Side-scan Sonar Imaging of the Colorado 

River, Grand Canyon

By Roberto Anima,1 Florence L. Wong,1 David Hogg,1

and Peter Galanis1

Open-File Report 2007-1216

2007

U.S. Department of the Interior

U.S. Geological Survey

1

 Menlo Park, Calif.
2

U.S. Department of the Interior

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia 2007

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Suggested citation:

Anima, Roberto, Wong, Florence L., Hogg, David, and Galanis, Peter, 2007, Side-scan 

sonar imaging of theColorado River, Grand Canyon: U.S. GeologicalSurvey Open-File 

Report 2007-1087, 15 p. [http://pubs.usgs.gov/of/2007/1216/].

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3

Abstract 

This paper presents data collection methods and side-scan sonar data collected along the 

Colorado River in Grand Canyon in August and September of 2000. The purpose of the 

data collection effort was to image the distribution of sand between Glen Canyon Dam and 

river mile 87.4 before and after the 31,600 cfs flow of September 6-8. The side-scan sonar 

imaging focused on pools between rapids but included smaller rapids where possible. 

Introduction 

Side-scan sonar data was collected within the Colorado River as part of a multifaceted 

scientific effort under the Grand Canyon Monitoring and Research Center (GCMRC) to 

provide information on the long-term changes of the river under the Glen Canyon Dam 

Adaptive Management Program (AMP). This program is designed to help the federal 

government understand the relationship between dam operations and the health of the river 

system so that it can meet its resource management obligations under the 1992 Grand 

Canyon Protection Act, the 1995 Glen Canyon Dam Environmental Impact Statement, and 

the 1996 Record of Decision.

Side-scan sonar has proven to be a useful tool in the marine environment to investigate oil 

and gas pipeline locations, shipwrecks, rock outcrops, and sediment distribution. An 

earlier attempt to collect side-scan sonar data along the Colorado River in Grand Canyon 

was undertaken in by Wilson in 1984 (1998, personal communication) who used onshore 

reference points on aerial photography as navigation controls for the side-scan sonar. Since 

this work, the advent of the Global Positioning System (GPS) has increased the feasibility 

and efficiency of side-scan sonar for the Grand Canyon

During this study the side-scan data bracketed the 31,600 cfs experimental flow of 

September 6-8, that followed the Low Steady Summer Flow (LSSF), 

(http://www.usgs.gov/newsroom/article_pf.asp?ID=478), with the first survey conducted 

August 28 to September 5, 2000 (R3-00-GC) and the second conducted September 10-18, 

2000 (R4-00-GC). Each survey proceeded from Glen Canyon Dam and ended at Diamond 

Creek, and included the same reaches of the corridor (Figure 1). Interest and time allowed 

for focusing our resources on the Tailwaters section (Glenn Canyon Dam to Lees Ferry, 

mile –15 to mile 0) to the Kaibab Bridge (mile 88.0). Distances and references along the 

river are in miles using the Grand Canyon Monitoring and Research Center’s web site. 

(http://www.gcmrc.gov/website/fist/viewer), and the Colorado River in Grand Canyon 

Guide (Stevens, 1983). Data collected during both surveys cover most of the pools that 

occur between rapids (Figure 1). Table 1 shows the reaches covered and the images 

included in this report. The accompanying DVD contains the reaches covered in this 

report. 

Purpose and Scope 

The purposes of this manuscript are to: 1) present the methods used in the data collection, 

2) present some limited data analysis showing how well the different bed material types can 

be identified in the images, and 3) deliver the images for potential future analysis by others.
4

Methods 

A 22-foot inflatable river raft (snout rig) was used to collect the data (Figure 2). A Klein 

500 kHz side-scan sonar tow fish was used to conduct the surveys above the Little 

Colorado River (LCR). The pre-LSSF (R3) survey found the Little Colorado discharging a 

large quantity of fine-grained sediment that attenuated the outgoing signal so much that 

operations were stopped. The survey switched to a 100 kHz tow fish for reaches between 

the LCR and Diamond Creek. The next survey (R4) used the Klein 500 kHz tow fish for 

the entire survey.

