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Open-File Report 03-265

Grand Canyon Riverbed Sediment Changes, Experimental Release of September 2000 - A Sample Data Set

by Florence L. Wong1, Roberto J. Anima1, Peter Galanis1, Jennifer Codianne2, Yu Xia3, Randy Bucciarelli4, and Michael Hamer5

1U.S. Geological Survey, Menlo Park, California 94025; 2Santa Clara Valley Water District, San Jose, California; 3Mason, Bruce & Girard, Inc., Portland, Oregon; 4Scripps Institution of Oceanography, La Jolla, California; 5City of San Leandro, California


of water released from Glen Canyon Dam, 1996 Figure 1. Open floodgates on the Glen Canyon Dam, Arizona, during a previous experimental flood.
An experimental water release from the Glen Canyon Dam into the Colorado River above Grand Canyon was conducted in September 2000 by the U.S. Bureau of Reclamation. The U.S. Geological Survey (USGS) conducted sidescan sonar surveys between Glen Canyon Dam (mile -15) and Diamond Creek (mile 220), Arizona (mile designations after Stevens, 1998) to determine the sediment characteristics of the Colorado River bed before and after the release. The first survey (R3-00-GC, 28 Aug to 5 Sep 2000) was conducted before the release when the river was at its Low Summer Steady Flow (LSSF) of 8,000 cfs. The second survey (R4-00-GC, 10 to 18 Sep 2000) was conducted immediately after the September 2000 experimental release when the average daily flow was as high as 30,800 cfs as measured below Glen Canyon Dam (Figure 2). Riverbed sediment properties interpreted from the sidescan sonar images include sediment type and sandwaves; overall changes in these properties between the two surveys were calculated.


Sidescan sonar data from the USGS surveys were processed for segments of the Colorado River from Glen Canyon Dam (mile -15) to Phantom Ranch (mile 87.7, Figure 3). The surveys targeted pools between rapids that are part of the Grand Canyon Monitoring and Research Center (GCMRC physical sciences study.

Maps interpreted from the sidescan sonar images show the distribution of sediment types (bedrock, boulders, pebbles or cobbles, and sand) and the extent of sandwaves for each of the pre- and post-flow surveys. The changes between the two surveys were calculated with spatial arithmetric and had properties of fining, coarsening, erosion, deposition, and the appearance or disappearance of sandwaves.

This report describes GIS spatial data files for this project and provides examples of the data from the Colorado River near mile 2 below the confluence of the Paria and Colorado Rivers. The complete data set includes sidescan sonar images and interpreted map files for each of the pre- and post-flow surveys and the changes between the segments of river listed in Table 1 below.

Table 1. Segments of Colorado River in survey.
mile id description
-15 to 0 tw Glen Canyon Dam to Lees Ferry
0 to 3 bp below Paria Riffle; Lees Ferry to Cathedral Wash
4 to 8 bc below Cathedral Wash
27 to 29 ts Tiger Wash to Shinumo Wash
30 to 32 ssc Shinumo Wash to South Canyon
36 to 39 tp Thirty-Six Mile to President Harding Rapid
44 to 47 phs President Harding Rapid to Saddle Canyon
47 to 52 sn Saddle Canyon to Nankoweap Rapid
60 to 61 slc Sixty Mile Rapid to Little Colorado River
62 to 69 blcr below Little Colorado River
85 to 87 zc Zoroaster Rapid to Cremation



Sidescan sonar images were processed with the USGS Mini Image Processing System (MIPS) <>, a set of software tools that are used to convert rectangular blocks of raw data to georeferenced images in UTM 12 coordinates in MIPS "raw" or .bil (band interleaved by line) format. The processed images have pixel values 0 to 255, indicating a range of sonar reflectance from low to high. The resolution of the sidescan images is 0.2 meter per pixel. The images were converted to TIFF format for use with illustration software.

Sidescan sonar TIFF images were imported to Adobe Photoshop where the color mapping was inverted so that original 0 to 255 pixel values are rendered as white (0, low reflectance) to black (255, high reflectance) (Figure 4). Bedrock and boulders, which have high sonar reflectance, image as dark reflectors whereas sand and gravel, which have low sonar reflectance, image as various shades of white to dark gray. Features interpreted from the pre- and post-flow sonar images were drawn as vector layers in Adobe Illustrator.

Vector layers from Adobe Illustrator files were exported to Arc shapefiles with the Avenza Mapublisher plugin. Registration tics were generated from the registration world file of the sidescan sonar images. The upper left tic coordinates and a scale of 567 supplied to Mapublisher produces registered shapefiles. The shapefiles were converted to Arc coverages for editing and tagging.

Because of intermittent GPS coverage in the Grand Canyon, most coverages required further manual registration. The image and vector files in UTM 12 coordinates were converted to Arizona State Plane coordinates for conformance to GCMRC requirements.

Areas of change were determined with with grid arithmetic. Each of the riverbed types was assigned a value: bedrock 1, boulders 2, pebbles_cobbles 4, sand 8, and shoreline 16. The pre- and post-survey polygon files were converted to grids and the R3-00-GC grid was subtracted from the R4-00-GC grid. The difference values of interest appear in Table 2. A similar calculation was used to determine areas of "new sandwaves" and "sandwaves lost".

