Fluorescent Tracer Experiment on Holiday Beach near 

Mugu Canyon, Southern California

By Nicole Kinsman, Alaska Department of Natural Resources, and J. P. Xu, U.S. Geological Survey

Open-File Report 2012–1131 

U.S. Department of the Interior

U.S. Geological Survey
Cover: Photograph of fluorescent tracer injection at the experimental Holiday Beach site, near Mugu Canyon in southern California (USGS 

photograph).

Back cover: Panoramic photograph of tracer delivery to Holiday Beach (USGS photograph).
Fluorescent Tracer Experiment on Holiday Beach near 

Mugu Canyon, Southern California

By Nicole Kinsman, Alaska Department of Natural Resources, and J. P. Xu, U.S. Geological Survey

Open-File Report 2012–1131 

U.S. Department of the Interior

U.S. Geological Survey
ii

U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2012 

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Suggested citation:

Kinsman, N., and Xu, J.P., 2012, Fluorescent tracer experiment on Holiday Beach near Mugu Canyon: 

U.S. Geological Survey Open-File Report 2012-1131. (Available at http://pubs.usgs.gov/of/2012/1131/.)

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endorsement by the U.S. Government. 

Although this report is in the public domain, permission must be secured from the individual 

copyright owners to reproduce any copyrighted material contained within this report.
iii

Contents

Abstract ......................................................................................................................................................................... 1

Introduction.................................................................................................................................................................... 1

Making Fluorescent Tracers .......................................................................................................................................... 3

Sand Source .............................................................................................................................................................. 3

Formulations .............................................................................................................................................................. 4

Production.................................................................................................................................................................. 6

Tracer Evaluation....................................................................................................................................................... 8

Field Experiment...........................................................................................................................................................10

Setting and Conditions..............................................................................................................................................10

Tracer Deployment and Monitoring...........................................................................................................................12

Results and Discussion.............................................................................................................................................15

Summary and Recommendations.................................................................................................................................19

Acknowledgments ........................................................................................................................................................21

References Cited..........................................................................................................................................................21

Figures

Figure 1. Map showing location of 2010 tracer experiment site on Holiday Beach near Mugu Canyon, 

southern California (USGS orthorecified aerial photograph, October 1, 2004). The Tracer

Dispersal/Sampling Region (blue rectangle) encompasses the area in which tracer grain counts 

were conducted. ........................................................................................................................................ 2

Figure 2. Histograms showing grain size distributions of sediment samples from around the experiment site. ........ 4

Figure 3. Illustration of the production steps involved in making coated fluorescent tracers (USGS photographs)... 7

Figure 4. Photographs of tracer material that has undergone abrasion testing for up to 39 days 

(USGS photographs). ................................................................................................................................ 8

Figure 5. Graph showing a theoretical calculation of the effect of coatings of various thicknesses is shown in 

the plots to the right with the densities of quartz and feldspar shown for reference. The result of 

repeated measures of the density of the sand and tracer used in this experiment is shown to the left...... 9

Figure 6. Graphs showing wave climate during and after the experiment, derived from the nearest National 

Data Buoy Center buoy, located in 110 meters of water, 30 kilometers to the west-northwest from 

the tracer release site. ............................................................................................................................. 10

Figure 7. Photograph of narrow, armored segment of coastline that lies to the east of the tracer release 

site (USGS photograph). ......................................................................................................................... 12

Figure 8. Graph showing profile of the tracer release site with locations of tracer injection shown......................... 12

Figure 9. Graphic representation of the sampling techniques used in this experiment. Manual visual 

inspection (a) and push cores (not shown) were used to produce the presented results in this study. 

Automated image analysis using a GPS-linked vertical depth profile camera (b) and surface camera 

(c) mounted on an ATV platform produces improved speed and an increased sampling density............ 13

Figure 10. Aerial photographs of the study area displaying the distribution of the tracer grain count 

measurements from hour 12 to hour 84 (USGS orthorecified aerial photograph, October 1, 2004). 

The tracer injection site is highlighted in orange. ..................................................................................... 14

Figure 11. Aerial photograph with location of push core transects relative to the tracer release profile 

and the rhythmic beach cusp morphology of the berm (USGS orthorecified aerial photograph, 
iv

October 1, 2004). ..................................................................................................................................... 15

Figure 12. Scatter plot of the spatial distribution of tracer counts from five sequential surveys, each conducted 

at low tides, after the tracers were released at h0 (about 3:30 p.m., September 8, 2010). The 

number of tracer grains at each survey point is displayed (on logarithmic scale) by both the color 

and the size of the plotted points. For clarity, the coordinates of the scatter plot are shifted 100 

meters diagonally for each survey. ........................................................................................................... 16

Figure 13. Histograms of vertical tracer grain counts in each push core sample arranged by transect location 

and distance across the shoreface. Push core samples of less than 8 cm are indicated by question 

marks (?). ................................................................................................................................................. 17

Figure 14. Histograms illustrating the across-shore distribution of tracer grains on the shoulder transect as a 

function of grain diameter......................................................................................................................... 19

Tables

Table 1. Three different categories of tracer formulations that were tested in the laboratory. ................................. 5

Table 2. Six fluorescent pigment colors tested in coating formulation. .................................................................... 5

Table 3. A summary of the measured grain size parameters from samples collected throughout the study area. 

