GEOMORPHIC RESPONSE OF SANDBARS TO THE MARCH 2008 HIGH-FLOW 

EXPERIMENT ON THE COLORADO RIVER DOWNSTREAM FROM GLEN 

CANYON DAM 

Paul E. Grams, Hydrologist, U.S. Geological Survey, Southwest Biological Science Center, 

Grand Canyon Monitoring and Research Center, Flagstaff, AZ, pgrams@usgs.gov 

Joseph E. Hazel, Geologist, Northern Arizona Univ., Flagstaff, AZ, Joseph.Hazel@nau.edu 

John C. Schmidt, Professor, Utah State Univ., Logan, UT, jack.schmidt@usu.edu 

Matt Kaplinski, Geologist, Northern Arizona Univ., Flagstaff, AZ, matt.kaplinski@nau.edu 

Scott A. Wright, Hydrologist, U.S. Geological Survey, California Water Science Center, 

Sacramento, CA, sawright@usgs.gov 

David J. Topping, Hydrologist, U.S. Geological Survey, Southwest Biological Science 

Center, Grand Canyon Monitoring and Research Center, Flagstaff, AZ, 

dtopping@usgs.gov 

Theodore S. Melis, Deputy Center Chief, U.S. Geological Survey, Southwest Biological 

Science Center, Grand Canyon Monitoring and Research Center, Flagstaff, AZ, 

tmelis@usgs.gov 

ABSTRACT: The completion of Glen Canyon Dam in 1963 drastically altered the downstream 

flow regime and resulted in more than a 90 percent reduction of sand supply to the Colorado 

River in Grand Canyon National Park. Sandbars that were maintained by annual floods and a 

large sediment supply are now fewer in number and smaller in area and volume. Efforts to 

maintain sandbars in the current era of dam management utilize controlled floods timed to occur 

during brief periods of sediment enrichment that result from tributary floods. Repeat surveys of 

22 sandbars made before and after controlled floods conducted in 1996, 2004, and 2008 

document changes in sandbar volume; and repeat surveys at more than 100 sites document 

changes in sandbar elevation and morphology for the 2008 event. Each of the controlled floods 

resulted in sandbar deposition that was followed by erosion in the 6-month post-flood period. 

Erosion rates are positively correlated with post-flood dam release volumes and negatively 

correlated with post-flood tributary sediment supply volume. October 2008 sandbar volume was 

similar or larger than sandbar volume in February 1996, before the first of the three controlled 

floods. Deposition during the 2008 controlled flood was also associated with increases in the 

quantity of backwater habitat, which is used by native and non-native fish. 

INTRODUCTION 

Prior to completion of Glen Canyon Dam in 1963, sand accumulated on the bed of the river 

during much of the summer and fall (Howard and Dolan, 1981; Topping and others, 2000). 

Annual snowmelt-driven spring floods typically redistributed this sediment to form expansive 

sandbars (Schmidt and Graf, 1990; Webb, 1996). These sandbars are a unique feature of the 

predam landscape, provided substrate for riparian vegetation, created beaches for recreational 

use, shaped aquatic habitat for native fish, and deposited fluvial terraces which buried 

archeological sites (Howard and Dolan, 1981; Kearsley and others, 1994; Stevens and others, 

1995). Completion of Glen Canyon dam in 1963 reduced the supply of sand to the Colorado 

River downstream from Lees Ferry, Arizona by more than 90 percent (Topping and others, 

2000). In addition, dam-regulated flows that are constrained to the range of powerplant 

2nd Joint Federal Interagency Conference, Las Vegas, NV, June 27 - July 1, 2010
operations limit the area over which deposition can occur during the infrequent periods of 

increased tributary sand supply. Sandbars in the post-dam era are fewer in number (Schmidt and 

Graf, 1990), smaller in areal extent of exposed sand (Schmidt and others, 1999; Hazel and 

others, 1999; Wright and others, 2005), and are lower in elevation (Schmidt and others, 1995). 

