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
work and a minimum number of technical personnel. Disadvantages include
the irregularity of their occurrence, the difficulty in distinguishing the
tracer from the sédiment 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.
Judge (1970) found that heavy minerai studies were unsatisfactory as
indicators of the direction of longshore transport for beaches between
Point Conception and Ventura, California, because of the lack of uniquê
minerai species and the lack of distinct longshore trends which could be
used to identify source areas. North of Point Conception, grain size and
heavy minerai distribution indicated a net southward movement. Cherry
(1965) concluded that the use of heavy minerais as an indicator of the
direction of Coastal sand movement north of Drakes Bay, California was
generally successful.
b.
Artificial Tracers. Artificial tracers may be grouped into two
general categories : radioactive or nonradioactive. In either case, the
tracers represent particles that are placed in an environment selected
for study, and are used for relatively short-term studies of sédiment
dispersion.
While particular experiments employ spécifie sampling methods and
operational characteristics, there are basic éléments in ail tracing
studies. These are: sélection of a suitable tracer material, tagging
the particle, placing the particle in the environment, and détection of
the particle.
Colored glass, brick fragments and oolitic grains are a few examples
of nonradioactive particles that hâve been used as tracers. The most comnnnly used stable tracer is made by coating indigenous grains with bright
colored paint or flourescent dye.
(Yasso, 1962; Ingle, 1966; Stuvier and
Purpura, 1968; Kidson and Carr, 1962; and Teleki, 1966.) The dyes make
the grains readily distinguishable among large sample quantities, but o
not significantly alter the physical properties of the grains. The dyes
must be durable enough to withstand short-term abrasion. The use of pamts
dyes as tracer materials offers advantages over radioactive methods in
that they require less sophisticated equipment to tag and detect the grains,
and do not require licensing or the same degree of safety précautions. However, less information is obtained for the same costs, and generally in a
ess timely matter.
When using nonradioactive tracers, samples must be collected and
removed from the environment to be analyzed later by physically counting
the grains. For fluorescent dyes and paints, the collected samples
viewed under an ultraviolet lamp and the coated grains counted.
For radioactive tracer methods, the tracer may be radioactive at *
lme of injection or it may be a stable isotope capable of being ^etected
by activation after sampling. The tracer in the grains may be mtroduced
4-151
short-term trends and provide qualitatively accurate historical background
information on transport. Their use requires a minimum amount of field
work and a minimum number of technical personnel. Disadvantages include
the irregularity of their occurrence, the difficulty in distinguishing the
tracer from the sédiment 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.
Judge (1970) found that heavy minerai studies were unsatisfactory as
indicators of the direction of longshore transport for beaches between
Point Conception and Ventura, California, because of the lack of uniquê
minerai species and the lack of distinct longshore trends which could be
used to identify source areas. North of Point Conception, grain size and
heavy minerai distribution indicated a net southward movement. Cherry
(1965) concluded that the use of heavy minerais as an indicator of the
direction of Coastal sand movement north of Drakes Bay, California was
generally successful.
b.
Artificial Tracers. Artificial tracers may be grouped into two
general categories : radioactive or nonradioactive. In either case, the
tracers represent particles that are placed in an environment selected
for study, and are used for relatively short-term studies of sédiment
dispersion.
While particular experiments employ spécifie sampling methods and
operational characteristics, there are basic éléments in ail tracing
studies. These are: sélection of a suitable tracer material, tagging
the particle, placing the particle in the environment, and détection of
the particle.
Colored glass, brick fragments and oolitic grains are a few examples
of nonradioactive particles that hâve been used as tracers. The most comnnnly used stable tracer is made by coating indigenous grains with bright
colored paint or flourescent dye.
(Yasso, 1962; Ingle, 1966; Stuvier and
Purpura, 1968; Kidson and Carr, 1962; and Teleki, 1966.) The dyes make
the grains readily distinguishable among large sample quantities, but o
not significantly alter the physical properties of the grains. The dyes
must be durable enough to withstand short-term abrasion. The use of pamts
dyes as tracer materials offers advantages over radioactive methods in
that they require less sophisticated equipment to tag and detect the grains,
and do not require licensing or the same degree of safety précautions. However, less information is obtained for the same costs, and generally in a
ess timely matter.
When using nonradioactive tracers, samples must be collected and
removed from the environment to be analyzed later by physically counting
the grains. For fluorescent dyes and paints, the collected samples
viewed under an ultraviolet lamp and the coated grains counted.
For radioactive tracer methods, the tracer may be radioactive at *
lme of injection or it may be a stable isotope capable of being ^etected
by activation after sampling. The tracer in the grains may be mtroduced
4-151