is very fine grained and mixed with varying percentages of silt and clay 

 (Table 2; App. B) . The area is also overlain by about 12 centimeters 

 (5 inches) of mud which could be a detriment to dredging. Seismic records 

 in the area show several buried stream channels close to core 34; it is 

 likely that the sand in core 34 is part of one of these small channels or 

 alternately is part of the ancestral delta of the Brazos River which en- 

 tered the gulf near this location in the past. The estimated sand volume 

 in area E is 2.1 million cubic meters (2.7 million square yards), based 

 on a thickness of 2.5 meters (8.1 feet); however, deep dredging close to 

 the shore could aggrevate the already serious erosion problems at Surfside 

 Beach. 



IV. SUMMARY AND RECOMMENDATIONS 



The primary objective of this study was to determine the geologic 

 character of the Texas inner shelf in order to evaluate the potential of 

 sandy sediments suitable for nourishment of eroding beaches. Several hun- 

 dred kilometers of high-resolution seismic reflection profiles were taken 

 to identify the primary stratigraphic subbottom reflectors, buried stream 

 channels, bars, and delta shoals in the area. Long cores were taken in 

 34 of the most promising sites and the seismic records were used to extrap- 

 olate the core stratigraphy to adjacent areas of the shelf. The major 

 findings and recommendations are listed below. 



a. The Pleistocene erosion surface is generally <_ 3 meters below the 

 sea floor, except for buried ancestral river channels, and because it is 

 primarily composed of indurated clay, is considered the lower boundary 

 for dredging of sand for beach nourishment. 



b. None of the ancestral stream channels cut into Pleistocene sedi- 

 ments and filled with Holocene sediments contain high quality sand. How- 

 ever, a buried channel west of High Island contains muddy sand and is 

 considered of marginal quality as a borrow site. 



c. Five sites were selected as containing possible borrow material 

 but only two, one at Galveston and one at San Luis Pass, were judged to 

 be of high potential. The Galveston site consists of lower shoreface 

 sand and a relict ebb tidal deltal complex; the San Luis Pass site com- 

 prises the modem outer bar and ebb tidal shoal complex. None of the 

 sites contain any artifacts or structures of known archeological signifi- 

 cance, and none contain obstructions that would interfere with dredging, 

 except the gas line in area A. 



d. Prior to project dredging, it is recommended that cores be taken 

 in a dense grid matrix to provide more detailed information on the three- 

 dimensional framework of the borrow site, as well as give additional 

 textural data for proper design of the beach fill. 



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