100 



well-documented westward net transport at Fire Island (Dean, 1986; Williams 

 and Meisburger, 1987). 



Dean (1987) has suggested that during the more rapid rate of sea level 

 rise up to 6,000 year BP, the shoreward shelf transport was not sufficient 

 to maintain a stable shoreline. However, with the relative sudden sea 

 level rise reduction by an order of magnitude, the same rates of shoreward 

 sediment transport generally led to reduced erosion rates and in some cases 

 to stable or accreting shorelines; Fig. 7.6 illustrates the concept. The 

 equilibrium mechanics associated with this concept are much different than 

 those employed by Bruun. Recognized are the natural variability of waves 

 and sediment sizes with sorting resulting in coarser sediment close to 

 shore. It is hypothesized that a particle of a given size is in 

 equilibrium when it is in a certain water depth at a particular distance 

 from shore. With sea level rise and assuming that the wave climate remains 

 the same, the sediment particle would tend to move landward rather than 

 seaward as required by the Bruun Rule. Fig. 7.7 illustrates this mechanism 

 of sedimentary equilibrium. 



With greater and greater sea level rise, the general situation will 

 shift toward erosion. Of primary importance is that to predict the 

 response to sea level change, each shoreline segment must be considered on 

 a case-by-case basis with due consideration of the sediment budget. The 

 components of the sediment budget are difficult to quantify. The best 

 basis for developing an appropriate response model for a shoreline segment 

 is an analysis of past response, including a focus on possible 

 anthropogenic effects. 



In discussing shoreline response models to sea level change and their 

 development and calibration, it is important to recognize and respect the 

 amount of "noise" in the system including that introduced 

 anthropogenically. Coastal structures and sand management practices at 

 navigational channel entrances are undoubtedly the main contributors to 

 shoreline perturbation by humans. The special attention to dociamentation 

 following storm activity should also be noted. Along the east coast of 

 Florida, in excess of 38 million cubic meters of beach compatible material 

 has been dredged from channel entrances and disposed at sea. Based on the 

 Bruun Rule, this amount is enough to offset 70 years of shoreline retreat 



