PART IV: DATA ANALYSIS AND DISCUSSION 



69. Reproductions of composite shoreline movement maps are enclosed 

 separately. These maps are useful in a qualitative way; i.e., they provide an 

 easy means of observing the changes that have occurred in the past. Because 

 of slight variations in shoreline position created in the printing process, 

 however, they should not be digitized for quantitative use in coastal manage- 

 ment, engineering, or research. To enable the data these maps represent to 



be so used, the following paragraphs describe the techniques used in this 

 study to quantify shoreline change. 



70. An analysis routine was used to average shoreline change parameters 

 for specified longshore distances. Because geographic point analyses were 

 based on latitude and longitude, a reasonable distance to use was one keyed to 

 those measures. Based on shore orientation, a 1-minute-latitude (about 2 km) 

 or -longitude (about 1.5 km) distance was selected to average long-term shore- 

 line changes. It deserves mention that the shoreline change rate given is 

 the average for the entire shoreline within the 1-minute coastal reach, not 

 the rate at particular sites 1 minute apart. The distinction is an important 

 one because measurements made at a constant alongshore interval seem to be 

 subject to a bias depending upon the particular interval chosen (Hayden et al. 

 1979). 



Analysis Methodology 



71. Shoreline change rates resulting from the following analyses, 

 although averages in space, are based on particular points in time. Nothing 

 is included that identifies what happened to the shoreline in the interval 

 between shoreline surveys; the analyses simply distribute the change uniformly 

 over the separating time increment. The rates given in this report are the 

 shore-normal rates of movement averaged for a fixed shore-length increment; 

 they were obtained using changes in plan area between successive latitude or 

 longitude boundaries 1 minute apart. For each survey set from time t a plan 

 area A(t) was specified using fixed latitude and longitude boundaries (three 

 of the boundaries used) and the shoreline (the fourth boundary) (Figure 27). 

 The latitude and longitude boundaries were invariant in time; only the shore- 

 line boundary changed. That change in shoreline position between surveys 



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