Table 2. Definition of Change Attribute
FROM_R3-00-GC TO_R4-00-GC
sand bedrock -7 erosion
sand boulders -6 coarsening
sand pebbles_cobbles -4 coarsening
pebbles_cobbles bedrock -3 erosion
pebbles_cobbles boulders -2 coarsening
boulders bedrock -1 erosion
bedrock boulders 1 deposition
boulders pebble 2 fining
bedrock pebbles_cobbles 3 deposition
pebbles_cobbles sand 4 fining
boulders sand 6 fining
bedrock sand 7 deposition



The Grand Canyon riverbed data are divided into pre- and post-release data sets, R3-00-GC and R4-00-GC, respectively. These data sets are further split into river segments, each of which includes the sonar images and related interpreted vector layers. The R4-00-GC river segments also have polygon files of changes noted between the two surveys. Each river segment, designated by xxx, is represented by the data files and their attributes described in the Table 3 below. The data file inventory appears in Table 4.

Table 3. Description of data files.
file name description attributes
r300xxx.tif, r400xxx.tif 0.2-meter resolution sidescan sonar images with pixel values 0 to 255. 0 represents nodata areas.
r300xxx, r400xxx polygon coverage of interpreted sediment types
values: bedrock, boulders, pebbles_cobbles, sand, shoreline
r300xxxsw, r400xxxsw polygon coverage of sandwave fields where present sedtype
values: starved_sand
chgxxxsw calculated polygon coverage of areas of bedform change between R3-00-GC and R4-00-GC change
values: new sandwaves, sandwaves lost
chgxxx calculated polygon coverage of areas of fining, coarsening, erosion or deposition between R3-00-GC and R4-00-GC change
values: coarsening, fining, deposition, erosion



The data sets have been assembled in a Arcview 3.2 project which displays a view of each of the R3-00-GC, R4-00-GC, and change data sets. A button tool permits the views to be synchronized to the window extent of any one of the three views (Figure 5 (76 kB)). For example, if the extent of the window in view "r400, azsp" is reset, the extent of the other two views are made to match by application of the button tool with the following Avenue script:

theView1 = av.GetProject.FindDoc ("r300, azsp")
theView2 = av.GetProject.FindDoc ("r400, azsp")
theView3 = av.GetProject.FindDoc ("r400-r300 change, azsp")


theExtent = theView2.GetDisplay.ReturnExtent
theView1.GetDisplay.SetExtent (theExtent)
theView3.GetDisplay.SetExtent (theExtent)



The segment of the Colorado River mapped in these images is approximately 17 miles downriver from Glen Canyon Dam where an experimental water release was conducted in September 2000. Maps of sediment type and bedforms from before (Figure 6) and after (Figure 7) the water release provide an idea of the the changes (Figure 8) that can be attributed to the increased stream flow during the release. The areas of the polygons of sediment type and bedforms for segment 'bp1a', downstream from where the Colorado River is joined by the Paria River, are provided in Tables 5 and 6 (only about half the segment is displayed in these maps). Within the limitations of the navigation, the calculations provide a qualitative view of the changes on the surface of the riverbed after the flow.

Table 5. Change in Extent of Sediment Types
polygon type R3-00-GC BP1A area (square meters) % of total R3 BP1A map area R4-00-GC BP1A area (sq m) % of total R4 BP1A map area difference
total BP1A area 179,000 179,600
bedrock 21,800 12% 14,500 8% -4%
boulders 19,900 11% 24,700 14% 3%
pebbles_cobbles 124,100 69% 118,900 66% -3%
sand 13,000 7% 21,400 12% 5%
sandwaves 42,900 24% 33,800 19% -5%
Table 6. Riverbed Change Characteristics
Change Description R3 to R4 change in BP1A (x 1000 sq m) change as % of BP1A area
fining boulders to pebbles/cobbles and/or to sand 14,800 8%
coarsening sand to pebbles/cobbles and/or to boulders 12,600 7%
deposition bedrock to sediment covered 10,900 6%
erosion sediment covered to bedrock 5,500 3%
sandwaves lost 21,700 12%
new sandwaves 14,700 8%

For this segment of the Colorado River near mile 2, areas of bedrock and pebbles or cobbles decreased after the water release. Areas of boulders and sand increased and sandwaves appeared to have decreased. The character of the changes fall into four types: (1) fining if a coarser sediment were replaced by a finer one, (2) coarsening if a finer sediment were replaced by a coarser one, (3) deposition if bedrock became sediment covered, and (4) erosion if sediment were removed to expose bedrock. Areas of fining and coarsening appear in subequal amounts. Areas of deposition are twice erosion for this sample area. Sandwaves disappeared from more areas than appeared in new areas.



FGDC-compliant metadata outline | Questions & Answers | Parseable text

R3-00-GC -

R4-00-GC -


Stevens, Larry, 1998, The Colorado River in Grand Canyon: A Comprehensive Guide to its Natural and Human History: Flagstaff, Arizona, Red Lake Books, 116 p.


For more information:

Florence L. Wong
Roberto J. Anima
Coastal and Marine Geology
U.S. Geological Survey
345 Middlefield Road MS 999
Menlo Park, California 94025


Mary McGann provided a helpful review of an earlier version of this report.

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government.

This report is adapted from a poster presented at the 23rd Annual ESRI International User Conference, San Diego, California, July 2003.


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