2008 High-Flow Experiment at Glen Canyon Dam—

Morphologic Response of Eddy-Deposited Sandbars and 

Associated Aquatic Backwater Habitats along the Colorado 

River in Grand Canyon National Park

Open–File Report 2010–1032

U.S. Department of the Interior

U.S. Geological Survey
Cover: Photograph of a Grand Canyon sandbar created as the result of the 2008 high-flow experiment at Glen 

Canyon Dam. To the left of the sandbar is a newly created backwater. (Photograph courtesy of Matthew Kaplinski, 

Northern Arizona University.)
Grand Canyon Monitoring and Research Center 

2008 High-Flow Experiment at Glen Canyon Dam—

Morphologic Response of Eddy-Deposited Sandbars and 

Associated Aquatic Backwater Habitats along the Colorado 

River in Grand Canyon National Park 

By Paul E. Grams, John C. Schmidt, and Matthew E. Andersen 

Open-File Report 2010–1032 

U.S. Department of the Interior 

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

KEN SALAZAR, Secretary 

U.S. Geological Survey 

Marcia K. McNutt, Director 

U.S. Geological Survey, Reston, Virginia 2010 

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

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Suggested citation: 

Grams, P.E., Schmidt, J.C., and Andersen, M.E., 2010, 2008 high-flow experiment at Glen Canyon Dam—morphologic 

response of eddy-deposited sandbars and associated aquatic backwater habitats along the Colorado River in Grand 

Canyon National Park: U.S. Geological Survey Open-File Report 2010-1032, 73 p. 

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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. 
iii

Contents 

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

Methods......................................................................................................................................................................... 7

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

Description of Approach............................................................................................................................................. 7

Selection of Study Sites ............................................................................................................................................. 8

Sandbar Surveys ......................................................................................................................................................11

Field Data Collection and Processing....................................................................................................................11

Morphologic Analyses ...........................................................................................................................................11

Remote Cameras......................................................................................................................................................12

Fish Sampling of Backwater Habitats........................................................................................................................13

Results..........................................................................................................................................................................13

Sandbar Surveys ......................................................................................................................................................13

Processes of Sandbar Morphologic Change that Affect Backwater Habitat ..........................................................13

Systemwide Changes in the Abundance and Size of Backwater Habitat ..............................................................29

Backwater Inventory .................................................................................................................................................37

Longitudinal Distribution of Backwater Habitats ........................................................................................................38

Observations of Fish in Backwater Habitats..............................................................................................................41

Conclusions and Management Implications .................................................................................................................42

Acknowledgements.......................................................................................................................................................44

References Cited..........................................................................................................................................................44

Appendix A. Data from Backwater Inventories Conducted Between February and September 2008...........................47

Appendix B. List of Sandbar Monitoring and Backwater Monitoring Study Sites, the Date and Time of Each Survey, 

and the Discharge at Time of Survey............................................................................................................................67

Appendix C. Relations Between Water Surface Elevation and Discharge for Study Sites............................................70

Figures 

1. Map of the Colorado River in Grand Canyon, Arizona, showing study sites and the locations of all backwaters 

identified in the backwater inventory................................................................................................................. 3

2. Diagrammatic illustration of typical reattachment bar, return channel, and backwater habitat.......................... 4

3. Discharge for the Colorado River at Lees Ferry, Arizona (USGS Station 09380000), for calendar year 2008 . 7

4. Matching oblique views photographed by remote camera looking from the right shore across to the sandbar 

and backwater at RM 45 left........................................................................................................................... 15

5. Maps of study site RM 45 left showing 1-m resolution DEMs derived from topographic and bathymetric 

mapping occurring from February to October 2008 ........................................................................................ 18

6. Relations between backwater size and discharge for RM 45 left during 2008................................................ 19

7. Maps of study site RM 3 left showing 1-m resolution DEMs derived from topographic and bathymetric 

mapping between February and April, 2008................................................................................................... 20

8. Relations between backwater size and discharge for RM 3 left during 2008.................................................. 21

9. Maps of study site RM 172 left showing 1-m resolution DEMs derived from topographic and bathymetric 

mapping between February and April, 2008................................................................................................... 24

10. Relations between backwater size and discharge for RM 172 left during 2008.............................................. 25

11. Two matching oblique views photographed by remote camera looking across the Colorado River to the RM 

65 left study site.............................................................................................................................................. 26
iv

12. Maps of study site RM 55 right showing 1-m resolution DEMs derived from topographic and bathymetric 

mapping between February and April, 2008................................................................................................... 27

13. Relations between backwater size and discharge for RM 55 right during 2008. A, Measured backwater area 

plotted as a function of discharge ................................................................................................................... 28

14. The number of backwaters present among the study sites for each survey period in 2008 as a function of 

discharge........................................................................................................................................................ 29

15. Plots showing calculated backwater volume and area for each of the five discharges analyzed in 2008 ....... 32

16. Plots showing total habitat area and volume for all study sites as functions of discharge in 2008.................. 33

