Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter.
Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 70
5
Sediment and Geomorphology
WHY SEDIMENT AND GEOMORPHOLOGY ARE IMPORTANT
Sediment is an integral part of the Grand Canyon river system. Sand
entering the Colorado River from the major tributaries moves through the
canyon with the river and is deposited as bars. When the bars are above the
water surface, they become the beaches on which the river runners camp.
Occasional movements of coarse substrate (debris flows) from tributaries
create the rapids that the boaters thrill to travel through. Sand and debris
flows provide habitat for riparian and aquatic communities. Thus, an un-
derstanding of the processes that create bars, beaches, and rapids is a
necessary part of the Glen Canyon Environmental Studies (GOES).
Amount of Sediment Is Not a Problem in the Grand Canyon
There is adequate sediment, of which sand is the dominant constituent,
entering the Colorado River below Glen Canyon Dam to maintain bars and
beaches. In fact, sand would not accumulate in the canyon if flow from the
dam were constant (BOR, 1993, p. 90) but would collect in the channel and
in low bars, with an elevation just below the elevation of the water surface.
Thus, the problem of sand in the Colorado River is not the amount of sand but
rather its distribution.
70
OCR for page 71
Sediment and Geomorphology
71
Management of Sediment
Maintenance of beaches above mean water level requires some pro-
cedure for raising the water level temporarily for beach-building flows. The
amount of discharge (height of water in the channel) will determine the height
of the beaches that are built by beach-building flows. Furthermore, beach
building will be most successful when there is a large supply of sand near the
upper end of the Grand Canyon. A sand budget must be maintained that
shows the amount and distribution of sand.
As we will discuss later in this chapter, the critical reach for sand man-
agement is between the Paria and the Little Colorado rivers. Research and
data collection should concentrate on that reach of river. Of secondary
concern is the reach from the Little Colorado River to Phantom Ranch. Much
less important in terms of sand management is the reach below Bright Angel
Creek.
Sand cannot be lifted onto beaches without occasional high flows (An-
drews, 1991~. The amount, duration, and scheduling of high flow are ele-
ments of management decisions that must be based on good scientific data
plus reliable physically based models. In general, higher and longer flows
create higher beaches. Beach-building flows should coincide with the
presence of high amounts of sand in the reach from the Paria to the Little
Colorado rivers; this sand will be lifted to beaches downstream by the high
flows.
At present, the sand supply from the Paria River is less well known than
that of the Little Colorado River. The Paria should be closely monitored so as
to reduce the uncertainty in the river's sediment transport record. A study of
the relationship of accuracy to frequency of sampling should be undertaken
for the Paria.
Rapids
Rapids in the Grand Canyon are created by debris flows from minor
tributaries throughout the canyon. Sands and gravels are eroded from the
debris flows, leaving behind the cobbles and boulders. The debris flows
narrow the area of flow and thus create the rapids.
The size of the materials removed from the debris flow deposits depends
on the peak flows that pass around and over the debris. Before the closing
of Glen Canyon Dam, the rapids were reworked by large annual floods and
OCR for page 72
72
River Resource Management in the Grand Canyon
by occasional massive floods. Thus, the rapids might constrict the channel,
but the amount of constriction was periodically reduced by annual and
occasional major floods.
Without inadvertent spills, as occurred in 1983, or deliberate flood flows,
Glen Canyon Dam would cause the rapids to increase in size. Without flood
flows, there would be no mechanism to remove the large material in the
debris flows (Cooley et al., 1977; Dolan, 1981; Kieffer, 1987~. Each time a
debris flow occurs at a site of an existing rapid, the new debris will further
constrict the channel. Over a period of time, rapids could become impass-
able, and river runners would need to portage around them. Thus an under-
standing and monitoring of the debris flows and their removal mechanism
were integral parts of GCES.
Sand as Substrate
Sand deposits are a substrate that supports riparian and aquatic
organisms in the canyon river corridor. Backwaters behind the beaches
provide habitat for warmwater-adapted fishes, such as the humpback chub
(Chapter 6~. Releases from Glen Canyon Dam are cold and swift, and the
backwaters reduce current velocity and may also give the water a chance to
warm. The bars and beaches support vascular plants and thus provide
habitat for terrestrial animals. Thus, an understanding of the physics of the
sand system and of the geomorphology of the canyon are important for
understanding the occurrence and abundance of the flora and fauna
throughout the canyon.
