Wave-refraction model 



The USACE-developed model RCPWave (Ebersole, Cialone, and Prater 1986) 

 provided the means to model wave refraction at East Pass Inlet. RCPWave. a linear wave 

 propagation model, addresses both refraction and diffraction by bottom contours. The 

 governing equations of the model are a modified form of the "mild slope" equation for 

 monochromatic, linear waves and the equation specifying irrotationality of the wave- 

 phase function gradient. The model accepts as input a representative wave field of wave 

 height period, and direction. The program then propagates the wave towards the shore 

 over a user-supplied bathymetry. 



The identical bathymetry used for the hydrodynamic modeling was input into the 

 wave model. Wave hindcast data from a station located approximately 9 miles due south 

 of the inlet in 52 ft of water provided the offshore wave conditions. Wave hindcast data 

 reduction produced representative wave conditions along 22.5-deg direction bands. The 

 procedure for finding the wave climate in the throat required two applications of 

 RCPWave. The first application brought the waves from deep water to the tips of the 

 jetties. The second application, performed with a finer resolution grid, started at the jetty 

 tips and propagated the wave through the throat. Figure 30 shows an example of both 

 model applications. In the figure, the wave rays were drawn through interpolation of the 

 model output. 



Figure 3 1 is a magnified view of Figure 30 in the area of the Old Pass shoal. The 

 figure illustrates the continued wave impact on Norriego Point despite the protection that 

 the jetties afford. Qualitatively, the angle with which the waves strike the point and the 

 magnitude of wave height before breaking suggest a significant amount of sediment 

 movement or at least sediment suspension. If an adverse wave climate occurs during 

 flood tide, currents may carry the wave-suspended sediment toward Old Pass. 



A program (or "calculator") evaluating sediment-transport potential by waves was 

 not available for this case study. This tool would help evaluate the hypothesis outlined in 

 the preceding paragraph. Development of these types of tools is part of the DMS work 

 unit. 



Conclusions concerning Old Pass shoal are incomplete. The preceding analysis has 

 indicated that tidal currents cross the channel at a right angle and show an accompanying 

 deceleration. However, sediment-transport contours indicate no gradients in the area. 

 Absence of sediment-transport gradients indicates little sediment deposition. The wave- 

 refraction diagrams show that wave activity may play a significant role in the physical 

 processes along the point. The synthesis of these facts prompts the hypothesis that waves 

 suspend sediment along the shoreline and currents transport the sediment toward the pass 

 where the sediment comes to rest. However, tools to evaluate this hypothesis are under 

 development. 



48 Chapter 4 DMS-Analytical Toolbox 