17. Cumulative frequency distributions showing the fraction of study sites as a function of the fraction of time a 

backwater is present for each of the four flow regimes associated with dam operations that followed the 2008 

HFE ............................................................................................................................................................... 36

18. Cumulative frequency distributions showing the fraction of study sites as a function of the fraction of time a 

backwater is present for the experimental fluctuating flows that occurred from January 3 to April 9, 2005, 

following the November 2004 HFE ................................................................................................................. 37

19. Downstream distributions of backwater habitat at differing discharges during 2008....................................... 41

20. Captures of fish species for the May (under fluctuating flows) and September (under experimental steady 

flows of 354 m3/s) backwater sampling periods in 2008 ................................................................................. 42

T bles a

1. Geomorphic classifications of backwaters in the inventory and among study sites between Lees Ferry and 

river mile 258 ............................................................................................................................................... 9

2. Humpback chub aggregation areas ........................................................................................................... 10

3. Processes of observed sandbar morphologic response associated with changes in return channel volume

................................................................................................................................................................... 14

4. Summary of backwater inventory results ................................................................................................... 38

5. Comparison between backwater inventory and surveys ............................................................................ 38

Conversion Factors 

Inch/Pound to SI 

Multiply By To obtain 

Length 

foot (ft) 0.3048 meter (m) 

mile (mi) 1.609 kilometer (km) 

Area 

square foot (ft2) 0.09290 square meter (m2) 

Volume 

cubic foot (ft3) 0.02832 cubic meter (m3) 

Flow rate 

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s) 
v

SI to Inch/Pound 

Multiply By To obtain 

Length 

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) 

Conversion of discharge from SI to Inch/Pound units for values used frequently in this report. 

Use in report m3/s ft3/s 

Peak discharge of 1996 HFE 1,274 45,000 

Peak discharge of 2004 and 2008 HFEs 1,203 42,500 

Discharge used in analyses 227 8,000 

Discharge used in analyses 283 10,000 

Discharge used in analyses 340 12,000 

Discharge used in analyses 453 16,000 

Discharge used in analyses 566 20,000 

Bottom of range of fluctuations for Flow Regime (FR) 1 198 7,000 

Top of range of fluctuations for FR 1 340 12,000 

Bottom of range of fluctuations for FR 2 283 10,000 

Top of range of fluctuations for FR 2 453 16,000 

Bottom of range of fluctuations for FR 3 311 11,000 

Top of range of fluctuations for FR 3 538 19,000 

Steady discharge for FR 4 351 12,400 

In this report, horizontal and vertical coordinate information is referenced in meters above the GRS80 ellipse defined by the 

North American Datum of 1983 (NAD 83). Elevation, as used in this report, refers to NAD83/GRS80 ellipsoid heights and not 

traditionally defined NAVD88 orthometric heights. 
vi
2008 High-Flow Experiment at Glen Canyon Dam— 

Morphologic Response of Eddy-Deposited Sandbars and 

Associated Aquatic Backwater Habitats along the 

Colorado River in Grand Canyon National Park 

By Paul E. Grams1, John C. Schmidt2, and Matthew E. Andersen1 

Abstract 

The March 2008 high-flow experiment (HFE) at Glen Canyon Dam resulted in sandbar 

deposition and sandbar reshaping such that the area and volume of associated backwater aquatic habitat 

in Grand Canyon National Park was greater following the HFE. Analysis of backwater habitat area and 

volume for 116 locations at 86 study sites, comparing one month before and one month after the HFE, 

shows that total habitat area increased by 30 percent to as much as a factor of 3 and that volume 

increased by 80 percent to as much as a factor of 15. These changes resulted from an increase in the area 

and elevation of sandbars, which isolate backwaters from the main channel, and the scour of eddy 

return-current channels along the bank where the habitat occurs. Because of this greater relief on the 

sandbars, backwaters were present across a broader range of flows following the HFE than before the 

experiment. 

Reworking of sandbars during diurnal fluctuating flow operations in the first 6 months following 

the HFE caused sandbar erosion and a reduction of backwater size and abundance to conditions that 

were 5 to 14 percent greater than existed before the HFE. In the months following the HFE, erosion of 

sandbars and deposition in eddy return-current channels caused reductions of backwater area and 

volume. However, sandbar relief was still greater in October 2008 such that backwaters were present 

across a broader range of discharges than in February 2008. 

Topographic analyses of the sandbar and backwater morphologic data collected in this study 

demonstrate that steady flows are associated with a greater amount of continuously available backwater 

habitat than fluctuating flows, which result in a greater amount of intermittently available habitat. With 

the exception of the period immediately following the HFE, backwater habitat in 2008 was greater for 

steady flows associated with dam operations of relatively lower monthly volume (about 227 m3

/s) than 

steady flows associated with dam operations of higher monthly volume. Similarly, there was greater 

habitat availability associated with lower monthly volume fluctuating flows (post-HFE through midApril) compared to higher monthly volume fluctuating flows (after mid-April 2008). 

