GEOMETRY OF PROFILES ACROSS INNER CONTINENTAL SHELVES 

 OF THE ATLANTIC AND GULF COASTS OF THE UNITED STATES 



by 

 Craig H. Everts 



I. INTRODUCTION 



A bathymetric profile, when projected over the Inner Continental 

 Shelf along most coastlines, displays a characteristic shape. The 

 profile, which is the intersection of the shelf bottom with a vertical 

 plane, is typically steep and concave-up near the coast. Farther sea- 

 ward it is generally planar with a gradual slope away from the coast. 

 Price (1954) separated this distinctive shelf geometry in the Gulf of 

 Mexico into the near-coast shorefaae sector and the more seaward ramp 

 sector. 



The geometric nature of the Inner Continental Shelves along open 

 and straight parts of the middle and southern Atlantic coast, and the 

 Gulf of Mexico coast, is described and quantified in this report. 

 Forty-nine shore-normal bathymetric profiles, at about a 100-kilometer 

 (62.5 miles) spacing, are presented. Each profile represents an 

 average of nine profiles taken along 12 kilometers (7.6 miles) of 

 adjacent coast. The shoreface and ramp sectors are discussed separately 

 because geometric evidence suggests the possibility of a different 

 origin for the two sectors. A means to approximate the two-part Inner 

 Continental Shelf profile as a function of easily obtained profile 

 elements is developed, and procedures to select the seaward-limiting 

 depth of the shoreface are suggested and evaluated. 



II. BACKGROUND 



One means of describing the Inner Continental Shelf profile is to 

 consider the profile as a continuous element. Bruun (1954), for 

 example, used a single-power' function in a study of shelf profiles 

 along the Danish and California coasts. 



Hayden, et al. (1975) applied an eigenvector method of analysis to 

 identify the characteristic forms of profiles to a distance of 365 

 meters (1,200 feet) offshore. Resio, et al . (1974) also used an 

 eigenvector analysis to characterize bathymetric variability in profile 

 shape, but to a greater distance offshore along the Atlantic and gulf 

 coasts. Resio, et al . discussed the two-segment form of the profiles, 

 but chose to analyze them as continuous features. They noted that the 

 break in profile shape from curvilinear to linear occurred in water 

 depths of 9 to 25 meters (30 to 80 feet) and always within 14 kilometers 

 (8.7 miles) of the shoreline. They also reported that the profile 

 break may represent a transition from a wave-dominated bottom region 

 near the coast to an offshore region where the wave influence is less. 



