collected. Near the reef lines and at depths not reached by the cores 

 under the gray sand blanket, the sand may be similar to the calcareous 

 sand of Section A. 



4. Suitability 



Corps of Engineers studies for Palm Beach, Broward, and Dade 

 Counties indicate a possible requirement of some 6 million cubic yards 

 of sand over a SO-year period; more than enough sand to meet these needs 

 exists in the study area. Indeed, enough sand-size material exists off- 

 shore in just the Miami grid to meet initial requirements (21.5 million) 

 and some years of annual nourishment . 



Sand comprising the beaches of Dade and Broward Counties has a high 

 carbonate content, but the aspect of the carbonate fraction existing 

 offshore in the Miami grid is different (see Figures 20 and 21). Shell 

 debris on the beaches is somewhat larger and much less delicate than the 

 shell occurring in the potential offshore borrow zones. This is due to 

 the difference in the type of organism contributing to the shell. Off- 

 shore the shell debris is from algae and foraminifers indigenous to the 

 quieter offshore zones, while onshore it comes from mollusks indigenous 

 to the high energy littoral zone (Figure 19) . Although median diameters 

 of beach and offshore sediment are not too dissimilar (Figure 17), the 

 compositional differences indicate there is some question if the offshore 

 sand-size material would maintain its integrity once placed on the beach; 

 that is, it might disintegrate under surf action. Therefore, while ample 

 material exists off Miami, the degree of its suitability can be determined 

 only through further study. 



Sediment comprising the shoreface terraces and the bottom offshore 

 in Section B are compositionally more suitable for beach fill but the 

 size characteristics (small median diameter) make the sediment not wholly 

 satisfactory for long-term projects. 



Section IV. SUMMARY AND CONCLUSIONS 



The southeastern coast of Florida between Cape Florida and Lake Park 

 is bordered by a narrow, shallow submarine shelf which is characterized 

 by two distinct morphological and sedimentary aspects, one dominant in 

 the north and the other dominant in the south. 



As part of a larger study, a subbottom exploration program covering 

 this 141 square mile shelf area was carried out by the -U. S. Army Corps 

 of Engineers in 1965. In this program 176 miles of continuous seismic 

 reflection profiles and 31 sediment cores were collected. 



The low coast bordering the southeastern Florida shelf is covered 

 by relatively thin sediment deposits consisting of late Pleistocene sands 

 and Holocene beach and dune sediments. Underlying these sediments are 



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