slope -dependent term in the transport rate equation in the present model 

 increases the transport rate on positive slopes. By calculating the wave 

 height distribution in the surf zone with a wave decay model, a more realistic 

 description of surf zone wave properties is obtained. Such calculation also 

 produces a difference in values of the optimum transport rate coefficient. 



Comparisons of model simulations 



510. A hypothetical beach profile with a dune having a slope of 1:4, no 

 distinct berm, and a foreshore slope of 1:15 to 0.6-m depth was used in the 

 model comparison. Seaward of 0.6 m, an equilibrium profile shape according to 

 Bruun (1954) and Dean (1977) (Equation 1) was used, where the shape parameter 

 A was determined from the design curve of Moore (1982) corresponding to a 

 median grain size of 0.25 mm. Water level was varied sinusoidally to go 

 through a maximum in a manner similar to a storm hydrograph and with a half- 

 period of 24 hr, and wave conditions were held constant with a wave height of 

 3 m and period of 10 sec. (see Figure 86 for an example surge hydrograph.) 

 Figure 82a shows that both numerical models produced similar amounts of 

 erosion. Figure 82b gives a detailed view of the dune and foreshore. 



511. The main difference between model results for this particular case 

 is the area over which material was deposited. The Kriebel model distributed 

 eroded material approximately evenly over the beach profile, whereas the 

 present model tended to deposit sand closer to the toe of the dune. Experi- 

 ments performed by Vellinga (1982) with a large wave tank showed time evolu- 

 tion of the profile qualitatively in agreement with the present model, but for 

 a shorter surge hydrograph. 



512. The dune face of the eroded profile was steeper for the present 

 model, whereas the Kriebel model produced direct translation of the initial 

 profile. Only a low-relief bar feature developed at the seaward end of the 

 profile in the present model because of the varying water level , which caused 

 the break point to move first shoreward and then seaward as the surge rose 

 then receded. Since the break point was not stationary, movement of the 

 transport rate maximum did not give the bar sufficient time to evolve . 



513. Wave period does not directly enter in the Kriebel model, but it 

 is of importance for the shoaling, breaking, and runup of waves in the present 

 model. Therefore, wave period was changed in the test case to 14 sec to 



216 



