Prepared in cooperation with Utah State University and Northern Arizona University 

Streamflow and Sediment Data Collected to Determine the 

Effects of Low Summer Steady Flows and Habitat 

Maintenance Flows in 2000 on the Colorado River between 

Lees Ferry and Bright Angel Creek, Arizona 

By John C. Schmidt, David J. Topping, David M. Rubin, Joseph E. Hazel, Jr., Matt Kaplinski, Stephen M. Wiele, 

and Sara A. Goeking 

Open-File Report 2007–1268
 

U.S. Department of the Interior 

U.S. Geological Survey 
Cover: Joe Hazel, Northern Arizona University, surveying the underwater part of the sandbar at river mile 

30.7 on September 6, 2000 (photograph by David J. Topping, U.S. Geological Survey); (background) Marble 

Canyon, Ariz. (photograph by Jeff Sorensen, Arizona Game and Fish Department). 
Streamflow and Sediment Data Collected to Determine 

the Effects of Low Summer Steady Flows and Habitat 

Maintenance Flows in 2000 on the Colorado River 

between Lees Ferry and Bright Angel Creek, Arizona 

By John C. Schmidt, David J. Topping, David M. Rubin, Joseph E. Hazel, Jr., Matt Kaplinski, Stephen M. 

Wiele, and Sara A. Goeking 

Open-File Report 2007–1268 

U.S. Department of the Interior 

U.S. Geological Survey 
U.S. Department of the Interior 

DIRK KEMPTHORNE, Secretary 

U.S. Geological Survey 

Mark D. Myers, Director 

U.S. Geological Survey, Reston, Virginia 2007 

Revised and reprinted: 2007 

For product and ordering information: 

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its natural and living resources, natural hazards, and the environment: 

World Wide Web: http://www.usgs.gov 

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Suggested citation: 

Schmidt, J.C., Topping, D.J., Rubin, D.M., Hazel, J.E., Jr., Kaplinski, M,, Wiele, S.M., and Goeking, S.A., 2007, 

Streamflow and sediment data collected to determine the effects of low summer steady flows and habitat 

maintenance flows in 2000 on the Colorado River between Lees Ferry and Bright Angel Creek, Arizona: U.S. 

Geological Survey Open-File Report 2007–1268, 79 p. 

Any use of trade, product, or firm names is for descriptive purposes only and does not imply 

endorsement by the U.S. Government. 

Although this report is in the public domain, permission must be secured from the individual 

copyright owners to reproduce any copyrighted material contained within this report. 

 ii
Contents 

Abstract................................................................................................................................................................................1

Introduction .........................................................................................................................................................................2

Background .........................................................................................................................................................................3

Dam Releases during the Study Period..........................................................................................................................6

LSSF Hypothesis and Study Design ................................................................................................................................6 

Methods ...............................................................................................................................................................................9 

Results ................................................................................................................................................................................15 

Discussion and Conclusions...........................................................................................................................................24 

References.........................................................................................................................................................................26

Figures 

1. Map showing the Colorado River in Marble and Grand Canyons .......................................................................31 

2. Diagram of a typical fan-eddy complex....................................................................................................................32

3. Diagram showing method of calculation of eddy deposition zones. ..................................................................33

4. Hydrograph showing releases from Glen Canyon Dam (as measured at the Lees Ferry gaging station) 

throughout the six periods of the low summer steady flows (LSSF) experiment....................................34

5. Stage and temperature at river mile 30.7 during the September 2000 habitat maintenance flows. .............35 

6. Cumulative size distributions of eddies in previous studies and low summer steady flows reaches ..........36 

7. Diagram showing a sample backwater opening in the upstream direction......................................................37 

8. Hydrographs of the (A), Colorado River at the Lees Ferry, (B) Lower Marble Canyon, (C) Grand Canyon, 

and (D) Diamond Creek gaging stations from April 1–October 1, 2000 .....................................................38

9. Hydrographs of three tributaries to the Colorado River: (A) the Paria River, (B) the Little Colorado River, 

and (C) House Rock Wash.................................................................................................................................39

10. Measurements of (A) suspended-sand and (B) silt and clay concentrations at the Paria River at Lees 

Ferry gaging station during the study period.................................................................................................40

11. Measurements of suspended-sediment concentration in House Rock Wash during the study period. ...41

12. Measurements of (A) suspended-sand and (B) silt and clay concentrations at the Little Colorado River 

near Cameron, Ariz., gaging station during the study period. ....................................................................42

13. Measurements of (A) suspended-sand and (B) silt and clay concentrations in the Colorado River at the 

Lower Marble Canyon and Grand Canyon gaging stations during the study period. ............................43

14. Measurements of (A) suspended-silt and clay concentration, (B) suspended-sand concentration, and 

(C) median grain size of suspended sand during the May and September habitat maintenance flows 

(HMF).....................................................................................................................................................................44

15. Measured surface (A) suspended-sand and (B) silt and clay concentrations (with smoothed curves) 

during May, July, and September 2000...........................................................................................................45

16. Depth-integrated measurements of suspended sediment (with smoothed curves) from the Lagrangian 

sampling trip during the September habitat maintenance flows (HMF)...................................................46

17. Computed cumulative sand transport during the study period..........................................................................47

18. Model-predicted versus measured instantaneous (A) sand and (B) silt and clay loads in the Paria River 

at Lees Ferry during the study period. ............................................................................................................48 

19. Suspended-sand rating curve used to estimate the concentration of suspended sand in the Little 

Colorado River. ....................................................................................................................................................49 

 iii
20. Mass-balance sand budget uncertainty envelopes for Marble Canyon and upper Grand Canyon during 

Periods 1–5...........................................................................................................................................................50

21. Mass-balance silt and clay budget uncertainty envelopes for Marble Canyon during Periods 1–5..........51

22. Fraction of bed area (in %) composed of each bed-texture class before and after the September habitat 

maintenance flows (HMF) in the three study reaches in Marble Canyon, as determined from sidescan sonar data...................................................................................................................................................52

23. Comparison of the sand budget and β at the Grand Canyon gaging station during Period 1......................53

24. Graphs showing temporal changes in the area and volume of fine sediment between the stages 

associated with discharges of 227 m3

/s and 708 m3/s at 17 study sites in Marble and upper Grand 

Canyons. ...............................................................................................................................................................54

25. Graphs showing temporal changes in the area and volume of fine sediment above the stage associated 

with the discharge of 708 m3

/s at 17 study sites in Marble and upper Grand Canyons .........................55

26. Graphs showing the temporal sequence of the mean (A) and median (B) area of mid-elevation finesediment deposits in larger eddies (i.e., in only the eddies larger than 1,000 m2

) between 1984 and 

2001........................................................................................................................................................................56

27. Graphs showing the temporal sequence of mid-elevation fine-sediment deposits, or the area of fine 

sediment inundated between the stages associated with discharges of 227 and 708 m3

/s, between 

1984 and 2000.......................................................................................................................................................57

28. Graph showing the cumulative fill ratio for mid-elevation fine-sediment deposits for four reaches and 

Marble Canyon, mapped at a common discharge of 227 m3

/s....................................................................58

29. Box-and-whisker plots showing the distribution of areas of mid-elevation fine-sediment deposits in 

larger eddies (i.e., in only the eddies larger than 1,000 m2

) in four reaches and Marble Canyon, 

mapped at a common discharge of 227 m3

/s. ................................................................................................59

30. Box-and-whisker plots of the distribution of fill ratios for mid-elevation fine-sediment deposits in larger 

eddies (i.e., in only the eddies larger than 1,000 m3

), mapped at a common discharge of 227 m3/s.. ..60

31. Histograms showing the number of eddies in which the area of low-elevation fine-sediment deposits 

increased or decreased by more than 200 m2 in each time interval, mapped at a common discharge 

of 227 m3

/s.............................................................................................................................................................61

32. Graphs showing the distribution of net normalized aggradation (NNA) in the four study reaches and 

Marble Canyon aggregate in response to the September 2000 habitat maintenance flows (HMF). ..62

33. Graphs showing the amount of erosion and deposition at scour-chain sites. ...............................................63

34. Map showing erosion and deposition at the river mile 30 study site within the first day of the September 

2000 habitat maintenance flows (HMF). .........................................................................................................64

35. Time series of backwater area (A) and the number of eddies with backwaters (B) .....................................65 

Tables 

1. Study site locations and geographic place names of the 19 fan-eddy complexes surveyed in March, 

June, August, and September 2000.................................................................................................................66 

2. Descriptions of the four study reaches included in photogeologic mapping based on two sets of aerial 

photographs acquired before and after the September 2000 habitat maintenance flows (HMF) .......67 

3. Error matrix of the agreement between areas surveyed by Northern Arizona University (NAU) and 

estimated by Utah State University (USU)......................................................................................................67 

4. Data from scour chains installed in August 2000 and recovered in September 2000......................................68 

5. Change in sediment mass during each of the five periods...................................................................................70 

 iv
 v

6. Bed area (in m2) and fraction of bed area (in %) composed of each bed-texture class before and after the 

September habitat maintenance flows (HMF) in the three study reaches in Marble Canyon, as 

determined from side-scan sonar data. .........................................................................................................71 

7. Area (m2

) and volume (m3) of fine sediment at each study site, within the high-elevation-eddy, midelevation-eddy, low-elevation-eddy, and main-channel zones. ................................................................72 

8. Percentage change in fine-sediment area and volume in each study site relative to the areas and 

volumes in March 2000, within the high-elevation-eddy, mid-elevation-eddy, low-elevation-eddy, 

and main-channel zones. ..................................................................................................................................75 

9. Volumes and rates of fine sediment either eroded or deposited in the eddy part of the fan-eddy complex 

at river mile 30 during the September 2000 habitat maintenance flows (HMF).......................................78 

10. Average response of the bed and eddy sandbars to various flow regimes of the low summer steady 

flows (LSSF) in different parts of the study area...........................................................................................79 

Conversion Factors 

SI to Inch/Pound 

Multiply By To obtain 

Length 

centimeter (cm) 0.3937 inch (in.) 

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi) 

Area 

square meter (m2) 10.76 square foot (ft2) 

Volume 

cubic meter (m3) 35.31 cubic foot (ft3) 

Flow rate 

cubic meter per second (m3/s) 35.31 cubic foot per second (ft3/s) 

Mass 

megagram (Mg) 1.102 ton, short (2,000 lb) 
Streamflow and Sediment Data Collected to 

Determine the Effects of Low Summer Steady Flows 

and Habitat Maintenance Flows in 2000 on the 

Colorado River between Lees Ferry and Bright Angel 

Creek, Arizona 

By John C. Schmidt, David J. Topping, David M. Rubin, Joseph E. Hazel, Jr., Matt Kaplinski, Stephen 

M. Wiele, and Sara A. Goeking1

Abstract 

The low summer steady flows (LSSF) experiment of 2000 further demonstrated that spike 

flows released from Glen Canyon Dam redistribute sand from the channel bed and lower elevation 

parts of eddy sandbars to channel-margin deposits and the higher elevation parts of eddy sandbars. 

Unfortunately, summer 2000 was a period of unusually low tributary influx of sediment and there 

was little fine sediment (i.e., sand and finer material) available for redistribution. Nevertheless, the 

low steady flows, which held releases from the dam steady at 230 m3/s (8,100 ft3/s), during the 

summer of 2000 effectively retained on the channel bed the little sediment that was supplied by 

tributaries, and a subsequent 4-day, 870 m3/s (30,700 ft3/s) spike flow caused modest increases in 

the area of the mid-elevation zone of eddy sandbars. 

 

1

 John C. Schmidt and Sara A. Goeking, Department of Watershed Sciences, Utah State University, Logan, Utah, 

84322-5210. David J. Topping, Grand Canyon Monitoring and Research Center, U.S. Geological Survey, Flagstaff, 

Ariz. David M. Rubin, U.S. Geological Survey, Marine Geology Team, Santa Cruz, Calif. Joseph E. Hazel, Jr. and 

Matt Kaplinski, Department of Geology, Northern Arizona University, Flagstaff, Ariz. Stephen M. Wiele, U.S. 

Geological Survey, Tucson, Ariz. 

 1
Introduction 

Since 1992, environmental management of the Colorado River in Glen, Marble, and Grand 

Canyons has been mandated by the Grand Canyon Protection Act of 1992 (GCPA; title XVIII, 

secs. 1801–1809, of Public Law 102-575). Releases of water from Glen Canyon Dam are the 

primary determinant of streamflow, sediment transport, water temperature, and disturbance to 

aquatic and riparian ecosystems downstream from the dam. Glen Canyon Dam also blocks the 

delivery of sediment from the upstream watershed to reaches downstream from the dam. Beginning 

in 1990, specific water-release patterns at the dam have been implemented to address downstream 

ecological concerns (U.S. Department of the Interior, 1995; National Research Council, 1996). 

These releases have also provided opportunities for scientific measurements of river processes. 

One such ecologically oriented water-release regime occurred between April 1 and 

September 30, 2000. During this period, the Bureau of Reclamation released low steady flows from 

the dam during the summer and released short-duration spike flows immediately preceding and 

following the low steady flows. The low summer releases were intended to benefit the endangered 

humpback chub (Gila cypha) and assist in compliance with the Endangered Species Act of 1973 

(Bureau of Reclamation, 2000). A spike flow in May was intended to create “ponding and other 

positive habitat conditions” at the confluence of the Little Colorado River (LCR), thereby allowing 

young humpback chub to “more quickly grow and survive” (Bureau of Reclamation, 2000). A high 

spike flow in early September was intended to adversely affect nonnative fish. Although the low 

steady flows were only one part of a longer period of experimental dam releases, the entire period 

is referred to by river managers as the low summer steady flows (LSSF) experiment because both 

the low steady flows and two spike flows were linked by similar biological objectives. 

Although the motivation behind the LSSF experiment was biological, the Physical 

Resources Program of the U.S. Geological Survey’s (USGS) Grand Canyon Monitoring and 

Research Center (GCMRC) developed a sediment measurement program in cooperation with 

Northern Arizona University (NAU) and Utah State University (USU). The goal of this 

collaborative effort was to measure influx, efflux, and change in the distribution of fine sediment in 

Marble Canyon and the eastern part of Grand Canyon. These measurements allowed calculation of 

fine-sediment budgets for different periods, because 

I – E = ΔS (1) 

where I is influx of fine sediment, E is efflux, and ΔS is change in storage. In this report, we 

summarize the measurements that comprise these budgets and compare values of ΔS computed by 

(1) based on field measurements of changes in the topography of fine-sediment deposits on the 

channel bed and along the channel margins. The study area is the river corridor between Glen 

Canyon Dam and USGS gaging station 09402500 (Colorado River near Grand Canyon, Ariz.; 

herein referred to as the Grand Canyon gaging station), located immediately upstream from Bright 

Angel Creek. The dam is located at river mile -15.82

, and the gage is located at river mile 88, 167 

river km downstream from the dam (fig. 1). 

 

2

 Locations in the river corridor are assigned by river mile upstream (negative values) or downstream (positive values) 

from Lees Ferry, Ariz. This measurement system was created by the USGS in 1921–23. We use revised locations of 

this measurement system, reported to the nearest 0.1 river mile (U.S. Geological Survey, 2006). 

 2
Background 

Study Area 

The study area consists of four parts: Glen Canyon, upper Marble Canyon, lower Marble 

Canyon, and upper Grand Canyon (fig. 1). Glen Canyon is that part of the river corridor between 

the dam and the confluence of the Colorado and Paria Rivers at river mile 0.8. Upper Marble 

Canyon extends to approximately river mile 40, and lower Marble Canyon extends from there to 

the confluence with the Little Colorado River at river mile 61.8. We use the informal term upper 

Grand Canyon to refer to the river segment between the LCR and the Grand Canyon gaging station. 