Locations of samples are shown in figure 1. The shoulder transect is located about 150 meters upcoast 

from the release site..............................................................................................................11
v 

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Volume

cubic foot (ft3) 28.32 liter (L)

cubic foot (ft3) 0.02832 cubic meter (m3)

SI to Inch/Pound

Multiply By To obtain

Length

millimeter (mm) 0.03937 inch (in.)

centimeter (cm) 0.3937 inch (in.)

meter (m) 3.281 foot (ft) 

meter (m) 1.094 yard (yd) 

kilometer (km) 0.6214 mile (mi)

kilometer (km) 0.5400 mile, nautical (nmi) 

Area

square centimeter (cm2) 0.1550 square inch (ft2) 

square centimeter (cm2) 0.001076 square foot (ft2)

square meter (m2) 0.0002471 acre 

square meter (m2) 10.76 square foot (ft2) 

Volume

cubic centimeter (cm3) 0.06102 cubic inch (in3) 

cubic meter (m3) 264.2 gallon (gal) 

cubic meter (m3) 35.31 cubic foot (ft3)

cubic meter (m3) 1.308 cubic yard (yd3) 

liter (L) 33.82 ounce, fluid (fl. oz)

liter (L) 2.113 pint (pt)

liter (L) 1.057 quart (qt)

liter (L) 0.2642 gallon (gal)

liter (L) 61.02 cubic inch (in3) 

Speed

centimeter per second (cm/s) 0.0328084 feet per second (ft/s)

centimeter per minute (cm/s) 0.0328084 feet per minute (ft/m)

Density (Thickness)

gram per cubic centimeter (g/cm3) 62.4220 pound per cubic foot (lb/ft3) 

The Kumbein phi scale for grain size also is used within this report. To find a metric diameter (D) in mm 

using a phi (φ) value, use the equation below. 

D = 2−φ
1 

Fluorescent Tracer Experiment on Holiday Beach near 

Mugu Canyon, Southern California

By Nicole Kinsman, Alaska Department of Natural Resources, and J. P. Xu, U.S. Geological Survey

Abstract

After revisiting sand tracer techniques originally developed in the 1960s, a range of fluorescent 

coating formulations were tested in the laboratory. Explicit steps are presented for the preparation of the 

formulation evaluated to have superior attributes, a thermoplastic pigment/dye in a colloidal mixture 

with a vinyl chloride/vinyl acetate copolymer. In September 2010, 0.59 cubic meters of fluorescent 

tracer material was injected into the littoral zone about 4 kilometers upcoast of Mugu submarine canyon 

in California. The movement of tracer was monitored in three dimensions over the course of 4 days 

using manual and automated techniques. Detailed observations of the tracer’s behavior in the coastal 

zone indicate that this tracer successfully mimicked the native beach sand and similar methods could be 

used to validate models of tracer movement in this type of environment. Recommendations including 

how to time successful tracer studies and how to scale the field of view of automated camera systems 

are presented along with the advantages and disadvantages of the described tracer methodology. 

Introduction

Littoral sands are in high demand for coastal management purposes such as beach 

replenishment. With projections of rising sea levels in the upcoming decades, this demand for sand 

resources likely will increase. On the U.S. West Coast much of this littoral sand is thought to be lost 

into various submarine canyons that incise across a narrow continental shelf and intercept littoral 

transport (for example, Monterey, Hueneme, and Mugu Canyons in California). Trapping this part of the 

littoral sand budget before it is lost into canyons has been proposed by many coastal managers (for 

example, Moffatt and Nichol, 2008). However, the proportion of sand in a littoral system that is lost into 

a canyon and the amount that is bypassed to the downcoast portion of the beach remains unquantified. 

Knowledge of this partition is a key prerequisite for the human interception of littoral sand in order to 

avoid potential negative consequences to downcoast beach stability and unnecessary costs. 

Mugu submarine canyon in southern California has been commonly cited as a near-complete 

sink at the downcoast boundary of the Santa Barbara Littoral Cell (Everts and Eldon, 2005; Patsch and 

Griggs, 2006). As part of a larger project to examine sand movement in the littoral zone near the head of 

Mugu submarine canyon, a fluorescent sand tracer study was conducted on an intertidal beach west 

(upcoast) of the canyon head (fig. 1). The results of this tracer experiment have been used to seed a 

numerical model that can be used to examine sand movement in the littoral zone near the head of Mugu 

canyon and to determine if sand is able to bypass the canyon head and in what quantities under 

predominant wave conditions (Xu and others, 2011).
2 

Figure 1. Map showing location of 2010 tracer experiment site on Holiday Beach near Mugu Canyon, southern California (USGS orthorecified 

aerial photograph, October 1, 2004). The Tracer Dispersal/Sampling Region (blue rectangle) encompasses the area in which tracer grain 

counts were conducted. 
3 

The first part of this report documents the processes and procedures of making fluorescent sand 

tracers from native beach sands. As noted by Ciavola (2004), there are few publications that detail sand 

marking techniques and the most well-known manual for creating coated tracers dates back to a halfcentury ago (Ingle, 1966). Therefore, the steps involved in tracer production are presented in detail for 

ease of use by future researchers. The second half of this report describes the deployment and ensuing 

surveys of the fluorescent sand tracers in the intertidal environment including recommendations for 

improved field studies of this type.

Making Fluorescent Tracers

Tracers have been incorporated into littoral zone studies as far back as 1902 for their ability to 

aid in qualitative and quantitative assessments of how sediments behave in coastal environments. The 

types of tracers used by these studies have taken a variety of forms (for a complete history, see Ciavola, 

2004; Black and others, 2007). Non-natural sand-sized tracers fall into three general categories: 

radioactive tagging, artificial grains, and colored sediments. Once an efficient method of obtaining high 

tracer recovery rates, radioactive marking (for example, Heathershaw and Carr, 1977) is no longer an 

acceptable practice due to negative environmental impacts. Artificial tracer grains that mimic native 

sand are prohibitively expensive for use in experiments that require large volumes of tracer. The 

coloring of native sediments is the oldest type of artificial tracer and remains the most widely accepted 

and least expensive option available to littoral studies today (2012). In the 1960s, the use of fluorescent 

pigments that glow under ultraviolet (UV) light made recovery and tracer counts easier, and the use of 

these pigments for tracer production became common practice (Zenkovich, 1965; Teleki, 1966). 

