80. If Equation 10 is inserted into Equation 12, one term results with 

 an exponent of the depth h as -1/2. This quantity is singular at the 

 shoreline where h = 0. Therefore, in practice, the equilibrium profile- 

 based portion of the model is terminated at some finite water depth and 

 connected to another model which operates landward of the connection point. 

 The Kriebel model uses simple geometrical and volume conserving procedures in 

 this landward section. In particular, a linear beach face slope is smoothly 

 connected with the equilibrium profile at the depth where the beach face 

 slope equals the slope of the equilibrium profile for the given water level 

 conditions. In the version of the model evaluated in Part V (Kriebel 

 1984a, b), two options are permitted for simulating dune erosion: one allows 

 representation of a wide, flat berm and the other a sloping beach that 

 directly connects to a dune. Kriebel (1986) includes a more realistic wave 

 runup limit, the formation of an erosional scarp, and a more realistic, 

 nearly vertical eroded dune face. 



Properties of the Kriebel model 



81. The Kriebel model satisfies a number of the criteria developed in 

 Part III for judging the quality of a dune erosion model. A critical 

 discussion will now be given based on general properties of the model. 



a_. Wave height and period do not explicitly appear in the model. 

 The wave height is used only in the determination of the wave 

 breaking point, hence the width of the surf zone. These 

 important parameters effectively disappear because of the 

 basic assumptions of the model, i.e., equilibrium profile, 

 shallow-water approximations to small amplitude wave theory, 

 and the spilling wave breaker assumption. Since wave 

 steepness or another criterion is not used to specify whether 

 erosion or accretion will occur, the model may predict erosion 

 when actually accretion or recovery would occur for the given 

 wave and beach conditions. 



b. The model requires specification of the water level through 

 time which it uses in a time-stepping manner. Both storm 

 duration and water level enter through the characteristics of 

 the hydrograph. 



c_. The model accounts for grain size or fall velocity through the 

 scale parameter A. Values of A were determined empirically 

 and thus can be used with relative confidence. 



d_. The initial profile is not required, although it can be used 

 if available. This is both a potential advantage and 

 disadvantage. On the one hand, an initial profile will 



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