Geomorphic Framework 

The distribution of fine sediment on the bed and along the margins of the Colorado River in 

the study area is determined by (1) the geomorphology of the river corridor, (2) the supply of fine 

sediment from tributaries, and (3) water releases from Glen Canyon Dam. The sites of finesediment storage are primarily determined by river corridor geomorphology and include the bed, 

eddy sandbars, and channel-margin deposits. Changes in fine-sediment storage occur as changes in 

bed elevation, changes in the topography of sandbars and channel-margin deposits, and changes in 

the proportion of the bed covered by fine sediment. Extreme changes in bed elevation and 

composition occurred in Glen Canyon soon after the dam was completed (Pemberton, 1976; Grams 

and others, 2007). Many studies have shown that the total area and number of sandbars and 

channel-margin deposits decreased after completion of the dam (Kearsley and others, 1994; Webb, 

1996). 

The distribution of river deposits along the channel edge is determined by the repeating 

hydraulic patterns created by debris fans that exist at the mouths of most tributaries. Schmidt and 

Rubin (1995) defined fan-eddy complexes as the sequence of hydraulic features that occurs 

wherever a tributary debris fan partially blocks the flow of the river, and this pattern is similar at 

each fan (fig. 2). The most upstream part of each fan-eddy complex is the ponded flow upstream 

from the fan, where the water-surface elevation is largely determined by the hydraulic control 

caused by the narrow channel and elevated bed of the rapid immediately downstream. Ponding may 

extend upstream between a few channel widths to a few kilometers (Kieffer, 1985) and varies with 

discharge. Differences in channel geometry cause some rapids to be “drowned out” at high flow, 

whereas the degree of hydraulic control at other sites may increase at flood stage (Kieffer, 1987). 

The bed of the ponded backwater is a large area of potential temporary storage of fine sediment 

(Howard and Dolan, 1981). 

Flow separation occurs immediately downstream from most rapids where the bank angle 

diverges abruptly from the orientation of the main flow (Schmidt, 1990). A zone of lateral 

recirculating flow (i.e., an eddy) exists along the bank downstream from the point of flow 

separation. Eddies effectively trap the suspended sediment load, and eddy sandbars composed of 

fine sediment typically are deposited in these zones of lateral flow recirculation. Sedimentary 

structures in these sandbars reflect the recirculating flow (Rubin and others, 1990, 1994). 

The entire eddy sandbar is not typically exposed at base flows, and some parts of eddy 

sandbars are of low elevation and always submerged. One metric of change in fine sediment 

storage in eddies is the area of eddy sandbars emergent at base flow or the area above some 

reference discharge. These measurements are meaningful because eddy sandbars do not migrate 

downstream and are fixed in location by the channel geometry that creates flow separation. Another 

 3
metric describing sandbar change is to compare sandbar area to the area of the entire eddy where 

deposition has historically occurred. This metric normalizes sandbar area because every eddy 

sandbar is divided by its local area of potential deposition. Because the area and length of eddies 

changes with flow, it is impossible to precisely define the area of potential eddy deposition without 

field observation at a wide range of discharges. This is impossible for a large study area. Schmidt 

and others (2004) proposed an objectively defined surrogate called the eddy deposition zone 

(EDZ). The EDZ is the composite area of each eddy where eddy sandbars have ever been emergent 

in any year of available aerial photography (fig. 3). The EDZ is smaller than the recirculating eddy 

itself because sandbars in some eddies have never been emergent at base flows in any historical 

aerial photograph. Schmidt and others (2004) termed the proportional area of an EDZ where an 

eddy sandbar occurred in a specific year a “fill ratio.” The “cumulative fill ratio” of a study reach is 

the total area of eddy sandbars measured at one time divided by the total area of all EDZs in that 

reach. 

The highest elevation parts of eddy sandbars sometimes merge downstream with linear 

banks of fine-sediment deposits that resemble flood plains (Schmidt and Graf, 1990). These 

“channel-margin deposits” typically have levees of low relief and form by deposition of suspended 

sediment as it moves away from the main flow, similar to deposits that occur on the floodplains of 

alluvial rivers. 

A mid-channel, or bank-attached, cobble bar often exists downstream from the zone of 

lateral flow recirculation. The debris on this bar has been eroded from the upstream debris fan 

(Webb and others, 1988, 1989, 1999; Grams and Schmidt, 1999; Pizzuto and others, 1999; Larsen 

and others, 2004). At moderate and low discharges, flow typically passes around the margins of 

these cobble bars and creates a riffle. 

Streamflow 

The seasonal and annual fluxes of water and fine sediment passing through the study area 

were highly variable before completion of Glen Canyon Dam (Topping and others, 2000a). The 

median discharge of the Colorado River at USGS gaging station 09380000 (Colorado River at Lees 

Ferry, Ariz.; herein referred to as the Lees Ferry gaging station) was 226 m3/s (7,980 ft3/s) for the 

predam period between May 8, 1921, and March 12, 1963, and the range of flows during the year 

was large. The 10% exceedence flow was 1,360 m3

/s (48,000 ft3/s), and the 90% exceedence flow 

of 127 m3/s (4,500 ft3/s) was an order of magnitude less (Topping and others, 2003). 

Operations of Glen Canyon Dam greatly reduced the magnitude of floods and increased the 

magnitude of base flows. The median discharge of the Colorado River for the period between 

March 14, 1963, and September 30, 2000, was 74% higher and the seasonal variation in flows was 

much less than during the predam period (Topping and others, 2003). The 10% exceedence flow 

for the postdam period was 708 m3

/s (25,000 ft3/s), and the 90% exceedence flow was 125 m3/s 

(4,400 ft3

/s). 

The era of environmental management began in summer 1990 during an 18-mo period 

when dam releases varied for 2-week periods to facilitate river-scale experiments to evaluate the 

downstream effects of dam releases that fluctuated on a daily basis for hydropower generation 

(Beus and Avery, 1992). The daily range in dam releases was thereafter constrained when the 

Secretary of the Interior adopted “interim operating criteria” in August 1991. Dam operations were 

modified only slightly after the 1996 signing of the Record of Decision (ROD) of the Operation of 

Glen Canyon Dam Final Environmental Impact Statement (U.S. Department of the Interior, 1995). 

In addition to constraining the magnitude of the daily peak discharge, the “interim operating 

 4
criteria” and ROD prohibited daytime dam releases less than 227 m3

/s (8,000 ft3/s) and nighttime 

releases less than 142 m3

/s (5,000 ft3/s). As a result, the magnitude of base flows increased 

throughout the 1990s, and flows less than the predam median discharge of 226 m3/s (7,980 ft3/s) 

rarely occurred. 

The ROD distinguishes two types of high-flow dam releases: (1) habitat maintenance flows 

(HMF), which are high steady releases that are approximately at the capacity of the powerplant, 

and (2) beach/habitat-building flows (BHBF), which are infrequent events exceeding powerplant 

capacity. The 7-d release of 1,274 m3/s (45,000 ft3/s) in 1996, referred to as the 1996 controlled 

flood, was the first BHBF released from the dam during the era of environmental management. 

Spike flows at the capacity of the powerplant in May and September 2000 were HMFs. 

Sediment Supply and Sediment Transport 

Between 1944 and completion of the dam, the annual load of fine sediment was 57 + 3 x 

106

 Mg at the Lees Ferry gaging station and 83 + 4 x 106 Mg at the Grand Canyon gaging station 

(Topping and others, 2000a). Approximately 40% and 35% of the annual fine sediment load 

passing the Lees Ferry and Grand Canyon gages, respectively, was sand. Thus, the average annual 

predam sand supply to Marble Canyon was approximately 24 x 106 Mg, and the average annual 

predam sand supply to the upstream end of Grand Canyon was approximately 26 x 106 Mg (Wright 

and others, 2005). 

After completion of Glen Canyon Dam, sand delivery to the part of Glen Canyon 

downstream from the dam decreased by about 99.5%. Sand delivery to the upstream end of Marble 

Canyon decreased by about 94%, and the Paria River is now the only major supplier of sand to 

Marble Canyon. Because some sand continues to enter the Colorado River from the LCR and 

smaller tributaries, sand transported past the Grand Canyon gage decreased by about 85% (Topping 

and others, 2000a). 

Seasonal differences in suspended-sand concentration at the Lees Ferry and Grand Canyon 

gaging stations were demonstrated by Topping and others (2000b) and imply that there was a 9-mo 

period between July and the following March when sand accumulated in the study area because 

more sand was delivered into Marble and upper Grand Canyons than was exported downstream 

(Topping and others, 2000a). Topping and others (2000a) also showed that sand only accumulated 

in the study area during the predam era when the discharge of the Colorado River was typically less 

than about 250 m3

/s (8,800 ft3/s). 

The role of tributary sand supply in determining the concentration of suspended sand in the 

Colorado River is now greater than during the predam period. Topping and others (2000b) showed 

that the dominant size of the fine sediment on the bed differs by a factor of four between times 

immediately following tributary fine-sediment resupply and periods when there is no tributary input 

of sediment. These changes in bed grain size occur because the finest part of tributary-supplied 

sediment is winnowed from the bed by subsequent clear-water dam releases. Topping and others 

(2000a, 2000b) and Rubin and others (2002) showed that newly input tributary sand is likely 

exported past the Grand Canyon gaging station within several months because suspended-sand 

transport is higher when the bed is enriched with finer sediment. Transport rates subsequently 

decline as the bed is winnowed and coarsens. 

Longitudinal changes in sand transport may cause longitudinal differences in eddy sandbar 

size. Wiele and others (1999) predicted that higher concentrations of suspended sand would create 

larger eddy sandbars for the same hydrologic event. Additionally, Schmidt (1999) showed that 

deposition rates during the 1996 controlled flood were larger downstream from the LCR, where 

 5
suspended-sand concentrations were greater. Conversely, small sandbars form or net sandbar 

erosion occurs where the concentrations of suspended sand are low. If a particular flood has a large 

increase in sand transport in the downstream direction, then there might also be an associated 

downstream increase in the size of the eddy sandbars that are formed by that flow. 

The sites of fine-sediment accumulation and evacuation may change longitudinally and with 

time. Sediment budgets calculated for the 1996 controlled flood suggest that the primary source of 

sand deposited at higher elevations in eddies and as channel-margin deposits in Marble Canyon was 

eroded sand from upstream eddies (Schmidt, 1999). This resulted in a net decrease in sandbar size 

in Marble Canyon during this flood. In contrast, the sand deposited at higher elevations in eddies in 

upper Grand Canyon appears to have been eroded from both upstream eddies and the channel bed. 

Sand storage on the channel bed and at low elevations along the channel margins is temporary, 

however. The sediment budgets on which these conclusions are based are subject to large error, 

however, and documenting the existence of changing longitudinal patterns of sediment sources and 

sinks was one objective of the study described herein. 

Dam Releases during the Study Period 

Releases from Glen Canyon Dam between April 1 and September 30, 2000, were 

distinguished as six periods. The durations of these periods ranged from 4 d to 3 mo. Before this 

experimental flow period, dam releases had followed the pattern of normal fluctuating-flow 

operations, decreasing in a stepwise manner from a relatively high range in August and September 

1999 to a relatively low range in February and March 2000 (fig. 4). Releases were maintained at a 

steady flow of 230 m3

/s (8,100 ft3/s) from March 25 through April 5, 2000. Releases from Glen 

Canyon Dam were increased to 485 m3/s (17,100 ft3/s) between April 6 and 8, and flows remained 

at this magnitude until May 3 when they were increased to about 870 m3

/s (30,700 ft3/s). These 

high releases were maintained until May 7. For purposes of this report, the period before the May 

HMF is referred to as Period 1 and the May HMF is referred to as Period 2. The beginning of 

Period 1 varies in this report. In the discussion of flow and sediment transport, flows beginning on 

August 15, 1999, are considered as part of Period 1 to place this period within a broader context of 

river processes during normal dam operations. April 1, 2000, is considered the beginning of Period 

1 for other components of the study. 

During Period 3, dam releases consisted mostly of steady releases of 480 m3/s (17,000 ft3/s), 

followed by 5 d of steady releases of 540 m3

/s (19,100 ft3/s) that then decreased in a stepwise 

manner to 230 m3/s (8,100 ft3/s) on May 31. Between June 1 and September 4, dam releases were 

held constant at 230 m3/s (8,100 ft3/s); this period is referred to as Period 4. Period 5, the 

September HMF, extended from September 5 through September 8, during which dam releases 

were increased to a steady 870 m3

/s (30,700 ft3/s) for 4 d. Dam releases were reduced to base flows 

on September 9, when Period 6 began. The maximum discharge of the HMFs in Periods 2 and 5 

was approximately 30% less than the maximum peak discharge of the 1996 controlled flood. 

LSSF Hypotheses and Study Design 

A comprehensive science plan was developed to evaluate the effects of the LSSF 

experiment on various components of the Colorado River ecosystem downstream from Glen 

Canyon Dam (Fritzinger and others, 2000). Only the sediment-studies part of this plan and 

associated guiding hypotheses are described herein. 

 6
Study Plan 

Changes in fine-sediment storage were determined in four study reaches, each 

approximately 3–8 km long, using a combination of reach-length aerial-photographic analyses and 

detailed ground surveys at selected study sites. These changes in fine-sediment storage were 

measured for Period 4 and Period 5. One purpose of this research program was to determine 

whether the distribution of sites of sediment storage and evacuation varied longitudinally. During 

Period 4, the location and magnitude of sediment storage change was expected to vary in relation to 

local and reach-scale channel geometry and distance downstream from those tributaries that 

delivered fine sediment during or immediately before the study period. During the September HMF 

(Period 5), the location and magnitude of sediment storage change was expected to vary in relation 

to bed conditions at the onset of this spike flow and in relation to the downstream increase in 

sediment flux that was anticipated would exist during the HMF. 

Data collected were sufficient to compute fine-sediment budgets for Marble and upper

Grand Canyons for Periods 4 and 5. To measure the influx of discharge and sediment supplied by 

tributaries, gaging stations were operated on the Paria River, House Rock Wash, and the LCR, 

where suspended-sediment samples were also collected. The proportion of the fine-sediment flux 

deposited at high elevations was estimated in Marble Canyon and in a reach in Grand Canyon 

immediately downstream from the LCR during Period 5. Various traditional and nontraditional 

methods were used to make measurements of changes in the volume and characteristics of fine 

sediment stored on the bed, in eddies, and in channel margins. This research approach provided the 

opportunity to evaluate how these methods could be integrated in the calculation of sediment 

budgets and to determine the level of precision and accuracy appropriate in measuring each 

component of such a budget. 

Sediment budgets for Marble Canyon that arose from this study were compared to those of 

Schmidt (1999) and Hazel and others (2000). These sediment budgets, including those arising from 

this study, were subsequently refined using topographic-based and grain-size-based approaches to 

constructing sediment budgets in Hazel and others (2006). Evaluations were conducted to 

determine whether the proportion of the total sediment flux deposited at higher elevations differed 

significantly between the 1996 controlled flood and the September 2000 HMF. These data are 

crucial for river managers because they quantify the “cost” of restoration floods (i.e., the fine 

sediment exported from Marble Canyon) in relation to the “benefit” of these floods (i.e., the 

volume of newly deposited fine sediment that benefits target species or is of value for riparian 

habitat, camping, or aiding in the preservation of archaeological sites). Lastly, the sediment budget 

for Period 4 was compared to the seasonal sediment budgets of Topping and others (2000a) to 

determine if flows of 230 m3

/s (8,100 ft3/s) were sufficiently low to cause net accumulation of fine 

sediment on the channel bed and in the lower elevation parts of eddies in Marble Canyon during, 

and for extended periods following, tributary inputs of fine sediment. The potential for seasonal to 

multiyear accumulation of fine sediment downstream from Glen Canyon Dam underlies the 

preferred alternative described by the U.S. Department of the Interior (1995). 

Thus, the sediment study plan and methods were guided by several expectations about river 

behavior. 

 7
Hypothesis 1: Accumulation of Sediment in Marble Canyon and Upper Grand Canyon during 

Period 4 

The steady flows less than 250 m3/s (8,800 ft3/s) released during Period 4 were 

expected to result in accumulation of sediment in the study area, based on the 

findings of Topping and others (2000a). The study goals were to measure the inflow 

and export of fine sediment and to measure changes in the size of fine sediment 

deposits. These measurements made it possible to determine the magnitude of 

accumulation that occurred upstream and downstream from the LCR, to determine 

the locations of accumulation of fine sediment, and to determine whether these 

locations differed in a systematic way downstream. Overall, it was expected that ΔS 

in (1) would be positive during Period 4. 