Figure 1 Study sites monitored in each controlled flood (red), and additional study sites 

monitored in 2008 (yellow). The Marble Canyon reach extends from Lees Ferry, Arizona to the 

Little Colorado River; the Grand Canyon reach extends from the Little Colorado River to 

Diamond Creek. 

Since 1996, three controlled floods have been conducted in the Colorado River downstream from 

Glen Canyon Dam (Figure 1). In this context, a controlled flood is defined as a planned release 

from the dam that exceeds the peak capacity of the hydroelectric powerplant (~940 m3

/s) by at 

least 30 percent (U.S. Department of the Interior, 1995). In the management context, these events 

have also been termed “beach habitat-building flows” and “high-flow experiments.” The central 

purpose of these experiments has been to determine whether controlled floods can be used to 

increase and maintain the amount of sand present in sandbars that are located in eddies and along 

the channel margins and thereby increase the number and size of beaches used by campers and 

sustain certain aspects of aquatic habitat. During the first controlled flood, conducted in March 

and April 1996, water was released at a rate of about 1,274 m3

/s (as measured at Lees Ferry, 

Arizona) for 7 days (Figure 2). Although this event resulted in an increase in sandbar elevations, 

2nd Joint Federal Interagency Conference, Las Vegas, NV, June 27 - July 1, 2010
measurements made of sand-storage change in eddies (Andrews and others, 1999; Hazel and 

others, 1999; Schmidt and others, 1999), measurements of sand flux (Topping and others, 1999; 

Rubin and others, 2002); and sand budgets (Schmidt, 1999; Hazel and others, 2006) indicated net 

erosion of sand from low-elevation (that is, below the stage associated with a discharge of 

approximately 227 m3/s) parts of eddies and the channel. The second controlled flood, with a 

shorter duration of 2.5 days and a slightly lower peak magnitude (1,187 m3/s at Lees Ferry), was 

conducted in November 2004 following tributary sediment input events from the Paria River 

(located 25 kilometers below the dam). The purpose of the 2004 controlled flood was to test 

whether it was possible to increase sandbar size without causing net erosion from eddies and the 

channel. Measurements of sand-storage change and sand flux showed that net deposition did 

occur in the upstream portion of Mable Canyon (from Lees Ferry to 69 km downstream of Lees 

Ferry) where pre-flood sediment enrichment was greatest (Topping and others, 2006). 

Downstream from this point, where sand enrichment was less, there was less deposition. 

0

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2004

2008

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2004 sandbar surveys

2008 sandbar surveys

DISCHARGE, IN CUBIC METERS PER SECOND

DAY RELATIVE TO DAY ONE OF CONTROLLED FLOOD

Figure 2 Discharge for the Colorado River at Lees Ferry, Arizona (USGS Station 09380000) for 

the 50 days preceding and the 250 days following each of the controlled floods. The dates of the 

pre-flood, post-flood and 6-month post-flood sandbar surveys are also shown. 

Tributary sediment inputs in 2006 and 2007 resulted in sand accumulation in all river segments 

between Lees Ferry and Diamond Creek. The March 2008 high-flow experiment (HFE) was 

conducted to determine whether a controlled flood conducted under these conditions of greater 

sand supply would result in net sandbar deposition over a greater portion of the river corridor in 

Marble Canyon and Grand Canyon. The average discharge of 1203 m3

/s during the 2008 HFE 

was about six percent lower than the average discharge during the 1996 controlled flood, but 

similar in magnitude and identical in duration to the 2004 controlled flood (Figure 2). Inflow 

from the Little Colorado River during the 2008 HFE increased the average magnitude of the 

2nd Joint Federal Interagency Conference, Las Vegas, NV, June 27 - July 1, 2010
event to 1,248 m3

/s downstream from the confluence, 49 m3/s less than the average flow during 

the 1996 controlled flood for that segment of the river. 