The sites monitored for this study represent about 20 percent of the 569 estimated number of 

potential sand-bounded backwaters that occur in eddies below Glen Canyon Dam in Grand Canyon 

 

1

 U.S. Geological Survey, Southwest Biological Science Center, Grand Canyon Monitoring and Research Center, Flagstaff, 

Arizona 

2

 Utah State University, Department of Watershed Sciences, Logan, Utah 

1
National Park. Data from fish sampling in backwaters, by seining, demonstrates that both native and 

nonnative species were present in the backwaters monitored for this study. 

Introduction 

In a landscape dominated by bedrock and talus, sandbars along the margins of the Colorado 

River in Grand Canyon are distinct features of the river corridor. Before completion of Glen Canyon 

Dam in 1963 (fig. 1), fine sediment, including sand, silt, and clay, accumulated during much of the 

summer and fall (Topping and others, 2000). This sediment was redistributed by annual spring floods 

and deposited at high elevations along the channel margin (Schmidt and Graf, 1990; Webb, 1996). The 

sand deposited by the annual floods provided substrate for riparian vegetation, created beaches for 

recreational use, and shaped aquatic habitat used by native fish (Kearsley and others, 1994; Stevens and 

others, 1995). Following completion of Glen Canyon Dam, the supply of sand to the Colorado River 

downstream from Lees Ferry, Arizona, was reduced by 94 percent (Topping and others, 2000; Wright 

and others, 2005). In addition, dam-regulated flows, typically constrained to the capacity of the 

hydropower plant, limit the area that is affected by river flows and thereby reduce the area of potential 

sandbar deposition during floods. Closure of Glen Canyon Dam resulted in three primary changes: (1) a 

greatly decreased sediment supply, (2) a greatly reduced flood magnitude, and (3) a greatly increased 

base flow (Topping and others, 2003). These dam-induced changes have resulted in fewer sandbars 

(Schmidt and Graf, 1990), decreased areal extent of exposed sand (Schmidt and others, 1999), and 

lower sandbar elevations (Schmidt and others, 1995). 

The largest proportion of the Colorado River’s sediment load in Grand Canyon is sand. 

Although completion of Glen Canyon Dam caused a large reduction in the supply of sand to Grand 

Canyon, sandbars remain in many zones of lateral flow separation—eddies—that occur downstream 

from rapids and in the lee of bank obstructions, such as debris fans, talus cones, and rock outcrops. Eddy 

sandbars have a characteristic morphology, because flow patterns in eddies are generally similar. 

Schmidt (1990) and Schmidt and Rubin (1995) proposed a nomenclature for these bars based on 

topography and relation to typical flow patterns at flood stages when the bars are inundated and active 

(fig. 2). 

2
Figure 1. Map of the Colorado River in Grand Canyon, Arizona, showing study sites (blue) and the locations of all 

backwaters (red and blue) identified in the backwater inventory. 

Eddy sandbars may be subdivided into reattachment bars and separation bars, and the primary 

eddy return-current channel (hereafter referred to as the return channel) occurs between them. 

Reattachment bars form beneath the central and downstream parts of the eddy, have the form of an 

upstream-projecting spit (called the bar platform), and are highest at their downstream end where they 

are attached to the bank (Rubin and others, 1990). Schmidt and Graf (1990), and Rubin and others 

(1990) showed that large reattachment bars that are emergent at base flow project far upstream. In 

contrast, if reattachment bars are small, the only part of the bar that is emergent at base flows is at the 

downstream end. The term “reattachment bar” arises because this downstream part of the bar occurs 

where the main downstream flow reattaches to the bank at times of bar inundation. 

The upstream parts of the reattachment bar are typically bounded by a deep channel that occurs 

between the bar and bank (fig. 2). This channel is maintained by upstream flow, or return current, that is 

concentrated along the bank of each eddy. Sand in return channels has been transported across the top of 

the bar platform and is efficiently swept upstream by the relatively higher velocity flows of this 

upstream current. This channel is referred to as the primary eddy return-current channel. 

3
Figure 2. Diagrammatic illustration of typical reattachment bar, return channel, and backwater habitat. Main 

channel flow is from left to right. The separation zone is the area where downstream flow separates from the 

bank, and the reattachment zone is the area where downstream flow reattaches to the bank. The small arrows 

indicate the region of recirculating flow within the eddy at flows during which the sandbar would be submerged. 

The dotted line is an example backwater closure line that separates the backwater from the main channel. 

Figure is modified from Schmidt and Graf (1990). 

During low flow, reattachment bars that are sufficiently large block eddy circulation into return 

channels. If the return channel is sufficiently deep, the inundated return channel becomes an embayment 

of stagnant water that is only connected to the main flow at the upstream end (fig. 2). Fisheries 

biologists refer to this stagnant flow feature as “backwater” aquatic habitat. The existence of this type of 

backwater habitat is therefore dependent on two key geomorphic attributes. First, the reattachment bar 

must be sufficiently large such that flow circulation at some discharges is blocked. Second, the return 

channel must be sufficiently large and deep that it is inundated at the same discharges when flow is 

blocked across the bar platform. 