Sand Source

To ensure that tracer grains accurately mimic the behavior of native sediments, sand for tracer 

production should be sourced locally from the study area. Holiday Beach was selected as the site for this 

experiment primarily because of its position relative to Mugu submarine canyon (fig. 1). Additionally, 

the beach is located within the boundaries of the Point Mugu Naval Air Station. The advantage of 

conducting this type of experiment on the premises of a security-controlled U.S. military base is that it 

minimizes the likelihood of the tracer being disturbed by anthropogenic activities. 

Sand for tracer production was collected in April 2010, approximately 5 months prior to the 

tracer release. At this time, access to the release site was limited, so 1.3 m3 of sand was bagged for 

production from a pile of sand located adjacent to the Public Beach parking area (fig.1); collected 

sediment was composed of road-overwash sand from a February 2010 storm event. Grain size analyses 

(obtained by sieving) of sand samples taken from the release site exhibited a uni-modal distribution of 

medium sand that is moderately well sorted with a mean grain size (D50) of 1.7–1.4 phi (310–390 μm in 

diameter). Grain size analyses of samples taken from the source pile exhibited strong agreement in grain 

size distribution with the source pile sand at the time of sand collection (black and gray bars, fig. 2).

However, grain size analyses of samples collected from the release site at the time of tracer injection in 

September 2010 indicate a shift toward fines in the grain size distribution (blue bars, fig. 2). This 

variance in the grain size distributions over time resulted in the tracer material having a different 

distribution than the native sand at the experiment site; variance could be reduced by minimizing the 

amount of time between sand collection and release, to minimize the effects of seasonal variation in the 

wave environment. 
4 

Figure 2. Histograms showing grain size distributions of sediment samples from around the experiment site. 

Formulations

Native beach sand can be fluorescently tagged by one of two methods: (1) by staining the grains 

with a fluorescent dye/ink, or (2) by covering the grains in a thin fluorescent coating (for specific 

examples of each see Ingle, 1966). Ideally, tracer stains and coatings should be insoluble in seawater, 

resistant to abrasion in the surf zone, resistant to fading or losing UV properties over the study duration, 

nontoxic to sea-life, affordable, and thin enough to not substantially alter the hydrodynamic properties 

of the original sand grains. Stained tracers are reported to have longer lifespans in the surf zone than 

coated tracers (Chapman and Smith, 1977), but they are not well-suited for use on beaches with a dark 

mineral component. Because of the typical mineral composition of California beaches, grain-coating 

methods were investigated to create the fluorescent sand tracers for this experiment. 

The creation of coated tracers involves the attachment of fluorescent pigments to native sand 

grains with the use of a binding agent. Few tracer studies adequately describe the types of fluorescent 

substances and binding agents that can be used for self-production. Multiple studies refer to the set of 

methods presented by Yasso (1966) (for example, Schwartz, 1966; Ciavola and others, 1997; Ferreira 

and others, 2002). Tracer production methods described by other studies involve paint/varnish binders 

(for example, Ciavola and others 1997a; Silva and others, 2007), plastic binders (for example, Jolliffe, 

1963) or resin binders (for example, Teleki, 1966; Boon 1970). Each one of these three categories of 

binders was tested in a laboratory phase of this tracer experiment (table 1). 
5 

Table 1. Three different categories of tracer formulations that were tested in the laboratory. 

Formulation Fluorescent Pigment Binding Agent Category Formulation Source

K1 

DayGlo® A/AX 

Pigments in Acrylic 

Laquer

A.R. Monteith Acrylic 

Laquer 202 Line 

(204-04, Red Orange)

Paint/Varnish Formulation #2, Yasso (1966)

K2 DayGlo® A-14N 

Pigment (Fire Orange)

Cytec Cymel U-227-8 

Butylated Ureaformaldehyde ResinResin 

Modified Formulation #3, 

Yasso (1966) and Procedure 5 in 

Ingle (1966) after Teleki

K3 DayGlo® A-14N 

Pigment (Fire Orange)

Wacker Vinnol H 15/45 

M Vinyl Copolymer 

Thermoplastic

Plastic Modified Formulation #5 and #7, 

Yasso (1966) and Teleki (1966)

In summary of this laboratory phase, Formulation K1(paint/varnish type) was very prone to 

clumping, the drying time was greater than 1 h, and both the acrylic lacquer and toluene required to thin 

the lacquer were expensive. Formulation K2 (resin type) also was prone to clumping, had an extended 

drying time, and required extra ventilation and handling measures due to the chemistry of the binding 

agent. Formulation K3 (plastic type) was initially made with Methyl Ethyl Ketone (MEK) and toluene 

following Yasso (1966). After consulting the literature on the selected thermoplastic, acetone was 

substituted for the toluene in a subsequent batch. Yasso Formulation #7 was modified with the use of a 

solution of raw pigment and solvent rather than acrylic lacquer, similar to Yasso Formulation #5. A 

vinyl chloride/vinyl acetate copolymer (Teleki 1966) was used in place of a carboxyl-modified vinyl 

copolymer. Formulation K3 coated evenly, did not clump and dried to the touch in less than 10 min 

during laboratory testing.