This paper reports results associated with the 2008 HFE and subsequent dam operations with 

respect to changes in sandbar size and extent and changes in associated backwater aquatic 

habitat. Sandbar deposition and post-controlled flood sandbar erosion rates for 2008 are 

compared with observations from the 1996 and 2004 controlled floods. These findings 

summarize results reported by Hazel and others (2010) and Grams and others (2010). 

METHODS 

The 2008 controlled flood was monitored by repeat topographic and bathymetric surveys of 

selected study sites that were analyzed to determine changes in sand storage volume and changes 

in backwater habitat volume. A total of 108 sites were surveyed four times in 2008. Surveys at 

41 sites included measurements of sandbar topography and channel bathymetry, while surveys at 

the remaining 67 sites consisted only of sandbar topography. Sandbar topography was surveyed 

by electronic total station and bathymetry was surveyed by multibeam sonar (Hazel and others, 

2010). 

Comparison between the three controlled floods was only possible for the subset of sites that 

were surveyed before and after the previous controlled floods. There were 7 sites in Marble 

Canyon that were surveyed before, immediately after, and six months after all controlled floods; 

and 15 sites in Grand Canyon surveyed before, immediately after, and six months after the 1996 

and 2008 controlled floods (Figure 1). The Marble Canyon reach extends from Lees Ferry 100 

km downstream to the Little Colorado River confluence. The Grand Canyon reach extends from 

the Little Colorado River confluence 264 km downstream to Diamond Creek. 

The volume of sand contained within study sites was calculated for the entire study site and for 

the portion of the study site above the stage of 227 m3

/s, referred to hereafter as the reference 

stage (Figure 3). This discharge was chosen as the reference stage because it is the discharge 

associated with the low end of normal hydroelectric powerplant operations. Total sand volume 

and sand volume above the reference stage were calculated between the topographic surface for 

that particular date and a predefined underlying minimum surface (Hazel and others, 2010). To 

allow comparison of study sites that are of different size, the sand volumes were normalized as 

ratio between the sand volume for a given measurement and the sand volume measured in 

February 1996. Erosion rates following each of the controlled floods were determined by 

summing the sandbar volume above reference stage by reach for the post-flood and 6-month 

post-flood surveys, calculating the difference in volume, and dividing that by the number of days 

between surveys. Post-flood erosion rates following each controlled flood were determined for 

14 sites in Marble Canyon and 20 sites in Grand Canyon. For the study sites that were 

monitored only in 2008, average sandbar elevation was calculated as the average surface 

elevation above the 227 m3

/s stage for the region common to all 2008 surveys. 

2nd Joint Federal Interagency Conference, Las Vegas, NV, June 27 - July 1, 2010
Figure 3 (A) Perspective view based on 1-m resolution digital elevation model of a typical eddy 

sandbar and adjacent channel showing pattern of recirculating flow, the reference stage of 227 

m3/s in white, and a typical backwater “closure” line in red. The portion of the sandbar above the 

reference stage and below the reference stage is illustrated. Mainstem flow is from bottom right 

to top left. (B) Cross-section view of eddy sandbar and channel illustrating the computational 

region for sand above reference stage and total sand (sand above reference stage plus sand below 

reference stage). 

Many sandbars along the Colorado River in Marble Canyon and Grand Canyon have the form of 

a bar platform that projects from the bank out towards the channel and upstream into a zone of 

lateral flow recirculation, or eddy (Figure 3). During high flows, the bar platform is submerged 

and flow circulates upstream along the bank in a return-current channel between the bar platform 

2nd Joint Federal Interagency Conference, Las Vegas, NV, June 27 - July 1, 2010
and the shoreline. At lower flows, the emergent bar is often separated from the bank by a 

channel of low-velocity or stagnant water. This return-current channel provides low-velocity and 

often warm-water habitat to native fish, including Humpback Chub (Gila cypha) and is known to 

fishery biologists as backwater habitat (Valdez and others, 2001). We calculated the volume of 

backwater habitat for each survey at each study site for five discharges (227, 283, 340, 453, and 

566 m3/s). This was done by determining the shoreline for each discharge, delineating the 

backwater by adding a closure line to separate the backwater from the main channel (Figure 3), 

and calculating the volume of water that would be contained in the backwater depression below 

the water surface associated with that discharge. These methods are described in more detail by 

Grams and others (2010). 