Side-scan sonar images were processed with the USGS Mini Image Processing system 

(MIPS) http://terraweb.we.usgs.gov/software/mips/, a set of software tools that are used to 

convert rectangular blocks of raw data to geo-referenced images in UTM 11 coordinates in 

MPS “raw” or bil (band interleaved by line) format. The processed images have pixel 

values of 0 to 255, indicating a range of sonar reflectance from low to high. The resolution 

of the side-scan sonar images is 0.2 meters per pixel. The images were converted to TIFF 

format for use with Adobe Photoshop and Adobe Illustrator software.

Side-scan sonar TIFF images were imported into Adobe Photoshop where pixel values 

were inverted so that bedrock and boulders, which have high sonar reflectance, appear as 

dark reflectors, whereas sand and gravel, which have low sonar reflectance, appear as 

various shades of white to dark gray. Because of intermittent GPS coverage, most images 

required further manual registration.

Navigation 

Navigation was attained in two ways. First, a Global Positioning System (GPS) collected 

Latitude and Longitude data using two GPS units. The antenna was mounted on a 

stationary frame that was located within 3.5 meters above the tow fish. The data were 

collected and stored on hard disk and optical drive for later processing. The orientation and 

steepness of the canyon walls, however, limited reception of satellite signals and in some 

cases introduced errors, perhaps due to reflection off the canyon walls.

The second method used aerial photographs as a backup to the GPS. Ortho-rectified aerial 

photograph coverage for the entire river allowed us to correlate features visible along the 

shoreline with the photographs. One person matched features along the shore that were 

visible on the aerial photographs and simultaneously marked the aerial photograph. The 

mark was called to the side-scan sonar operator who placed a time mark on the side-scan 

sonar record, and marked a GPS fix on the hand held units. The aerial photograph data 

proved invaluable where the GPS signal was either lost or reflected on the canyon walls.

The side-scan sonar images were given number designations, i.e., r4-00-blcr1a. Each 

designation includes the survey number (r3, r4) and the year (-00-). The letters and 

numbers that follow represent the area covered, (i.e., blcr, below the Little Colorado River, 

and zc, Zoraster Canyon to Cremation). The number shows the line number run in the area. 

The brackets drawn on each image indicate where along the track line the pre-and postsurvey lines match up.
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Table 1 showing letter designations for each area surveyed. River miles are commonly 

used along the Colorado River as reference points and are used here. 

River Mile Pre-flow Data Post-flow Data

TW Tailwaters (0 to –15 

miles)

Mile –15.7 to –14.5 r3-00-tw1d

r3-00-tw1c

r4-00-tw1c_A

r4-00-tw1c_B

Mile -14.9 to Mile –13.5 r3-00-tw1d r4-00-tw2b

Mile –13.0 to Mile –10 r3-00-tw2a r4-00-tw2b_A

r4-00-tw3a

Mile –10.0 to Mile –6.0 r3-00-tw3a

r3-00-tw3a_B

r3-00-tw4a

r400tw3a

r400twr4a_A2

r400tw4a_B

Mile –6.0 to Mile 0 r3-00-tw4a

r3-00-tw5a_A & B

r4-00-tw5a_B

r4-00-5a_C

r4-00-tw5b_A & B

BP Paria River to 

Cathedral Wash (1 to 3 

miles)

r3-00-bp1a r4-00-bp1a

BCH Below Cathedral 

Wash (Miles 3.5 to 7.9)

r3-00-bch1A

r3-00- bch1B_B

r4-00-bch1_A

r4-00-bch1B-B

Between 6 Mile Wash 

and below Mile 6

r3-00-bch1B_C r4-00-bch1_B-C

TS – Tiger Wash to 

Shinumo Wash (Miles 

26to Mile 29.2)

r3-00-ts1a r4-00-ts1a_A

r4-00-ts1a_B

SSC - Shinumo Rapid to 

South Canyon (Miles 

29.4 to 31.6)

r3-00-ssc1a

r3-00-ssc2

r4-00-ssc1a

r4-00-ssc2a

r4-00-ssc2b 

r4-00-ssc2c

r4-00-ssc2e

r4-00-ssc2b_2

TP – 36 Mile Rapid to 

President Harding Rapid

(Miles 36 to 38)

r3-00-tp1a r4-00-tp1a_A

PHS – President 

Harding to Saddle 

Canyon (Miles 44.8 to 

46.4)

r3-00-phs2-A & B r4-00-phs1c_B

SN – Saddle Canyon to 

Nankoweap Rapid 

(Miles 47.5 to 50.6)

r3-00-sn2_A r4-00-sn1a_A

SLC – Sixty Mile Rapid 

to the Little Colorado 

(Miles 60.6 to 61.7)