Although return channels create the greatest proportion of backwater habitat, other geomorphic 

features create zones of low velocity or stagnant flow elsewhere. Occasionally, backwaters form 

adjacent to reattachment bars but downstream from the reattachment zone and beyond the return 

channel. Backwaters are also found on separation bars, which occur upstream from the return channel 

and typically mantle the debris fan that creates lateral separation eddies. Areas of low velocity 

occasionally form near separation bars at low discharges, but these areas typically have a larger waterexchange rate with the main channel flow than do inundated return channels. Other areas of stagnant 

water or low velocity flow occur near emergent gravel bars and other channel obstructions. 

The use of backwater habitats by endangered native humpback chub (Gila cypha) has been 

documented by monitoring efforts since the early 1990s (Valdez and others, 2001). Because of the 

federally listed endangered status of humpback chub, backwaters are a major focus of ecological 

investigation to better understand the use and role of these habitats in the life history of various native 

and nonnative fish species. Scientists and managers have hypothesized that backwater habitats of the 

mainstem Colorado River may be especially important for humpback chub and other native fish species 

4
because they offer potentially warmer water temperatures under conditions of low velocity, which likely 

promote growth of juvenile life stages. Schmidt and Brim-Box (2004) described backwaters in the 

Green River (a tributary of the Colorado River located in the upper Colorado River Basin) and showed 

that their abundance is dependent on channel geomorphology and discharge. On the Green River, 

backwaters occur both in canyons with debris fans and near emergent bank-attached bars in alluvial 

segments of the river system, such as the Uinta Basin. The latter type of backwaters are critical habitat 

for nursery-age Colorado pikeminnow (Ptychocheilus lucius). Backwaters associated with debris fans 

and eddy bars occur in Desolation and Grey Canyons of the Green River, but their importance to upper 

Colorado River Basin humpback chub populations is less, because the temperature of the mainstem flow 

is much warmer than below Glen Canyon Dam in Grand Canyon (Valdez and Clemmer, 1982; Valdez 

and others, 1990). In Grand Canyon, backwaters may provide seasonally warmer habitats (summer and 

fall) in contrast to the mainstem temperatures, which are cool throughout the year. In some situations in 

Grand Canyon, however, competition or predation with nonnative species may be such that backwater 

habitats are disadvantageous where, for example, native fish congregate in backwaters and subsequently 

are consumed by predaceous nonnative fishes. In winter, backwater temperatures may be colder than 

water in the main channel and therefore may be less suitable habitat for juvenile native fish. 

One of the current goals of native fish management in Grand Canyon National Park is to 

maintain or increase the availability of backwaters because of their potential role in providing habitat for 

juvenile native fish. Previous studies on the relation between backwater habitats and flow regime in 

Grand Canyon have shown that flows larger than the capacity of the Glen Canyon Dam powerplant, 

such as the 1996 controlled flood (see Webb and others, 1999), cause redistribution of eddy sandbars 

(Schmidt and others, 1999) and short-term increases in the area of backwater habitat (Brouder and 

others, 1999; Goeking and others, 2003). Goeking and others (2003) analyzed historical aerial 

photographs taken as early as the mid-1930s and found that backwater area in specific eddies was highly 

variable among the different years of available photographs. They found that there may be significant 

changes in the number and size of backwaters over short (~ 1 yr) time periods, but they also found that 

significant changes in backwater area were not evident over multiyear or decadal time scales. The 

implication of these findings is that reattachment bar platforms are sufficiently large in many eddies, 

and return-current channels are sufficiently large, that backwaters persist as habitat over multiyear or 

decadal time scales, although the locations of specific backwaters change from year to year. Goeking 

and others (2003) also found that backwaters do not necessarily exist if reattachment bars are very large 

and fill the return-current channel, as was seen in many eddies in the mid-1930s aerial photographs. 

Since 1990, three experimental controlled floods exceeding the capacity of the Glen Canyon 

Dam powerplant have been released. Administratively, these releases are termed high-flow experiments 

(HFE), defined as planned releases from the dam that exceed the peak capacity of the hydroelectric 

powerplant (~940 m3

/s) by at least 30 percent (U.S. Department of the Interior, 1995). The primary 

purpose of these experiments has been to determine whether HFEs have the potential to effectively 

increase and maintain sandbars and related habitats that are located in eddies and along the channel 

margins. During the first HFE, conducted in March and April 1996, approximately 1,274 m3/s were 

released for a period of 7 days. Although this test did result in sandbar deposition, measurements made 

of sand-storage change in eddies (Hazel and others, 1999; Schmidt and others, 1999) and a calculation 

of sand mass balance (Topping and others, 1999; Schmidt, 1999) both indicated net erosion of sand 

from low-elevation (below the stage associated with a discharge of approximately 227 m3

/s) parts of 

eddies and the channel. In a study based on examination of aerial videography following this flood, 

Brouder and others (1999) reported that the number of backwaters increased between Lees Ferry and 

Diamond Creek (fig. 1) because bar platforms were elevated and return channels were excavated. They 

5
also stated that the number of backwaters decreased during the months following the controlled flood, 

when normal hydropower plant operations resumed (referred to as Modified Low Fluctuating Flows, as 

described in the 1996 Record of Decision on Glen Canyon Dam operations, see U.S. Department of the 

Interior, 1996), but they did not quantify the magnitude of this decrease. Reduction in backwater area 

was caused by infilling of return channels and erosion of bar platforms. 