RESULTS 

Each of the three controlled floods resulted in increases in sandbar volume above the 227 m3

/s 

reference stage in Marble Canyon and Grand Canyon (Figure 4). The median sandbar volume 

above reference stage following the 2008 controlled flood was similar to the median volume 

above reference stage following the 1996 and 2004 controlled floods in Marble Canyon and was 

also similar to the median volume above reference stage following the 1996 controlled flood in 

Grand Canyon. However, a greater number of the study sites had larger sandbars following the 

2008 event relative to the 2004 event in both Marble Canyon and Grand Canyon, shown by the 

position of the upper quartile (Figure 4). The antecedent sandbar size, which is the total sand 

volume in the study sites preceding a controlled flood, was generally greater for the 2008 

controlled flood than for the other controlled floods. Because of this, the increase in total sand 

volume during the 2008 event was smaller compared to the increases that occurred during the 

1996 and 2004 events in Marble Canyon. Thus, for the 7 sites that were monitored before and 

after all events in Marble Canyon, sandbar volume above reference stage was similar following 

each of the controlled floods, despite differing antecedent total sand storage volumes. A similar 

comparison is not possible for Grand Canyon, because no sites were monitored in 2004. 

There was a greater difference in behavior between the controlled floods for changes in total 

sand volume within the study sites. Although the measure of total sand volume includes the 

volume above the reference stage, the response in this zone is dominated by changes below that 

stage, where 80 percent or more of the sand occurs (Hazel and others, 2006). The 1996 

controlled flood resulted in a large decrease in total sand volume for the study sites in Marble 

Canyon, as reported by Hazel and others (1999). While decreases in total sand volume also 

occurred at the Marble Canyon study sites during the 2004 and 2008 controlled floods, these 

decreases were much less than occurred in 1996 (Figure 4). Total sand volume for the study sites 

located in Grand Canyon increased slightly during both the 1996 and 2008 controlled floods. 

Thus, the deposition above the reference stage that occurred in 2008 was not systematically 

linked with erosion in eddies and the main-channel bed below the reference stage, as was 

observed during the 1996 controlled flood. 

Sandbars eroded substantially following each of the three controlled floods (Figure 4). 

Following the 1996 and 2008 floods, erosion occurred relatively rapidly during summer 

fluctuating flows that peaked at about 560 m3

/s or greater (Figure 2). The 1 year period 

following the 2004 controlled flood did not include a sustained period of equally high flows and 

erosion was not documented until October 2006 (Figure 4). 

2nd Joint Federal Interagency Conference, Las Vegas, NV, June 27 - July 1, 2010
0

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NORMALIZED VOLUME OF SAND ABOVE REFERENCE STAGE

A. Marble Canyon

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B. Grand Canyon

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NORMALIZED TOTAL SAND VOLUME

C. Marble Canyon

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10/15/2008

D. Grand Canyon

Figure 4 Sandbar volume normalized by the volume measured in February 1996, before the 

1996 controlled flood. (A) Normalized sandbar volume above reference stage in Marble Canyon, 

(B) Normalized sandbar volume above reference stage in Grand Canyon, (C) Normalized total 

sandbar volume in Marble Canyon, and (D) Normalized total sandbar volume in Grand Canyon. 

In each plot, the shaded region shows the upper and lower quartiles, the line shows the median 

value, the whiskers show the range of all data within 1.5 times the distance between the bounds 

of the upper and lower quartiles. Outliers outside this range are shown with unique symbols. 

Because values are normalized to the February 1996 survey, all values for that date equal one 

(thick blue line). Pre-flood measurements are all shown in blue, post-flood measurements are all 

shown in red, 6-month post-flood measurements are all shown in green, measurements made 

between controlled floods are shown in gray. 