Hypothesis 2: Evacuation of Fine Sediment from Marble Canyon and Upper Grand Canyon 

during Normal Dam Operations 

Flows higher than 250 m3/s (8,800 ft3/s) were hypothesized to result in net export of 

sand from the study area, based on the same logic described in the preceding 

expectations. Thus, it was expected that ΔS would be negative for other periods. 

Hypothesis 3: Relative Effectiveness of High Flows in Depositing Eddy Sandbars and 

Creating Backwaters 

In light of the anticipated accumulation of fine sediment during Period 4, the 

transport of suspended sediment was expected to be greater and the grain size of the 

suspended sediment was expected to be finer in September than in May. Therefore, 

eddy sandbars were expected to be larger immediately after the September HMF 

than after the May HMF. 

Hypothesis 4: Evaluation of the Relative Roles of Sediment Transport, Reach Scale 

Geometry, and Local Site Geometry in Determining the Magnitude and Location of 

Deposition and Erosion during High Flows 

Detailed measurements of changes in sediment storage within short reaches 

provided the opportunity to describe how these changes differ longitudinally as the 

sediment flux presumably increased downstream. The role of reach-scale channel 

geometry in controlling the location of fine-sediment erosion and deposition was 

also evaluated. 

Hypothesis 5: Evaluation of Rubin and Topping’s (2001) Metric of Relative Bed-sediment 

Coarseness (β) to Describe Average System Behavior 

Rubin and Topping (2001) suggested that β can be calculated from sedimenttransport measurements and be used as a measure of upstream changes in fine 

sediment accumulation. β is a nondimensional measure of the average bed-surface 

grain-size that interacts with the suspended sand in the flow. β uses the 

concentration and grain size of the sand in suspension to compute the average 

upstream grain size of the sand on the bed. All measurements necessary to calculate 

 8
β and to determine the upstream changes in storage that cause β to change were 

collected. 

Methods 

Tributary Influxes and Sediment Transport of the Colorado River 

Sediment influxes were measured on the Paria River, House Rock Wash, and the LCR. 

Stream-flow gaging stations on the Paria River and LCR were in place before the beginning of this 

study. Gaging of House Rock Wash began on July 25, 2000, when a downward looking acoustic 

stage gage was installed. This tributary is the largest entering the Colorado River between the Paria 

River and the LCR. Because of the remoteness and flashiness of House Rock Wash, discharge 

measurements were not made there, and the relation between stage and discharge was computed 

using the USGS multidimensional surface-water modeling system (McDonald and others, 2001). 

Between August 15, 1999, and October 31, 2000, 96 suspended-sediment measurements 

were made near USGS gaging station 09382000 (Paria River at Lees Ferry, Ariz., herein referred to 

as the Paria River gaging station), and 48 suspended-sediment measurements were made near 

USGS gaging station 09402000 (Little Colorado River near Cameron, Ariz., herein referred to as 

the LCR gaging station). Of the samples collected near the Paria River gaging station, 17 were 

collected by the equal-width increment (EWI) method (Edwards and Glysson, 1988), 77 were dip 

samples, and 2 were collected by an automatic pump sampler. Of the samples collected near the 

LCR gaging station, 3 were collected by either the EWI or equal-discharge increment (EDI) 

methods, 2 were dip samples, 38 were collected by an automatic pump sampler, and 5 were 

collected by a U-59 single-stage sampler. Five suspended-sediment samples were collected in 

House Rock Wash between July 25 and October 31, 2000, using a U-59 single-stage sampler. 

Suspended-sediment concentration and grain size in the Colorado River were determined 

from cross-sectionally integrated suspended-sediment measurements. Between August 15, 1999, 

and September 30, 2000, 238 measurements were made at USGS gaging station 0938100 

(Colorado River above Little Colorado River near Desert View, Ariz.; herein referred to as the 

Lower Marble Canyon gaging station) located at river mile 61.4, and 340 measurements were made 

at the Grand Canyon gaging station. Of the samples collected at the Lower Marble Canyon gaging 

station, 79 were collected by the EWI method using a D-77 bag sampler and 159 were collected by 

the EDI method using a D-77 bag sampler. Of the samples collected at the Grand Canyon gaging 

station, 7 were collected by the EWI method using a D-77 bag sampler and 333 were collected by 

the EDI method using a D-77 bag sampler. In addition to the samples collected at these two gaging 

stations, 12 cross-sectionally integrated suspended-sediment measurements were made with a D-77 

bag sampler using the EWI method near river mile 30.2 just before, during, and immediately after 

the September HMF. 

To determine longitudinal changes in the spatial distribution of channel and eddy sources of 

suspended fine sediment before, during, and after Period 4, suspended-sediment samples were 

collected downstream from Lees Ferry on river trips in May, July, and September 2000. Between 

May 11 and May 16, 21 surface dip samples were collected in the center of the channel. Dam 

releases during this river trip were 480 m3

/s (17,000 ft3/s). Between July 26 and July 31, 18 surface 

dip samples were collected in the center of the channel. Dam releases during this trip were 230 m3

/s 

(8,100 ft3

/s). Between September 6 and 8, 91 single-vertical depth-integrated samples and 37 

surface dip samples were collected in the center of the channel using a sampling scheme wherein 

the same parcel of water was tracked between Lees Ferry and river mile 100 during 3 d of traveling 

 9
at the mean flow speed and camping for only those hours when navigation was not feasible because 

of darkness. Because the goal of the trip was to sample the same water parcel as it traveled 

downstream, this sampling trip is hereafter referred to as the “Lagrangian sampling trip.” 

Characteristics and Changes in the Area of the Bed Covered by Fines and the Size of Fine 

Sediment on the Bed 

Changes in the area of the bed covered by fine sediment were determined from towed sidescan sonar surveys conducted by R.J. Anima before and after the September HMF (Wong and 

others, 2003). Details of the side-scan sonar system used in these surveys are described by Anima 

and others (1998). Before and after the September HMF, side-scan sonar data were collected in 

three reaches in Marble Canyon: the Lees Ferry, Redwall Gorge, and Point Hansbrough reaches 

(fig. 1). These data were positioned using a handheld Global Positioning System (GPS) receiver 

and reference to aerial photographs. The spatial accuracy of the side-scan sonar data was 

subsequently improved by matching shoreline features present in the side-scan sonar data with 

equivalent features in 2002 orthorectified digital aerial photography. Once an adequate number of 

ground control points were located in the side-scan sonar data, several geometric correction 

algorithms were applied using standard GIS image-processing software. The effectiveness of each 

algorithm for producing an image that most closely matched the shoreline features in the aerial 

photography was compared, and the rubber-sheeting algorithm was found to produce the best 

results. Ground control point positioning was only possible along the edges of the side-scan sonar 

data, where the shoreline was detectable. Not all images contained complete shoreline features 

(e.g., the side-scan sonar swath captured only one shore, or neither shore was visible in places 

where the river was wider than the sample swath). In these situations, it was difficult or impossible 

to identify the true locations of the features observed in the side-scan sonar data, and some river 

segments contained no ground control points. This is not desirable when using the rubber-sheeting 

model (or most other geometric correction models), and as expected, it produced distortions and 

some data loss. 

The grain size of bed sediment was monitored using three techniques: physical samples, 

observational samples, and calculated indices of bed sediment size. Sediment samples were 

collected with a pipe dredge, and an underwater video microscope recorded observations of 

surficial sediment. Indices of grain size were calculated from the concentration and grain size of 

suspended sediment at the Grand Canyon gaging station using the β technique of Rubin and 

Topping (2001). 

Using an underwater microscope system composed of a microscopic lens installed on a 

digital video camera and housed in a heavy pressure case (Chezar, 2001; Rubin and others, 2006, in 

press), several thousand in situ images of surficial bed sediment were collected. The entire system 

was lowered to the riverbed using a winch. A digital video recording console on the surface vessel 

was used to acquire and record images of the riverbed. The mean grain size of each sample was 

determined by viewing digital videotapes of the bed images on a computer using a video-editing 

program. We extracted frames that showed usable images of bed sediment, and frames were 

considered usable when no sediment was blurred in the image. Blurring is caused by movement of 

the camera owing to currents, turbidity, or change in boat position. The selected usable frames were 

converted from picture files to text files to obtain grain-size data. A spatial autocorrelation 

algorithm (Rubin and others, 2001; Rubin, 2004) was used to process the text files and determine 

the mean grain size of each sample. Samples were aggregated into 15 groups that distinguished 

samples collected before and after the September HMF, and the mean grain size was computed for 

 10
each of the 15 groups before and after the September HMF. Values of β were compared to 

observed systemwide trends in suspended sediment and bed sediment to evaluate this metric’s 

ability to describe average system behavior. 

Changes in the Topography of Fine-Sediment on the Bed, in Eddy Sandbars, and in 

Channel-margin Deposits 

Changes Measured by Ground Surveys and Bathymetry 

The topography of eddy sandbars, channel-margin deposits, and the bathymetry of the bed 

were measured in March, June, August, and September 2000 to evaluate changes in location and 

magnitude of fine-sediment storage in parts of 19 fan-eddy complexes. One measurement site was 

in Glen Canyon, 13 sites were in Marble Canyon, and 5 sites were in upper Grand Canyon (fig. 1). 

Measurements bracketed both HMFs. The volume and area of fine sediment above the stage of 

specific reference discharges were compared. Kaplinski and others (1995) and Hazel and others 

(1999) described annual and more frequent surveys at the same long-term study sites between July 

1991 and February 1997. Study site reference numbers indicate river mile location (table 1). 

The primary area of interest within each site was the eddy sandbars immediately 

downstream from each constriction. Nearby channel-margin deposits and the main-channel bed 

immediately downstream from each constriction and directly offshore from surveyed eddy sandbars 

were also measured at most sites. For computational purposes, the dividing line separating the main 

channel and eddy was taken as the topographic base of the eddy sandbar. This dividing line 

typically occurs offshore from the location of the streamline dividing downstream channel flow and 

recirculating flow. 

Surveys of terrestrial and shallow subaqueous topography were conducted using electronic 

total stations and conventional survey techniques. River bathymetry was surveyed using highresolution single-beam and multibeam echo sounders (Kaplinski and others, 2000); although, there 

were technical problems with the multibeam system during the June surveys that prevented bed 

topography from being measured at most sites. 

The repeat surveys allowed precise assessment of topographic change. As many as 2,000 

ground points, between 2 x 104

 and 3 x 104 single-beam bathymetric points, and between 8 x 106

and 10 x 106

 multibeam bathymetric points were collected at each site to define the topography. 

The point data have a horizontal error of less than 0.25 m and vertical error that varies from 5 cm or 

less for points acquired with a total station to 10 cm or less for bathymetric points. Point data were 

referenced, in meters, to established survey marks with the Grand Canyon Monitoring and 

Research Center’s geodetic control network. The network references the National Spatial Reference 

System (Zilkoski and others, 1997) and uses the 1983 Arizona State Plane Coordinate System, 

central zone. 

Topographic surfaces and change detection at each site were generated using surface 

modeling software. Single-beam and multibeam point data were resampled at 2-m intervals, and the 

multibeam data were converted to a 2-m point grid derived from a triangulated irregular network 

(TIN) using the Delaunay method of triangulation. The combined ground-based and bathymetric 

data typically corresponded to an average density of one point per 1 to 5 m2

. These combined 

points were used to calculate a TIN surface for both terrestrial and subaerial portions of each of the 

19 fan-eddy complexes. Fine-sediment volumes below the 227 m3

/s (8,000 ft3/s) stage were 

determined by subtracting the measured values from a minimum surface TIN, which was derived 

 11
from a regularly spaced grid of minimum point values generated from a 10-yr dataset containing as 

many as 25 surveys at each study site (Hazel and others, 2006). 

We computed fine-sediment storage changes in eddy sandbars for three elevation zones 

related to the stages of three types of dam releases. The high-elevation zone is emergent above a 

flow of 708 m3/s (25,000 ft3/s) and is only inundated by BHBFs and some HMFs. The midelevation zone is the area inundated by flows of 227 (8,000 ft3

/s) to 708 m3/s (25,000 ft3/s), the 

typical operating range for Glen Canyon Dam during most months. The low-elevation zone is 

below the stage of 227 m3

/s (8,000 ft3/s) and is always inundated during the typical flow regime. 

This zone includes deeper, continuously inundated portions of the eddy and main channel. The 

elevations for the stage of each reference discharge were derived from previously determined stagedischarge relationships for each site (Hazel and others, 1999). The high-elevation zone is 

equivalent to the postdam flood deposits and the mid-elevation zone is equivalent to the 

fluctuating-flow deposits of Schmidt and others (2004). 

The methods described here permitted detection of changes in sediment storage, as well as 

analyses of sediment transfer among elevation zones. Changes in area and volume were normalized 

and expressed as a percentage of the topography surveyed in March 2000, using the following 

formula. 

% change = 100*[(VTx – VTx+1)/Vi], (2) 

where VTx is the volume or area at time x, VTx+1 is the volume or area at time x+1, and Vi is the 

volume or area in March. Areas are reported for the mid-elevation and high-elevation zones only. 

Low-elevation eddy and main channel areas did not change appreciably. 

Direct comparison of topographic changes caused by the May and September 2000 HMFs 

was problematic because the time interval between the surveys bracketing the May HMF 

(conducted in March and June) was much greater than that for the September HMF. The maximum 

time interval between the pre-HMF (March) survey at a study site and the onset of the May HMF 

was 46 d, and the maximum interval between the end of the May HMF and the post-HMF (June) 

survey at a study site was 34 d. During this period, there were 24 d of steady, moderately high 

discharge at 487 m3

/s (17,200 ft3/s) before the May HMF and 23 d of steady discharge (also at 487 

m3

/s) after the HMF, followed by the 3-mo period of steady flow at 230 m3/s (8,100 ft3/s) that 

began June 1. Thus, considerable change in the deposits at the study sites may have occurred that 

was unrelated to the May HMF. In contrast, the September HMF was immediately preceded and 

followed by the low, steady discharge of 230 m3/s, which resulted in minimal modification of the 

deposits of fine sediment at the study sites, and the time interval between measurements was small. 

Daily Changes in Sand Storage as Measured by Ground Surveys at River Mile 30.7 

The eddy sandbar and nearby channel at river mile 30.7 were surveyed daily during the 

September HMF to examine daily and hourly rates of topographic change. This eddy is located in a 

relatively narrow part of Redwall Gorge in upper Marble Canyon. The area of the eddy within the 

study boundary is 8,523 m2

, and it is one of the largest in the local area (Schmidt and others, 2004). 

A pre-HMF survey was conducted on September 4, when the discharge was about 237 m3

/s (8,400 

ft3/s). The site was surveyed three times on September 5, with the first survey occurring as the flow 

increased from about 538 m3

/s (19,000 ft3/s) to 722 m3/s (25,500 ft3/s). The rising limb of the HMF 

arrived at approximately 5:30 a.m. on September 5 (fig. 4) and took about 7 h to reach peak 

discharge, a rate of approximately 91 m3/s (3,200 ft3/s) per hour. The second survey occurred when 

the flow reached its maximum stage. The total stage change during the rising limb of the HMF was 

 12
3.7 m (12 ft) (fig. 5). The site was surveyed once more that day, and surveys were repeated twice 

per day thereafter. The post-flood survey was conducted on September 9, when flow had returned 

to about 233 m3

/s (8,200 ft3/s). The longest interval between surveys was 18 h. Volumes were 

calculated for the entire eddy area. 

Aerial Photograph Analysis of Eddy Sandbars and Channel-margin Deposits 

The area of fine sediment in the mid-elevation zone was mapped from aerial photographs in 

four study reaches covering 21.4 km of the river before and after the September HMF. These study 

reaches (table 2) were shorter than and totally encompassed by the 55 km previously mapped by 

Schmidt and Leschin (1995), Schmidt and others (1999), Sondossi (2001), and Sondossi and others 

(2002). These earlier studies described the distribution of fine sediment for several years between 

1984 and 1997, including changes in the area of fine sediment caused by the 1996 controlled flood 

(Schmidt, 1999). 

