fluctuations of sand level at a site (Everts, 1973), and thus provides 

 data useful in beach fill and groin design. 



Methods for obtaining beach and nearshore profiles, and the accu- 

 racy of the resulting profiles are discussed in Section 4.514. 



4.824 Tracers . It is often possible to obtain evidence on the direction 

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

 tracer materials which move with the sediment. Fluorescent tracers were 

 used to study sand migration in and around South Lake Worth Inlet, Florida. 

 (Stuiver and Purpura, 1968.) Radioactive sediment tracer tests were con- 

 ducted 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, and in addition 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 biblio- 

 graphy: (Duane and Judge, 1969; Bruun, 1966; Galvin, 1964; and Huston, 

 1963); models of tracer motion: (James, 1970; Galvin, 1964; Hubbell and 

 Sayre, 1965; and Duane, 1970); and use in engineering problems: (Hart, 

 1969; Cherry, 1965; Cummins, 1964; and Duane, 1970). 



a. Natural Tracers . Natural tracers are used primarily for back- 

 ground 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) devel- 

 oped a technique for the study of surface textures of sand grains with 

 electron microscopy, and applied the technique to the study of sand trans- 

 port along the Atlantic shore of Long Island. Naturally occurring radio- 

 active materials in beach sands have also been used as tracers. (Kamel, 

 1962.) 



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