In the past, sand has covered archeological sites and thus has protected
them. Periodic erosion of the sand through local flooding was offset by
deposition of new sand from the annual floods of the Colorado River. Without
the high annual floods and occasional rare large floods in the Colorado River,
local erosion on the beaches and bars will not be offset by deposition without
some inclusion of high flows in the management plan for the dam. Local
runoff now creates gullies and thus exposes ancient sites. Only flood flows
can reverse this trend (Hereford et al., 1991~.
SEDIMENT STUDIES OF GCES PHASE I
GCES began in 1982 in response to concerns about the effects of Glen
OCR for page 73
Sediment and Geomorphology
73
Canyon Dam on the resources of the Grand Canyon. The planners of Phase
I of GCES recognized that sediment is a major resource of the Grand Canyon
river corridor. The daily fluctuations of flow from Glen Canyon Dam (Chapter
4) were thought to erode the beaches and thus diminish the resources for
river runners as well as the native fishes and riparian biota of the canyon.
Almost as soon as GCES Phase I was organized, exceptionally high
runoff occurred (in 1983~. The resulting unusual spill from the dam radically
altered the canyon and its beaches in ways that were difficult to anticipate.
Thus, the high flows disrupted the original plans for GCES Phase 1.
Bureau of Reclamation Model
GCES Phase I included studies of sediment movement through the Grand
Canyon and emphasized modeling of flow and sediment transport. Modeling
was undertaken by the Bureau of Reclamation (BOR), which planned to adapt
a preexisting steady-state program to model the flow through the canyon
(Randle and Pemberton, 1987~. The movement of flood waves was modeled
by a series of steps involving different discharges. Thus, the flow was allowed
to vary, but the shape of the flood wave was held constant.
The BOR modeled sand movement by using the hydraulics developed by
the water-routing model with calibration to sand discharge relationship at
various control points in the canyon. The gauge below the Little Colorado
River and the long-term gauge at Phantom Ranch (Bright Angel Creek) were
to be the anchors of the model, and other temporary gauges were used to
supplement the data base.
There were two major flaws in the BOR approach to modeling in GCES
Phase 1. First, a steacly-state model cannot predict the attenuation of a flood
wave as it moves down a river. The second major flaw was that the sand
discharge relationships at several measurement sites in the canyon could not
be differentiated from each other. Thus, the model was necessarily calibrated
to identical relationships at different sites, which led to the conclusion that the
sand input and output would be the same throughout the reach of the canyon
modeled. Thus, there was no basis for estimating the variation in storage of
sand within reaches of the canyon.
GCES Phase I monitored the beaches, their geometry, and theirvolume.
There was, however, no strategy for relating these results to the water- and
sediment-routing model.
OCR for page 74
74
River Resource Management in the Grand Canyon
Early Assumptions Concerning Sediment Movement
GCES started with the assumption that beaches were being eroded
throughout the Grand Canyon and that the cause was fluctuating flows
released from Glen Canyon Dam. The judgments stated above were those
of the river boatmen, but they strongly influenced the GCES researchers.
These assumptions influenced the decisions concerning what should be
studied, how it should be studied, and, more importantly, the conclusions
from GCES Phase 1. Part of the learning experience of GCES Phase I was to
set research goals as scientific hypotheses to be tested rather than ass-
umptions to be verified.
Coordination and Communication
"Unfortunately, the critical linkage of sediment/water flow in the main
channel was pursued predominantly as an exercise in its own right, largely
divorced of concerns about sediment sources and sinks and with inadequate
attention to modeled sediment movement to beaches, riparian habitats, and
so on" (NRC, 1987, pp. 88-89)-so stated the National Research Council
(NRC) committee in its assessment of the sediment work in GCES 1. Good
work was performed and excellent data were collected, but there was little
coordination among the different elements of the research team. Elements
were added to the plan as time showed that the original plan would not
provide sufficient information. The spill of 1983 radically altered the work plan
but did not lead to full integration of the study team.. New projects were
added to study newly perceived problems, but each project remained
essentially an independent entity. There was little coordination of results and
little exchange of information among research teams. The water and sand
modeling was not related to the beach studies, and there was no mechanism
for the results of one to be integrated into the work plan of the other.
