CORRELATION OF SHORELINE TYPE WITH OFFSHORE 

 CONDITIONS IN THE GULF OF MEXICO 



W. Armstrong Price 

 Agricultural and Mechanical College of Texas 



Contract N7onr-48706 

 Task NR 388-009 



The project on which I have been working is an attempt to correlate shoreline type with 

 offshore conditions. It has been limited to the Gulf of Mexico where there is a broad or fairly 

 broad continental shelf. So far I have been working necessarily on the basic science phase of 

 the problem. Next will come the applied phase which has special interest for the Navy. The 

 objective of that phase is to find some of the index conditions in the offshore area, which would 

 indicate the type of shoreline that you would expect if you landed on a little-known coast, and 

 vice-versa : knowing something about the shoreline, you could predict what you would encounter 

 off shore. This applied phase can be started now because much of the basic information which 

 I needed has just arrived. 



The shoreline is the place where land and ocean meet. Under peacetime conditions, the 

 geography and physiography of the land are easily determinable. For our project we should 

 find out what the ocean has done in modifying the land surface, or in controlling any extensions 

 of the land which are taking place contemporaneously, such as deltaic growth. That is a tradi- 

 tional, well-known situation with geologists and geomorphologists. 



My previous experience was in the study of the deltaic Pleistocene coastal plains of the 

 Gulf of Mexico, trying to learn their nature— that is, what were the characteristics easily de- 

 terminable from the surface so as to find out the normal, and then discover the abnormal on a 

 small scale, for example, surface anomalies of the oil-field structure type and size. For in- 

 stance, the deltaic plains have characteristic slopes depending on such factors as the energy of 

 the streams that deposited them, the coarseness of grain and volume of the sediment, and the 

 slope of the land. We have found that each of the five successive deltaic plains of the Gulf 

 coast has its own slope and own topographic characteristics. After determining the normal 

 characteristics of the plains, the objective was to find the abnormalities caused by structural 

 uplift. These appear as domes, up-warped ridges, and scarps. 



In coming to this project of the offshore area, I thought that we might find some such 

 basic control. Adopting the viewpoint of the oceanographer, a strictly geophysical one, my ap- 

 proach was to determine the wave-energy relationships on the continental shelf, get actual 

 figures on the energy, and determine spectra of wave energy across the shelf; that is: (a) the 

 total energy of the deep water wave as it approaches the edge of the continental shelf, and (b) 

 the degree to which that energy is dissipated as it crosses the shelf. With this done, we might 

 find out what the residual energy does to the shoreline. In other words, would it be possible 

 some day to set up a classification of shorelines and shelf zones based on the amount of energy 

 used in developing them? Of course there would be many other factors to consider besides 

 those mentioned, and we would find many varieties and sub-varieties of coasts, but might there 

 not be a basic relationship between the amount of energy and the type of shoreline ? 



At first I used relative energy values, as it took considerable time to find the right peo- 

 ple to make the numerical energy computation on a regional basis. The usual approach of the 

 oceanographer is extremely time-consuming and expensive— to determine in detail the amounts 

 of energy that are going to be thrown against a single structure built at the shoreline. There- 

 fore, we had to find a method of determining the energy from a regional standpoint. 



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