The use of multiple colors is useful for the concurrent tracking of sediments from different 

temporal or spatial tracer injections. DayGlo® Color Corp., a pigment company, offers a line of products 

that includes a total of 10 A and AX fluorescent pigment colors and 13 different D fluorescent dye 

colors. During the laboratory testing phase, tracer batches were produced using a coating of Formulation 

K3 in six fluorescent colors (table 2). These tracers were examined under UV light prior to large-scale 

production. 

Table 2. Six fluorescent pigment colors tested in coating formulation (USGS photograph). 

DayGlo® name DayGlo® ID Visible color Ultraviolet color

Fire Orange1,2 A-14N Orange Orange 

Arc Yellow1 AX-16-N Dark Yellow Yellow

Signal Green AX-18-N Green Yellow-Green

Horizon Blue A-19 Blue Blue

Carona Magenta A-21 Pink Orange-Pink

Columbia Blue1 D-298 Not Visible Blue

1

Produced as a tracer for use at the Holiday Beach study site. 2Shown under UV light in the embedded image. 

Observations under UV light revealed a similarity in some fluorescent colors that could inhibit 

the differentiation of tracers, particularly with automated image analysis techniques. An additional 

feature of UV-based tracer detection is that it makes possible the use of pigments that cannot be seen in 

the visible spectrum. This presents opportunities for the use of tracer grains in field experiments on 

more populated beaches without causing a visual disturbance or inviting human tampering. 
6 

Production

Tracer production was conducted at the U.S. Geological Survey (USGS) Marine Facility in 

Santa Cruz, California, during May-June 2010. Initial laboratory test batches of 1,000 cm3 were scaled 

up to 2–3 ft3 batches and a total of 1.3 m3 of fluorescent sand was created over a period of 4 nonconsecutive days by two workers. Coating was performed using a 3.5 ft3 capacity cement mixer to 

ensure uniform coverage and a fast drying time (Silva and others, 2007). Larger batches could be 

produced on a shorter timescale with the use of a high capacity cement mixer as long as the time within 

the mixer is increased to allow for adequate drying. Weather conditions during this process consisted of 

low winds, temperatures of approximately 70±10°F, and approximately 75±15 percent humidity. 

The method for preparation and application of the coating is illustrated in figure 3: 

1. Combine 2 L of acetone with 800 mL of pigment/dye powder to create the pigment mixture. 

2. Very gradually combine 200 mL of Vinnol H 14/45 M powder into a 1 L acetone/1 L MEK 

mixture until fully dissolved, to create the binding agent. Stir continuously to avoid clumping. 

3. Add pigment mixture to binding agent and blend to a colloidal state. 

4. Pour fluorescent tagging formulation over about 2.5 ft3

 (0.071 m3) of dry sand in a rotating 

cement mixer. Allow to coat and dry in rotating mixer for 10–15 min. 

5. Pour tracer sand onto a tarp and air dry while manually breaking apart any remaining clumps 

with a rake or shovel. 

Experimentation involving slight variations to the proportions of components in the described 

preparation is recommended to attain a coating appropriate for the mineral composition, angularity, and 

grain-size distribution of the native sand. For example, inadequate fluorescence per grain can be 

rectified by the addition of more pigment powder in step 1. The quantities presented above created the 

highest quality fluorescent tracer out of the sand from Holiday Beach. 
7 

Figure 3. Illustration of the production steps involved in making coated fluorescent tracers (USGS 

photographs). 

Adverse environmental factors, such as hot weather and high humidity, led to a noticeable 

increase in the amount of clumping during the drying process. This clumping could be reduced by the 

addition of extra acetone or by extending the amount of drying time in the cement mixer to 30 minutes. 

Additionally, the formation of “gooey” aggregates and uneven coating occurred when too much MEK 

was used in proportion to the resin powder. This variation in pigment behavior between different colors 

was observed during the production process. This was most likely a result of changing environmental 

factors or the suspension of pigments in resin mixtures that did not contain an ideal ratio of liquid 

components during batch experimentation. 

There are several obstacles associated with the presented tracer preparation. The use of 

chemicals such as acetone and MEK requires adequate storage facilities, safe handling, and use of 

protective gear during the formula mixing process. Masks with organic vapor filters are necessary for 

protection from the chemical fumes as well as fine particulate components, such as the pigment powders 

and resin. In some locations, the release of large quantities of organic vapors associated with this tracer 

preparation will require the acquisition of an environmental permit from the local air-quality regulating 

body. These factors may inhibit the on-site production of this type of tracer on many beaches in the 

United Status. 
8 

Tracer Evaluation

The performance of the tracer grains and the merits of the selected formulation were evaluated in 

the laboratory and during the course of the field experiment on Holiday Beach. The tracers were tested 

for seawater insolubility, abrasion resistance, and fade resistance. The toxicity and price of the tracer 

also are presented. A comparison of the original native sand to the tracers provides a summary of the 

hydrodynamic differences and limitations to the coating method of tracer production. 

In regard to seawater insolubility, the technical literature for Vinnol H 15/45 M recommends 

using this polymer over other polymers for marine applications, stating that films of Vinnol H 15/45 M 

are highly resistant to water. This agrees with the findings of Teleki's (1966) review of tracer binding 

agents, which describes vinyl chloride/vinyl acetate copolymer thermoplastics as not affected by 

saltwater, alkalies, or non-oxidizing acids. Teleki (1966) also reported that this type of binding agent 

does not react with soluble salts in beach sand, retains fluorescence well, is ideally suited for quartz rich 

beaches, and has excellent resistance to the absorption of sea water, even under prolonged submersion. 