Leadership for GCES
GCES I was organized around the capabilities and approaches of
governmental agencies. Each agency pursued its work independently, with
little sense of overview. This resulted partly from the fact that each agency
was considered an expert in its field, and the GCES leadership was not
OCR for page 75
Sediment and Geomorphology
75
sufficiently empowered to overrule the judgment of individual agencies forthe
benefit of GCES (Chapter 2~.
For sediment research the agencies were asked to propose projects that
would address the general goals of GCES. There was no a priori statement
of tasks, with work plans, and with requests for agencies to perform the work
as designed by GCES. Thus, for example, the BOR worked on its water and
sediment model without anyone asking how the model and its results would
fit into the solution of the problems to be addressed by GCES 1.
NRC Committee Recommendations After GCES ~
At the end of GCES 1, the NRC committee made several suggestions
concerning future GCES work. Several suggestions were particular to sed-
iment work. Others, though more general, had direct bearing on it. The
particular sediment-related suggestions were summarized as follows: "Future
work by the Department of the Interior should seek to look for connections
between research disciplines in the planning phases of the study, initiate
studies of tributary processes because they are the main source of sediment
in the Colorado River main stem, include in future hydrologic research
empirical approaches es well as modeling approaches, link sediment studies
to biological and hydrological monitoring and research, and institute
geomorphic studies to supplement the hydraulic studies of the Colorado
River system in the Grand Canyon" (NRC, 1987, p. 8~. The GCES team
implemented some of these suggestions. In particular, the tributary sources
of sediment were given more emphasis. Both empirical and physically based
modeling replaced the original modeling effort. The general problems of
coordination and integration persisted. Different groups collecting similar
data at a site dicl not always communicate their findings or plans to each
other. There seemed to be no understanding that the data collection could
be better coordinated, so that the overall results of GCES could be achieved
with less effort. There seemed to be little attempt by researchers to query
each other before a river trip to determine whether there were data that could
be collected for general use or that could be collected in a slightly different
manner or format for the benefit of others. As an example, the slopes of the
bar faces were studied, but bar topography was documented separately and
without acknowledgment of the values of computing bar face slopes for use
by others.
OCR for page 76
76
River Resource Management in the Grand Canyon
WHAT IS NEEDED CONCERNING SEDIMENT
AND GEOMORPHOLOGY
Sediment Budget
The perception of the problems concerning sand in the Grand Canyon
changed over the life of GOES. One of the concepts that instigated GOES
was the belief that fluctuating flows from the Glen Canyon Dam were causing
a loss of the sand bars, which are the camping beaches on which the public
depends in their trips through the canyon. It was thought that steady flows
would reduce the removal of sands and improve the condition of the canyon
as a whole.
About 790,000 tons of sand enterthe Colorado River annuallythrough the
Paria, and another 1,600,000 tons enter through the Little Colorado River.
Kanab Creek contributes 300,000 tons per year, and other minor tributaries
arm debris flows from side canyons contribute about 700,000 tons of Sara per
year. Thus, there is on average, over 3 million tons of sand delivered per year
to the river corridor (BOR, 1993, Appendix D). If the releases from Glen
Canyon Dam were constant, about 11,400 cubic feet per second (cfs) would
correspond to a release of 8.25 million acre-feet (ma] per year as specified
by the Law of the River, and 15,200 cfs would carry the average inflow to Lake
Powell (11 mat per year). A steady flow of 15,200 cfs would carry about
550,000 tons of sand per year to the Little Colorado River, and some 1.13
million tons per year past Phantom Ranch and out of the canyon into Lake
Mead (BOR, 1993, Appendix D). Thus, with steady flows, sand would ac-
cumulate in the canyon (almost 2 million tons per year). It would accumulate
in the main channel, however, and not on the beaches and bars.
Wave action eventually would cause all bars to erode to the elevation of
the water if flows were steady. If steady flow persisted, more of the bottom
of the channel would be covered with sand and a new equilibrium condition
would developthatwould carrythe sand through the Grand Canyon with bars
at water level. The only variation in this condition would be temporary,
following storm flows from the Paria and Little Colorado rivers, which might
deposit sand at higher elevations.
Sediment Budget by Reach
The problem of sand management varies in different parts of the canyon.