r3-00-slc1_a r4-00-slc1_a

BLCR – Below the 

Little Colorado to 

Tanner Rapid (Miles 62 

to 68.5)

r3-00-blcr 2a, 3a, 4a 

r3-00-blcr 5a_A

r4-00-blcr 1a

r4-00-blcr 2A

r4-00-blcr2a_A

Mile 63.8 to Mile 68.9 r3-00-blcr5a_B 

r3-00-blcr6a_B 

r3-00-blcr 6a_A

r4-00-blcr2_B

upper part of r4-00-blcr3a

lower section of r4-00-blcr3a

upper r4-00-blcr3b

ZC – Zoraster Rapid to 

Bright Angle Rapid 

(Miles 86.1to 88)

r3-00-zc2a_A

r3-00-zc2a_B

r4-00-zc1a
6

Features shown on images 

The accompanying DVD contains files with pre- and post- high flow images side by side. 

The pre-flow image is on the left with the post-flow image on the right. The river miles are 

based on river miles posted on the GCMRC web site. The Lees Ferry area (Figure 3) 

shows nearly all the various features found along the river bottom.

The reflectivity of bedrock exposures is dark to black, typically exhibiting discernable 

parallel bedding planes (Figure 4). In many reaches, bedrock is partially overlain by 

boulders, cobbles, pebbles, or sand (Figure 5). 

Boulders (grain diameter > 256 mm) appear as large discontinuous features in talus and 

debris fans. The smallest boulders are comparable in size to a single sonar pixel and are 

perhaps to small to be resolved clearly, but larger boulders can be resolved individually 

(Figure 5). Larger boulders commonly have a “sonar shadow” (white area) behind them 

due to the rock deterring any imaging beyond the rock reflector. 

Boulders may look like layered bedrock where boulders become distorted in linear bands as 

a result of current-induced heave and yaw of the side-scan sonar tow fish, a change in boat 

speed, or a combination of both (Figure 6). Bedrock and boulders can be distinguished in 

undistorted images, because boulders and cobbles appear as individual objects, whereas 

bedding planes in the bedrock are clearly exposed as continuous features (Figure 6). 

Sand (diameter between 0.625 and 2.0 mm), pebbles (diameter between 2 and 64 mm), and 

cobbles (diameter between 64 and 256 mm) are smaller than the sonar pixels and therefore 

cannot be resolved individually. In the sonar images, sand appears as very nearly white or 

grey in color (Figures 3, 6, and 7). Sand often occurs as sub-aqueous dunes, with pebbles 

or cobbles exposed in the dune troughs (Figure. 5). 

Dunes up to 40 m in wavelength and 1 m in height were found in reaches that contained 

large amounts of sand (Figures 3, 6, and 7). In underwater video surveys (Anima, et. al., 

1998), small-scale ripples are often observed superimposed on dunes, but such ripples are 

too small to be resolved by the sonar system used in this work. 

Pebbles and cobbles have stronger acoustic reflections than sand and therefore appear 

darker (Figure 7). In some cases, pebbles and cobbles have a mottled texture, perhaps due 

to spatial variations in grain size, topography, or the presence of sand patches partially 

covering the coarser bed material. Some dunes have a dark reflectance suggesting that they 

are composed of pebbles. Underwater video also shows that some dunes are composed of 

gravel, confirming that dune morphology is not sufficient to identify a sand bed. Pebbles 

are widespread and are the predominant bed type in some reaches of the river. Pebbles and 

cobbles are the predominant feature along the tail waters section of the river above Lees 

Ferry. 

Changes in bed material 

The September 2000 LSSF experiment caused the bed material to change at some sites. We 

observed a number of such changes including: areas where a fine-grained veneer of sand 

was removed; large areas of change from sand to pebbles and cobles; and areas of change 

from pebbles and cobbles to sand; and changes in dune size (fig. 8 & 9). Figures 8 & 9 

show examples of changes observed along the riverbed and can be seen along most 

segments of the river.
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Conclusions 

Side-scan sonar gave us the ability to cover a very large area of the riverbed very quickly. 

The images show very good resolution, and bed features can be identified from survey to 

survey. Navigation using GPS was adequate for most of the canyon survey, but glitches in 

the navigation data did occur. With thought and planning, GPS coverage could be 

improved.