2nd Joint Federal Interagency Conference, Las Vegas, NV, June 27 - July 1, 2010
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80

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Marble Canyon

Grand Canyon

EROSION RATE, IN METERS PER DAY

MEAN OF DAILY DISCHARGE FOR PERIOD BETWEEN SURVEYS, 

IN CUBIC METERS PER SECOND1996 2004 2008

A.

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Marble Canyon

EROSION RATE, IN METERS PER DAY

PARIA RIVER SAND INPUT, IN METRIC TONS

1996

2004

2008

B.

Figure 5 (A) Rate of sandbar erosion as a function of the mean of mean daily discharge for 

period between post-flood surveys and 6-month post-flood surveys for sites in Marble Canyon, 

Eastern Grand Canyon, and combined Central and Western Grand Canyon. Each year is 

associated with a single mean of daily discharge, as indicated. (B) Rate of sandbar erosion as a 

function of the total magnitude of Paria River sand inputs that occurred in the period between 

post-flood surveys. 

Erosion rates may be affected by the relative magnitude of release volumes and by mainstem 

sediment concentrations, which could result in deposition in some parts of eddies at the same 

time as flood-formed deposits erode. Because both average dam releases and sediment supply 

varied among the three post-flood periods, it is not possible to decouple the relative influence of 

these factors. Erosion rates for the post-flood periods are, in fact, positively correlated with 

average dam releases and negatively correlated with Paria River sand inputs (Figure 5). The 

greater average dam releases that occurred following the 1996 controlled flood were associated 

with the highest average erosion rates among the study sites in Marble Canyon and Grand 

Canyon. The lower average dam releases that occurred following the 2004 controlled flood were 

associated with the lowest average sandbar erosion rates. Alternatively, the high erosion rates 

observed in 1996 were also associated with the post-flood period of least Paria River sand input. 

In 2004, when erosion rates were lowest, the Paria River supplied over 600,000 metric tons of 

sand in a six month period. 

Sand deposition and scour during controlled floods alters the morphology of deposits within 

eddies. Where deposition on a reattachment bar is accompanied by scour in the eddy returncurrent channel, increases in backwater habitat area and volume may occur (Grams and others, 

2010). This type of morphologic response occurred frequently enough among the 108 sites 

monitored before and after the 2008 controlled flood to cause increases in backwater area and 

volume (Figure 6). These changes increased the volume of available backwater habitat for all 

flows. However, because backwater habitat before the controlled flood was most abundant at 

low flows, there was a larger proportional increase in available habitat at high flows. As sandbars 

2nd Joint Federal Interagency Conference, Las Vegas, NV, June 27 - July 1, 2010
eroded between April and October 2008, backwater volume also decreased. Increases in 

backwater size are generally associated with sandbar deposition (Figure 7). There is not, 

however, a linear relation between the magnitude of sandbar deposition and increase in 

backwater volume. For some sites, deposition results in enlarged backwaters, while for other 

sites deposition may either not affect backwater size or may decrease backwater size. Similarly, 

decreases in sandbar elevation are generally associated with decreases in backwater volume, but 

not uniquely. There are several cases where backwater volume decreased when sandbars 

increased in size and where backwater volume increased as sandbars eroded. 

0.01

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BACKWATER VOLUME, IN CUBIC METERS

227 m3/s 283 m3/s 340 m3/s 453 m3/s 566 m3/s

Feb.Apr.MayOct.Feb.Apr.MayOct.Feb.Apr.MayOct.Feb.Apr.MayOct.Feb.Apr.MayOct.

Figure 6 Volume of backwater habitat as a function of discharge for each of the four 

sandbar/backwater surveys made in 2008. The February (blue) survey shows conditions before 

the March 2008 controlled flood, the April survey (blue) shows conditions after the controlled 

flood, the May survey shows conditions two months after the controlled flood (gray), and the 

October survey (green) shows conditions six months after the controlled flood. 