OCR for page 77
Sediment and Geomorphology
77
In the first 16 miles, from Glen Canyon Dam to Lees Ferry and the mouth of
the Paria River, there is almost no sand inflow (38,600 tons per year from
minor tributaries). Therefore, the sand storage in that reach is declining.
Sand transport past the mouth of the Paria therefore is a net loss to the reach
above. This can be ameliorated only by sand augmentation, which presently
seems unlikely (Chaptered. Otherwise, all sand in thefirst 16 miles eventually
will move downstream, and there will be no beaches in that reach.
In the next 61 miles, between the mouth of the Paria and the mouth of the
Little Colorado, the only significant sand supply is from the Paria. The
distribution of sand in that reach is dynamic, and the capacity of the water
much exceeds that required to move the sand downstream. This is the
critical reach, and the problem of sand management is to keep as much sand
as possible on the beaches and out of the main channel.
Below the Little Colorado River, almost the total supply of sand is
available in the Colorado River. The first 26 miles, between the Little Colorado
to Bright Angel Creek, will, however, have periods of beach erosion when
sand supply to the Colorado River from the Little Colorado is below normal.
Beach erosion should be considered normal during periods of sand supply
deficit, and sand accumulation should be expected during periods of high
sand transport from the Little Colorado.
Any strategy that improves the reach from the Paria to the Little Colorado
probably also will improve the reach just downstream from the Little
Colorado. This is because the flows from the Paria and the Little Colorado
are correlated; high flows and high transport of sand usually occur from both
in the same year. Thus, when there is a supply in the upper reach to be
managed, there usually is a supply in the reach just below the Little Colorado
also.
The Paria, which is much smaller than the Little Colorado (Chapter 4),
may not increase the main river flow sufficiently to transport the sand that it
delivers. Thus, much of the sand contributed by the Paria will tend to remain
in the channel immediately below the river's mouth. In contrast, the peak
flows from the Little Colorado combined with flows from the Paria and with
dam releases often exceed the power plant capacity of 31,500 cfs from Glen
Canyon Dam and will deposit materials on the beaches throughout the
system downstream from the Little Colorado. In particular, if the Little
Colorado peak coincides with high flow from Glen Canyon Dam, a sizable
peak of discharge and transport can occur.
The most critical piece of information in the sand budget will be the
amount of sand in the main channel between the Paria and the Little Col
OCR for page 78
78
River Resource Management in the Grand Canyon
orado. There should be some decision criterion that triggers the release of
beach-building flows sufficient to deposit sand from the main channel onto
the beaches in the reach above the Little Colorado. The amount of sand in
storage in that reach should be a part of the triggering, as well as the water
stored in Luke Powell. When both are above normal, beach-building flows
can and should be planned.
Sand Distribution Between Main Channel and Beaches
Beaches form where ecldies can remove sand from the main channel.
Beaches often form below rapids, which create eddies downstream. Know-
lecige of the mechanism of eddy formation, the variation of the mechanism
with discharge, and the process for transfer of suspended sand across the
eddy fence (a vertical plane that clivides an eddy field from other parts of the
channel flow that are moving in a downstream direction) into the eddy field
(an area of flowing water where motion occurs in a circular fashion or in a
reverse direction to the rest of the channel) is needed.
Preliminary evidence seems to indicate that the transfer of suspended
sand from the main channel across the eddy fence is fairly rapid (Dawdy,
personal communication, 1993~. Therefore, the bars will not be eliminated as
long as there is suspended sand in the main channel. Eventually, the bar
within an eddy will develop to a height about equal to the steady water level.
Thus, a strategy must be developed not only for predicting the movement of
sand across the eddy fence but also for predicting the deposition of sand on
the beaches at higher elevations during beach-building flows.
The river stage heights of the beach-building flows will determine the
height of the camping beaches. The greaterthe flows, the higher the beaches
will be and the greater the amount of sand that will be stored on the beaches.
An understanding of the eddy system and its role in beach building is an
integral part of managing the resources of the Grand Canyon.
