Accretion/Erosion Prediction 



Ho/Lo 



1.0000^ 



0.1000= = 



0.0100 



0.0010 



0.0001 



Hq/wT 



10.0 



Figure 10. Classification of erosion and accretion events in the 



field using deepwater wave steepness and dimensionless fall 



speed, with wave height taken as mean wave height 



within the context of the other plotted points. For example, day 1 of the 

 Santa Barbara data described what would be considered as recovery waves with 

 Hgo = 0.21 m and Tp = 18 sec, yet the profile eroded. This point plotted at 

 the bottom left side of Figure 10, far from other erosional events. Several 

 mild accretionary events from the Scripps Beach data set plot on or near the 

 erosion side of the separation line, suggesting that factors other than direct 

 wave action contributed to produce the profile change and that the profile 

 change may have been mixed. Kriebel , Dally, and Dean (1987) used a finite- 

 width band rather than a single separation line to denote possible areas of 

 mixed or ambiguous transport. In general, however, it is judged that the 

 criterion given by Equation 2 is applicable to distinguish erosion and accre- 

 tion events in nature for the more extreme events. Since engineering applica- 

 tions involving cross -shore sand transport, such as beach fill design, 

 must consider extreme and not weak or mixed events. Figure 10 appears to be 

 suitable as a first-order estimator for such purposes. 



74 



