152 



Our understanding of processes at a particular site, post facto, has 

 improved vastly. However, prediction of future shorelines, in any given 

 situation, at best remains a hazardous guess except in a few well defined 

 situations. In many cases therefore, simple modeling based on inundation 

 and the Bruun Rule are used for predicting long-term trends (Kana et al., 

 1984) . The problem seems to lie with the fact that our ability to predict 

 sediment motion along the coastline under a changing wave climate on a 

 long-term basis remains rudimentary, and is in fact the subject of major 

 ongoing research effort in coastal engineering. It may take an additional 

 decade or two before confidence in long-term prediction reaches acceptable 

 levels . A part of the difficulty is not so much with relating hydrodynamic 

 forcing to sediment motion, as with synoptic data necessary to obtain 

 reliable (hindcast) hydrodynamic (currents, waves, winds) information. 

 Furthermore, structures interrupt sediment motion. Modeling of 

 sediment- structure interaction is still under research, although some 

 useful modeling work has been done in this context (Kraus , 1983). 



In the subject of estuarine mouth or inlet response to changing 

 oceanographic conditions, much more work has been done on sandy inlets than 

 on inlets where the material is fine-grained. In general, simplified 

 description of inlet response can be examined by considering inlet 

 hydraulics as characterized by the repletion coefficient concept (Keulegan, 

 1967) and inlet sedimentary response via O'Brien's (1969) equilibrium 

 relationship for inlet stability. 



The repletion coefficient, K, is defined as 



K = -^_ (ll|0)V2 

 ao^Ab ' F ' 



where A^, = inlet flow area, A^ = bay area, a = tidal frequency, aQ = tidal 

 amplitude in the sea, g = acceleration due to gravity and F = impedance. 

 F accounts for bottom resistance in the channel as well as head losses 

 associated with flow entrance and exit (Keulegan, 1967; Mehta and Ozsoy, 

 1978). Sea level rise will influence several terms, including A^, 

 (increase), A^ (increase, unless bay is bounded by vertical walls), a^ 