Flood Waves
Peaks attenuate as they travel downstream. The attenuation can be
predicted quitewell with the modelsdeveloped bythe USGS for GOES (Smith
and Wiele, in press). The flood wave changes shape as it moves down-
stream, and the travel time of the wave varies as it moves downstream (Figure
OCR for page 79
Sediment and Geomorphology
79
5.1~. The leading edge of the wave steepens as the wave moves downstream,
whereas the falling edge becomes less steep. As peaks attenuate and peak
stages are lower, the beaches that the wave can build will be at a lower
elevation. Also, brief peaks deposit less sand. An understanding of this
interaction between sand deposition and beach-building flows should be
developed, so that the sand resource can be managed throughout the
system.
U.S. Geological Survey Effort on Sediment Modeling
The U.S. Geological Survey (USGS) has developed a water-routing model
that can predict the transformation of the flood wave down the channel. The
steepening of the wave front, flattening of the back of the wave, lowering of
the peak, and increase in discharge at the trough can be modeled. Thus, for
any time at a given site, the USGS model can be used to predict the elevation
of water level, given a history of discharge (Smith and Wiele, in press).
The linking of discharge to sand transport is more tenuous. The USGS
uses a reach-averaged cross section to model the stage. It uses the
percentage of bottom covered by sand as input to its sediment transport
prediction. There seems to be no periodic updating of the cross section as
sand is predicted to accumulate or erode. The model is calibrated to the
sediment collection sites in the canyon, which are the source of information
on percentage of the bottom covered by sand in the reaches upstream from
each measurement site. The model is an improvement over the steady-state
model of GOES 1, but it still is the weak link in the modeling needs for
managing sand.
USGS Effort on Eddy Modeling
Eddy modeling is farther along than main channel modeling, although it
was less well understood when GOES began. There has been more
emphasis on this aspect of sediment modeling than on any other, and there
have been more workers attacking the problem from different aspects. Also,
there seems to be good communication among workers studying geo-
morphic and mathematical aspects of ecidy formation, circulation, and bar
building.
OCR for page 80
80
60 - .
50
40
° 30
-
a)
20
10
O
River Resource Management in the Grand Canyon
D
/~
, .
./
B
\~ ~
o
50
100 150 200
River mile
FIGURE 5.1 Travel time as a function of river mile for discharge waves during Research Flows
B and D (solid line) compared to predicted travel times [dashed line with single dots (b) and
dashed line Idol. The smaller-amplitude discharge wave of Research Flow B had a lower phase
speed and therefore is the lower of the two solid lines. SOURCE: U.S. Geological Survey
(1991~.
Linking of Sediment Modeling and Eddy Modeling
At the present time, there still is a need for linking the main channel water
and sand discharge with the eddy system and the growth of bars. The
deficiency at this time appears to be more in the main channel sand modeling
than in the eddy modeling. Some first-approximation results based on the
connection of the sand transport model and the eddy circulation model
should be developed to predict the growth of bars.
NAU Beach and Bar Studies
Northern Arizona University (NAU) has an extensive program on mapping
of bars (Beus et al., 1994~. There seems to be little attempt at quantitatively
relating these measurements to the building of bars or to using the data for
scheduling beach-building flows. Various data collection efforts should have
been coordinated with each other. The types of data collected should have
OCR for page 81
Sediment and Geomorphology
81
been determined by GCES management, so that the NAU data could have
been used by other researchers.
WHERE WE STAND NOW
The GCES has added considerably to our understanding of the physics
of sand movement in the Colorado River below Glen Canyon Dam, but there
is still much that needs to be understood. Among the GCES findings related
to sediment are:
· There is a sufficient amount of sand reaching the Colorado River to
maintain the beaches. The problem is one of management of the sand in the
river.
· Beach-building flows that are greaterthan normal maximum operating
flows are necessary to place sand on the beaches to develop camping sites.
· The transformation of the flood wave as it travels downstream from
Glen Canyon Dam can be modeled, so that stage and discharge at any point
and at any time along the Colorado downstream from the dam can be
estimated.
· The critical reach for sand budget and beach stability is that from the
Paria to the Little Colorado.
· Rapids in the Grand Canyon will continue to grow, with no mechanism
to rework rapicis, unless controlled floods are part of the management plan.
