numerical models proposed prior to the present work, that of Kriebel (1982) 

 (see also Kriebel and Dean 1985a, Kriebel 1986) comes closest to satisfying 

 the five criteria listed above. The Kriebel model was critically evaluated 

 and determined to be the best available tool for estimating erosion on U.S. 

 coasts (Birkemeier et al . 1987). The Kriebel model satisfies criteria a. and 

 b. , and, in part e. , but not criteria c. and d. The model was originally 

 developed and verified using cases from the CE data set, as well as an 

 erosional event associated with Hurricane Elena, and has since been used in 

 engineering studies (Kriebel and Dean 1985b, Kraus et al . 1988). Development 

 of the present model was stimulated by the success of the Kriebel model. 



385. In the following, a short overview of the structure of the 

 numerical model is given as an introduction before its various components are 

 discussed in detail. Changes in the shape of the beach profile are assumed to 

 be produced by breaking waves; therefore, the cross -shore transport rate is 

 determined from local wave, water level, and beach profile properties. The 

 equation expressing conservation of beach material is solved to compute 

 profile change as a function of time. 



386. The wave height distribution is calculated across the shore by 

 applying small -amplitude wave theory up to the point of breaking, and then the 

 breaker decay model of Dally (1980) is used to provide the wave height in 

 regions of breaking waves. The profile is divided into specific regions 

 according to the wave characteristics at the given time -step for specification 

 of transport properties. The distribution of the cross -shore transport rate 

 is then calculated from semi-empirical relationships valid in different 

 regions of transport. At the shoreward end of the profile, the runup limit 

 constitutes a boundary across which no material is transported, whereas the 

 seaward boundary is determined by the depth at which no significant sediment 

 motion occurs. Once the distribution of the transport rate is known, profile 

 change is calculated from the mass conservation equation. The described 

 procedure is carried out at every time-step in a finite-difference solution 

 scheme using the current incident wave conditions and water level, and 

 updating the beach profile shape. 



387. First, the wave model is described and calculations compared with 

 measurements from the CRIEPI data set. Then the various transport relations 



157 