The second HFE, with a shorter peak duration of 2.5 days and a slightly lower peak magnitude, 

was conducted in November 2004, following tributary sand inputs from the Paria River (located 25 km 

below the dam) to determine if it was possible to build sandbars without causing net erosion from the 

eddies and the channel. This second high-flow experiment was specifically released following tributary 

sand enrichment and was designed with a shorter peak duration on the basis of results from the 1996 

HFE, as summarized by Rubin and others (2002). Measurements of sand-storage change and sand flux 

past mainstem stream gages at various locations below the Paria River show that net deposition did 

occur in some upstream segments where pre-HFE sand enrichment was greatest (Topping and others, 

2006). In downstream segments where sand enrichment was less, net erosion occurred. Tributary sand 

production (mostly from the Paria River, fig. 1) in 2006 and 2007 resulted in sand accumulation in all 

river segments between Lees Ferry and Diamond Creek (fig. 1). 

The March 2008 HFE was conducted to determine whether a third high flow conducted under 

these conditions of relatively high sand enrichment would result in net sandbar deposition over a greater 

portion of the river corridor between Lees Ferry and Diamond Creek. The average discharge of 1,203 

m3

/s during the March 2008 HFE was about 6 percent lower than the peak of the 1996 test but identical 

to the November 2004 dam release. The 2008 HFE was much shorter than the 1996 experiment but was 

the same duration as the 2004 HFE (fig. 3). Hazel and others (2010) report on sandbar response 

measured during all three HFEs. 

The purpose of this report is to describe changes in sandbar morphology caused by the 2008 

HFE and subsequent operations, to describe how those changes affected backwater habitats, and to 

provide some general information about the presence or absence of native and nonnative fish found in 

backwaters following the 2008 experiment. 

6
Figure 3. Discharge for the Colorado River at Lees Ferry, Arizona (USGS Station 09380000), for calendar year 

2008. The March 4–8, 2008 HFE is shown in addition to the times of the four survey trips and the three fishseining trips. Also shown are the time durations of four distinct flow regimes (FR1, FR2, FR3, and FR4) that 

occurred in the period following the HFE through October 2008. 

Methods 

Description of Approach 

As described above, backwater habitats are dynamic features whose size depends on topographic 

characteristics of the reattachment bar (or other bars that block circulation into an embayment) and river 

stage, which determines the proportion of the embayment where stagnant flow occurs. Thus, a 

multimonth, or multiyear, backwater monitoring program requires resurvey of the topographic 

characteristics of the bar platform and return channel and must account for differences in river stage at 

the time of surveys. Additionally, the influence of steady or varying river stage on backwater 

distribution requires determination of backwater size and frequency at a range of discharges. Evaluation 

of how the habitat varies across a range of flows for a given eddy and associated sandbar morphology 

requires describing the eddy-bar topography and determining the local stage-discharge relation so that 

site-specific topographic models that account for the size of backwaters can be constructed and 

analyzed. This approach allows the development of discharge-dependent relations for backwater size 

and abundance similar to the method proposed by Goeking and others (2003). The large site-to-site 

variability in eddy, sandbar, and backwater characteristics led us to collect data for a relatively large 

7
sample of the population of sites where backwaters are expected to occur in Grand Canyon National 

Park. 

Selection of Study Sites 

Our first step in determining the number and distribution of sample sites was to assess the size 

and characteristics of the population of all backwaters in Marble and Grand Canyons (fig. 1). Although 

sandbars in Grand Canyon National Park have been the subject of ongoing research and monitoring 

(Wright and others, 2005; Hazel and others, 2006b) and the potential importance of backwater habitats 

has been recognized (Valdez and others, 2001), before this study there did not exist a comprehensive 

and field-verified catalog of locations where backwaters have historically occurred. 

Three datasets were considered with which to evaluate the population of all backwaters and with 

which to devise a sampling strategy. This effort was necessary because previous studies of sandbar 

response (Hazel and others, 1999; Schmidt and others, 1999) and backwater dynamics (Goeking and 

others, 2003) demonstrated large site-to-site variability and because preliminary data indicated the likely 

existence of hundreds of potential backwater locations. First, detailed topographic information was 

collected at 46 sites by Hazel and others (2010) for the purpose of measuring sandbar response to the 

2008 HFE. Because backwaters have the potential to form at each of these sites, they were analyzed in 

our study as well. These sites are referred to herein as the sandbar monitoring sites (SBM). The second 

set of data describing backwaters were fish-seining efforts between 2003 and 2007. During this period, 

one river trip was conducted each year in late summer for the purpose of seining backwaters to 

determine the presence or absence of fish. On these trips, each backwater present at the time of 

visitation was seined. The location, number of fish caught, and species of fish caught were recorded. 