The technical literature for Vinnol H 15/45 M also highlights the polymer’s excellent adhesion 

to mineral substrates and high film strength, two important elements to resisting abrasion in the surf 

zone. To test this resistance in the laboratory, a sample of the Fire Orange tracer grains was placed into 

a hexagonal rock tumbler with salt water and abraded for approximately 1 month. Samples of the 

tumbled tracer material were pulled out at regular intervals (fig. 4) and visible fluorescent material was 

still present on most of the grains at the end of this test. 

Figure 4. Photographs of tracer material that has undergone abrasion testing for up to 39 days (USGS 

photographs).

A direct test of fade resistance or loss of UV fluorescence was not conducted; however, the 

technical literature for the DayGlo® A/AX pigments cites an outdoor fluorescent lifespan of more than 

3–6 months depending on the pigment (AX pigments have a longer lifespan in direct sunlight than A 

pigments). The partial solubility of these thermoplastic pigments in acetone, a primary component used 

in the coating process, may reduce the fluorescent lifespan. The effects of partial solubility are expected 

to be minimal based on communications with the DayGlo® laboratory. DayGlo® D pigments are organic 

dyes not housed in thermoplastics; they are expected to have shorter fade times but are available in a 

wider range of colors. Based on the dye class of D-298 (Columbia Blue), the fade time for the D 

pigments is around 500 h. The use of vinyl thermoplastic as a binding agent helps to maximize the lightfastness of the selected dyes and pigments, and the expected fluorescent fade times are acceptable for 

any planned study duration of less than 1 month. 

The pigments and dyes in the described formulation are contained in the binding agent once 

properly dried. The Vinnol H 15/45 M Material Safety Data Sheet reports “no expected damaging 

effects to aquatic organisms.” The MEK and acetone used in the production process are evaporated 
9 

before introduction to the marine environment. To remove any traces of MEK or acetone impurities left 

on the coated sand, the tracer may be rinsed prior to release at the study site. 

Of the tracer formulas that were tested and considered, Formulation K3 was the least expensive 

option. Cost was reduced with the substitution of acetone for toluene (this also decreased odor and 

drying time). The direct use of pigments is recommended over the use of acrylic lacquers because price, 

odor, and clumping of tracer grains are all reduced. The average price for the required production 

materials in 2010 U.S. dollars is approximately $650.00/m3, with variations due to choice of fluorescent 

color. 

Tracers composed of coated native sediments repeatedly have been found to have hydraulic 

properties similar to those of the original uncoated particles (Ingle, 1966; Madsen, 1987). This is 

especially true for very thin coatings; the strength of the binding agent in the presented formulation 

allows the coating to be very thin and still resist abrasion. Yasso (1966) reported that vinyl 

thermoplastic formulations resulted in coatings of less than 0.013 mm. The quartz-rich sand used in the 

experiment at Holiday Beach was sieved before and after the coating process (fig. 2). The apparent 

coarsening trend in the grain-size distribution of the tracer relative to the sand in the original source pile 

can be partially attributed to the coating thickness but is more likely a result of the loss of fines, or 

winnowing of the tracer sand during production and transport. 

A theoretical calculation of the rate at which tracer density varies with grain size under different

coating thicknesses (fig. 5) predicted that the density of the tracers in this experiment (median diameter 

of 0.33 mm) would be an average 0.29g/cm3

 less than the native sand. The measured variation in density 

(fig. 5) was slightly less (approximately 0.20 g/cm3) than the estimated amount. This may be explained 

by a presence of heavier mafic minerals in the sand composition, the winnowing and loss of the fines or 

tracer coatings that were thinner than predicted.

Figure 5. Graph showing a theoretical calculation of the effect of coatings of various thicknesses is shown in the 

plots to the right with the densities of quartz and feldspar shown for reference. The result of repeated 

measures of the density of the sand and tracer used in this experiment is shown to the left. 
10

Field Experiment

Setting and Conditions

The experiment site is a beach located at the eastern end of the Santa Barbara Channel in 

southern California (fig. 1). The area lies within the Santa Barbara littoral cell which has a net longshore 

drift rate of approximately 803,000 m3

/yr to the east/southeast (Patsch and Griggs, 2008). Just 

downcoast of the experiment site, Mugu submarine canyon extends almost to the beach near the 

entrance of Mugu Lagoon and is the presumed terminus or primary sand trap of the Santa Barbara 

littoral cell.

Surface currents in the region near the study area are bidirectional along the coast, with mean 

current speeds generally less than 10 cm/s (Harms and Winant, 1998). Meteorological data from two 

National Oceanic and Atmospheric Administration buoys located just offshore from the study area 

indicate that dominant winds are from the west/northwest. The wave regime in the area also is 

characterized by westerly/northwesterly seas with occasional long-period, southerly swells (Xu and 

Noble, 2009). Over the course of the tracer experiment (September 7–11, 2010) weak, southerly swells 

typical of the summer wave climate were interrupted by two pulses of strong westerly sea events (fig. 

6).

Figure 6. Graphs showing wave climate during and after the experiment, derived from the nearest National 

Data Buoy Center buoy, located in 110 meters of water, 30 kilometers to the west-northwest from the tracer 

release site.
11

The region experiences mixed semi-diurnal tides with a mean diurnal range of approximately 1.7 

m. The tracer experiment was conducted during spring tides with a semidiurnal range of 1.3–2.1 m. The 

width of the study area beach from the low water line to upper berm is approximately 30–40 m 

including an intertidal shoreface of 8–13 m wide. 