DISCUSSION AND CONCLUSIONS 

Each of the three controlled floods resulted in sandbar deposition above the reference stage (the 

stage associated with a discharge of 227 m3

/s) at the monitored study sites. Sandbar size 

following a flood is likely determined by site characteristics, flood stage, flood duration, and 

sand concentration during the flood. Antecedent sandbar size and the magnitude of deposition 

during each event varied among the controlled floods. However, for the 7 sites monitored before 

and after all events in Marble Canyon and the 15 sites monitored before and after the 1996 and 

2nd Joint Federal Interagency Conference, Las Vegas, NV, June 27 - July 1, 2010
2008 events in Grand Canyon, the post-flood sand volume above the reference stage was similar 

following each event. This suggests that water stage, which was essentially the same for each of 

the controlled floods, may play an important role in determining post-flood sandbar size, at least 

within the range of sand supply conditions that existed for these three controlled floods. The 

1996 controlled flood resulted in a large net decrease in the total sand volume contained at the 

study sites in Marble Canyon, while the 2004 and 2008 controlled floods resulted in smaller 

decreases in total sand volume. Neither the 1996 nor the 2008 controlled floods resulted in 

decreases in the total sand volume at study sites in Grand Canyon. Thus, even under conditions 

of high sediment enrichment, such as existed in 2004 (Topping and others, 2006) and 2008, 

deposition above the reference stage was associated with some loss of sand below the reference 

stage at the sites in Marble Canyon. For these controlled floods that were conducted following 

tributary sediment inputs, the loss of total sand volume at the study sites in Marble Canyon 

approximately balanced the gains in total sand volume that occurred during periods of tributary 

supply, resulting in no net decrease in total sand volume at the study sites. 

1000

2000

3000

Feb. to Apr.

Apr. to May

May to Oct.

KWATER VOLUME 

D, IN CUBIC METERS

-3000

-2000

-1000

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CHANGE IN MAXIMUM BAC

FOR INDICATED TIME PERIO

CHANGE IN AVERAGE SAND ELEVATION 

FOR INDICATED TIME PERIOD, IN METERS

Figure 7 Change in maximum backwater volume plotted as a function of change in average sand 

elevation for the time periods between the 2008 sandbar/backwater surveys. Maximum 

backwater volume is the maximum volume across all discharges for the given measurement. 

Deposition of sandbars during the 2008 controlled flood resulted in increases in the number and 

size of aquatic backwater habitats. Although increases in the quantity of backwater habitats are 

generally associated with increases in average sandbar elevation and decreases in the quantity of 

backwater habitat are generally associated with decreases in average sandbar elevation, there is 

2nd Joint Federal Interagency Conference, Las Vegas, NV, June 27 - July 1, 2010
not a direct linear relation. These results demonstrate that controlled floods result in sandbar 

deposition and increases in backwater habitat. However, the magnitude of habitat increase is not 

necessarily proportional to the magnitude of sandbar deposition. 

Following each of the three controlled floods, sandbars eroded. In 2008, the median volume of 

sand above the reference stage at the study sites in Marble Canyon 6 months after the controlled 

flood was similar to the median volume above the reference stage before the controlled floods. 

However, in Grand Canyon, median sandbar volume above the reference stage was still greater 6 

months after the controlled flood than it was prior to the event. The rate of sandbar erosion 

following the controlled floods varied among the events and was positively correlated with the 

magnitude of average dam releases and inversely related to the magnitude of Paria River sand 

inputs for Marble Canyon. Erosion rates were lowest following the 2004 controlled flood when 

average dam releases were low and Paria River sand inputs were high. Erosion rates were 

highest following the 1996 controlled flood when average dam releases were high and there was 

very little sand supplied by the Paria River. 