The cumulative size distributions of EDZs in the longer study reaches mapped in previous 

studies were compared with those of the shorter study reaches mapped in this study to evaluate 

whether the distributions were similar between these two datasets. Similarity is a prerequisite for 

comparisons of the 2000 data with data from previous years. The cumulative size distributions of 

eddies within these two datasets (fig. 6) were not similar in the Lees Ferry and Point Hansbrough 

study reaches. Thus, revised metrics for the shorter study reaches were computed for all the years 

presented in previous studies. 

Interpretations were made of photographs acquired between August 29 and 31 and between 

September 15 and 18, 2000, when discharge was 227 m3

/s (8,000 ft3/s). These photographs were 

provided by the GCMRC as 18-cm resolution, black-and-white, digital imagery. The distribution of 

fine sediment was delineated from both photographic series using on-screen digitizing methods in 

ArcInfo. Shadows at some sites prevented unambiguous identification of the boundary between 

water and wet sand, and survey data in these places were used to aid in mapping the edge of water. 

Map units were similar to those defined by Schmidt and Leschin (1995), Schmidt (1999), and 

Schmidt and others (2004). We differentiated between channel-margin deposits and eddy sandbars 

based on the criteria of Schmidt (1990), Rubin and others (1990), and Schmidt and Rubin (1995). 

GIS databases that include separate data layers obtained from different years of aerial 

photographs may contain several types of errors, including mapping and interpretation errors, 

spatial transformation errors, and errors in change-detection algorithms. The first two sources of 

error can occur in any specific data layer, whereas the other sources of error emerge in comparing 

the distribution of deposits among different years. The accuracy and precision of the maps 

produced in this study were estimated in two ways. First, the estimation of error within each data 

layer was quantified by Schmidt and others (2004), who compared a remote-sensing approach for 

delineating deposits in the mid-elevation zone with the extent of these deposits surveyed with total 

stations at 13 eddy sandbars in Marble and upper Grand Canyons. The error was assumed to be the 

same as those calculated by Schmidt and others (2004), since the methods used here were the same. 

To estimate the accuracy of the algorithm for interpreting change among data layers, areas where 

the algorithm predicted erosion, no change, or deposition were compared with the areas surveyed at 

seven sites. 

A major objective of this study was the detection of temporal changes in the distribution 

and size of eddy sandbars and channel-margin deposits. Thus, the area of eddy sandbars and 

channel-margin deposits were measured, and fill ratios were determined. Absolute changes in eddy 

sandbars were determined by counting the number of eddy sandbars that significantly increased, 

 13
did not change, or significantly decreased in area between August and September 2000. 

Significance in these calculations was defined as a change greater than 200 m2

, which represents 

the minimum detectable change of our methods. We also determined the mean and median size of 

eddy sandbars in each reach in each year of photography, the fill ratio of each EDZ in each reach, 

and the reach cumulative fill ratio. Net normalized aggradation (NNA) was defined as 

NNA = (Ad – Ae) / AEDZ (3) 

where Ad is the area of significant deposition during a time period, Ae is the area of significant 

erosion during the same time interval, and AEDZ is the area of the eddy deposition zone (Schmidt 

and others, 1999). Schmidt and others (2004) provide an extensive explanation of these metrics. 

Robustness of the analyses used in this study was also evaluated. The overall accuracy of 

the algorithms used to compare the areas of sandbars before and after the September HMF was 

64.1% (table 3). The off-diagonal of the error matrix in table 3, which includes areas where 

deposition occurred yet the algorithm predicted erosion (0.4% of the total area) and vice versa 

(0.1% of the total area), indicates that the algorithm did not always detect small amounts of erosion 

or deposition but rarely produced predictions opposite to the actual change. This indicates that the 

algorithm did not detect many of the small-scale changes in elevation measured by detailed ground 

surveys. 

Assessment of Reworking in Eddy Sandbars Using Scour Chains 

In August, 67 scour chains were installed to assess the amount of scour and fill at 18 sites 

during the September HMF. Each site consisted of two to four transects, with three to four chains 

comprising each transect (table 4). Transects were oriented perpendicular to the local edge of water 

at 878 m3/s (31,000 ft3/s) and extended toward the center of the eddy. The location of each chain 

was surveyed in August and September before and after the HMF. Chains were 1 m long. 

Assessment of Changes in Backwater Area Among Years 

Areas of ponded flow shoreward from emergent sandbars, such as the inundated but 

stagnant flow area of flooded eddy return-current channels, were delineated on aerial photographs 

taken before and after the September HMF. These areas are locally called “backwaters” by aquatic 

ecologists working in Grand Canyon, and that term is used here. Thus, these backwaters are not the 

same as the areas of mainstem flow ponded upstream from debris fans in fan-eddy complexes. The 

size and distribution of backwaters as depicted on aerial photographs were mapped for the flow 

conditions at the time the photographs were taken. Backwaters were defined as those areas 

enclosed by shoreline on three sides and only open to exchange of flow with the main current at 

one end of the embayment. The line drawn from the edge of the sandbar that forms the streamward 

side of the embayment was drawn at an angle of approximately 45° to the mean current direction 

(fig. 7). Backwaters were differentiated between those whose opening was oriented upstream and 

those oriented downstream. 

 14
Results 

Spatial and Temporal Trends in Discharge and Suspended Sediment

Measurements of Discharge and Suspended Sediment in Tributaries 

There was little inflow from tributaries during summer and fall 2000, and the hydrographs 

of the four mainstem gaging stations did not differ greatly from that measured at the dam (fig. 8). 

Small differences in discharge between the Lees Ferry and Lower Marble Canyon gaging stations 

reflect small inflows from the Paria River (fig. 9A), House Rock Wash (fig. 9C), and other small 

tributaries in Marble Canyon. Inflow from the LCR was below normal for the study period (fig. 

9B). The largest inflows during the study period occurred after August 15 well downstream of the 

study area, between the Grand Canyon gaging station and USGS gaging station 09402400 

(Colorado River above Diamond Creek near Peach Springs, Ariz.), which is located approximately 

224 km downstream from the Grand Canyon gaging station (compare fig. 8C and 8D). Although 

the LSSF study design anticipated that substantial tributary sediment would be supplied to the 

Colorado River during Period 4, there was little inflow of suspended sediment from any of the 

tributaries (Figs. 10, 11, and 12). 

Trends in Suspended Sediment in the Colorado River during the May and September HMFs 

Comparison of the suspended-sediment data collected at the Lower Marble Canyon and 

Grand Canyon gaging stations during the two HMFs (fig. 13) suggests that the upstream sand 

supply in Marble Canyon during the May HMF was greater than during the September HMF. 

Though the concentrations of suspended silt and clay during the two HMFs were comparable at the 

Lower Marble Canyon gaging station (fig. 14A), the concentration of suspended sand was 

approximately 30% lower during each day of the September HMF than during each day of the May 

HMF (fig. 14B). This was true despite the fact that suspended sand was slightly finer during the 

latter portion of the September HMF than during the May HMF (fig. 14C). Observations made 

during the Lagrangian sampling trip and subsequent observations in spring 2001 suggests that 

small-scale flooding occurred on Nankoweap and Kwagunt Creeks, two small tributaries that enter 

the Colorado River in Marble Canyon between the Point Hansbrough and Tapeats Gorge study 

reaches (fig.1), during the latter portion of the September HMF, and these tributaries probably 

supplied the finer-grained sediments at this time. While there was less sand in suspension in Marble 

Canyon during the September HMF, approximately 80% of the sand that was eroded from Marble 

Canyon during the September HMF was derived from sources upstream from river mile 30. 

Furthermore, the sand in suspension was much coarser at river mile 30 than it was at either the 

Lower Marble Canyon or Grand Canyon gaging stations during each day of the September HMF 

(fig. 14C). The differences between the May and September HMFs were less pronounced at the 

Grand Canyon gaging station than at the Lower Marble Canyon gaging station. After day one of the 

September HMF, the upstream supply of sand appears to have been comparable during both events, 

and the upstream supply of silt and clay actually increased temporarily during day two of the 

September HMF in response to upstream tributary activity. 

As the upstream supply of sediment became depleted during the May and September HMFs, 

the suspended sediment coarsened over time while the concentration of suspended sediment 

decreased. This process was observed everywhere suspended sediment was measured during the 

two HMFs, as was the case during both the 1996 controlled flood (Rubin and others, 1998; Topping 

 15
and others, 1999; Topping and others, 2000b) and an HMF in November 1997 (Topping and others, 

2000b). Coarsening of the suspended sediment over time during these two HMFs occurred because 

of both a decrease in the concentration of silt and clay and a coarsening of the sand in suspension. 

Comparison of the Longitudinal Patterns of Suspended Sediment in May, July, and 

September 

Analysis of the surface dip samples collected in May, July, and September indicate that the 

pattern of the downstream increase in suspended sand was similar during all three periods, with a 

rapid increase in concentration at the mouth of the Paria River and a more gradual increase in 

suspended-sand concentration from the mouth of the Paria River downstream (fig. 15A). Because 

no substantial new tributary sand was supplied to the Colorado River during any of these sampling 

trips, this downstream increase in suspended-sand concentration reflected the progressive erosion 

of sand from the eddies and channel in the downstream direction during each period. During the 

May and July trips, approximately half of the sand exported past the Lower Marble Canyon gaging 

station was eroded from the upstream half of Marble Canyon. During the September HMF, 

approximately 80% of the sand exported from Marble Canyon was eroded from the upstream half 

of Marble Canyon. 

Analysis of the suspended silt and clay data yields a similar result, with the exception being 

the July trip, when larger tributary effects on the silt and clay concentrations were evident 

immediately downstream from the Paria River and LCR (fig. 15B). During all three trips, roughly 

half of the suspended silt and clay that was exported from Marble Canyon was from the upstream 

half of Marble Canyon. 

Lagrangian Sampling Trip during the September HMF 

Because the goal of this river trip was to repeatedly sample the same parcel of water moving 

downstream on each of the 3 d, sampling did not begin on day one because we anticipated a rapid 

temporal decrease in suspended-sediment concentration at the onset of the flood. Such a rapid 

decrease in concentration would increase the error associated with imperfect tracking of the same 

parcel of water as it moved downstream. 

After an initial rapid increase in the concentration of suspended sand between Lees Ferry 

and river mile 10, suspended-sand concentrations gradually increased further downstream. Slight 

decreases were measured between the last measurement of an evening and the first measurement of 

the next morning (fig. 16A), because the parcels of water sampled on different days were different 

parcels of water. Similarly, the concentration of suspended silt and clay gradually increased in the 

downstream direction, and there was a rapid increase in suspended silt and clay concentration 

immediately downstream from the LCR. As the concentration of suspended sand increased 

downstream, the grain size of the suspended sand got finer (fig. 16B). Comparison of the data 

collected throughout the Lagrangian sampling trip, at river mile 30, and at the Lower Marble 

Canyon gaging station suggests that more than half of the sand that was eroded upstream from river 

mile 30 during the September HMF was eroded between the Paria River and river mile 10. 

Computation of the Mass-Balance Sediment Budgets 

Using both the model of Topping (1997) and suspended-sediment measurements, the 

cumulative fine-sediment supply for the Paria River was computed for the entire study period. 

Tributary influxes of fine sediment from the other two measured tributaries, House Rock Wash and 

 16
the LCR, were computed using suspended-sediment measurements only (fig. 17A). The cumulative 

fine-sediment export past the Lower Marble Canyon and Grand Canyon gaging stations was 

computed using measurements of suspended-sediment concentration (fig. 17B). Cumulative finesediment influxes to and effluxes from the study area were thus computed for Periods 1 through 5. 

Fine-sediment Input to Marble Canyon 

Instantaneous loads of sand, silt, and clay in the Paria River computed using the model of 

Topping (1997) compared favorably with those measured during the two periods of historical daily 

sediment data, October 1947–September 1976 and July–December 1983, with the model-predicted 

sand loads being better than the model-predicted silt and clay loads (Topping, 1997). Uncertainties 

used in the model computations for the period of August 15, 1999, through October 31, 2000, were 

20% for sand and 50% for silt and clay (fig. 17A). Comparison of the model-predicted and 

measured instantaneous sand loads and silt and clay loads indicate that these uncertainties are 

reasonable (fig. 18A, B). 

Data collected at the gaging station on House Rock Wash were used to estimate the supply 

of sand and the supply of silt and clay from the smaller tributaries during Periods 4 and 5. Data 

collected at gaging stations installed subsequent to this study during 2001–02 on other small 

tributaries suggest that House Rock Wash contributes between 1.5 and 2 times the amount of fine 

sediment to Marble Canyon than does the combined influx of Badger Creek, Tanner Wash, North 

Canyon Wash, and Shinumo Wash (D.J. Topping, unpubl. data). Together with House Rock Wash, 

these small tributaries comprise approximately 55% of the tributary drainage basin area to Marble 

Canyon downstream from the Paria River. Observations made in these small tributaries in July 

2000 and measured streamflow at the Lower Marble Canyon gaging station together indicate that 

no substantial floods occurred before July 2000 on Badger Creek, Tanner Wash, or Shinumo Wash. 

One large flood probably occurred in June on North Canyon Wash, and one moderate flood 

occurred before July 25 on House Rock Wash. To account for these tributary inputs, the sand loads, 

and silt and clay loads computed for House Rock Wash were doubled, with uncertainties assumed 

to be 50%. 

Fine-sediment Export from Marble Canyon 

Sand export and silt and clay export from Marble Canyon during Periods 1 through 5 were 

computed by multiplying the measured concentrations of suspended sediment in these size classes 

at the Lower Marble Canyon gaging station by the discharge of water; uncertainties of 20% were 

assumed (fig. 17B). Only one suspended-sediment measurement was made during the period 

between October 1999 and March 2000; measurements of suspended-sand and suspended-silt and 

clay concentration observed at the Grand Canyon gaging station were thus used to estimate 

suspended-sediment concentrations at the Lower Marble Canyon gaging station during this period. 

In addition to computing the sediment efflux from Marble Canyon, the suspended-sediment data 

collected near river mile 30 were used to compute the sediment export from the upstream half of 

Marble Canyon during the September HMF. 

Sand Input to Upper Grand Canyon 

During each of the five periods, the sand input to upper Grand Canyon was computed by 

combining the computed sand efflux past the Lower Marble Canyon gaging station, including 

uncertainties, with an estimate of the sand supplied by the LCR (fig. 17A). A suspended-sand rating 

 17
curve was developed to estimate the suspended-sand concentration as a function of discharge at the 

LCR gaging station. Data used in this rating curve were 138 suspended-sand measurements made at 

this gaging station between 1997 and 2001 (fig. 19). Uncertainties used for the estimates of the 

sand supplied by the LCR were 30%. No estimates of the silt and clay load of the LCR were made 

because of the much greater uncertainty associated with computing silt and clay loads by a ratingcurve approach. Thus, no silt and clay budget could be constructed for upper Grand Canyon. 

Sand Export from Upper Grand Canyon 

Sand export from upper Grand Canyon during Periods 1 through 5 was computed by 

multiplying the measured suspended-sand concentrations at the Grand Canyon gaging station by 

the discharge of water. Uncertainties were 10% because of the greater number of sedimenttransport measurements at this gaging station. 

Mass-Balance Sediment Budgets for Periods 1 through 5 

Sediment budgets for the first five periods of the LSSF experiment are consistent with 

hypotheses concerning sediment transport described at the beginning of this report (figs. 20 and 21, 

table 5). The mass balance for sand was negative in Marble Canyon in Periods 1, 2, 3, and 5 and 

was positive in Period 4. The mass balance for sand in upper Grand Canyon was indeterminate in 

Periods 1, 2, 3, and 5 and was positive in Period 4. Thus, influxes of tributary fine sediment did not 

remain in Marble Canyon during Period 1 but were typically more than 250 m3/s (8,800 ft3/s). 

Instead, they were transported past the Lower Marble Canyon gaging station within a few months 

after tributary inflows. Accumulation only took place during Period 4 when discharges were less 

than about 250 m3/s (8,800 ft3/s). However, because tributary-derived influxes of fine sediment 

were much lower than average during summer 2000, less sand accumulated during Period 4 than 

was eroded during the May HMF (Period 2) and the transitional moderate dam releases of Period 3. 

