WSP00018

• File Number: 8220.101.10
• Description: Colorado River-Water Projects-Glen Canyon Dam/Lake Powel-Glen Canyon Adaptive Management
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 1/1/2003
• Author: USGS-GCMRC
• Title: Variations in Sand Storage Measured at Monumented Cross Sections in the CO River Between Glen Canyon Dam and Lava Falls Rapid Northern Arizona 1992-99
• Water Supply Pro - Doc Type: Report/Study

ted Ihat cross sections could be used to provide an
assessment of the sand storage in Ihe channel. the
storage conditions for possible bar-building high
releases. and Ihe effectiveness of those releases in
scowing stored sand and rebuilding sandbars,

Purpose and Scope

The purpose of this report is 10 document locations
of the 131 monumented cross sections. the measure-
ment dates during the study period June 1992 to
September 1999. and the methods ot' data collection
and processing. and to present a general assessment
of the variability in cross-sectional area, A subset of Ihe
data. referred 10 as the primary daIa set, was used
to illustrate the temporal and spatial variability in
cross-sectional area, In addition. a subset of the
primary data set consisting of data from measurements
made on or nearly on the same day at secIions
downstream from Ihe Pari a and Little Colorado Rivers.
referred 10 as the matching-date daIa set. was used to
further explore the eft'ects of hydro-logic conditions on
the changes in cross-secIional area. All cross-section
measurcment data are available electronically as ASCI!
files from the Arizona District Office of Ihe USGS
(address on back of Iitle page),

Acknowledgments

The authors thank the many people who provided
assisIance throughout the life of this project. In panic-
ular. we acknowledge Julia B, Graf, USGS (retired), for
her guidance and leadership in eSIablishing the
foundations upon which this project was developed,
We also thank Dave Anning, Greg Fisk. and Gail
Cordy of the USGS for their help in the preparation of
Ihis report.

Description of ,the Study Area

The study area includes the Colorado River
between Glen Canyon Dam and Lava Falls Rapid,
which is about 195 miles downstream from Glen
Canyon Dam in nonhel11 Arizona. The study area
encompasses parts of Glen Canyon National
Recreational Area and Grand Canyon National Park

(tig, I), In Ihis report. disIances along Ihe Colorado
River are expressed in river miles. and all other
measurements are expressed in metric units.

Physical and Hydrological Conditions

For much of its length Ihrough Ihe sJudy area. Ihe
Colorado River is con tined by bedrock. by large blocks
of talus, or by alluvial dcbris fans that are composed of
sediment too coarse to be transported except during
high tlows, Flow depths in the thalweg of the river
range from about 1,5 10 32 m at a discharge of
708 mJ/s, Depths can change abruptly. and there are
near-vertical drops of as much as 15 m in gorges
fanned in the meIamorphic and igneous rock (Wilson.
1986). Between Lees Ferry (river mile 0) and Diamond
Creek (river mile 226). the elevation of the river
decreases about 542 m, Much of Ihe decrease in
elevation occurs in short. steep reaches. many of which
are the well-known rapids of the Colorado River,
Although Ihe average gradient between Lees Ferry and
Diamond Creek is 0.0015. the gradient of many of Ihe
short reaches exceeds 0,0 I (Schmidt and Graf, 1990),
Many of the reaches between rapids have gradients less
Ihan 0,0005 (Birdseye. 1923l.
In the study area. tributaries of the Colorado Rivcr
can be categorized as those having headwaters above
the (im and those having headwaters below the rim,
The Paria and Colorado Rivers are tributaries having
headwaters above Ihe rim; their drainage basins include
large plateau areas. and they supply mosI of the
suspended sediment to the Colorado River within the
sllIdy area, Tributaries having headwaters below the
rim have drainage basins largely within Ihe inner
canyon and can transport tine sediment as well as large
boulders ill debris !lows (Cooley and others. 1977;
Webb and others. 1989), The debris !lows from these
smaller tributaries define the longitudinal protile and
control the geomorphic framework of the Colorado
River by forming rapids (Webb, ]996). In addition, the
debris fans direcIly control the formation and stability
of most sandbars (Schmidt. 1990; SchmidI and Graf.
1990: Schmidt and Rubin. 1995),
In general. the channel pattern of the Colorado
River through the sJudy area is dominated by an
alternating rapid-pool sequence (Howard and Dolan.
1981), Flow through the constrictions created by the
debris-tlow deposits at the mouths of tributaries forms
the rapids, Flow through rapids ends in pools (Dolan

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4 Variations in Sand Stor~ge ,.,1a'~~red in the Colorado River Between Glen Canyon Dam and Lava Falls Rapid, Northern Arizona, 1992-99