PART IX: SUMMARY AND CONCLUSIONS 



160. Borrow source exploration in a subaqueous environment requires 

 consideration of a number of geological factors. The most important of these 

 are historical geology, geomorphology , stratigraphy, and lithology. A sub- 

 stantial part of the data needed to assess these factors must, in most cases, 

 be obtained by a field collection effort. 



161. Certain geomorphic features of marginal marine and inner continen- 

 tal shelf environments have been found to contain sand- size sediment poten- 

 tially usable for beach fill. These features are barrier island inlet shoals, 

 linear shoals, cape- and estuary-associated arcuate shoals, relict fluvial 

 channels, and shoal retreat massifs. 



162. Field exploration for borrow sites involves geophysical and 

 sediment-sampling operations. The geophysical operations make use of Fathom- 

 eters, side-scan sonar, and seismic reflection profilers. Sediment samples 

 are obtained with grab or dredge samplers for surficial sediments and vibra- 

 tory corers for sub-bottom sampling. 



163. Existing geophysical methods and equipment are adequate for borrow 

 source exploration; however, improvements are needed to increase economy, 

 flexibility, noise suppression, and range of available equipment. Methods and 

 equipment for obtaining sub -bottom sediment samples are adequate but highly 

 expensive. Improvements in economy, and greater reliability of penetration 

 achievement, are ongoing research and development goals. 



164. Procedures for designing borrow source exploration programs are 

 based on past experience in design and conduct of exploration programs. The 

 main elements of the design are initial layout of trackline patterns, core 

 site selection, selection of personnel and equipment, schedules, and cost 

 estimates . The program should be flexible and amenable to changes made in the 

 field based on review of the data as it becomes available. 



66 