Thus, less fine sediment was available for entrainment in Marble Canyon at the start of the 

September HMF than at the start of the May HMF. 

Characteristics and Changes in Bed-Sediment Area and Grain Size 

Side-scan Sonar Mapping of Changes in Bed Texture 

Using the methods described in Anima and others (1998) and Wong and others (2003), 

areas of similar bed texture were identified and classified by R.J. Anima in the side-scan sonar data 

collected in the three Marble Canyon reaches before and after the September HMF. Four bedtexture classes were identified: sand, finer gravel (i.e., pebbles and cobbles), boulders (i.e., coarser 

gravel), and bedrock. The sand and finer-gravel classes were further subdivided based on whether 

they occurred in main-channel or eddy environments (table 6). Near-equivalent areas of 

interpretable side-scan sonar data were collected during the pre- and post-HMF trips in the Lees 

Ferry and Redwall Gorge reaches. The area of interpretable side-scan sonar data collected during 

the post-HMF trip in the Point Hansbrough reach was only approximately 58% of the area in which 

interpretable side-scan sonar data were collected in this reach during the pre-HMF trip. 

The September HMF caused the area of sand covering the bed to increase and the area of 

fine gravel to decrease, based on comparison of the side-scan sonar data in the three reaches in 

Marble Canyon (fig. 22). The area of the bed composed of boulders and bedrock did not 

significantly change during this period. These findings are similar to those of Anima and others 

 18
(1998), who showed that during the 1996 controlled flood the area of sand on the bed increased 

despite the fact that the volume of sand on the bed and in the lower elevation parts of eddy sandbars 

decreased (Andrews and others, 1999; Hazel and others, 1999; Schmidt, 1999). Because the 

discharge during Period 5 was not high enough to entrain boulders, the small differences in the area 

of bed composed of boulders and bedrock illustrates of the error associated with interpretation of 

side-scan sonar data and incorporation into a GIS.

Direct Measurements of Bed-Sediment Grain Size 

The mean grain size of the fine sediment on the surface of the bed coarsened as a result of 

the September HMF (Period 5), and 12 of the 15 sample sites coarsened. The fine sediment on the 

bed coarsened by an average of 0.16 mm in the upstream 93 km of the study area. The greatest 

increase in mean grain size was 1.02 mm at river mile 1.75, although this value is anomalous 

relative to the average for the 12 sites that coarsened. Mean grain size decreased at only two sites as 

a result of the September HMF. These sites are located at river miles 65 and 68, where mean grain 

size decreased by 0.15 mm and 0.04 mm, respectively. One site out of 15, located at river mile 

59.95, experienced no change in grain size. Among the four sites downstream from river mile 60, 

sediment became coarser at two sites and became finer at two sites.

Evaluation of Relative Bed Sediment Coarseness (β) to Describe Average System Behavior 

Temporal trends in the grain size of the sand component of the bed largely tracked trends in 

the sand budget (fig. 23). Bed-grain size was computed using the method of Rubin and Topping 

(2001). The sand component on the bed abruptly fined following upstream tributary floods during 

August–September 1999 and then subsequently coarsened until early April 2000, when the sand 

component of the bed sediment was extremely coarse. Day-to-day variability of β values was 

relatively small compared to monthly trends. 

Changes in the Topography of Fine Sediment Deposits on the Bed and along the Channel 

Margins 

The source of the difference between tributary influx of fine sediment and transport past the 

Grand Canyon gaging station is the fine sediment that is either evacuated or accumulated on the 

bed, in sandbars, and in channel-margin deposits. Although the sediment budgets described in the 

previous section demonstrate that there was some degree of sand evacuation from Marble Canyon 

during Periods 1, 2, 3, and 5, this pattern of channel change is not necessarily reflected in the 

changes in eddy sandbars or distribution of fine sediment on the bed in every short reach. Similarly, 

accumulation of sand in Marble Canyon and upper Grand Canyon during Period 4 does not 

guarantee that accumulation occurred in every short reach, nor do those budgets demonstrate the 

elevation zone where accumulation occurred. Thus, we made field measurements of changes in fine 

sediment deposits and analyzed changes on aerial photographs to compare large-scale changes in 

ΔS predicted by (1) with patterns of change measured in short reaches or at specific sites. 

We measured changes in fine-sediment deposits in two ways: precise measurement of 

topographic change in a few places and imprecise measurement of change in many places. The 

precise measurements were made by ground and bathymetric survey and the imprecise 

measurements were made by mapping the area of every fine-sediment deposit in four study 

reaches. Each approach has its limitations. Neither approach is a rigorously developed sampling 

 19
scheme, and neither approach is a comprehensive census of the change of every fine-sediment 

deposit in the study area. 

Changes in Fine-Sediment Storage as Measured by Ground Surveys

Despite a large degree of variability in topographic change from site to site, the average 

responses of eddy sandbars indicates that fine sediment was redistributed from the bed and lowelevation parts of eddies to the mid-elevation zone during the HMFs. These were the same periods 

when ΔS in Marble Canyon was negative. In contrast, sand was redistributed from the midelevation zone to lower elevations during the low steady flows of Period 4 when ΔS was positive in 

Marble Canyon and upper Grand Canyon. 

The average response of the mid-elevation zone to the May and September HMFs was an 

increase in the mean volume of fine sediment. Between March and June, the average volume of 

fine sediment in the mid-elevation zone increased from 787 to 924 m3 in upper Marble Canyon and 

increased from 2,370 to 2,697 m3 in lower Marble Canyon (table 7). Although the measurement 

interval was large and does not uniquely isolate the effect of the May HMF, measurements at river 

mile 30.7 (described below) and field observations indicate that most of the deposition in the midelevation zones occurred during Period 2. The proportional increase in fine sediment in the midelevation zone was significant in relation to the volume of these deposits measured in March 2000. 

Deposition between March and June resulted in a 47% and 51% increase in the volume of fine 

sediment in the mid-elevation zone in upper and lower Marble Canyons, respectively (table 8). 

Deposition in the mid-elevation zone also occurred between August and September, the period 

spanning the September HMF. The average change in volume in this zone was +409 m3

 and +859 

m3 in upper and lower Marble Canyons, respectively (table 7). 

In contrast to mid-elevation zone changes, the low-elevation zone was depleted of fine 

sediment during the HMFs in upper Marble Canyon, where the average volume of fine sediment at 

low-elevation decreased by 20% (table 8), from 13,628 to 6,701 m3

 (table 7). There were too few 

measurement sites from which to calculate average change in lower Marble Canyon or upper Grand 

Canyon between March and June at low elevation. Measurements were only made at two sites in 

lower Marble Canyon, where one site increased in volume (river mile 47) while the other decreased 

(river mile 51), and at one site in upper Grand Canyon (river mile 62), where aggradation occurred. 

Fine sediment at low elevation was also evacuated during the September HMF. 

Measurements suggest that this pattern may have occurred in lower Marble Canyon, as well as 

upper Marble Canyon, because the two sites in lower Marble Canyon lost fine sediment as well as 

the four measured sites in upper Marble Canyon. 

Mid-elevation fine sediment deposits were typically eroded during the low flows of Period 

4, when the average volume decreased from 924 to 698 m3

 in upper Marble Canyon and from 2,697 

to 2,315 m3

 in lower Marble Canyon. Some of this fine sediment was presumably transferred to the 

low-elevation zone because the average volume of sand in this zone increased by +7,346 m3 in 

upper Marble Canyon and by 1,270 m3

 in lower Marble Canyon (table 7). 

The average changes disguise significant site-to-site variability (fig. 24). Substantial 

aggradation occurred in the mid-elevation zone during both the May and September HMFs at some 

sites, such as at river miles 30, 51, 55, and 65 (tables 7 and 8). Elsewhere, however, the volume of 

fine sediment in this zone decreased during the May HMF, such as at river miles 3, 45, and 68, and 

during the September HMF at river miles 50 and 87. 

Topographic changes of the main channel bed and low-elevation zones of eddies reflected a 

high degree of site-to-site variability. Some sites that aggraded during Periods 2 and 3 eroded 

 20
during the low steady flows of Period 4, such as at river miles 30, 51, and 62 (table 7). In contrast, 

other sites experienced fine-sediment evacuation during Periods 2 and 3 and aggraded during 

Period 4, such as at river miles 22, 32, and 35. One site, at river mile 47, aggraded during Periods 2, 

3, and 4, but was eroded during Period 5. 

Changes in the area and volume of fine sediment in the high-elevation zone at the 19 study 

sites were insignificant because this zone was not inundated by the HMFs. Surveys conducted since 

1990 indicate that the volume of fine sediment in the high-elevation zone significantly increased 

only during the 1996 controlled flood and slowly and steadily decreased thereafter (fig. 25). This 

pattern continued during the LSSF when redistribution of sand was caused by wind. 

The effects of the overall LSSF experiment were not significantly different among upper 

Marble Canyon, lower Marble Canyon, and upper Grand Canyon (tables 7 and 8). Therefore, the 

ground surveys at the 19 study sites provided no evidence of longitudinal differences in eddy 

sandbar response or the relative proportion of fine sediment transferred among the bed, eddy 

sandbars, or channel-margin deposits amongst any of the periods of the LSSF. 

Changes in Fine-Sediment Storage as Measured by Aerial Photograph Analysis 

Analysis of aerial photographs provides an opportunity to independently evaluate whether 

the average changes calculated from the precise ground survey measurements were representative 

of changes averaged for longer reaches. Although Hazel and others (1999) demonstrated that the 

area of new deposits created by the 1996 controlled flood decreased despite measured increases in 

volume, the average change in area of mid-elevation fine sediment deposits was similar to the 

average changes in volume during both HMFs in upper and lower Marble Canyon and in upper 

Grand Canyon (tables 7 and 8). Thus, we assumed that measured increases in the area of midelevation sand interpreted from aerial photographs indicated that the same area had increased in 

volume. 

The measurements made from aerial photographs for the September HMF indicate that the 

average trends calculated from the detailed measurement sites were representative of average 

system response (fig. 26). The average of the three reaches in Marble Canyon indicated that an 

increase in sandbar area had occurred, which is the same trend as indicated by measurements of 

area and volume in upper and lower Marble Canyon from ground surveys. Nevertheless, significant 

variability also exists at the reach scale. For example, the average and median area of eddy 

sandbars in the mid-elevation zone decreased slightly in the Lees Ferry and Point Hansborough 

reaches but increased in the Redwall Gorge and Tapeats Gorge (figs. 27 and 28). 

Site-to-site variability is even larger than the reach-scale variability, as indicated by the 

differences in the area of fine sediment at mid-elevation among eddies in a reach (fig. 29), the 

proportion of each eddy filled with those deposits (fig. 30), the number of eddies that were 

significantly aggraded or eroded (fig. 31), and the different distributions of net normalized 

aggradation (NNA) (fig. 32) in each reach caused by the September HMF. The NNA metrics for 

the September 2000 HMF indicate that the Lees Ferry reach experienced more erosion, relative to 

the amount of deposition, than any other reach (fig. 32). 

Amount of Reworking in Eddy Sandbars as Determined by Scour Chain Recovery 

Surveys of scour chains before and after the September 2000 HMF show that statistics 

describing net change of eddy sandbar topography disguise the magnitude of scour and fill that 

took place at different times and in different parts of the same eddy. Based on all recoverable scour 

chains, both offshore and nearshore sites within about 20 m of the shoreline experienced only 

 21
deposition (fig. 33). However, a few scour chains ranging from 18 to 87 m from the shoreline at 

878 m3

/s (31,000 ft3/s) were not recovered, thus indicating that some sites experienced more than 1 

m of scour (table 4). For example, one chain at the Carbon Creek fan-eddy complex (river mile 65) 

was not recovered, yet freshly deposited sand was observed at the site and net deposition of 80 cm 

was measured by ground surveys. Therefore, this site experienced at least 1 m of scour followed by 

at least 1.8 m of fill. 

Changes in Fine-Sediment Storage as Measured by Ground Surveys: Daily Changes at One 

Study Site 

Measurements of topographic change of the eddy sandbar at river mile 30.7 during the 

September HMF further illustrate the dynamic processes of scour and fill that caused the 

topographic changes described above. Although the details of these processes undoubtedly differ 

from site to site, they further illustrate that net topographic change may result from deep scour or 

thick fill in some parts of eddies. Initially, the eddy sandbar at river mile 30.7 was rapidly eroded. 

Subsequently, there was gradual deposition, punctuated by a smaller erosion event between the first 

and second days of the HMF. Erosion of 7,630 m3 of sand occurred on the rising limb of the HMF 

on September 5 (table 9). As a result, a semicircular depression more than 3 m deep was formed in 

the middle to upstream portion of the reattachment sandbar (fig. 34). This erosion event and the 

resulting semicircular depression probably was the result of a subaqueous mass failure. This mass 

failure of the sandbar occurred solely beneath the water surface, and the high-elevation portion of 

the sandbar was not affected. At least some of this eroded material was not immediately transported 

downstream and temporarily filled part of the main channel, where more than 2 m of fine sediment 

accumulated. The next survey was performed 3 h later when this 2-m-thick deposit on the bed had 

been scoured. On September 6, an additional 4,340 m3

 of sand was eroded from the eddy. This 

erosion occurred upstream from the area of slumping the day before. Deposition of fine sediment 

during the following 2 d replaced about half of the sand scoured from the eddy. This deposition was 

greatest on the upstream part of the reattachment sandbar near the reattachment point and in the 

upstream depression resulting from the failure on September 5. Much of the eddy sandbar platform 

in this area was gradually covered with 1–2 m of sand. 

The overall response at this eddy sandbar to the September HMF varied among the different 

elevation zones. Deposition of 580 m3

 of fine sediment in the mid-elevation zone resulted in a 40% 

increase in fine-sediment volume and a 16% increase in fine-sediment area (table 8). However, 

3,060 m3 of fine sediment was scoured from the low-elevation zone in the eddy, constituting a 23% 

volume decrease. The net effect of the September HMF was a loss of 2,520 m3 of fine sediment 

from the eddy (table 9). The main channel experienced a net volume increase of 1,135 m3 of fine 

sediment, or a 16.6% increase, because of additional slumping of fine sediment from the eddy 

(table 8). 

Rapid failure of eddy sandbars has been documented during normal dam operations (Cluer, 

1995), during the 1996 controlled flood (Andrews and others, 1999; Konieczki, and others, 1997), 

and during the 2-d 1997 test flow of 878 m3

/s (Hazel and others, 2000); although, this process may 

not be common. Andrews and others (1999) suggested rapid erosion resulted from high deposition 

rates and mass failure of over-steepened, unconsolidated sandbar slopes, and models suggest that 

sandbar failure is not a result of declining sand concentration (Wiele and others, 1999). Further 

study is needed to resolve the processes involved in eddy sandbar response to changes in dam 

operations. When mass failures occur during the onset of high flows, the aggradation that follows 

may not replace the sand that was initially eroded from eddy sandbars (Schmidt, 1999). 

 22
Characteristics of Eddy Sandbars during the LSSF in Relation to Characteristics Observed 

since 1984 

The increases in the mean and median area of eddy sandbars in the mid-elevation zone 

caused by the September 2000 HMF were small in the context of the longer term record since 1984. 

Increases in sandbar area at mid-elevation did not return sandbars to the size they had been in 1984. 

In some cases, sandbars were not restored to the sizes they had been in 1990. 

The longer history of sandbar change reflects progressive loss of fine sediment since 1984. 

The total area of fine-sediment deposits in the mid-elevation zone in all study reaches decreased 

significantly from 1984 to 1990 (fig. 27A). Thereafter, the study reaches have responded in 

somewhat different ways. In the Redwall Gorge, Point Hansbrough, and Tapeats Gorge reaches 

there was no significant difference in eddy sandbar area in the mid-elevation zone between 1990 

and 2000. Between April 1996 and August 2000, mean eddy sandbar area and total fine-sediment 

area in the mid-elevation zone increased in all reaches to conditions similar to those in 1990 (Figs. 