Each year, the beaches in the study area undergo a geomorphic winter-summer cycle. This 

pattern is most dominantly characterized by the development of a flatter berm as a result of accretion in 

the lower-energy summer months, which effectively increases the beach slope in front of the berm. In 

the winter, most of the summer berms are eroded by high energy waves, effectively reducing the overall 

beach slope in the foreshore. 

Table 3 provides a temporal and spatial overview of grain size parameters for the coastal 

sediments from throughout this study. The study area is composed of medium sand beaches that are 

moderately well-sorted with fine to very fine sand (decreasing in diameter with depth) in the offshore. 

Mean grain size on the shoreface increased from east to west as the beach narrows around an exposed, 

armored bend in the coastline (figs.1 and 7) and decreases again on the more sheltered beach near the 

head of Mugu Canyon. In April and September, mean grain size increased with distance from the swash 

zone to the berm. At the berm top, the observed decrease in grain size is most likely due to aeolian 

deposition. Temporal changes in the grain-size parameters at the release site are characterized by an 

approximately 90 μm decrease in the mean diameter over a 5 month period, likely a result of accretion 

in a lower energy summer wave climate.

Table 3. A summary of the measured grain size parameters from samples collected throughout the study area.

Locations of samples are shown in figure 1. The shoulder transect is located about 150 meters upcoast from 

the release site.

Sampling date No. Location D50 Grain size Sorting 

Regional grain sizes 

April 2010 A1 Upper Beach Armored Segment 1.2 φ Medium sand Well sorted

A2 Upper Beach Firing Range 1.3 φ Medium sand Moderately well sorted

A3 Storm Overwash Release Site Road 1.5 φ Medium sand Moderately well sorted

September 

2010

O1 Offshore 10 ft depth 2.9 φ Fine sand Moderately sorted

O2 Offshore 20 ft depth 2.9 φ Fine sand Moderately sorted

O3 Offshore 35 ft depth 3.3 φ Very fine sand Moderately well sorted

O4 Offshore 50 ft depth 3.8 φ Very fine sand Well sorted

Tracer

April 2010 - Undyed Source Sand 1.5 φ Medium sand Moderately well sorted

- Dyed Tracer Sand 1.3 φ Medium sand Moderately well sorted

Release site grain 

sizes 

A4 Upper Beach Release Site 1.4 φ Medium sand Moderately well sorted

A5 Swash Zone Release Site 1.7 φ Medium sand Moderately well sorted

September 

2010

- Berm Top Shoulder Transect 1.9 φ Medium sand Moderately well sorted

- Upper Beach Shoulder Transect 1.6 φ Medium sand Moderately sorted

- Lower Beach Shoulder Transect 1.9 φ Medium sand Moderately well sorted

- Swash Zone Shoulder Transect 2.0 φ Medium sand Moderately sorted
12

Figure 7. Photograph of narrow, armored segment of coastline that lies to the east of the tracer release site 

(USGS photograph). 

Tracer Deployment and Monitoring

At low tide on September 7, 2011, tracer sediments were placed into shallow ditches across the 

shoreface at the Holiday Beach tracer release site (fig. 8). A volume of 0.2 m3 Columbia Blue tracer was 

injected near the swash zone and 0.05 m3 of Arc Yellow tracer was deployed just beneath the berm. The 

bulk of the tracer sediments, 0.34 m3

 colored Fire Orange, were placed in a 1 m wide, 0.1 m deep trough 

on the mid-shoreface. 

Figure 8. Graph showing profile of the tracer release site with locations of tracer injection shown. 
13

The intended method of tracer monitoring for this experiment was an innovative two-camera 

setup that utilizes rapid on-site digital image analysis (algorithm for UV grain counts modified after 

Rubin, 2004) to capture a three-dimensional view of the tracer distribution at a grid of sampled locations 

on the shoreface. The general setup of the instrumentation is similar to the all-terrain vehicle (ATV)-

mounted SADAM system used by Pinto and others (1994) for automated surface grain counts. In this 

experiment the surface camera (fig. 9C) was a miniature USGS eyeball imaging system (Chezar, 2001) 

with a UV LED light source modification. An additional vertical profiling camera (fig. 9B, after 

REMOTS, Rhoads and Germano, 1982) collected automated grain counts to a depth of 10 cm in tandem 

with the surface counts. The primary advantages of this system are that it is fast and that it samples the 

distribution of tracers throughout the mixing layer as opposed to just on the surface. The importance of 

sampling beyond the surface in tracer studies in order to capture a three-dimensional measure of of 

sediment movement is now widely recognized (Kraus and others 1982; Caviola and others 1997a). 

Figure 9. Graphic representation of the sampling techniques used in this experiment. Manual visual inspection 

(a) and push cores (not shown) were used to produce the presented results in this study. Automated image 

analysis using a GPS-linked vertical depth profile camera (b) and surface camera (c) mounted on an ATV 

platform produces improved speed and an increased sampling density.

Following the deployment of the tracer sediments, the release site was revisited for sampling at 

the next lower low tide, approximately 12 h later. Initial use of the ATV-mounted automated dualcamera system resulted in low grain counts of less than 1 tracer grain per image with the surface 

camera. A manual examination of the shoreface with UV light indicated that low returns were not a 

result of an absence of tracer material, but that the field of view on the camera was not adequately sized 

to capture useful automated grain counts following initial dispersal of the material. Because of these low 
14

returns, a method of grain counts based on visual inspection (fig. 9A) with a hand-held UV light sources 

was adopted. 

Manual surface grain counts were conducted on a grid of cross-beach transects every 20 m along 

the shoreline in each direction away from the profile where tracer injection occurred (fig. 10). On 

average, there were at least four grid points on each cross-beach transit. At each grid point a visual 

count of tracer grains within a 3×3 in. area was conducted in triplicate and the average of these three 

counts was recorded. The geographic position of each observed grid point was recorded with a handheld 

Global Positioning System (GPS) receiver.