The records from these five trips provide an estimate of the number and locations of backwaters present 

for this period. These data did not distinguish the geomorphic conditions that gave rise to each 

backwater. In addition, only backwaters present at those specific river stages at the time of visitation 

were sampled, and no discharge-dependent descriptions of backwaters are available for that sample 

group. The third set of data that identifies potential backwater locations represented an attempt to 

estimate the population of all backwaters. This characterization was provided by automated inspection 

of the shoreline visible on digital aerial photographs collected in May 2002 and May 2005, at an 

approximately steady flow of 227 m3

/s (T.M. Gushue, U.S. Geological Survey, and M.J. Breedlove, 

Utah State University, unpub. data, 2009). The data resulting from the image analysis provide, for two 

points in time and two river stages, an additional estimate of potential backwater locations. Thus, 

discharge-dependent relationships could not be estimated from these data. 

To develop a sampling strategy made on the basis of backwater population characteristics, the 

latter two datasets were merged and coregistered in a geographic information system (GIS) such that for 

each potential backwater location the presence or absence of a backwater was recorded on each of the 

2003-2007 seining trips and for each of the two image sets analyzed. This resulted in a list of 687 

potential backwater locations. These data were visually inspected in a GIS with orthorectified images 

from 2004 and 2005 as background, and classified according to backwater type. Our classification (table 

1) is the first that we are aware of that explicitly distinguishes the geomorphic context of backwater 

habitats. The primary criteria used to classify the backwaters were the characteristics of the geomorphic 

feature separating the embayed backwater from the main channel. Sand-bounded backwaters were 

defined as those where the backwater is separated from the main channel by the reattachment bar 

platform, parts of emergent separation bars, or by any other sand deposit. As described in the 

introduction, the majority of sand-bounded backwaters occur near reattachment bars (table 1). There are 

also backwaters that are not bounded from the main channel by sand, but are formed by irregularities in 

8
bedrock or talus along the bank and, in some cases, gravel bars. This inventory includes backwaters in 

all reaches of the river from Lees Ferry downstream to river mile3

 (RM) 258, the approximate upper 

extent of Lake Mead (fig. 1). 

Table 1. Geomorphic classifications of backwaters in the inventory and among study sites between Lees Ferry 

and river mile 258. Locations along the Colorado River in Grand Canyon are referenced by the convention of 

river mile, which is distance downstream from Lees Ferry, Arizona along the channel centerline. 

Sand-bounded backwaters associated with eddies Code Number in 

inventory 

Number of 

study sites 

Reattachment Bar: Located downstream from debris fan, bar spit 

projects upstream into eddy. Backwater occurs in return channel. 

rb 333 87 

Bedrock-formed Reattachment Bar: Same form as reattachment bar 

but located in eddy formed by bedrock bank irregularity rather than 

debris fan. 

rb-br 36 2 

Reattachment Bar Extension: Zone downstream from reattachment 

point where backwater may occur in location other than return 

channel. 

rb-ext 34 1 

Gravel Bar Reattachment Bar: Same form as reattachment bar but 

located in eddy caused by a gravel bar rather than a debris fan. 

rb-gb 15 2 

Separation Bar: Located immediately downstream from debris fan, 

backwaters may form in irregularities along sand bank or as a result of 

sand spit projecting into eddy. 

sb 70 3 

Upper Pool: Zone of recirculating or low velocity flow in ponded 

flow upstream from debris fans; backwaters may occur when sand spit 

projects into eddy. 

up 81 10 

Subtotal of all sand-bounded backwaters in eddies 569 105 

Other backwaters 

Channel Margin Sand: Sand deposits generally outside of eddies; 

backwater may form along shoreline bounded from main channel by 

river parallel bar form. 

cm 173 0 

Bank Irregularity: Zone of recirculating flow or low velocity flow 

caused by bank irregularities such as bedrock or talus; small 

embayments may be separated from the main channel by bedrock, 

talus, or gravel, but may also include small sand spits. 

bank 68 0 

Gravel Bar: Low-velocity or stagnant flow bounded from the main 

channel by a gravel bar. 

gb 36 0 

Small tributary mouth: Bank irregularity may result in formation of 

backwater. 

st 34 0 

Subtotal of other backwaters 311 0 

Total 880 105 

 

3

 Locations along the Colorado River in Grand Canyon are referenced by the convention of river mile, which is distance 

downstream from Lees Ferry, Arizona along the channel centerline. 

