sediment transport during a different season and under different oceano- 

 graphic climate. Long-range wave and weather forecasts indicated sea and 

 swell conditions of 6 to 8 feet 90 percent of the time. These waves are 

 within the operational range of the LARC XV amphibious vehicle. Based 

 on preliminary analysis of the earlier September-October data, two simul- 

 taneous line injections of gold-tagged sand were made along Range 158 in 

 depths of 6 to 14 feet mean lower low water and 21 to 27 feet mean lower 

 low water. Returning to shore after injection, the LARC XV developed 

 mechanical problems which could not be repaired at sea nor on the beach. 

 Tracing components had to be transferred to the backup LARC V. Sea and 

 breakers then rose to heights of 12 to 16 feet and stayed that high until 

 the field study was terminated several days later. These high waves pre- 

 vented safe operation of the backup vehicle in the sea, and tracing was 

 confined to the beach. Tracing data indicated the tagged sand did not 

 return to the beach. 



Static tests with the mobile detector were conducted to determine, 

 empirically, the ability of the system to detect burial based upon 

 attenuation of gamma photons emitted by the gold. Small quantities of 

 tagged sand were buried at 10-, 6-, and 3-inch depths and covered with 

 dead sand. The spectrum obtained, readout and photographed at the site, 

 is shown in Figure 24. 



Section IV. COMPARISON OF THE RIST SYSTEM WITH OTHER 

 ARTIFICIAL TRACING METHODS 



1 . General 



Discussions of sediment tracing experiments invariably generate 

 comparisons of particular programs, or comparisons between specific 

 aspects of particular programs. Kidson and Carr (1962) present an ex- 

 cellent summary of methods used in marking beach sediments for tracing 

 experiments. The purpose of this section is to relate the RIST study 

 to other sediment-transport studies, to review reported transport- study 

 methods, and briefly describe their procedures and scope. 



Artificial tracers may be grouped into two major categories: stable 

 and radioactive. In either case, the tracers represent particles that 

 are placed in an environment selected for study, and are used for rela- 

 tively short-term studies of sediment dispersion. Stable particles con- 

 sist of crushed colored glass, crushed bricks, and anything else that is 

 unlike the natural sediment. Naturally occurring sedimentary material, 

 painted or coated with a bright paint or fluorescent dye, has also been 

 used to study sediment transport (Ingle, 1966; Stuiver and Purpura, 

 1969) . Activity may be induced in radioactive tracers in a number of 

 ways. Labeling may involve neutron activation of an element in a mineral: 

 for example, phosphorus- 32 prepared by this method was used with limited 

 success on the California coast (Inman and Chamberlain, 1959) . Radio- 

 active material has been placed in holes drilled in a large pebble. It 

 has been incorporated in molten glass which, when hardened, is crushed 



36 