Figure 10. Aerial photographs of the study area displaying the distribution of the tracer grain count 

measurements from hour 12 to hour 84 (USGS orthorecified aerial photograph, October 1, 2004). The tracer 

injection site is highlighted in orange.

Surface distribution of tracer grains was observed at successive low tides (an approximately 12-h 

interval) using the visual inspection technique for a total duration of 84 h (h12 – h84). Because of

military training operations in the restricted use-area surrounding Holiday Beach, interrupted surveys 

(h12) and restricted access combined with unfavorable light conditions (h48 and h72) resulted in some 

gaps in observation. 
15

A very limited number of Arc Yellow and Columbia Blue tracers were identified by visual 

inspection during the h12 observation. The low number non-Flame Orange tracer observations may be 

attributed to a combination of three factors: (1) a sufficient volume of these tracer colors was not 

deployed, (2) a significant portion of the tracer material deployed in the swash zone was carried 

offshore by wave action, and/or (3) these colors, while tested with the automated camera system, are 

less visible to the naked eye under UV light. As a result of the low recovery rate for these tracer colors, 

only Flame Orange tracer counts were made at successive observation times and an observed 

distribution of these tracers has been included in the remainder of this report. 

In addition to the surface counts, push core samples were taken 24 h after the tracer release along 

three cross-beach transects near the release site. The transects were located at the cusp (five samples), at 

the horn (eight samples), and at the shoulder (seven samples) of the same berm feature, as shown in 

figure 11. Each push core was vertically sub-sampled into 1-cm sections in the laboratory and the 

number of tracer grains in each section was visually counted. Four push core samples from the shoulder 

transect were sieved in the laboratory and a visual count of tracer sediments within the grain-size 

distribution was conducted (method after Komar, 1977).

Figure 11. Aerial photograph with location of push core transects relative to the tracer release profile and the 

rhythmic beach cusp morphology of the berm (USGS orthorecified aerial photograph, October 1, 2004).

Results and Discussion

The field surveys of surface tracer counts, illustrated in figures 10 and 12, exhibit a complex 

dispersal pattern that appears to include both advection and diffusion processes. The number of tracers 

observed near the initial release site decreased rapidly with time. Concurrently, the total area of the 

shoreface where tracers were observed expanded with time as the tracer grains were dispersed by wave 

action; the length of beach where tracers were observed increased from 500 m at h24 to more than 1,000 

m at h84 contributing to a decrease in the net tracer density. 
16

Figure 12. Scatter plot of the spatial distribution of tracer counts from five sequential surveys, each conducted at 

low tides, after the tracers were released at h0 (about 3:30 p.m., September 8, 2010). The number of tracer 

grains at each survey point is displayed (on logarithmic scale) by both the color and the size of the plotted 

points. For clarity, the coordinates of the scatter plot are shifted 100 meters diagonally for each survey. 

In this experiment, a spatial integration method was used to analyze tracer advection (Madsen, 

1987). To quantify alongshore transport of the tracer material, centroids were computed using the 

center-of-mass concept (Silva and others, 2007) for each individual survey. The centroid positions did 

not exhibit a unidirectional movement of the tracer material. Twelve hours (h12) after the tracer release, 

the centroid moved about 50 m upcoast. At h24 the centroid moved 150 m farther upcoast, with an 

average velocity of transport of 20 cm/min (figure 12). 

From h36 through the remainder of the experiment observations, the centroid movement 

reversed to a downcoast direction. At h36, h60, and h84, the centroid migrated in the downcoast 

direction 50, 100, and 50 m, respectively. Thus, the centroid was located near the initial release site at 

h84 after a downcoast transport with an average velocity of 6 cm/min.

The upcoast migration and subsequent reversal of the centroid can be readily explained by the 

strong westerly wave events illustrated in figure 6. Because the region is more typically characterized by 

a summer wave climate similar to the conditions in the latter half of the experiment, the slower, 

downcoast movement of the centroid may be used as a representation of the typical alongshore sediment 

advection at this location.

The results of the across-shore vertical sampling are summarized in figure 13. The presence of 

tracer grains throughout the push cores indicated a mixing depth (or transport thickness, Balouin and 

others, 2005) of at least 8 cm. This estimate is corroborated by the fact that there was no layer of tracers 

left at the release location—all tracers initially placed in a 10 cm deep pit were completely mixed and 

removed.
Figure 13. Histograms of vertical tracer grain counts in each push core sample arranged by transect location and distance across the shoreface. 

Push core samples of less than 8 cm are indicated by question marks (?). 
18

Many tracer studies that rely on surface observations alone have assumed uniform distribution 

down to burial depth; the results of the push core grain counts in this experiment highlight the 

importance of using a three dimensional approach. The majority of push core samples exhibited 

considerable variation in the number of tracer grains with depth. Only 17 percent of the push cores that 

contained any tracer had a near uniform vertical distribution and, as seen in many of the histograms in 

figure 13, the total number of tracer grains at depth was often 2–4 times greater than the number of 

grains observed in the top 1 cm interval.

The across-shore distribution of tracer material suggests an initial onshore movement of the 

tracer as the centroid migrated upcoast, this pattern also can be observed in figure 12. One explanation 

for this pattern is an onshore movement of sand associated with the high energy wave event, another 

explanation could be that advection dominates in the upper one-half of the intertidal zone where wave 

surges prevail and that diffusive processes dominate on the lower one-half shoreface where breaking 

waves are more prevalent over a typical tidal cycle.

