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7. SHORELINE RESPONSE MODELING 



7 . 1 INTRODUCTION 



A potential dominant effect of relative sea level rise is shoreline 

 erosion. An erosional trend on a developed coastline always requires a 

 decision to: 1) retreat, 2) stabilize through coastal structures, or 3) 

 stabilize through nourishment. Each of the above can be costly; accepting 

 that under a given scenario of relative shoreline stability, sea level 

 rise, etc. there is an "optimal" choice, it follows that an inappropriate 

 choice could be inordinantly expensive. Given that eustatic sea level rise 

 affects shorelines on a global basis, that the human rate of shoreline 

 development is increasing and that some projections of future sea level 

 rise are much greater than in the past, it becomes important to attempt to 

 predict the shoreline response to such a rise. 



Shoreline response to sea level change depends not only on the rate of 

 change, but also on antecedent conditions and the degree and type of 

 disequilibrium of the shoref ace . The dominant engineering approach to 

 predicting shoreline response is the so-called "Bruun Rule" which considers 

 only cross-shore conditions and an offshore "closure depth" seaward of 

 which there is no sediment exchange. The Bruun Rule yields a simple 

 relationship resulting in horizontal shoreline retreat of approximately 

 50-100 times the rise of sea level. This chapter presents a more complete 

 consideration of the sediment budget on the shoreface and attempts to 

 remove some of the limitations of the Bruun Rule. Specific cross -shore 

 components not included by Bruun but which could be of significance are: 

 1) shoreward transport of sediment across the shoreface, 2) deposition of 

 suspended sediment, and 3) biogenic production of sediment. An important 

 factor relating to shoreward sediment transport is the history of sea level 

 change over the past -20,000 years, with the last 6,000 years or so 

 representing a relative still stand. 



7.2 LITERATURE REVIEW 



Prior to discussing the models for shoreline response, it is 

 instructive to review estimates of sea level rise over the last 



