Two approaches may be taken for the estimation of storm impact on the 

 beach profile; one will be called the design- storm approach and the other the 

 storm-ensemble approach . The design storm is either a hypothetical or a 

 historical event which produces a specified storm surge hydrograph and wave 

 condition at the project. Surge is a water level rise caused by wind stress 

 and atmospheric pressure variation; waves also produce a rise in mean water 

 level at the shore called setup. The time average, on the order of an hour, 

 of surge, wave setup, and tide is called the stage. In stage -frequency analy- 

 sis, the design storm may have a certain frequency of occurrence, for example, 

 a 100-year storm. The problem with the design storm approach for use in dune 

 erosion modeling is that beach change is sensitive to storm duration, surge 

 shape, and wave height and period, in addition to peak stage. The maximum 

 water level associated with the surge of a design storm may produce less 

 erosion than a storm of lower surge but longer duration, or than a storm of 

 lower surge but higher waves. 



The solution to the problem of the many- to -one relation between beach 

 erosion and stage frequency is to use the storm- ensemble approach, i.e., to 

 calculate erosion for a large number of storms (treating hurricanes and 

 extratropical storms independently) and key the erosion to the frequency of 

 storm occurrence (Scheffner 1988, 1989). This yields an erosion- or reces- 

 sion-frequency of occurrence curve. At present, the classes must be treated 

 independently because they have different physical characteristics. For 

 example, hurricanes are infrequent events of short-duration and high inten- 

 sity, whereas extratropical storms are more frequent and usually of longer 

 duration and lower intensity than hurricanes. The storm-ensemble approach is 

 recommended for project design, although it requires a storm data base and is 

 much more computationally intensive than the design storm approach. 

 Here, the response of nourished beach profiles to a representative hurricane 

 and an extratropical storm (northeaster) is calculated to examine predictions 

 of the model to storms of differing waves and water levels (surge and dura- 

 tion). Kraus and Larson (1988) investigated profile response to a single 

 severe hurricane. In the present work, the two storms were constructed to 

 produce erosion resulting from a 2-5 year event for the mid-Atlantic Ocean 



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