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 accuracy of the resulting profiles are discussed in Section 4.514.
4.824 Tracers. It is often possible to obtain evidence on the direction
of sédiment movement and the origins of sédiment deposits by the use of
tracer materials which move with the sédiment. Fluorescent tracers were
used to study sand migration in and around South Lake Worth Inlet, Florida
(Stuiver and Purpura, 1968.) Radioactive sédiment tracer tests were conducted to détermine whether potential shoaling material passes through or
around the north and south jetties of Gaiveston Harbor.
(Ingram, Cummins,
and Simmons, 1965.)
Tracers are particles which react to fluid forces in the same manner
as particles in the sédiment whose motion is being traced, yet which are
physically identifiable when mixed with this sédiment. Ideally, tracers
must hâve the same size distribution, density, shape, surface chemistry,
and strength as the surrounding sédiment, and in addition hâve a physical
property that easily distinguishes them from their neighbors.
Three physical properties hâve been used to distinguish tracers:
radioactivity, color, and composition. Tracers may be either naturally
présent or introduced by man. There is considérable literature on recent
investigations using or evaluating tracers including reviews and bibliography: (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 background information about sédiment origin and transport directions, i.e.,
for studies which involve an understanding of sédiment patterns over a
long period of time.
Studies using stable, nonradioactive natural tracers may be based
on the presence or absence of a unique minerai species, the relative
abundance of a particular group of minerais within a sériés of samples,
or the relative abundance and ratios of many minerai types in a sériés
of samples. Although the last technique is the most complex, it is often
used, because of the large variety of minerai types normally présent in
sédiments and the usual absence of singularly unique grains. The most
suitable natural tracers are grains of a spécifie rock type originating
from a localized spécifie 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
électron 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 hâve also been used as tracers.
(Kamel,
4-150
data useful in beach fill and groin design.
Methods for obtaining beach and nearshore profiles, and the accuracy of the resulting profiles are discussed in Section 4.514.
4.824 Tracers. It is often possible to obtain evidence on the direction
of sédiment movement and the origins of sédiment deposits by the use of
tracer materials which move with the sédiment. Fluorescent tracers were
used to study sand migration in and around South Lake Worth Inlet, Florida
(Stuiver and Purpura, 1968.) Radioactive sédiment tracer tests were conducted to détermine whether potential shoaling material passes through or
around the north and south jetties of Gaiveston Harbor.
(Ingram, Cummins,
and Simmons, 1965.)
Tracers are particles which react to fluid forces in the same manner
as particles in the sédiment whose motion is being traced, yet which are
physically identifiable when mixed with this sédiment. Ideally, tracers
must hâve the same size distribution, density, shape, surface chemistry,
and strength as the surrounding sédiment, and in addition hâve a physical
property that easily distinguishes them from their neighbors.
Three physical properties hâve been used to distinguish tracers:
radioactivity, color, and composition. Tracers may be either naturally
présent or introduced by man. There is considérable literature on recent
investigations using or evaluating tracers including reviews and bibliography: (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 background information about sédiment origin and transport directions, i.e.,
for studies which involve an understanding of sédiment patterns over a
long period of time.
Studies using stable, nonradioactive natural tracers may be based
on the presence or absence of a unique minerai species, the relative
abundance of a particular group of minerais within a sériés of samples,
or the relative abundance and ratios of many minerai types in a sériés
of samples. Although the last technique is the most complex, it is often
used, because of the large variety of minerai types normally présent in
sédiments and the usual absence of singularly unique grains. The most
suitable natural tracers are grains of a spécifie rock type originating
from a localized spécifie 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
électron 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 hâve also been used as tracers.
(Kamel,
4-150