evaluate its effect on the simulation. The result with the present model was 

 formation of a gently sloping, wide bar of low height; the amount of dune 

 erosion was approximately the same for both models. 



514. To illustrate the difference between model predictions, another 

 example was simulated in which the water level variation was contrived to 

 promote bar formation. The same initial beach profile and wave conditions 

 were used as in the previous case, but the water level variation consisted of 

 an instantaneous rise of 2 m (surge) at the start of the simulation. The 

 simulation period was 48 hr , and the result is displayed in Figure 83(a and 

 b) . A distinct bar was developed by the present model, reducing the incident 

 wave energy at the dune and thus reducing the amount of dune erosion compared 

 with the Kriebel model. The shoreward slope of the bar is quite steep due to 

 constancy of the incident wave conditions. 



515. Summary . In general, the two models produce similar dune erosion 

 if wave and water level conditions are such that bar development is limited. 

 However, if conditions allow a bar to form, the present model will predict a 

 smaller amount of nearshore erosion than the Kriebel model. The beach profile 

 shape seaward of the dune toe is probably more realistically described in the 

 present model where the area of material deposition is more concentrated, 

 implying a narrower surf zone as the water level increases. 



Simulation of Beach Profile Accretion 



Background and review 



515. Most development work with the numerical model was focused on 

 simulating beach profile response to erosional waves and water levels, since 

 prediction of erosion is of immediate engineering importance. Although berm 

 construction was discussed in the data analysis and geometric properties of 

 the berm quantified, initial model development was not primarily directed 

 toward simulating accretionary stages of a beach. Transport rates from the 

 LWT experiments that resulted in berm buildup were determined from profile 

 surveys, together with some associated characteristics of the transport rate 

 distribution. However, due to lack of suitable test cases having sufficient 

 information of the wave height distribution across the shore, it was not 



218 