The differences in tracer distribution from horn to cusp allude to the role of local circulation 

patterns around this type of beach morphology. Uprush against the horn and shoulder is in contrast to 

the swift backrush flows that typically occur perpendicular to the cusp and may account for the 

decreased tracer deposition along the cusp transect. Furthermore, the observation of grains atop the 

berm only at the convergence point is further evidence of this pattern. Although this type of 

interpretation can only be speculative in this study, it demonstrates the potential to use tracer studies to 

not only calculate traditional rates of littoral drift but also to validate complex nearshore hydrodynamic 

circulation models.

The results of the across shore distribution of tracer sediments by grain size are presented in 

figure 14. At each location across the beach, the distribution of tracers by size closely follows the native 

sand distribution. A high ratio of coarser tracers on the upper beach, relative to lower down, in 

conjunction with the tracer diameters on the lower one-half of the shoreface being skewed towards 

fines, indicates that the tracers are undergoing the same across shore size sorting that is seen in the 

native beach sand. Both of these patterns are evidence that the tracer grains and the uncoated sand are 

behaving in a hydrodynamically similar way.
19

Figure 14. Histograms illustrating the across-shore distribution of tracer grains on the shoulder transect as a 

function of grain diameter. 

Summary and Recommendations

Like other contemporary sand tracer studies, we found that minor modifications to the 

formulations and methods presented by Yasso (1966) resulted in a suitable fluorescent coating for the 

USGS tracer study at Mugu Canyon. The selected formulation for use in this study consists of sand 

evenly coated in a thin layer of DayGlo® thermoplastic pigments/dyes in a colloidal mixture with 

Wacker Vinnol H 15/45 M, a vinyl chloride/vinyl acetate copolymer thermoplastic. The measured

density of the tracer grains were slightly less than the native sand, as predicted, but the tracer

performance in the field indicated that the differences in the hydrodynamic properties of the tracer

grains were at an acceptably low level for the tracer to mimic the behavior of the native beach sand. 

Based on the results of the grain-size analysis, studies that seek to use a similar methodology would be 

advised to collect native beach sand from the beach close to the time of tracer deployment to minimize 

the effects of seasonal grain-size variability. A preferred method of tracer preparation would be on-site.

The results of the field experiment demonstrated the importance of selecting an appropriately

sized field of view or observation window for automated tracer grain detection methods. Manual grain 

counts and laboratory analysis were time consuming so further development of the automated system 
20

would streamline experimental observations and improve recovery rates. The overall results of the tracer 

monitoring post-injection were quantitatively inconclusive due to the limitations of the observation 

methods. By assuming that the tracers were fully mixed with native sand within a 10 cm mixing depth, 

an estimated tracer recovery rate using the manual method (White, 1998) can be computed based on a 

40 m beach width, the beach length, grain size, and a nominal sediment porosity value (0.65). This 

recovery rate was the highest (71 percent) at h24, and decreased to 50, 31, and 33 percent for the 

surveys at h36, h60, and h84, respectively. Only the h24 recovery rate fell into the “good” tracer 

experiment criteria (>60 percent) as defined by White (1998). 

Calculations of required tracer volume should include a consideration of the camera field of 

view. Equation 1 is presented as a guideline to assist researchers in selecting a minimum volume of 

tracer (Vtracer) based on study site characteristics and the scale of the observation window. 

This equation will yield an approximation of the minimum volume of tracer required for observations of 

more than one tracer grain/surface image. Because recovery rates decrease as a function of time, the 

recovery rate should be selected as a function of the duration of the field experiment. 

Based on the experimental counts of tracer per observation window (58 cm2 field of view) and 

using the beach characteristic assumptions from the recovery rate calculation, the average grain counts 

would have been less than 0.6 grain per image at all experimental time steps if the automated camera 

system (6 cm2

 field of view) had been used. This is consistent with the extremely low number of tracers 

(typically zero) observed in images that were collected with the camera system at h24. To achieve

meaningful tracer observations (an average tracer grain count of more than one per image), the 

minimum field of view for the automated camera system would have needed to be at least 52 cm2 for 

the 0.34 m3 volume of tracer with a 30 percent recovery rate by h96. Conversely, using the volumetric 

beach assumptions above, we can calculate that this experiment would have required an initial tracer 

injection of 0.8 m3 for the designed camera to be effective with a 100 percent recovery rate. Given the 

actual recovery rates, which account for sand lost to the nearshore, an initial tracer volume of 2.4 m3 

(more than 7× the amount deployed) would have been necessary to obtain useful measurements with the 

designed camera system.

A preliminary modeling study that investigated the movement of the tracers described in this 

field experiment over a 1 week period and in a range of typical nearshore wave climates concluded that 

the tracer material would not bypass the canyon head (Xu and others, 2011). Depending on the relative 

strengths of surfzone currents at the head of Mugu Canyon and in the downcoast direction, the modeled 

path of tracers is either onto the offshore shelf or into the canyon head. A longer term field investigation 

with an adjusted camera system could be used to verify these model results. 
21

Acknowledgments

The authors would like to acknowledge Hank Chezar and Joanne Ferreira from the USGS 

Pacific Coastal and Marine Science Center for their significant roles in the field component of this tracer 

experiment as well as in the development and testing of the camera system. Steve Granade and Martin 

Ruane, from the Ventura County Naval base, were instrumental in facilitating the execution of the beach 

experiment within rules of the restricted use areas. The manuscript benefited from the insightful reviews 

by Lissa MacVean and Li Erikson from the USGS Pacific Coastal and Marine Science Center. This 

study is funded by the Coastal and Marine Geology Program of the U.S. Geological Survey. 

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