26, 28). In the Redwall Gorge reach, the area of mid-elevation fine-sediment increased substantially 

soon after the 1996 controlled flood and then decreased by August 2000, with changes during this 

period being more pronounced in eddy sandbars than in channel-margin deposits (fig. 27C). This 

trend is similar to that determined by averaging change measured at the 19 study sites (fig. 26). All 

reaches exhibited their lowest mean and median eddy sandbar sizes in the mid-elevation zone in 

April 1996. The volume of fine sediment in the mid-elevation zone was typically less in 2000 than 

in 1996, although the volume of sand at a few sites was nearly as large as those measured at other 

times in the 1990s (fig. 24). 

The 1984–2000 time series of sandbar area shows that the Lees Ferry reach has experienced 

erosion of greater magnitude and persistence than the other reaches. Between 1990 and 1996, the 

total area of fine sediment in the Lees Ferry reach continued to decline. The loss of fine-sediment 

area in this reach between 1990 and 2000 was greatest in channel-margin deposits (fig. 27B). The 

greatest decrease in total fine-sediment area occurred between March and April 1996, when the 

1996 controlled flood redistributed fine sediment to the high-elevation zone (Schmidt and others, 

2004). By August 2000, the area of fine sediment in the Lees Ferry reach remained significantly 

less than in 1990, while the total fine-sediment area in the three downstream reaches was not 

significantly different from the 1990 area. 

Eddy sandbars at mid-elevation filled less of the eddy deposition zone in April 1996 than at 

any other time, and increased between April 1996 and August 2000 (figs. 28 and 30). Only the 

Redwall Gorge reach showed an increase in fill ratio because of the September 2000 HMF (fig. 28). 

By September, the fill ratios in the Redwall Gorge and Point Hansbrough reaches were near 1984 

levels; although, both the cumulative and site-specific fill ratios of the Lees Ferry and Tapeats 

Gorge reaches had significantly decreased. 

Different flow regimes since 1984 have caused sandbar area and fill ratios to be more or 

less similar to each other, as reflected in the magnitude of the inter-quartile range (fig. 29). Eddy 

sandbars within each reach were more similar to each other immediately following the 1996 

controlled flood than at any other time. The variability of eddy sandbar area increased after the 

1996 controlled flood in all reaches except Lees Ferry. 

The reach-to-reach variability in sandbar response to flow regime change is further 

illustrated by different distributions of the number of eddies where significant erosion or deposition 

occurred in each reach. In addition, similar flow regime changes caused different proportional 

changes in the study area. The 1996 controlled flood and September 2000 HMF caused different 

styles of change in eddy sandbar area. The larger 1996 controlled flood caused decreases in the area 

 23
of mid-elevation sand in all reaches, but increases in sandbar area in this elevation zone occurred in 

September 2000 in the Redwall Gorge. 

Changes in Backwater Area 

The total area of backwater (i.e., eddy return-current channel) habitat increased in all 

reaches during the September HMF except in the Redwall Gorge reach, where backwater area 

decreased slightly (fig. 35). The number of backwaters also increased significantly in the Tapeats 

Gorge and Redwall Gorge reaches. The number and total area of backwaters within each reach in 

September 2000 were comparable to those in 1984, when these study reaches contained more and 

larger backwaters than at any other time during the period of record examined by Goeking and 

others (2003). Therefore, backwater area has not been greatly affected by the long-term declines in 

eddy sandbar area in Marble and Grand Canyons. 

Discussion and Conclusions 

The LSSF experiment can be evaluated in two ways: as a demonstration project and as 

opportunity to refine scientific understanding. As a demonstration project, one goal of the LSSF 

was to restrict the downstream transport of fine sediment by decreasing dam releases in the summer 

when tributary resupply of fine sediment was anticipated. Another purpose of the LSSF was to 

redistribute the tributary-supplied fine sediment to channel-margin deposits and eddy sandbars 

during the September HMF. This demonstration project was of limited success because tributary 

inflows were unusually low in summer 2000. The May and September HMFs did significantly 

increase the volume and area of fine sediment in eddy sandbars in the mid-elevation zone, but the 

magnitude of the increase was small relative to other observed increases in deposit volume and area 

since 1984. The two HMFs did not reverse the long-term trend of decreasing eddy sandbar volume 

in Marble and upper Grand Canyons. 

In terms of improving scientific understanding, the LSSF was generally successful in the 

sense that integrated measurements were made of main-channel and eddy processes. Measurements 

of main-channel fine-sediment storage, eddy fine-sediment storage, and associated sediment 

budgets show that fine sediment was exported from Marble Canyon when dam releases were 

greater than approximately 250 m3

/s (8,800 ft3/s), and that fine sediment accumulated in Marble 

Canyon when dam releases were less than 250 m3

/s. These results demonstrate that tributarysupplied fine sediment is exported from Marble Canyon during all but the lowest dam releases, and 

that interannual accumulation is likely to occur only if discharge is restricted to less than 

approximately 250 m3

/s. Values of β reflect these trends and also indicate that the bed sand was 

coarsest and the sand supply was the most depleted in Marble and upper Grand Canyons in June 

2000 than compared to any previous time. Thus, it was not surprising that the volume or area of 

eddy sandbars changed little during the September HMF. 

Comparison of the sand mass balance with measured changes in components of ΔS 

demonstrate that sand is stored in and is transferred among different elevation zones by different 

flow regimes (table 10). Sand accumulated in the mid-elevation zone during the two HMFs, and 

sand was eroded from the low-elevation zone by the same flows. In contrast, sand was eroded from 

the mid-elevation zone and accumulated in the low elevation zone during Period 4. Thus, changes 

in sand volume at low elevation in eddies mirror changes in the large-scale, sand mass balance. In 

contrast, changes in the area of sand on the bed increased during periods when evacuation of sand 

occurred. 

 24
At smaller spatial scales, reach and site-scale differences appear to determine if net 

evacuation or accumulation of sand occurs in eddies. Thus, reach average or larger scale metrics 

disguise the fact that there are always eddies that lose sand when most nearby eddies gain sand, and 

vice versa. In fact, during Period 5 when the mid-elevation zone was accumulating sand in most 

areas, eddy sandbars near Lees Ferry and Point Hansborough typically lost sand. Thus, the inherent 

characteristics of site-to-site variability in eddy sandbar response to changing flows and sediment 

supply must be considered in development of robust metrics that describe systemwide change in 

key sediment-related resources, such as the area of campsites. 

The effects of the May and September HMFs differed with respect to the fine-sediment 

supply and the consequent effects on fine-sediment storage in eddy sandbar and channel-margin 

deposits. Because of the small amount of fine sediment supplied by tributaries between the May 

and September HMFs, less fine sediment was available for transport and deposition during the 

September HMF than during the May HMF. The difference in upstream fine-sediment supply 

between the two HMFs was most pronounced during the first day of high discharge, whereas the 

fine-sediment supply was similar between the two HMFs after the first day. Thus, the recent 

influxes of tributary fine sediment were exhausted quickly during the rising limb and first day of 

the September HMF. Following this initial period, the predominant source of the fine sediment 

exported from Marble Canyon during the September HMF was the eddy sandbars, as was the case 

during the 1996 controlled flood (Schmidt, 1999; Hazel and others, 2006). Measurements of eddy 

sandbar scour and fill corroborate this pattern. For example, detailed surveys at an eddy sandbar at 

river mile 30.7 documented rapid erosion followed by gradual deposition of fine sediment during 

the September HMF, but an overall net loss of fine sediment. Similarly, scour-chain data from the 

mid-elevation zone indicated that most eddies experienced erosion followed by deposition, and 

low-elevation parts of eddy sandbars experienced net erosion during the September HMF. This 

result is expanded upon in Hazel and others (2006). 

Samples of suspended and bed sediment illustrated a downstream increase in sediment 

transport throughout the duration of the LSSF experiment. The concentration of suspended 

sediment increased and the grain size of the suspended sediment decreased over the upstream 161 

km on all three sampling trips (May, July, and September). The increase in suspended-sand 

concentration was most pronounced downstream from the Paria River and was more gradual 

throughout the rest of Marble and upper Grand Canyons. Similarly, the increase in suspended-silt 

and clay concentration was most pronounced downstream from the LCR. No new tributary finesediment input occurred during the suspended-sediment sampling trips, so the increasing 

concentration reflected the progressive erosion of stored fine sediment from the bed of the main 

channel and eddies, even during the low steady flows in July. Suspended-sediment data show that 

most of the fine sediment eroded during the September HMF was eroded from upper Marble 

Canyon. These changes in suspended sediment resulted from a downriver increase in the amount of 

suspended sediment in the eddies and main channel and a downriver decrease in the grain size of 

the fine sediment on the bed, thus causing the median grain size of suspended sediment to decrease 

and the concentration of suspended sediment to increase. Grain size of the surficial bed sediment 

also coarsened during the September HMF, especially in the upstream 93 km nearest Lees Ferry. 

Reach-scale maps of the distribution of fine sediment support the conclusion that 

downstream increases in suspended-sand concentrations represent the erosion of sand stored in 

channel-margin and eddy sandbar deposits. While none of the reaches experienced significant 

changes in fine-sediment area because of the LSSF experiment, net normalized aggradation values 

were negative only in the Lees Ferry reach, indicating that this reach experienced more erosion than 

 25
deposition. The Lees Ferry reach contained significantly less fine sediment in 2000 than in 1990; in 

contrast, this trend did not occur in the three downstream reaches. Only in the Lees Ferry reach has 

a substantial decline in the area of mid-elevation fine sediment in eddies continued through 2000, 

indicating that fine sediment from this reach continues to be exported downstream.

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 26
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 27
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 29
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 30
Figures 

Figure 1. Map showing the Colorado River in Marble and Grand Canyons. U.S. Geological Survey 

gaging stations are located at (1) Colorado River at Lees Ferry, Ariz., station 09380000, (2) Colorado 

River above Little Colorado River near Desert View, Ariz., station number 09383100, (3) Colorado 

River near Grand Canyon, Ariz., station number 09402500, (4) Paria River near Lees Ferry, Ariz., 

station number 09382000, (5) House Rock Wash, Ariz., (6) Little Colorado River near Cameron, Ariz., 

station number 09402000, and (7) Colorado River above Diamond Creek near Peach Springs, Ariz., 

station number 09402400. Each of the 19 fan-eddy complexes surveyed in March, June, August, and 

September 2000 are indicated with asterisks. Boxes enclosed areas of comprehensive 

photogeologic mapping. 

 31
Figure 2. Diagram of a typical fan-eddy complex. 

 32
Figure 3. Diagram showing method of calculation of eddy deposition zones. 

 33
0

200

400

600

800

1,000

AUG 1999

SEP 1999

OCT 1999

NOV 1999

DEC 1999

JAN 2000

FEB 2000

MAR 2000

APR 2000

MAY 2000

JUN 2000

JUL 2000

AUG 2000

SEP 2000

OCT 2000

INSTANTANEOUS DISCHARGE, 

IN CUBIC METERS PER SECOND

PERIOD 1 23 4 5

Figure 4. Hydrograph showing releases from Glen Canyon Dam (as measured at the Lees Ferry 

gaging station) throughout the six periods of the low summer steady flows (LSSF) experiment. 

 34
Figure 5. Stage and temperature at river mile 30.7 during the September 2000 habitat maintenance 

flows. These measurements were made every 15 minutes at a temporary stage gage installed on 

river left across from the sandbar. 

 35
Figure 6. Cumulative size distributions of eddies in previous studies and low summer steady flows 

reaches. (A) Lees Ferry study reach. (B) Redwall Gorge study reach. (C) Point Hansbrough study 

reach. (D) Marble Canyon aggregated sample. (E) Tapeats Gorge study reach. 

 36
Figure 7. Diagram showing a sample backwater opening in the upstream direction. The upstream 

boundary of the backwater was drawn at an angle of approximately 45° with respect to the maincurrent direction. 

 37
Figure 8. Hydrographs of the (A), Colorado River at the Lees Ferry, (B) Lower Marble Canyon, (C) 

Grand Canyon, and (D) Diamond Creek gaging stations from April 1–October 1, 2000. 

 38
Figure 9. Hydrographs of three tributaries to the Colorado River: (A) the Paria River, (B) the Little 

Colorado River, and (C) House Rock Wash. 

 39
Figure 10. Measurements of (A) suspended-sand and (B) silt and clay concentrations at the Paria 

River at Lees Ferry gaging station during the study period. 

 40
10,000

100,000

1,000,000

AUG 1999

SEP 1999

OCT 1999

NOV 1999

DEC 1999

JAN 2000

FEB 2000

MAR 2000

APR 2000

MAY 2000

JUN 2000

JUL 2000

AUG 2000

SEP 2000

OCT 2000

SUSPENDED SAND

SUSPENDED SILT AND CLAY

CONCENTRATION, 

IN MILLIGRAMS PER LITER

HOUSE ROCK WASH IN RIDER CANYON

Figure 11. Measurements of suspended-sediment concentration in House Rock Wash during the 

study period. 

 41
Figure 12. Measurements of (A) suspended-sand and (B) silt and clay concentrations at the Little 

Colorado River near Cameron, Ariz., during the study period. 

 42
Figure 13. Measurements of (A) suspended-sand and (B) silt and clay concentrations in the 

Colorado River at the Lower Marble Canyon and Grand Canyon gaging stations during the study 

period. 

 43
Figure 14. Measurements of (A) suspended-silt and clay concentration, (B) suspended-sand 

concentration, and (C) median grain size of suspended sand during the May and September habitat 

maintenance flows (HMF). 

 44
Figure 15. Measured surface (A) suspended-sand and (B) silt and clay concentrations (with 

smoothed curves) during May, July, and September 2000. 

 45
Figure 16. Depth-integrated measurements of suspended sediment (with smoothed curves) from 

the Lagrangian sampling trip during the September 2000 habitat maintenance flows (HMF). (A) 

Concentrations of suspended sand and suspended silt and clay. (B) Median grain size of suspended 

sand. 

 46
Figure 17. Computed cumulative sand transport during the study period. (A) Sand supply from the 

Paria River, Little Colorado River, and House Rock Wash. Uncertainties are shown for the Paria 

River and Little Colorado River sand supplies. (B) Sand export past the Lower Marble Canyon and 

Grand Canyon gaging stations, with uncertainties. 

 47
Figure 18. Model-predicted versus measured instantaneous (A) sand and (B) silt and clay loads in 

the Paria River at Lees Ferry during the study period. 

 48
0.1

1

10

100

1,000

10,000

100,000

0.001 0.01 0.1 1 10 100 1,000

EWI OR EDI MEASUREMENTS

DIP SAMPLES

PUMP SAMPLES

U-59 SAMPLES

SUSPENDED-SAND CONCENTRATION,

IN MILLIGRAMS PER LITER

INSTANTANEOUS WATER DISCHARGE,

IN CUBIC METERS PER SECOND

LITTLE COLORADO RIVER NEAR CAMERON

Figure 19. Suspended-sand rating curve used to estimate the concentration of suspended sand 

in the Little Colorado River. 

 49
Figure 20. Mass-balance sand budget uncertainty envelopes for Marble Canyon and upper Grand 

Canyon during Periods 1–5. (A) Period 1, (B) Period 2 (May habitat maintenance flows), (C) Period 3, 

(D) Period 4, and (E) Period 5 (September habitat maintenance flows). The demonstrable sand mass 

balances in each reach lie within these uncertainty envelopes. 

 50
Figure 21. Mass-balance silt and clay budget uncertainty envelopes for Marble Canyon during 

Periods 1–5. (A) Period 1, (B) Period 2 (May habitat maintenance flows), (C) Period 3, (D) Period 4, 

and (E) Period 5 (September habitat maintenance flows). The demonstrable silt and clay mass 

balances in this reach lie within these uncertainty envelopes. 

 51
Figure 22. Fraction of bed area (in %) composed of each bed-texture class before and after the 

September habitat maintenance flows (HMF) in the three study reaches in Marble Canyon, as 

determined from side-scan sonar data. LF is Lees Ferry study reach. RG is Redwall Gorge study 

reach. PH is Point Hansbrough study reach. 