9
The inventory of backwater habitats was verified in the field to confirm and expand the catalog 

of potential backwater locations. The locations of all backwaters in the original remotely sensed catalog 

were plotted on a set of maps, and these sites were inspected in the field on each survey trip, described 

below. An inventory was also conducted in July 2008. New backwater sites identified in the field were 

added to the database and revisited on subsequent trips. Because the presence of a backwater habitat is a 

function of water-surface elevation, or discharge, as well as topography, it is not possible to have a 

constant reference frame for determining backwater presence in an environment where flows fluctuate 

hourly within a trip and the flow regimes vary between trips. The inventory was designed to minimize 

the dependence of the observation on the discharge at the immediate time of observation by using four 

different categories for fluctuating flow conditions. These categories are (0) no backwater present for 

any discharge within the range of current flow fluctuations; (1) backwater present only for the lower 50 

percent of the range of current flow fluctuations; (2) backwater present only for the upper 50 percent of 

the range of current flow fluctuations; and (3) backwater present across the full range of current flow 

fluctuations. For the inventory conducted during steady dam releases in September 2008, these 

categories were prefixed with an indication of whether a backwater was present (P) or absent (A) at the 

time of observation. The numerical classification used in the inventory conducted during steady flow in 

September indicates whether a backwater would be present (1) at flows lower than the steady discharge, 

(2) at flows greater than the steady discharge, or (3) at flows both lower and greater than the steady 

discharge. 

On the basis of our assessment of the population of all backwaters in Grand Canyon estimated 

from the datasets described above, 62 additional study sites were selected from among the catalog of 

identified potential backwater locations (appendix A). These sites are referred to herein as backwater 

monitoring (BWM) sites. Because most sand-bounded backwaters occur near reattachment bars and 

because reattachment bars that project into eddies are the bar form most likely to be affected by HFE 

deposition and erosion, this geomorphic setting was the focus of our study. A limited sample of other 

bar forms were included among the study sites, however. We made an effort to locate study sites 

throughout Grand Canyon National Park in approximate proportion to the frequency of backwaters 

identified in our inventory. However, in river segments where humpback chub are known to occur in 

greatest abundance (table 2), more sample sites were selected than strictly in proportion to the frequency 

of backwaters identified in the inventory. Study sites were established throughout the river ecosystem 

downstream from Lees Ferry, including three sites downstream from Diamond Creek. However, 

because the segment downstream from Diamond Creek was not monitored on the May through October 

2008 trips, the analyses of the data presented in this report are restricted to the river corridor between 

Lees Ferry and Diamond Creek (approximately 15 and 240 miles below Glen Canyon Dam, fig. 1). 

Table 2. Humpback chub aggregation areas (Valdez and Ryel, 1995) 

Aggregation Site from RM to RM 

1. 30-mile 29.8 31.3 

2. LCR inflow 57.0 65.4 

3. Lava to Hance 65.7 76.3 

4. Bright Angel Creek inflow 83.8 92.2 

5. Shinumo Creek inflow 108.1 108.6 

6. Stephen Aisle 114.9 120.1 

7. Middle Granite Gorge 126.1 129.0 

8. Havasu Creek inflow 155.8 156.7 

9. Pumpkin Spring 212.5 213.2 

10
Sandbar Surveys 

Field Data Collection and Processing 

The purpose of the field surveys for both the SBM and BWM sample sites was to collect 

topographic data that would enable construction of a three-dimensional computer topographic surface 

model of each sandbar and predict the existence and size of backwaters, when present, for a range of 

discharges associated with dam operations. Thus, we sought to define continuous functions wherein 

backwater area is a function of river discharge. Development of these discharge-dependent functions 

required collection of precise and repeatable measurements of location and elevation on each sandbar, 

along the shoreline upstream and downstream from the sandbar, and in the adjacent eddy, including the 

return channel. The upper and lower elevation of the surveyed area was constrained by our focus on 

backwater changes between the elevations associated with stages of 227 m3/s and 566 m3/s, because 

these discharges are the typical range of Glen Canyon Dam hydropower plant operations. The upstream 

and downstream bounds of the survey were determined by the extent of each eddy, with the purpose that 

each survey covered the length of the zone of recirculating flow from upstream of the separation zone to 

downstream of the reattachment zone (fig. 2). These criteria were followed for all the new BWM sites 

established in 2008. The data collection boundary for the SBM sites (Hazel and others, 2010) 

encompassed these criteria and typically covered a larger area. 

All sites were surveyed following protocols described in Hazel and others (2008). Each study 

site was surveyed using an electronic total station referenced to two geodetically referenced control 

points (for the BWM sites, geodetic referencing was done following the 2008 field data collection). 

Field technicians occupied desired topographic or other positions, and location information was stored 

on digital data collectors. Distinct breaks in slope were captured, and water surface elevations and high 

water marks were surveyed. High-water marks that were surveyed included the peak river stage reached 

in the preceding 24 hours, the peak flow level reached in the preceding month, and the peak flow level 

reached by the March 2008 HFE. Most sites were surveyed a total of four times during river trips that 

were conducted February 2 to 19, March 28 to April 14, May 17 to June 3, and September 20 to October 

26 (appendix B). Hereafter, we refer to each data collection period as the February, April, May, and 

October 2008 measurements. The September to October period included two separate river trips; each 

site was surveyed once during this period. 

Morphologic Analyses 

The sandbar survey data were analyzed to compute erosion and deposition between 

measurements, compute the area and volume of associated backwaters at different river stages, and 

determine spatial patterns of erosion and deposition. These analyses required the following sequence of 

processing steps for each measurement site: (1) processing of the raw survey data to create surface 

models, (2) translation and rotation of raw survey data and surface models from local coordinates to 

Arizona State plane coordinates (this step was not necessary for the SBM sites, where data were 

collected in State plane coordinates), (3) construction of relations between water stage and discharge, 

(4) delineation of backwaters and computation of backwater area and volume for a suite of discharges 

for each survey, (5) computation of sandbar erosion and deposition between surveys, and (6) creation of 

maps showing spatial patterns of erosion and deposition. 

