Cable Attached 

 To Winch 



Figure 19. Front view of lightweight vibracorer mounted on a barge 



If it is necessary to obtain deep cores, or if there are cemented or very 

 hard sediments in the subsurface, rotary coring is necessary. Truck- or skid- 

 mounted drilling rigs can be conveniently used on beaches or on barges in 

 lagoons and shallow water. Offshore, rotary drilling becomes more complex 

 and expensive, usually requiring jack-up drilling barges or four-point anchored 

 drill ships (Figure 20). An experienced drilling crew can sample 100 m of the 

 subsurface in about 24 hr. Information on drilling and sampling practice is 

 presented in HQUSACE (1972) and Hunt (1984). 



Sediment Movement and Surface Forms 



Of great importance in investigations of geologic history is tracing sedi- 

 ment movement. This includes identifying the locations of sediment sources 

 and sinks, quantifying sediment transport rates, and discovering the pathways. 

 Sediment transportation is influenced by grain properties such as size, shape, 

 and density, with grain size being most important. Differential transport of 



46 



Chapter 3 Field Data Collection and Observation 