 52
Figure 23. Comparison of the sand budget and β at the Grand Canyon gaging station during 

Period 1. β values were calculated relative to the mean for data from 1944–2000.

 53
Figure 24. Graphs showing temporal changes in the area and volume of fine sediment between 

the stages associated with discharges of 227 m3

/s and 708 m3/s at 17 study sites in Marble and upper 

Grand Canyons. Vertical bars indicate the period of the LSSF experiment. (A) Fine-sediment area in 

sites in upper Marble Canyon. (B) Fine-sediment volume in sites in upper Marble Canyon. (C) Finesediment area in sites in lower Marble Canyon. (D) Fine-sediment volume in sites in lower Marble 

Canyon. (E) Fine-sediment area in sites in upper Grand Canyon. (F) Fine-sediment volume in sites in 

upper Grand Canyon. 

 54
Figure 25. Graphs showing temporal changes in the area and volume of fine sediment above the 

stage associated with the discharge of 708 m3

/s at 17 study sites in Marble and upper Grand 

Canyons. Vertical bars indicate the period of the LSSF experiment. (A) Fine-sediment area in sites in 

upper Marble Canyon. (B) Fine-sediment volume in sites in upper Marble Canyon. (C) Fine-sediment 

area in sites in lower Marble Canyon. (D) Fine-sediment volume in sites in lower Marble Canyon. (E) 

Fine-sediment area in sites in upper Grand Canyon. (F) Fine-sediment volume in sites in upper Grand 

Canyon. 

 55
Figure 26. Graphs showing the temporal sequence of the mean (A) and median (B) area of midelevation fine-sediment deposits in larger eddies (i.e., in only the eddies larger than 1,000 m2

) 

between 1984 and 2001. LF is Lees Ferry study reach. RG is Redwall Gorge study reach. PH is Point 

Hansbrough study reach. TG is Tapeats Gorge study reach. MC is Marble Canyon aggregate. NAU 

(n=12) and NAU (n=14) are two samples of the population of eddy sandbars in Marble Canyon 

surveyed by Northern Arizona University (NAU). 

 56
Figure 27. Graphs showing the temporal sequence of mid-elevation fine-sediment deposits, or the 

area of fine sediment inundated between the stages associated with discharges of 227 and 708 m3

/s, 

between 1984 and 2000. (A) The total area of fine sediment per unit river length. (B) The area of 

channel-margin deposits per unit river length. (C) The area of fine-sediment deposits within larger 

eddies (i.e., in only the eddies larger than 1,000 m2) per unit river length. LF is Lees Ferry study reach. 

RG is Redwall Gorge study reach. PH is Point Hansbrough study reach. TG is Tapeats Gorge study 

reach. MC is Marble Canyon aggregate. 

 57
Figure 28. Graph showing the cumulative fill ratio for mid-elevation fine-sediment deposits for 

four reaches and Marble Canyon, mapped at a common discharge of 227 m3

/s. LF is Lees Ferry study 

reach. RG is Redwall Gorge study reach. PH is Point Hansbrough study reach. TG is Tapeats Gorge 

study reach. MC is Marble Canyon aggregate. 

 58
Figure 29. Box-and-whisker plots showing the distribution of areas of mid-elevation fine-sediment 

deposits in larger eddies (i.e., in only the eddies larger than 1,000 m2

) in four reaches and Marble 

Canyon, mapped at a common discharge of 227 m3

/s. (A) Lees Ferry study reach. (B) Redwall Gorge 

study reach. (C) Point Hansbrough study reach. (D) Marble Canyon aggregate. (E) Tapeats Gorge 

study reach. 

 59
Figure 30. Box-and-whisker plots of the distribution of fill ratios for mid-elevation fine-sediment 

deposits in larger eddies (i.e., in only the eddies larger than 1,000 m2

), mapped at a common 

discharge of 227 m3/s. (A) Lees Ferry study reach. (B) Redwall Gorge study reach. (C) Point 

Hansbrough study reach. (D) Marble Canyon aggregate. (E) Tapeats Gorge study reach. 

 60
Figure 31. Histograms showing the number of eddies in which the area of low-elevation finesediment deposits increased or decreased by more than 200 m2

 in each time interval, mapped at a 

common discharge of 227 m3

/s. (A) Lees Ferry study reach. (B) Redwall Gorge study reach. (C) Point 

Hansbrough study reach. (D) Marble Canyon aggregate. (E) Tapeats Gorge study reach. 

 61
Figure 32. Graphs showing the distribution of net normalized aggradation (NNA) in the four study 

reaches and Marble Canyon aggregate in response to the September 2000 habitat maintenance 

flows (HMF). (A) Lees Ferry study reach. (B) Redwall Gorge study reach. (C) Point Hansbrough study 

reach. (D) Marble Canyon aggregate. (E) Tapeats Gorge study reach. 

 62
Figure 33. Graphs showing the amount of erosion and deposition at scour-chain sites. (A) 

Thickness of scour (negative values) and fill (positive values) that occurred at a total of 67 scourchain sites during the September 2000 habitat maintenance flows (HMF). (B) Graph showing the net 

elevation change at each scour-chain site during the September 2000 HMF. LF is Lees Ferry study 

reach. RG is Redwall Gorge study reach. PH is Point Hansbrough study reach. TG is Tapeats Gorge 

study reach. MC is Marble Canyon aggregate. 

 63
Figure 34. Map showing erosion and deposition at the river mile 30.7 study site within the first day 

of the September 2000 habitat maintenance flows (HMF). Contours represent topography at the 

beginning of the HMF; contour interval is 1 m. Dashed outline is the eddy boundary used in finesediment volume calculations. Flow in the main channel (right side of map) is from top to bottom. 

 64
Figure 35. Time series of backwater area (A) and the number of eddies with backwaters (B). LF is 

Lees Ferry study reach. RG is Redwall Gorge study reach. PH is Point Hansbrough study reach. TG is 

Tapeats Gorge study reach.

 65
Tables

Table 1. Study site locations and geographic place names of the 19 fan-eddy complexes surveyed 

in March, June, August, and September 2000. (Note: This table uses the terms separation and 

reattachment sandbars; however, for simplicity, these terms are not used elsewhere in the text. For 

definitions, please see Schmidt (1990) or Schmidt and Graf (1990).) 

Site location Geographic Type of 

(river mile) place name eddy sandbar 

-6 -6 Mile reattachment sandbar 

3 Above Cathedral reattachment sandbar 

8 Jackass Canyon separation sandbar 

16 Hot Na Na Wash separation sandbar 

22 22-Mile Wash reattachment sandbar 

30 Fence Fault reattachment sandbar 

32 South Canyon undifferentiated eddy sandbar 

35 Nautiloid Canyon both separation and reattachment sandbars 

43 Anassazi Bridge undifferentiated eddy sandbar 

45 Eminence both separation and reattachment sandbars 

47 Saddle Canyon reattachment sandbar 

50 50-Mile both separation and reattachment sandbars 

51 51-Mile reattachment sandbar 

55 55-Mile reattachment sandbar 

62 Crash Canyon reattachment sandbar 

65 Carbon Creek both separation and reattachment sandbars 

68 Tanner Canyon undifferentiated eddy sandbar 

81 Grapevine undifferentiated eddy sandbar 

87 Cremation separation sandbar 

 66
Table 2. Descriptions of the four study reaches included in photogeologic mapping based on two 

sets of aerial photographs acquired before and after the September 2000 habitat maintenance flows 

(HMF). 

Reach Lees Ferry Redwall Gorge Point Hansbrough Tapeats Gorge 

Reach length (km) 3.3 4.7 4.9 8.5 

Mean size of eddies, in m 10,718 3,064 7,011 6,676 2

Number of eddies 11 20 26 54 

Number of eddies larger than 1,000 m 8 12 9 41 2

Number of NAU survey sites in reach 1 2 2 2 

Number of scour-chain transects 4 5 4 5 

Table 3. Error matrix of the agreement between areas surveyed by Northern Arizona University 

(NAU) and estimated by Utah State University (USU). 

Area, in square meters, surveyed by NAU

Erosion No Change Deposition 

Erosion 1,994 1,213 95 Area, in square meters, 

No change mapped by USU 1,166 9,141 4,940 

Deposition 17 872 3,673 

Percentage of total area, as surveyed by NAU

Erosion No Change Deposition 

Erosion 8.6% 5.3% 0.4% Percentage of total 

No change 5.0% 39.6% 21.4% area, as mapped 

Deposition 0.1% 3.8% 15.9% by USU

Overall accuracy = 64.1%

 67
Table 4. Data from scour chains installed in August 2000 and recovered in September 2000. Chains 

were not recovered at sites noted below as scoured. 

Reach Location & type Chains Deposition (cm) Erosion (cm) Net change (cm) 

Lees Paria Eddy 1--1--1 0 SCOURED -100 

Ferry separation sandbar 1--1--2 0 SCOURED -100 

1--1--3 2 0 2 

1--1--4 2 0 2 

 1--1--5 2 0 2 

Lees River right below bend 1--2--1 2 0 2 

Ferry channel margin 1--2--2 1.5 0 1.5 

1--2--3 6 0 6 

 1--2--4 12 -8 4 

Lees River left between 1--3--1 49 -28 21 

Ferry debris fan 1--3--2 12 0 12 

undifferentiated eddy 1--3--3 0 -13 -13 

 sandbar 1--3--4 0 0 0 

Lees River left below 1--4--1 25 0 25 

Ferry debris fan 1--4--2 4 -11 -7 

reattachment sandbar 1--4--3 0 -12 -12 

 1--4--4 10 0 10 

Lees Silver Grotto 2--1--1 20 0 20 

Ferry separation sandbar 2--1--2 42 0 42 

2--1--3 67 0 67 

2--1--4 87 0 87 

 2--1--5 87 -34 53 

Redwall River right downstream 2--2--1--1 21 0 21 

Gorge from Silver Grotto 2--2--1--2 31 0 31 

undifferentiated eddy 2--2--1--3 40 0 40 

 sandbar 2--2--1--4 35 -9 26 

Redwall River right downstream 2--2--2--1 47 0 47 

Gorge from Silver Grotto 2--2--2--2 78 0 78 

undifferentiated eddy 2--2--2--3 74 0 74 

 sandbar 2--2--2--4 46 -17 29 

Redwall 30-mile 2--3--1 61 0 61 

Gorge reattachment sandbar 2--3--2 47 0 47 

2--3--3 27 -17 10 

2--3--4 26 0 26 

 2--3--5 58 0 58 

Redwall South Canyon 2--4--1 4 0 4 

Gorge separation sandbar 2--4--2 6 0 6 

 2--4--3 17 0 17 

Point 43-Mile 3--1--1 30 0 30 

Hans- reattachment sandbar 3--1--2 38 0 38 

brough 3--1--3 24 0 24 

 3--1--4 16 0 16 

 68
Table 4. Data from scour chains installed in August 2000 and recovered in September 2000. Chains 

were not recovered at sites noted below as scoured.—Continued 

Point Eminence 3--2--1--1 0 SCOURED -100 

Hans- reattachment sandbar 3--2--1--2 70 -24 46 

brough 3--2--1--3 0 SCOURED -100 

Point Eminence 3--2--2--1 6 0 6 

Hans- reattachment sandbar 3--2--2--2 2 0 2 

brough 3--2--2--3 4 0 4 

Point Eminence 3--2--3--1 38 0 38 

Hans- separation sandbar 3--2--3--2 42 0 42 

brough 3--2--3--3 27 0 27 

Tapeats 60-mile 4--1--1 9 0 9 

Gorge reattachment sandbar 4--1--2 21 0 21 

4--1--3 19 -39 -20 

 4--1--4 16 0 16 

Tapeats River right below 60-mi 4--2--1 29 0 29 

Gorge reattachment sandbar 4--2--2 7 -30 -23 

Tapeats River left abv. LCR 4--3--1 0 SCOURED -100 

Gorge reattachment sandbar 4--3--2 0 SCOURED -100 

Tapeats River left Tapeats Gorge 4--4--1 63 0 63 

Gorge reattachment sandbar 4--4--2 55 0 55 

4--4--3 38 0 38 

 4--4--4 10 0 10 

Tapeats Carbon Creek 4--5--1 180 SCOURED 80 

Gorge reattachment sandbar 4--5--2 52 0 52 

4--5--3 68 0 68 

 4--5--4 0 SCOURED -100 

 69
Table 5. Change in sediment mass during each of the five periods. Demonstrable erosion is shown 

in bold-face type, demonstrable accumulation is shown in normal type, no demonstrable change is 

shown in italics. 

Period Change in sand mass 

(metric tons) 

Change in silt and clay mass 

(metric tons) 

Marble Canyon Upper Grand Canyon Marble Canyon 

Period 1 -920,000+490,000 -520,000+680,000 -410,000+690,000 

Period 2 (May HMF) -340,000+65,000 +46,000+94,000 -59,000+12,000 

Period 3 -140,000+25,000 -19,000+42,000 -18,000+3,500 

Period 4 (low, steady flows) +31,000+18,000 +8,100+7,900 -9,000+32,000 

Period 5 (Sept HMF) -220,000+45,000 -12,000+66,000 -65,000+12,000 

 70
Table 6. Bed area (in m2

) and fraction of bed area (in %) composed of each bed-texture class 

before and after the September habitat maintenance flows (HMF) in the three study reaches in 

Marble Canyon, as determined from side-scan sonar data. The sand and finer-gravel classes are 

further subdivided between main-channel and eddy environments. 

Reach Bed-texture class Pre-HMF 

Area (m2

) 

Post-HMF 

Area (m2) 

Pre-HMF 

Fraction (%) 

Post-HMF 

Fraction (%) 

Lees Ferry Eddy sand 1,460 2,180 0.9 1.1 

 Main-channel sand 11,440 19,720 7.0 10.4 

Total sand 12,900 21,900 7.9 11.5 

 Eddy finer gravel 2,170 2,850 1.3 1.5 

 Main-channel finer gravel 111,350 126,770 68.5 66.6 

Total finer gravel 113,520 129,620 69.8 68.1 

Boulders 17,490 22,440 10.8 11.7 

Bedrock 18,750 16,490 11.5 8.7 

Total 162,660 190,450 100.0 100.0 

 Eddy sand 5,800 13,120 2.1 4.7 

 Main-channel sand 41,080 76,570 14.5 27.0 

Redwall 

Gorge 

Total sand 46,880 89,690 16.6 31.7 

 Eddy finer gravel 5,360 2,320 1.9 0.8 

 Main-channel finer gravel 48,930 40,240 17.3 14.2 

Total finer gravel 54,290 42,560 19.2 15.0 

Boulders 117,200 58,650 41.5 20.7 

Bedrock 64,130 92,340 22.7 32.6 

Total 282,500 283,240 100.0 100.0 

Point Eddy sand 5,840 4,120 6.4 7.8 

Hansbrough Main-channel sand 11,950 25,790 13.2 48.8 

Total sand 17,790 29,910 19.6 56.6 

 Eddy finer gravel 11,550 180 12.7 0.3 

 Main-channel finer gravel 34,030 7,440 37.6 14.1 

Total finer gravel 45,580 7,620 50.3 14.4 

Boulders 3,190 2,530 3.5 4.8 

Bedrock 24,080 12,810 26.6 24.2 

Total 90,640 52,870 100.0 100.0 

 71
Table 7. Area (m2

) and volume (m3) of fine sediment at each study site, within the high-elevationeddy, mid-elevation-eddy, low-elevation-eddy, and main-channel zones. Data were collected in 

March, June, August, and September 2000.