The density of the data collected posed a post-processing problem. The time required to 

process the data into the images reported here was time consuming, and because these were 

back to back surveys posed an even greater amount of time and work. This data set proves 

the viability of the system in these extreme conditions. It can be done. Greater time needs 

to be anticipated and a team of experienced processors needs to be ready to begin the 

processing in order to get a faster turnaround time.

Because of the extreme heat conditions in the canyon required steps to be taken to keep the 

electronics needed to complete the surveys cool. This was achieved by building cases that 

were able to use the cold river water as a cooling medium for the electronics.

Many would argue that the navigation controls were not adequate to determine centimeter 

scale changes to the bed material. We don’t argue this point, however, to attain a quick 

look at overall changes in bed texture and how the bed changes over tens of river miles, 

side-scan sonar is a very good tool.

Acknowledgements 

The Grand Canyon Monitoring and Research Center funded this work. Pete Dartnell, Phil 

Davis, and Dave Rubin (all USGS) reviewed this manuscript. We would like to thank Lars 

Neimi, Brian Derker, Stuart Reider, Steve Bledsoe, and other river guides for sharing their 

knowledge and helping with this project. Without them we would likely still be on the 

rocks at some point along the river. We would also like to thank Michael and Kelly Hamer, 

and Joseph Rios, for their assistance in the field, and Nenah Board and Yu Xia, for their 

help in organizing the data.

References 

Anima, R.J., Marlow, M.S., Rubin, D.M., Hogg, D.J., 1998, Comparison of sand 

distribution between April 1994 and June 1996 along six reaches of the Colorado 

River in Grand Canyon, Arizona. U.S. Geological Survey Open-File Report # 98-

141, 33 pages.

Stevens, L., 1983, The Colorado River in Grand Canyon, Red Lake Books, P.O. Box 

1315, Flagstaff, AZ. 86002. Third edition, 3rd printing, 1990. Library of Congress 

Catalog Card Number: 83-61589.

Wilson, 1998, Telephone conversation discussing the methods used during his survey.
8

Figures 

Figure 1. Map showing areas of side-scan sonar coverage between Glen Canyon Dam 

and river mile 87.5.
9

Figure 2. A 22-ft snout rig inflatable boat was used to collect side-scan data. White plastic 

waterproof boxes housed all electronics. The side-scan tow fish was raised and lowered 

using the lifting fame at the bow of the vessel.

Figure 3. Three side-scan lines were merged to make this mosaic of the Lees Ferry reach 

(miles 0 to –0.3). Lines were merged using MIPS software. Variations in reflectivity of 

riverbed features create the differing textural patterns. Refer to Figures 4 and 7 for 

additional details of each area enclosed in the boxes.
10

Figure 4. Images of bedrock. A. Bedrock with clear stratification. B. Bedrock partially 

covered with boulders and other sediment.
11

Figure 5. Sections of lines R3-00-SLC-1 and R4-00-SLC1 (between miles 60 and 61). 

Numbers identify the following bed features: (1) Bedrock with bedding planes is inferred 

from strong reflections (dark) and parallel continuous structure. (2) Pebbles or cobbles 

(dark) with patches of sand (light) are inferred to make a mottled pattern. (3) Boulders are 

inferred where reflectors are strong (dark) and individual objects can be resolved. (4) Sand 

is inferred where the bed appears light in color and uniformly smooth in texture. (5) Dunes 

composed of sand are inferred where dunes are relatively light. (6) Dunes composed of 

pebbles are inferred where dunes are relatively dark. (7) Dunes with sand crests and 

pebble or cobble troughs are inferred where troughs are dark.
12

Figure 6. Sections of lines R3-00-Sn_2_A and R4-00-Sn_1_A exhibit examples of an area 

of distorted boulders and bedrock due to yawing of the side-scan tow fish.
13

Figure 7. Sonar image containing features interpreted as dunes composed of sand, flat or 

rippled bed of sand, and flat bed of pebbles or cobbles.
14

Figure 8. Lees Ferry to Cathedral Wash reaches showing areas of change in bed texture 

and bedforms in the pre- and post-LSSF. M represents more sand cover; L represents less 

sand cover; and BFC represents areas of bedform change.
15

Figure 9. Below Cathedral Wash reaches also showing areas of change in bed texture and 

bedforms in the pre- and post-LSSF. M represents more sand cover; L represents less 

sand cover; and BFC represents areas of bedform change.