Several methods have been used to study sand movements. Fluorescent dyes 

 tagged onto sand grains have been used extensively, and most of the infor- 

 mation concerning sediment transport has been obtained with this method. 

 There are, however, fundamental difficulties that limit the utility of 

 fluorescent tags in obtaining meaningful data from dynamic systems such 

 as the ocean. Perhaps the most serious are the limited number of samples 

 that can be obtained after injection of the tagged sand and the inability 

 to 'predict sampling points. 



Naturally occurring minerals have been utilized as indicators of sand 

 transport; however, unless the source of the mineral is well defined and 

 known to be the exclusive source, the data obtained are often misleading. 

 With radioisotope tracers, which have been used to a lesser extent, use- 

 ful studies of sand transport have been made in laboratory flumes and 

 wave basins, but definitive information can come only from field tests 

 (See Addendum C-l) 



Field testing is divided into three major efforts: preparing and dispen- 

 sing the tracer in a test area, which are discussed elsewhere, surveying 

 the test area, and treating the data. Both radioactive and fluorescent 

 tracing systems have common problems relative to data treatment. Radio- 

 isotope tracing does, however, offer considerable advantage over the 

 fluorescent tracing during sampling since in situ measurements are made 

 and a large number of data points can be obtained. In addition, readout 

 data are available to assist in the determination of sample points, and 

 thus one is able to follow the progress of the transport system on a real- 

 time basis. A number of radionuclides were considered for use in sedi- 

 ment transport studies, and the half -life, energy of the radiation, bio- 

 logical hazard, and tagging method specific to various elements were 

 evaluated. While no single radionuclide was found to meet all the re- 

 quirements that would make it ideal for all tracing experiments, primary 

 consideration was given to those radioisotopes that have a low biological 

 hazard. This characteristic was especially important during the early 

 phases of the field testing when data could be collected -to serve as a 

 basis for determining the concentration or dilution of tagged sand that 

 may occur during tracing studies. Also, radiation exposure to be ex- 

 pected could be determined. Such data could then be used to determine 

 hazards associated with the use of other radionuclides in tagging sediment. 



After tagged sand has been placed in the ocean, as a point source or as a 

 line source, surveys are made to determine transport. This is done either 

 by collecting grab samples and taking them to a laboratory for counting or 

 by making the measurements on the ocean floor. Since the in situ measure- 

 ment yields data rapidly, it was considered to be the more promising method 

 for gathering information for littoral transport studies. 



Selecting the Radioisotope 



Some of the nuclear properties considered in selecting the radioisotope for 

 further evaluation were half -life, type of radiation, and radiation energy. 



C-4 



