not been confirmed. The model, as scaled, cannot correctly simulate this type of geotechnical failure, if 

 indeed this was the cause of the prototype profile shape after 40 waves. 



97. An RMS variation between profiles was calculated for the vertical variations between prototype 

 and model using the formulation: 



RMSVariation= a/-^(/ip-/i„)^ (13) 



where hp and hm are the prototype and model profile elevations at equivalent horizontal positions. The 

 RMS variation for the comparison after 40 waves was 0.70 m, which impUes a reproduction accuracy of 

 ±0.35 m. 



98. The profile comparison after 370 waves (Figure 10) is somewhat better, having an RMS variation 

 of 0.49 m. The berm in the model was not eroded as much as in the prototype, and not as much sediment 

 was moved to the region seaward of the breakpoint bar. The profile comparison in the surf zone and in the 

 vicinity of the bar is quite good. 



99. The center-line profile after 1,650 waves (Figure 10) represents the equilibrium condition for this 

 test. The RMS variation for the 1,650 wave comparison was 0.44 m when the model center-line profile was 

 used. This RMS variation was slightly reduced to 0.40 m when the average profile (Figure 9) was used in 

 the comparison. The model did not succeed in eroding the final portion of the berm on the upper portion 

 of the revetment. There are two possible explanations for this. First, the concrete revetment in the model 

 had a rough finish that, when scaled to prototype, would be much rougher than the concrete revetment 

 used in the prototype tests. This may have limited the extent of wave runup in the model due to frictional 

 effects. Wave runup may also have been influenced by the difference between prototype and model in the 

 off'shore portion of the profile which could have affected wave characteristics. 



100. Another difference between model and prototype is that the model did not succeed in moving 

 enough sediment to seaward of the breakpoint bar, and consequently the scouring in the surf zone was not 

 as severe as evidenced in the prototype. 



101. The observed difference between prototype and model in the region offshore of the bar is most 

 likely a result of the scaling relationship selected. This scaling relationship works best for regions 

 dominated by turbulence-induced sediment transport. Because the model sand grains are not scaled 

 according to the geometric length scale, they undergo a transition from suspended mode to bed-load mode 

 of transport before this transition occurs in the equivalent prototype flow regime. With the selected scaling 

 criteria, the bed-load mode of transport is not properly scaled in the model; consequently the model sand 

 grains are at rest under scaled conditions that still result in offshore sediment transport in the prototype. 

 This concept is further examined in the next subsection. 



102. The observed difference between prototype and model in the surf zone may be related to the 

 aforementioned differences in the offshore portion of the profile. If the offshore bar has a sediment storage 

 capacity under a given wave condition, and sediment to meet this capacity must come primarily from the 



41 