The sandbar results presented here are based on 22 study sites that were monitored before and 

after each of the three controlled floods that have occurred since 1996. The degree to which 

these results are representative of the estimated hundreds of sandbars that occur in Marble and 

Grand canyons is uncertain. Schmidt and others (1999) reported that the sign and magnitude of 

deposition above the reference stage reported for these sandbar study sites was consistent with 

results based on mapping from aerial photographs over longer reaches. However, 80 percent or 

more of the sand in active storage is below the reference stage (Hazel and others, 2006). In some 

cases, changes in sand volume for this set of study sites has been shown to be consistent with 

reach-scale trends in sand storage (Schmidt, 1999; Hazel and others, 2006); while for other 

cases, changes in sand volume over short reaches has been shown to be inconsistent with reachscale sediment budgets (Topping and others, 2006). It is likely that the sites are most 

representative when there are large system-wide perturbations, such as controlled floods or large 

tributary sediment inputs that are likely to result in similar responses over long river segments. 

The relation between sandbar response at these discrete study sites and reach-scale response is 

under continued investigation. 

In summary, these results demonstrate that the 3 controlled floods resulted in repeated sandbar 

deposition at the sites monitored, that sandbar deposition is also associated with increases in 

backwater habitat, and that sandbars eroded substantially within 6 months after each of the 

controlled floods. Despite erosion, the median sandbar size at the monitored sites was similar or 

slightly larger in October 2008, 6 months after the third controlled flood than before the first 

controlled flood in February 1996. Whether the approach of using controlled floods and the sand 

supplied by tributaries to build and maintain sandbars is sustainable over decadal time scales 

remains uncertain. The outcome will depend on dam operations between controlled floods, 

which are largely determined by legal requirements for water delivery, and other factors that are 

difficult to predict such as river basin hydrology and tributary sediment production. 

REFERENCES 

Andrews, E.D., Johnston, C., Schmidt, J., and Gonzales, M., 1999, Topographic evolution of sand bars in Grand 

Canyon during the experimental flood, in Webb, R.H., Schmidt, J.C., Valdez, R.A., and Marzolf, G.R., eds., 

2nd Joint Federal Interagency Conference, Las Vegas, NV, June 27 - July 1, 2010
The 1996 controlled flood in Grand Canyon: scientific experiment and management demonstration: American 

Geophysical Union Monograph. 

Grams, P.E., Schmidt, J.C., and Andersen, M.A., 2010, 2008 High-Flow Experiment at Glen Canyon Dam: 

Morphologic Response of Eddy-Deposited Sandbars and Associated Aquatic Backwater Habitats along the 

Colorado River in Grand Canyon National Park, : U.S. Geological Survey Open-File Report 2010–1032, 73 

p. 

Hazel, J.E., Jr., Grams, P.E., Schmidt, J.C., and Kaplinski, M., 2010, Sandbar response in Marble and Grand 

Canyons, Arizona, following the 2008 high-flow experiment on the Colorado River: U.S. Geological Survey 

Scientific Investigations Report 2010–5015, 52 p. 

Hazel, J.E., Kaplinski, M., Parnell, R., Manone, M., and Dale, A., 1999, Topographic and bathymetric changes at 

thirty-three long-term study sites, in Webb, R.H., Schmidt, J.C., Marzolf, G.R, and Valdez, R.A., eds., The 

Controlled Flood in Grand Canyon: American Geophysical Union. 

Hazel, J.E., Jr., Topping, D.J., Schmidt, J.C., and Kaplinski, M., 2006, Influence of a dam on fine-sediment storage 

in a canyon river: Journal of Geophysical Research v. 111, no. F3, doi: 10.1029/2004JF000193. 

Howard, A., and Dolan, R., 1981, Geomorphology of the Colorado River in the Grand Canyon: Journal of Geology, 

v. 89, no. 3, p. 269-298. 

Kearsley, L.H., Schmidt, J.C., and Warren, K.D., 1994, Effects of Glen Canyon Dam on Colorado River sand 

deposits used as campsites in Grand Canyon National Park, USA: Regulated Rivers, Research and 

Management, v. 9, p. 137–149. 

Rubin, D.M., Topping, D.J., Schmidt, J.C., Hazel, J., Kaplinski, M., and Melis, T.S., 2002, Recent sediment studies 

refute Glen Canyon Dam hypothesis: Eos (American Geophysical Union Transactions), v. 83, p. 273, 277–

278. 

