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SECT. 7. SHORELINE RESPONSE MODELING 



The shoreline response to sea level change can be investigated using 

 historical data. Historical U.S. shoreline changes have been compiled into 

 a computerized data base, the coastal erosion information system (CEIS) , 

 based upon measurements from old maps, charts, and aerial photographs, 

 covering at least a 40- to 50-year period (May et al., 1982, 1983). The 

 data have been averaged into 3' x 3' latitude -longitude grid cells. While 

 spatial coverage is fairly continuous over large areas, the shoreline 

 displacement history typically does not have more than 6 or 7 time 

 measurements. Rates of less than 0.6-1.0 m/yr (over a 25- to 40 -year 

 interval) lie within the uncertainty. Other problems with data quality 

 have been encountered. Therefore, it may be desirable to check the CEIS 

 data against independent measurements. Furthermore, the data show high 

 spatial variability. The United States is covered by 71 tide-gage stations 

 with records covering 20 years or longer, which have fairly continuous time 

 series but are spatially discontinuous. 



Initially, the records for each tide -gage station can be matched with 

 the corresponding CEIS cell that encloses it. In order to obtain more 

 extensive coverage, sea levels can be averaged over coastal segments 

 demonstrating a similar sea level behavior, or by linear interpolation 

 between stations. The CEIS data can be smoothed further by using 3- to 

 5 -cell running means. The optimum smoothing scale can be assessed by 

 sensitivity studies. The shoreline displacement can be divided into both 

 inundation and erosion components. The relative contribution of inundation 

 or erosion can be assessed at each tide station, or along coastal segments. 

 The observed average displacement rate can then be compared with those 

 predicted by various models , such as the Bruun rule , or a sediment budget 

 analysis, for historical rates of sea level rise. 



REFERENCES 



Aubrey, D.G. (1985). "Recent sea levels from tide gauges: Problems and 

 prognosis," in Glaciers, Ice Sheets, and Sea Level: Effect of a 

 CO2- induced climatic change, DOE/ER/60235-1, U.S. Department of 

 Energy, Washington, D.C. , 73-91. 



