. The low pressure system which drove 

 the storm remained along the eastern seaboard for over a week, generating 35- 

 to 50-knot winds from the north and northeast from 6 March to 8 March. These 

 gales caused a surge on the Atlantic side of the Outer Banks near Oregon 

 Inlet and a drawdown on the east side of Pamlico Sound. The head difference 

 at the inlet caused a large flow into the bay through an entire tidal cycle on 

 7 March, which, together with setup, created flooding in nearby Roanoke Island 

 and the mainland. 



41. The storm simulations used the historical tides developed during 

 calibration as initial and boundary conditions for the nearshore and offshore 

 models. The initial conditions for a VJTFM storm run were supplied by data 

 sets (dubbed "hotstarts") saved during tidal cor^putations. Hotstarts contain 

 the free-surface elevations and horizontal velocities at every point in a 

 grid, which enables one to start WTFM calculations with this Information as a 

 realistic, dynamic initial condition. The same tidal boundary conditions were 

 also used during storm simulations, so that the tide appears throughout each 

 storm hydrograph. Hence, computed hydrographs can be directly compared with 

 historical marigrams. . ■. ■. - ,. 



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