spacing. A l8ss detailed trackline configuration is the "open rectangle' 

 pattern sho'^Ti on the left side of Figure A-5. Spacing of parallel lines 

 nay be at 1, 2, or 3 miles. Either a single pattern is used or two 

 patterns are crossed to produce a grid as illustrated. Segments between 

 grids or open rectangle surveys are covered by "reconnaissance" lines 

 which are usually zigzag but may be altered to conform to shoreline and 

 inner shelf configuration. Reconnaissance lines are adequate for tracing 

 regional subbottom reflecting horizons between grids and for detecting 

 any large sedinient accumulations crossed. 



A few tentative core locations may be selected during the planning 

 stage, but rxist core sites are picked after the geophysical survey has 

 been run and the records examined. This allows for a better selection than 

 than one based on the generally meager information available during the 

 planning stage. 



If field survey work is to be let on contract, flexibility is gained 

 by splitting the work into a minimum number of survey miles and cores and 

 optional incremental work (Figure A-3) . At the- discretion of the Coastal 

 Engineering Research Center, the whole or any part of the optional work 

 may be subsequently ordered depending on the outcome of the minimum work. 

 The value of flexible planning was illustrated by a recent Sand Inventory 

 Survey in Long Island Sound. One grid area, near Bridgeport, Connecticut, 

 was selected primarily on the basis of a need for sand in that particular 

 place. After first survey results, it was apparent that prospects for 

 suitable sand were not good in the grid area. However, a nearby recon- 

 naissance line indicated considerable sediment accumulation, and a single 

 core on the line revealed several feet of sand. Optional survey miles and 

 cores were available, and a small grid was constructed around the spot with 

 favorable indications. It was thus possible to delineate a sand deposit 

 that could provide the material needed in the Bridgeport area. 



3. Sur'.'ey Operations 



Since most of the sand inventory work is within 10 miles of the 

 shore, the sur\,'ey vessel need not be large, and accurate continuous posi- 

 tion control poses no special technical problems. 



General practice in sand inventory surveys has been to run the 

 geophysical profiles for a limited area and then to study the records 

 before selecting core locations and prescribing optional work. Coring and 

 additional tracklines of geophysical data can then be completed, and the 

 vessel can go to work in the next area. This mode of operation permits 

 the contractor to shift his base along the coastline without being obliged 

 to return for cleanup work. 



To identify the uppermost strata revealed by sonic profiles, it is 

 necessary to obtain samples of the material. This is done by coring 

 through the overburden, or by surface sampling if the subbottom reflectors 

 can be traced to an exposure. On the average, in CERC surveys, one core 



A-8 



