adjacent project shorelines. This study was conducted to provide a 

 detailed survey (using seismic reflection data and long cores) of the 

 shelf off Galveston County and Surfside Beach to determine the location, 

 character, and volume of sand having potential value as fill for nourish- 

 ment of eroding beaches. 



Scope . 



The study area (Fig. 3) covers about 850 square kilometers (330 square 

 miles) of the Gulf of Mexico from High Island (94°20'W., 29°30'N.) west 

 about 85 kilometers (55 miles) to Freeport (95°20'W., 28°55'N.), and 

 centered about Galveston, Texas. It includes parts of the Texas Inner 

 Continental Shelf off Bolivar Peninsula, Galveston Island, Follets Island, 

 and Surfside Beach. The area of data collection extends seaward a maxi- 

 mum of about 8 kilometers (5 miles) from the shoreface (water depths from 

 about 3 to 15.5 meters or 10 to 50 feet). Data collected consist of about 

 435 kilometers (270 miles) of seismic reflection profiles and 34 cores 

 ranging in length from 2.2 to 6.1 meters (7.3 to 20 feet). The mean core 

 length is 4.9 meters (16 feet). These data were supplemented by logs of 

 engineering borings taken along the Freeport and Galveston jetties and 

 across San Luis Inlet. Additional information on the subbottom geology 

 was also derived from several hundred trackline kilometers of seismic 

 records taken along shore-normal transects as part of a joint U.S. Geolog- 

 ical Survey (USGS) and the University of Texas, Bureau of Economic Geology 

 (TBEG) program. Also, a TBEG map showing surficial sediment distributions 

 based on several hundred grab samples was used. Pertinent scientific and 

 technical literature and hydrographic maps were also used. Especially 

 informative were the TBEG environmental atlases by Fisher, et al . (1972, 

 1973) and McGowen, et al . (1976). 



II. BACKGROUND 



1 . Equipment and Field and Laboratory Procedures . 



a. Geographic Positioning System . An electronic positioning system, 

 the Motorola Mini -Ranger III, was used to accurately determine position 

 of the research survey vessels during both phase I of seismic surveying 

 and phase II of taking cores. The system determines the position of the 

 survey vessel with respect to two known reference points on shore and is 

 restricted to line-of -sight operation. The stated accuracy is ±3 meters. 

 The basic system consists of a master mobile unit mounted on board the 

 vessel and two shore-based transponders. The master unit interrogates 

 each transponder separately and the elapsed time between the transmitted 

 pulse and the transponder reply pulse is converted to a measurement of 

 distance. Each distance (range) from the two transponders at the known 

 shore stations is displayed, in turn, on the range console. This range 

 information, together with the known locations of the shore stations, is 

 then trilaterated and plotted on hydrographic charts to obtain the posi- 

 tion (fix) of the survey vessel. Navigational fixes during the seismic 

 survey were obtained about every 2 to 4 minutes and each fix was keyed 

 to the seismic records by an event mark on the records. 