RECOMMENDATIONS
GCES has improved our understanding of sand movement and storage
below Glen Canyon Dam. GCES sponsored the development of a more
physically based analysis of the sediment transport and the eddy circulation
system of the Colorado River system. GCES also acivanced our under-
standing of the bar-building system of the Colorado River. New knowledge
of changes of bar area and volume over time has given more insights into the
change of the Grand Canyon river corridor and bar slope failure is better
understood as a result of physically based modeling. The qualitatively rapid
interchange of sand between the main channel and the eddy systems has
been defined. The need for beach-building flows has been presented and is
generally accepted by researchers. Several kinds of continuing research and
monitoring will enhance the potential for beneficial management of sediment
OCR for page 82
82
transport:
River Resource Management in the Grand Canyon
· Study of the rate of sand interchange between the main channel and
the eddy systems that create beaches.
· Development of a mechanism for determining the initiation of beach-
building flows.
· Development of quantification of the magnitude and duration of beach-
building flows.
~ Study of the rate at which sand is deposited on beaches during beach-
building flows.
· Creation of a procedure for determining sand budgets in different parts
of the canyon downstream from Glen Canyon Dam.
Less emphasis should be placed on collection of qualitative geomorphic
data and more on the understanding of sediment transport processes, es-
pecially through the use of quantitative, physically based models of the
system. For example, problems in using the Sediment Transport and River
Simulation (STARS) water-routing model along with sediment rating curves
to determine sediment transport through the Grand Canyon might have been
identified earlier if more thought had been given to what was needed and how
the modeling efforts would be used to meet those needs.
If the present data collection methods of the U.S. Geological Survey
cannot provide adequate accuracy, support of the USGS program should be
shifted to monitoring the amount of change of sand volume in the critical
reaches. If the amount of sand and the change in volume in the main channel
cannot be measured with accuracy, the BOR should rethink its priorities for
study of sediment transport and develop an alternative method for de-
termining the timing and magnitude of beach-building flows.
Management should coordinate the research and monitoring, even
across agency lines. There should be more communication among the work-
ing groups. At the very least, each research team should know who is
collecting data, where the collection will occur, and the methods that will be
used. Data should be exchanged. Before going into the Grand Canyon, each
team should ask whether it can collect data for other researchers.
OCR for page 83
Sediment and Geomorphology
83
REFERENCES
And rows, E.D. 1991. Sediment transport in the Colorado River basin. Pp.
54-74 in Colorado River Ecology and Dam Management. Washington,
D.C.: National Academy Press.
Beus, S.S., M.A. Kaplinski, J.E. Hazel, Jr, and L. Kearsley. 1994. Monitoring
the Effects of Interim Flows from Glen Canyon Dam on Sand Bar
Dynamics and Campsite Size in the Colorado River Corridor, Grand Can-
yon National Park, Arizona. Draft Final Report, U.S. Geological Survey.
Bureau of Reclamation. 1993. Operation of Glen Canyon Dam. Draft
Environmental Impact Statement, U.S. Department of the Interior, Wash-
ington, D.C.
Cooley, M., B. Aldridge, and R. Euler. 1977. Effects of the catastrophic flood
of December 1966, north rim area, eastern Grand Canyon, Arizona. U.S.
Geological Survey Professional Paper 980.
Dawdy, D.R. 1993. Personal communication between David Dawdy and
Jonathan l~lelson at GOES research meeting, October 14, Boulder, Colo.
Dolan, R., and A. Howard. 1981. Geomorphology of the Colorado River in
the Grand Canyon. Journal of Geology 89:269-298.
Hereford, R., H. Fairley, K. Thompson, and J. Balsom. 1991. The Effect of
Regulated Flows on Erosion of Archaeologic Sites at Four Areas in
Eastern Grand Canyon National Park, Arizona: A Preliminary Analysis.
U.S. Geological Survey, Reston, Va.
Kieffer, S.W. 1987. The Rapids and Waves of the Grand Canyon. USGS
Open-File Report 87-096, U.S. Geological Survey, Reston, Va.
National Research Council. 1987. River and Dam Management.
Washington, D.C.: National Academy Press.
Randle, T.~., and E.L. Pemberton. 1987. Results and Analysis of STARS
Modeling Efforts of the Colorado River in Grand Canyon. Final Report,
U.S. Bureau of Reclamation, Washington, D.C.
Smith, d.D., and S. Wiele. In Press. Flow and Sediment Transport in the
Colorado River Between Lake Powell and Lake Mead. Boulder, Colo.:
USGS Water Resources Division.
Representative terms from entire chapter:
colorado river
