sediment movement and the origins of sediment deposits by the use of tracer 

 materials which move with the sediment. Fluorescent tracers vere used to 

 study sand migration in and around South Lake Worth Inlet, Florida (Stuiver 

 and Purpura, 1968). Radioactive sediment tracer tests were conducted to 

 determine whether potential shoaling material passes through or around the 

 north and south jetties of Galveston Harbor (Ingram, Cummins, and Simmons, 

 1965). 



Tracers are particles which react to fluid forces in the same manner as 

 particles in the sediment whose motion is being traced, yet which are 

 physically identifiable when mixed with this sediment. Ideally, tracers must 

 have the same size distribution, density, shape, surface chemistry, and 

 strength as the surrounding sediment; in addition they must have a physical 

 property that easily distinguishes them from their neighbors. 



Three physical properties have been used to distinguish tracers: 

 radioactivity, color, and composition. Tracers may be either naturally 

 present or introduced by man. There is considerable literature on recent 

 investigations using or evaluating tracers, including reviews and bibliography 

 (Duane and Judge, 1969; Bruun, 1966; Galvin, 1964a; Huston, 1963), models of 

 tracer motion (James, 1970; Galvin, 1964b; Hubbell and Sayre, 1965; and Duane, 

 1970b), and use in engineering problems (Hart, 1969; Cherry, 1965; Cummins, 

 1964; and Duane, 1970b). 



(1) Natural Tracers . Natural tracers are used primarily for 

 background information about sediment origin and transport directions; i.e., 

 for studies which involve an understanding of sediment patterns over a long 

 period of time. 



Studies using stable, nonradioactive natural tracers may be based on the 

 presence or absence of a unique mineral species, the relative abundance of a 

 particular group of minerals within a series of samples, or the relative 

 abundance and ratios of many mineral types in a series of samples. Although 

 the last technique is the most complex, it is often used because of the large 

 variety of mineral types normally present in sediments and the usual absence 

 of singularly unique grains. The most suitable natural tracers are grains of 

 a specific rock type originating from a localized specific area. 



Occasionally, characteristics other than mineralogy are useful for 

 deducing source and movement patterns. Krinsley et al., (1964) developed a 

 technique for the study of surface textures of sand grains with electron 

 microscopy and applied the technique to the study of sand transport along the 

 Atlantic shore of Long Island. Naturally occurring radioactive materials in 

 beach sands have also been used as tracers (Kamel, 1962). 



One advantage of natural tracers is their tendency to "average" out short- 

 term trends and provide qualitatively accurate historical background 

 information on transport. Their use requires a minimum amount of field wark 

 and a minimum number of technical personnel. Disadvantages include the 

 irregularity of their occurrence, the difficulty in distinguishing the tracer 

 from the sediment itself, and a lack of quantitative control on rates of 

 injection. In addition, natural tracers are unable to reveal short-term 

 changes in the direction of transport and changes in material sources. 



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