High-elevation fine sediment 

(above stage associated with discharge of 708 m3 Location /s) 

 Area, in square meters Volume, in cubic meters 

March June August September March June August September 

Glen Canyon 

River mile -6 418 524 387 430 353 402 339 379 

 

Upper Marble 

Canyon 

River mile 3 132 133 132 134 89 89 85 87 

River mile 8 786 804 753 799 547 556 515 553 

River mile 16 102 104 106 99 42 34 42 43 

River mile 22 334 337 331 509 516 500 529 541 

River mile 30 509 500 496 530 724 697 682 702 

River mile 32 744 750 728 749 825 795 770 811 

River mile 35 766 751 765 778 1,106 1,074 1,106 1,096 

mean 482 483 473 514 550 535 533 548 

standard deviation 298 298 289 295 384 373 376 379 

 

Lower Marble 

Canyon 

River mile 43 2,536 2,508 2,552 2,550 2,933 2,855 2,923 2,930 

River mile 45 2,979 2,973 3,063 3,048 3,448 3,310 3,482 3,456 

River mile 47 1,130 1,060 1,130 1,200 1,059 986 1,058 1,076 

River mile 50 1,738 1,782 1,713 1,823 3,073 3,034 3,016 3,109 

River mile 51 5,187 5,458 5,148 5,399 5,030 5,033 5,012 5,030 

River mile 55 5,640 5,629 5,548 5,832 3,780 3,782 3,762 3,807 

mean 3,202 3,235 3,192 3,309 3,221 3,167 3,209 3,235 

standard deviation 1,834 1,903 1,802 1,899 1,297 1,323 1,294 1,294 

 

Upper Grand 

Canyon 

River mile 62 291 332 279 333 230 237 225 237 

River mile 65 687 684 655 751 400 373 403 407 

River mile 68 2,154 2,099 2,441 2,179 1,215 1,179 1,130 1,226 

River mile 81 1,486 1,499 1,473 1,580 1,395 1,314 1,364 1,424 

River mile 87 340 360 331 344 325 341 315 318 

mean 992 995 1,036 1,037 713 689 687 722 

standard deviation 807 777 919 815 547 514 521 558 

 72
Table 7. Area (m2

) and volume (m3) of fine sediment at each study site, within the high-elevationeddy, mid-elevation-eddy, low-elevation-eddy, and main-channel zones. Data were collected in 

March, June, August, and September 2000.—Continued

Mid-elevation fine sediment 

(between stages associated with discharges of 227 and 708 m3 Location /s) 

 Area, in square meters Volume, in cubic meters 

March June August September March June August September 

Glen Canyon 

River mile -6 3,472 4,055 3,798 3,127 588 1373 628 449 

 

Upper Marble 

Canyon 

River mile 3 2,014 1,703 1,017 2,063 1,776 443 1,731 1,792 

River mile 8 1,331 1,400 1,041 1,403 438 453 306 452 

River mile 16 794 746 749 867 199 197 138 237 

River mile 22 1,631 1,884 1,581 1,697 1,313 1,877 1,292 1,837 

River mile 30 2,930 2,879 2,769 3,405 1,449 2,675 1,338 2,029 

River mile 32 1,877 2,174 1,739 2,950 154 204 106 667 

River mile 35 1,184 2,050 686 1,721 181 621 0 734 

mean 1,680 1,834 1,369 2,015 787 924 698 1,107 

standard deviation 691 664 733 884 699 963 727 750 

 

Lower Marble 

Canyon 

River mile 43 1,544 1,584 1,543 1,689 883 921 963 1,088 

River mile 45 6,004 4,204 5,794 5,916 4,137 2,569 3,947 4,376 

River mile 47 5,036 5,770 4,958 5,999 3,250 3,163 3,243 6,491 

River mile 50 1,948 2,814 1,859 1,313 675 2,035 566 0 

River mile 51 2,938 4,670 3,030 3,093 1,364 3,125 1,407 2,806 

River mile 55 4,849 5,733 4,638 4,912 3,912 4,369 3,763 4,426 

mean 3,720 4,129 3,637 3,820 2,370 2,697 2,315 3,174 

standard deviation 1,828 1,660 1,750 2,083 1,573 1,167 1,506 2,429 

 

Upper Grand 

Canyon 

River mile 62 784 750 789 740 281 402 253 323 

River mile 65 5,328 6,790 4,895 5,753 1,440 4,127 1,173 3,081 

River mile 68 2,434 2,113 1,960 2,699 2,889 2,585 2,897 3,015 

River mile 81 609 663 597 630 440 644 399 782 

River mile 87 386 342 408 331 384 326 380 309 

mean 1,908 2,132 1,730 2,031 1,087 1,617 1,020 1,502 

standard deviation 2,076 2,691 1,870 2,281 1,111 1,683 1,110 1,424 

 73
Table 7. Area (m2

) and volume (m3) of fine sediment at each study site, within the high-elevationeddy, mid-elevation-eddy, low-elevation-eddy, and main-channel zones. Data were collected in 

March, June, August, and September 2000.—Continued

Low-elevation fine sediment 

(below the stage associated with discharge of 227 m3 Location /s) 

 Area, in square meters Volume, in cubic meters 

March June August September March June August September 

Glen Canyon 

River mile -6 8,553 NA NA 8054 8,802 NA NA 9,691 

 

Upper Marble 

Canyon 

River mile 3 20,654 NA NA 20,008 34,650 NA NA 33,888 

River mile 8 NA NA NA NA NA NA NA NA 

River mile 16 13,575 NA NA NA 9,552 NA NA NA 

River mile 22 8,886 7,417 10,277 7,272 5,262 4,085 5,543 5,357 

River mile 30 12,978 12,398 12,253 9,922 6,842 7,094 3,183 7,977 

River mile 32 13,431 14,861 13,673 14,195 7,328 6,390 6,955 5,308 

River mile 35 12,503 26,624 20,665 7,726 18,134 9,234 40,508 464 

mean 13,671 15,325 14,217 11,824 13,628 6,701 14,047 10,599 

standard deviation 3,836 8,144 4,519 5,332 11,266 2,122 17,709 13,299 

 

Lower Marble 

Canyon 

River mile 43 7,487 NA NA 7,007 37,812 NA NA 29,981 

River mile 45 43,393 NA NA 30,076 20,876 NA NA 17,703 

River mile 47 46,014 48,669 47,574 38,624 24,496 25,642 29,099 25,035 

River mile 50 3,801 NA NA 3,642 4,550 NA NA 8,581 

River mile 51 59,644 48,956 63,241 48,920 36,043 38,595 37,679 34,630 

River mile 55 42,771 NA NA 34,183 47,264 NA NA 47,675 

mean 33,852 48,812 55,407 27,075 28,507 32,119 33,389 27,268 

standard deviation 22,724 203 11,078 18,011 15,123 9,159 6,067 13,592 

 

Upper Grand 

Canyon 

River mile 62 13,115 13,965 11,659 14,023 6,303 7,769 4,232 4,310 

River mile 65 23,088 NA NA 20,980 14,463 NA NA 17,013 

River mile 68 17,482 NA NA 11,655 12,245 NA NA 8,476 

River mile 81 297 NA NA NA 2,839 NA NA NA 

River mile 87 252 NA NA NA 4,254 NA NA NA 

mean 10,847 NA NA 15,553 8,021 NA NA 9,933 

standard deviation 10,278 NA NA 4,847 5,083 NA NA 6,476 

 74
Table 8. Percentage change in fine-sediment area and volume in each study site relative to the 

areas and volumes in March 2000, within the high-elevation-eddy, mid-elevation-eddy, lowelevation-eddy, and main-channel zones. 

High-elevation fine sediment 

(above stage associated with discharge of 708 m3 Location /s) 

 Area, in square meters Volume, in cubic meters 

June August September June August September 

Glen Canyon 

River mile -6 25.36 -7.42 2.87 13.88 -3.97 7.37 

Upper Marble 

Canyon 

River mile 3 0.76 0 1.52 0 -4.49 -2.25 

River mile 8 2.29 -4.2 1.65 1.65 -5.85 1.1 

River mile 16 1.96 3.92 -2.94 -19.05 0 2.38 

River mile 22 0.9 -0.9 52.4 -3.1 2.52 4.84 

River mile 30 -1.77 -2.55 4.13 -3.73 -5.8 -3.04 

River mile 32 0.81 -2.15 0.67 -3.64 -6.67 -1.7 

River mile 35 -1.96 -0.13 1.57 -2.89 0 -0.9 

mean 0 -1 8 -4 -3 0 

standard deviation 2 3 20 7 4 3 

Lower Marble 

Canyon 

River mile 43 -1.1 0.63 0.55 -2.66 -0.34 -0.1 

River mile 45 -0.2 2.82 2.32 -4 0.99 0.23 

River mile 47 -6.19 0 6.19 -6.89 -0.09 1.61 

River mile 50 2.53 -1.44 4.89 -1.27 -1.85 1.17 

River mile 51 5.22 -0.75 4.09 0.06 -0.36 0 

River mile 55 -0.2 -1.63 3.4 0.05 -0.48 0.71 

mean 0 0 4 -2 0 1 

standard deviation 4 2 2 3 1 1 

 

Upper Grand 

Canyon 

River mile 62 14.09 -4.12 14.43 3.04 -2.17 3.04 

River mile 65 -0.44 -4.66 9.32 -6.75 0.75 1.75 

River mile 68 -2.55 13.32 1.16 -2.96 -7 0.91 

River mile 81 0.87 -0.87 6.33 -5.81 -2.22 2.08 

River mile 87 5.88 -2.65 1.18 4.92 -3.08 -2.15 

mean 4 0 6 -2 -3 1 

standard deviation 7 7 6 5 3 2 

 75
Table 8. Percentage change in fine-sediment area and volume in each study site relative to the 

areas and volumes in March 2000, within the high-elevation-eddy, mid-elevation-eddy, lowelevation-eddy, and main-channel zones.—Continued 

Mid-elevation fine sediment 

(between stages associated with discharges of 227 and 708 m3 Location /s) 

 Area, in square meters Volume, in cubic meters 

June August September June August September 

Glen Canyon 

River mile -6 16.79 9.39 -9.94 133.5 6.8 -23.64 

Upper Marble 

Canyon 

River mile 3 -15.44 -49.5 2.43 -75.06 -2.53 0.9 

River mile 8 5.18 -21.79 5.41 3.42 -30.14 3.2 

River mile 16 -6.05 -5.67 9.19 -1.01 -30.65 19.1 

River mile 22 15.51 -3.07 4.05 42.96 -1.6 39.91 

River mile 30 -1.74 -5.49 16.21 84.61 -7.66 40.03 

River mile 32 15.82 -7.35 57.17 32.47 -31.17 333.12 

River mile 35 73.14 -42.06 45.35 243.09 -112.71 305.52 

mean 12 -19 20 47 -31 106 

standard deviation 29 19 22 99 39 147 

Lower Marble 

Canyon 

River mile 43 2.59 -0.06 9.39 4.3 9.06 23.22 

River mile 45 -29.98 -3.5 -1.47 -37.9 -4.59 5.78 

River mile 47 14.58 -1.55 19.12 -2.68 -0.22 99.72 

River mile 50 44.46 -4.57 -32.6 201.48 -16.15 -121.04 

River mile 51 58.95 3.13 5.28 129.11 3.15 105.72 

River mile 55 18.23 -4.35 1.3 11.68 -3.81 13.14 

mean 18 -2 0 51 -2 21 

standard deviation 31 3 18 93 9 82 

 

Upper Grand 

Canyon 

River mile 62 -4.34 0.64 -5.61 43.06 -9.96 14.95 

River mile 65 27.44 -8.13 7.98 186.6 -18.54 113.96 

River mile 68 -13.19 -19.47 10.89 -10.52 0.28 4.36 

River mile 81 8.87 -1.97 3.45 46.36 -9.32 77.73 

River mile 87 -11.4 5.7 -14.25 -15.1 -1.04 -19.53 

mean 1 -5 0 50 -8 38 

standard deviation 17 10 10 82 8 55 

 76
Table 8. Percentage change in fine-sediment area and volume in each study site relative to the 

areas and volumes in March 2000, within the high-elevation-eddy, mid-elevation-eddy, lowelevation-eddy, and main-channel zones.—Continued

Low-elevation fine sediment 

(below the stage associated with discharge of 227 m3 Location /s) 

 Area, in square meters Volume, in cubic meters

June August September June August September 

Glen Canyon 

River mile -6 NA NA -5.83 NA NA 10.1 

Upper Marble 

Canyon 

River mile 3 NA NA -3.13 NA NA -2.2 

River mile 8 NA NA NA NA NA 

River mile 16 NA NA NA NA NA 

River mile 22 -16.53 15.65 -18.16 -22.37 5.34 1.81 

River mile 30 -4.47 -5.59 -23.55 3.68 -53.48 16.59 

River mile 32 10.65 1.8 5.69 -12.8 -5.09 -27.57 

River mile 35 112.94 65.28 -38.21 -49.08 123.38 -97.44 

mean 26 19 -15 -20 18 -22 

standard deviation 59 32 17 22 75 45 

Lower Marble 

Canyon 

River mile 43 NA NA -6.41 NA NA -20.71 

River mile 45 NA NA -30.69 NA NA -15.2 

River mile 47 5.77 3.39 -16.06 4.68 18.79 2.2 

River mile 50 NA NA -4.18 NA NA 88.59 

River mile 51 -17.92 6.03 -17.98 7.08 4.54 -3.92 

River mile 55 NA NA -20.08 NA NA 0.87 

mean -6 5 -16 6 12 9 

standard deviation 17 2 10 2 10 40 

 

Upper Grand 

Canyon 

River mile 62 6.48 -11.1 6.92 23.26 -32.86 -31.62 

River mile 65 NA NA -9.13 NA NA 17.63 

River mile 68 NA NA -33.33 NA NA -30.78 

River mile 81 NA NA NA NA NA NA 

River mile 87 NA NA NA NA NA NA 

mean 6 -11 -12 23 -33 -15 

standard deviation NA NA 20 NA NA 28 

 77
 78

Table 9. Volumes and rates of fine sediment either eroded or deposited in the eddy part of the faneddy complex at river mile 30 during the September 2000 habitat maintenance flows (HMF). Amount 

of scour, fill, and net change is in cubic meters; rates are in cubic meters per hour. 

 Scour Fill Net change Scour rate Fill rate 

Rate of net 

change 

Survey Interval (m3) (m3) (m3) (m3/hour) (m3/hour) (m3/hour) 

Pre-HMF Day 1 (11am) 7,629 796 -6,833 - - - 

Day 1 (11am) Day 1 (2pm) 652 2,516 1,864 217 839 621 

Day 1 (2 pm) Day 1 (5 pm) 575 776 201 192 259 67 

Day 1 (5 pm) Day 2 (9 am) 4,344 2,329 -2,015 272 146 -126 

Day 2 (9 am) Day 2 (3 pm) 985 1,389 404 164 232 67 

Day 2 (3 pm) Day 3 (9 am) 1,317 1,869 552 73 104 31 

Day 3 (9 am) Day 3 (3 pm) 443 1,075 632 74 179 105 

Day 3 (3 pm) Day 4 (9 am) 596 1,356 760 33 75 42 

Day 4 (9 am) Day 4 (3 pm) 421 974 553 70 162 92 

Day 4 (3 pm) Post-HMF 452 1,744 1,292 - - - 

 

Pre-HMF Post-HMF 5,282 2,766 -2,516 
Table 10. Average response of the bed and eddy sandbars to various flow regimes of the low summer steady flo

parts of the study area. “NA” indicates no data available, “?” indicates indeterminate response, “-“ indicates loss 

or volume, and “+” indicates increase or gain in area or volume. 

Mass balance Area of 

sand on 

bed 

Finesediment 

grain size 

on bed 

β Eddy bars at midelevation 

(determined from 

ground surveys) 

Eddy bars at mid-elevation 

aerial photogra

Period Marble 

Canyon 

upper 

Grand 

Canyon 

Marble 

Canyon 

Marble 

and 

upper 

Grand 

Canyons 

Upper 

Marble 

Canyon 

Lower 

Marble 

Canyon 

Lees 

Ferry 

reach 

Redwall 

Gorge 

reach 

Poi

Hansbo

rea

1 - ? NA NA fines NA NA NA NA NA 2 - ? NA NA coarsens + + NA NA NA 3 - ? NA NA coarsens NA NA NA NA NA 4 + + + coarsens coarsens - - NA NA NA 5 - ? NA NA coarsens + + - + - 

Eddy bars at low 

elevation 

Backwater 

area 

Period Upper 

Marble 

Canyon 

Lower 

Marble 

Canyon 

Marble 

Canyon 

Period 1 - NA NA 2 NA NA NA 3 + + NA 4 - - + 

79