Static methods do not allow calculation of the temporal behavior of the 

 profile in achieving the equilibrium shape. An engineering model to simulate 

 time -dependent dune erosion was presented by Kriebel (1982, 1986) and Kriebel 

 and Dean (1985), although it rests in major part on the static profile shape 

 given by Equation 1. The model is based on a relation for the cross -shore 

 sand transport rate expressed in terms of the breaking wave height and has 

 been shown to produce correct orders of magnitude of foreshore and dune 

 erosion (Birkemeier et al . 1987). A modified version of the Kriebel and Dean 

 model has been successfully employed in engineering studies of storm- induced 

 beach erosion and fill design on the north New Jersey coast (Kraus et al . 

 1988), for which a methodology was developed for calculating beach recession 

 vs. frequency of storm occurrence relationships (Scheffner 1988). Time -depen- 

 dent calculation of the rapid beach erosion accompanying a storm is expected 

 to provide a more realistic prediction of eroded volume than a static method, 

 since static methods pertain to a longer duration of wave action, implying a 

 probable overestimation. 



The Kriebel and Dean model includes the following simplifications: 

 (1) independence of profile change on wave period; (2) limited capability to 

 reproduce beach recovery on the foreshore; and (3) over-schematization of the 

 beach profile. In contrast, beaches respond to changes in wave steepness 

 (involving wave period), recovery may begin prior to the end of a storm (e.g., 

 Sonu 1970, Kriebel 1987), and bars grow and move seaward during storms. Bar 

 growth is a natural defense mechanism of the beach to break the incident waves 

 and reduce erosive wave energy close to shore. Thus, improvements in modeling 

 capabilities are needed for application to beach fill design. 



The capability to predict the time rate of change of a beach fill adjust- 

 ing to its equilibrium shape under varying waves and water level would promote 

 an efficient project design "template" which could be used to estimate, for 

 example, the greatest longevity of a fill of fixed total volume for a given 

 wave climate, amortization of initial and maintenance costs vs. life expectan- 

 cy, and the behavior of a fill under seasonal patterns of waves and water 

 level where accretionary processes must also be modeled. 



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