95 



the measured. As expected, considering smaller groups of profiles, the 

 errors were larger. 



Hands (1983) has evaluated the Bruun Rule employing a series of 

 25 profiles along 50 km of the Lake Michigan eastern shore over a 7 -year 

 period. During this period, the water level rose by 0.51 m and then fell 

 by 0.31 m. Fig. 7.4 from Hands shows that the shoreline responded to the 

 changes in water level, although with a lag. Hands recommends that in the 

 absence of other information the "depth of limiting motion" be taken as 

 twice the significant wave height. 



Everts (1985) presented a sediment budget approach which encompassed 

 and extended beyond the Bruun Rule. The method was applied to Smith 

 Island, Virginia, and a 75 km segment of the Outer Banks of North Carolina 

 to determine the portion of the shoreline retreat explainable by sea level 

 rise. It was found that 55% and 88% of the measured shoreline retreat was 

 attributable to sea level rise at Smith Island and the Outer Banks, 

 respectively. The remaining component was interpreted to be due to 

 gradients in longshore sediment transport. The sediment budget approach 

 applied by Everts recognizes the limitations of the Bruun Rule and the need 

 to consider a more complete framework for representing and interpreting 

 shoreline response to sea level rise. 



Dean and Maurmeyer (1983) have generalized the Bruun Rule to barrier 

 island systems that retreat as a unit filling in on the bay side to 

 maintain their width as they erode on the ocean side. Employing the 

 notation of Fig. 7.5, the shoreline recession, R, due to a sea level rise, 

 S, is 



(L + W + L ) 

 R = S —^ , — (7.4) 



\ -^ 



\ 



It is clear from Eq . 7.4 that the recession will always predict a greater 

 erosion than the Bruun Rule because: 1) a greater horizontal dimension is 

 being elevated with sea level rise (the entire active barrier island 



