65. In a scoping mode, or if the offshore contours are parallel to the 

 trend of the shoreline and the extent of the project to be modeled is small 

 (for example, shoreline change at a single detached breakwater), the simple 

 wave transformation routine (internal model) in GENESIS can be used to 

 refract, shoal, and diffract waves. GENESIS will transform the waves from the 

 depth of the offshore gage or hindcast point and produce the pattern of 

 breaking waves alongshore for calculating the longshore sand transport rate. 



66. If offshore contours are irregular or the project is of wide 

 extent, a specialized wave transformation program must be used to propagate 

 the waves from offshore to nearshore for use by GENESIS. Any wave model can 

 be used to provide the required information. At CERC, the model RCPWAVE 

 (Regional Coastal Processes WAVE model) (Ebersole, Cialone , and Prater 1986) 

 is used to supply the needed nearshore wave information. 



67. Shoreline change is sensitive to wave direction, and this quantity 

 is the most difficult to estimate. If information on wave direction is not 

 available, wind direction from a nearby meteorological station, buoy, Coast 

 Guard station, or airport may be useful, as well as consideration of possible 

 fetches. The effects of the coastal boundary layer and daily and seasonal 

 trends in wind speed, gustiness, and direction should be taken into account. 



68. The wave input interval (time step), statistics of the waves, and 

 the period to be covered must also be determined. For shoreline change model 

 calibration and verification, either hindcast data or the actual wave record 

 occurring over the simulation interval should be used, if available. In 

 simulations involving long periods and wide spatial extent, it may be imprac- 

 tical to handle a wave data file covering the full simulation period. 

 Instead, a shorter wave data file can be used and repeated, a capability 

 provided by GENESIS. The shorter record is fabricated by comparing statistics 

 of the total available wave data set (gage or hindcast) by year, season, and 

 month. Typical quantities that should be preserved are average significant 

 wave height and period, maxima of these quantities, average wave direction, 

 and occurrence of storms. For example, a 5 -year record might be composed of 



1 year of more frequent storms (but not the extreme year as that would not be 

 representative), a year of relatively low waves, and 3 years judged to be 

 "typical . " 



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