Aftar verification, the affects of the jetties are estimated with the models 

 for both tide and storm conditions. 



Approach 



4. The numerical hydrodynamic code used in this study is iJIFM, the WES 

 Implicit Flooding Model (Butler, in preparation). WIFM employs finite dif- 

 ference methodo to approximate the vertically integrated Navier-Stokes equa- 

 tions. Several special features of WIFM are important to this study. The 

 flooding and drying of tidal flats and low-lying lands are accurately simulated 

 in WIFM. Variably spaced finite difference grids are used to maximize accuracy 

 in the hydrodynamic simulationss without increasing computer costs. WIFM can 

 approximate jetties, and other small topographic details, as thin barriers 

 betveen computaticnal cells. The implicit formulation used in WIFM's solution 

 scheme allows for larger time-steps than do explicit solution schemes, 



5. The hydrodynamic features of the Carolina coast and Oregon Inlet 

 are simulated to three levels of accuracy in this study by the use cf three 

 different finite difference grids that cover different portions of the study 

 area (Figure 2). The three grids can be linked together, wherein an internal 

 boundary in a larger grid can provide boundary conditions to the next small- 

 est grid. The offshore grid (Figure 3) approximates the entire Carolina 

 coast with 3,186 cells, making computaticns with it inexpensive. This grid 

 extends seaward to the continental shelf in order to model the effects of 

 long-wave shoaling caused by the shelf. Oregon Inlet is only approximated by 

 one cell in the offshore grid, so computations from this model can only 

 provide rough estimates of hydrodynamics in the sounds. The nearshore grid 

 (Figure 4) models the Outer Banks in much finer detail with 9,009 cells. 

 Tides and surges can be accurately simulated throughout the bays and inlets 

 with this grid. Oregon Inlet is modeled with enough detail in this grid to 

 allow for calculations with crude jetty approximations. This grid provides 

 all boundary conditions to the mosu detailed of the three grids used in this 

 study, the shore process grid. 



6. The shore process grid (Figure 5) covers less than 85 square miles 

 around Oregon Inlet with A, 620 computational cells. This model provides high 

 resolution at the inlet and in the surf zone. The shore process model predicts 

 circulation patterns at the inlet, predicts effects of jetties on inlet flow. 



