serve as elemental conditions that can be combined in a time series of varying 

 conditions to approximately replicate natural conditions. 



Comparison with the Kriebel Model 



Overview 



507. Presently, there is only one other known numerical model available 

 to the engineering community that allows simulation of time -dependent changes 

 in beach profile produced by breaking waves, the model developed by Kriebel 

 (1982, 1986) and Kriebel and Dean (1985a). Simulations were performed with 

 the present model and the Kriebel model for hypothetical cases to evaluate 

 differences in calculated profile response. The Kriebel model does not 

 simulate bar formation and, a priori, is expected to produce more erosion than 

 the present model. Furthermore, the Kriebel model was developed to simulate 

 profile behavior during erosional conditions, particularly dune erosion, with 

 no capability for simulating berm buildup in its original formulation. 



508. Since the two models differ in structure and purpose and contain 

 different parameters, direct comparison using identical parameter values is 

 not possible. For example, in the present model wave height is calculated at 

 grid points across the shore, requiring specification of two empirical 

 parameters. In the Kriebel model, wave height is assumed to be related to 

 water depth in a fixed ratio. To facilitate comparison, parameter values were 

 used as given by calibration against the LWT data for the respective models. 

 Parameter values for the Kriebel model were taken from Case 300 which was used 

 for calibration (Kriebel 1986). 



Calibration 



509. Parameter values in the present model were identical to those 

 obtained from calibration against seven of the LWT cases. Even though the 

 transport relationships are similar in the two models, values of the transport 

 rate coefficient K resulting from the calibration were quite different (in 

 the present model, K=l . 6 10'^ m'/N; in the Kriebel model, K=8 . 7 10"^ mVw) . 



The transport rate coefficient is basically a calibration parameter deter- 

 mining the time scale of profile change, and its value is affected by the 

 amount of smoothing applied in the model. Also, incorporation of a bottom 



215 



