and 



= 3 ac + b {3) 



where g is a computed quantity. The concavity parameter is obtained 

 from the figure in Appendix D or 



('-!) 



f = 2.8 i - ^ . (4) 



Points on the profiles in Figure 4 and in Appendix C are depth- 

 distance values obtained using equation (IJ. The values a, b, c, and d 

 are relatively easy to obtain from the profiles, and appear to provide 

 a first-order mathematical approximation of the profile when used in 

 equation (I). Table 1 presents the values of parameters used in equation 

 (L) for each of the 49 profiles (Fig. 1; App. C) . 



3 . L imit Depth of Shore-Parallel Contours . 



The seaward limit of shore-parallel contours, and the depth where the 

 rms values change significantly are shown in Table 2. The rms values 

 on the landward parts of the profiles averaged 0.6 to 1.0 meter (2 to 3 

 feet) on profiles along the Atlantic coast, and 0.2 to 0.3 meter (0.7 to 

 1.0 foot) along the Gulf of Mexico coast. The ratio of the rms values 

 of the near-coast profile segment to the rms values farther seaward are 

 given in the table. Figure 6 shows two representative rms depth curves 

 plotted against distance from shore. The curve on profile line 1 shows 

 a well-defined change in the rms depth values; the profile line 48 curve 

 suggests no obvious difference in rms along the profile (see bathymetry 

 in Figs. 2 and 3) . 



V. DISCUSSION 



Profile Characteristics . 



Steep and concave-up shoreface sectors, and gently dipping and planar 

 ramp sectors are ubiquitous off the mid and south Atlantic, and Gulf of 

 Mexico, barrier island coasts. Values of individual geometric slope 

 parameters in many instances tend to vary in a consistent manner in an 

 alongshore direction, or remain constant and exhibit little alongshore 

 variation over a long coastal reach (Table 1). The consistency of trend 

 between different parameters is not so obvious. This is especially true 

 for the properties of the shoreface and ramp which appear to be mostly 

 unrelated. 



a. Ramp Slope . The ramp slope, a (Table 1), in the direction 

 normal to shore, varies only slightly from the mean slope of 0.00041 

 along most of the Atlantic coast. However, as the Continental Shelf 



