Applications in Peace anil War 



15 



locality by jetting clown to the underlying 

 rocks. 



Of more basic importance to the oil in- 

 dustry is an understanding of the mechan- 

 ism of formation and accumulation of 

 petroleum in marine sedimentary rocks. 

 Almost every type of environment in which 

 oil-bearing sedimentary rocks were laid 

 down in past geologic ages now exists be- 

 neath the ocean. By studying detailed 

 characteristics of the sediments being de- 

 posited in these environments the subma- 

 rine geologist can greatly aid in the search 

 for new oil pools. Much oil, for example, 

 occurs in ancient coral or shell reefs. By ob- 

 serving the ways in which reefs of the pres- 

 ent day vary in character laterally and verti- 

 cally it becomes easier to predict from well 

 logs and geophysical data the character of 

 the rocks concealed far below the surface 

 and the directions in which drilling should 

 be extended. In addition, much oil occurs 

 in "traps" formed by impervious sediments 

 on the sea floor as controlled by depth of 

 water, distance from shore, and waves and 

 currents. 



BEACH EROSION AND CONTROL 



It is estimated that a strip of land averag- 

 ing one foot in width over the entire 52,000 

 miles of shore line of the United States, or 

 approximately 6,400 acres or 10 square 

 miles, is annually lost by beach erosion. 

 In some regions, such as in the Chesapeake 

 Bay area, the unprotected shores of devel- 

 oped and agricultural lands are cut back 

 as much as fifteen feet or more per year. 

 By conservative estimates, shore erosion 

 and control costs the people of the United 

 States about 100 million dollars annually. 

 The State of New Jersey alone has spent 

 a million dollars a year for the past twenty 

 years to protect its beaches. This is a small 

 part of the total value of the shore front 

 property. At Atlantic City, which is largely 

 dependent on the maintenance of some 

 10,000 feet of beach, the shore front prop- 

 erty is valued at about 200 million dollars. 

 There are three major types of shore 

 control problems. The first concerns sta- 

 bilization and rehabilitation of developed 



beach areas by building protective struc- 

 tures to resist the attack of the sea, and 

 to regain at least a part of the shore already 

 lost. In many areas, highways, homes, hotels 

 and business establishments have been lo- 

 cated immediately adjacent to the beach 

 with little allowance for encroachment by 

 the sea. With the passage of time normal 

 beach erosion occurs and the structures are 

 endangered or damaged. 



Another type of problem results from 

 dredging deep navigation channels into 

 rivers or harbors. A natural inlet channel 

 has a depth in equilibrium with the rate 

 of material transport along shore and with 

 the tidal flow characteristics of the inlet. 

 This equilibrium is destroyed by deepening 

 the channel and the natural forces tend to 

 re-establish the equilibrium by filling the 

 dredged area. If jetties are built to prevent 

 refilling of the dredged channel the natural 

 movement of material along shore will be 

 stopped and the down-drift beaches will 

 rapidly become eroded. 



A third type of problem arises when 

 breakwaters are built to construct or im- 

 prove harbors which impede the natural 

 long-shore movement of beach materials. 

 This often results in starvation of the down- 

 drift shore and in excessive accretion of 

 materials on the up-drift side of the harbor 

 mouth. The latter may shoal the harbor 

 mouth itself unless provision is made to 

 maintain or re-establish the movement of 

 materials around the harbor entrance. 



To solve shore control problems one must 

 know the sources and rates of supply and 

 removal of sedimentary materials and 

 understand the processes which cause ero- 

 sion and transportation. Materials will be 

 brought into and out of the area by long- 

 shore drift and by motion between the 

 beach and the adjacent sea bottom. Rivers 

 and streams may carry material into the 

 area and the wave erosion of sea cliffs back 

 of the beach also furnishes material to the 

 beach. Wind action often removes materials 

 to form barren dune areas inland from the 

 shore. 



Waves are the principal source of energy 

 changing the shoreline. Waves produce a 