Schmidt, J.C., 1999, Summary and synthesis of geomorphic studies conducted during the 1996 controlled flood in 

Grand Canyon, in Webb, R.H., Schmidt, J.C., Marzolf, G.R, and Valdez, R.A., eds., The Controlled Flood in 

Grand Canyon: Geophysical Monograph 110, American Geophysical Union, p. 329-341. 

Schmidt, J.C., and Graf, J.B., 1990, Aggradation and degradation of alluvial sand deposits, 1965 to 1986, Colorado 

River, Grand Canyon National Park, Arizona, Professional Paper 1493, U. S. Geological Survey, 74 p. 

Schmidt, J.C., Grams, P.E., and Leschin, M.F., 1999, Variation in the magnitude and style of deposition and erosion 

in three long (8-12 km) reaches as determined by photographic analysis., in Webb, R.H., Schmidt, J.C., 

Marzolf, G.R, and Valdez, R.A., eds., The Controlled Flood in Grand Canyon: Geophysical Monograph 110, 

American Geophysical Union, p. 185-203. 

Schmidt, J.C., Grams, P.E., and Webb, R.H., 1995, Comparison of the magnitude of erosion along two large 

regulated rivers: Water Resources Bulletin, v. 31, p. 617-631. 

Stevens, L.E., Schmidt, J.C., Ayers, T.J., and Brown, B.T., 1995, Flow regulation, geomorphology, and Colorado 

River March development in the Grand Canyon, Arizona: Ecological Applications, v. 5, no. 4, p. 1025-1039. 

Topping, D.J., Rubin, D.M., Nelson, J.M., Kinzel, P.J.I., and Bennett, J.P., 1999, Linkage between grain-size 

evolution and sediment depletion during Colorado River floods, in Webb, R.H., Schmidt, J.C., Marzolf, G.R., 

and Valdez, R.A., eds., The 1996 Controlled Flood in Grand Canyon: Washington, D.C., American 

Geophysical Union, p. 71-98. 

Topping, D.J., Rubin, D.M., and Vierra, L.E.J., 2000, Colorado River sediment transport 1. Natural sediment supply 

limitation and the influence of Glen Canyon Dam: Water Resources Research, v. 36, no. 2, p. 515-542. 

Topping, D.J., Rubin, D.M., Schmidt, J.C., Hazel, J.E. Jr., Wright, S.A., Kaplinski, M., Draut, A.E., and Breedlove, 

M.J., 2006, Comparison of sediment-transport and bar-response results from the 1996 and 2004 controlledflood experiments on the Colorado River in Grand Canyon: Proceedings of the 8th Federal Interagency 

Sediment Conference, Reno, Nevada, April 2006, ISBN 0-9779007-1-1. 

U.S. Department of the Interior, 1995, Operation of Glen Canyon Dam Final Environmental Impact Statement: Salt 

Lake City, Utah, Bureau of Reclamation, Upper Colorado Region, 337 p., appendices. 

Valdez, R.A., Hoffnagle, T.L., McIvor, C.C., McKinney, T., and Leibfried, W.C., 2001, Effects of a test flood on 

fishes of the Colorado River in Grand Canyon, Arizona: Ecological Applications, v. 11, no. 3, p. 686-700. 

Webb, R.H., 1996, Grand Canyon, a century of change: rephotography of the 1889-1890 Stanton expedition: 

Tucson, Arizona, The University of Arizona Press, 290 p. 

Wright, S.A., Melis, T.S., Topping, D.J., and Rubin, D.M., 2005, Influence of Glen Canyon Dam operations on 

downstream sand resources of the Colorado River in Grand Canyon, in Gloss, S.P., Lovich, J.E., and Melis, 

T.S., eds., The state of the Colorado River ecosystem in Grand Canyon: U.S. Geological Survey Circular 

1282, p. 17–31. 

2nd Joint Federal Interagency Conference, Las Vegas, NV, June 27 - July 1, 2010