Following each data-collection trip, the raw survey data were imported into survey software 

(Sokkia Mapping Software for the SBM sites and Eagle Point for the BWM sites). The data were 

inspected for errors and edited. The points and break lines were then used to construct a triangular 

irregular network (TIN) surface model. For the SBM sites, which were collected in State plane 

11
coordinates, the surface model was then exported as a grid of points with 1.0-m spacing. These grids 

were imported into GIS software (ArcMap 9.2), where digital elevation models (DEMs) with 1.0-m grid 

spacing and TIN surfaces were created. The BWM sites required translation and rotation, which were 

accomplished by exporting the surface models and raw data from Eagle Point as AutoCad drawing files, 

which were then imported into Trimble Geomatics Office, where the coordinate transformation was 

performed. Terramodel was then used to export from the AutoCad data files 1.0-m resolution grids, 

which were imported into the GIS software as described above. 

For each sandbar survey, backwater area was determined for five discrete discharges chosen to 

encompass the range of most common dam operations. This required that a relation between discharge 

and water stage be developed for each site. For the SBM sites, which have been surveyed multiple times 

over the past several years, stage and discharge relations were already available (Hazel and others, 

2006a). For the BWM sites, stage-discharge relations were constructed using the data collected during 

this study. For each site surveyed, water surface elevations and high-water marks were plotted as 

functions of discharge. The discharge for the time of survey and the surveyed high-water indicators was 

determined by routing flow downstream from the nearest upstream stream-gaging station using an 

unsteady one-dimensional streamflow model (Wiele and Griffin, 1997). A second-order polynomial fit 

was applied to the data for each site using least-squares regression (appendix C). 

The sandbar topography and the stage-discharge relations were used to determine whether 

backwater habitat existed across a range of discharges and to compute the backwater area and volume 

when backwaters were present. The topographic contour lines corresponding to discharges of 227, 283, 

340, 453, and 566 m3

/s were determined from the triangular integrated network (TIN) surface. If a 

backwater was present within the survey area boundary, then the area of the backwater was outlined as a 

polygon feature defined by the corresponding contour line and an additional backwater “closure” line 

(fig. 2). The intent of the backwater closure line is to separate the region of stagnant flow in the 

backwater from the higher velocity current in the adjacent eddy. Although it was not possible to observe 

flow conditions across the range of discharges for each survey, observations were made at each site at 

the time of survey. These observations included a field description of the sandbar, the backwater (if 

present), and the closure line that would separate the backwater from the eddy on the basis of flowvelocity criteria. These observations were used during analysis to guide the delineation of backwater 

area. This polygon provides the measurement of backwater area. The volumetric difference between the 

polygon of backwater area and the underlying sandbar surface provides the measurement of backwater 

volume. The volume thus measured is the volume of water required to fill the backwater for the 

specified discharge. Backwaters with an area less than 2 m2

 were excluded from the analysis. Several 

study sites were observed to have backwaters at multiple locations. Where this occurred, each backwater 

location was delineated and tracked separately through the data analysis. Thus, the number of backwater 

locations exceeds the number of study sites. 

To evaluate changes in backwater area and volume in the context of changes in sandbar volume 

and morphology, maps showing erosion and deposition between successive surveys were constructed 

and volumes of sandbar change were computed. The erosion and deposition, or “difference” maps were 

constructed by calculating the difference between successive surveys in a raster environment. Areas and 

volumes of erosion and deposition were calculated only for the region of overlap common to all four 

surveys. 

Remote Cameras 

Remotely deployed cameras were used to document daily changes in sandbar and backwater 

morphology that occurred between field surveys. Twelve of the sites were monitored with digital 

12
cameras that were programmed to take five photographs daily at approximately 8 a.m., 10 a.m., 12 p.m., 

2 p.m., and 4 p.m. These cameras captured photographs daily from the date of installation through the 

study period (appendix B). An additional 19 sites were monitored by analog film cameras that took 

photographs once daily for variable periods of time determined by the number of exposures available 

per roll of film and the time interval between site visits when exposed films could be recovered and 

changed (appendix B). 

Fish Sampling of Backwater Habitats 

Sampling backwaters for fish was accomplished by two approaches, full sampling and 

supplemental sampling. Full sampling was conducted with a full staff of experienced fisheries biologists 

that accompanied physical scientists and surveyors on monitoring trips. These trips were launched in 

May and September 2008, coinciding with the survey trips. The supplemental trips were conducted in 

April and July and were led by science professionals assisted by youth volunteers participating in the 

Grand Canyon Youth program. These supplemental trips visited fewer sites, but provided valuable 

additional information. The April trip sampled only sites downstream from Diamond Creek and 

occurred shortly before the full trip conducted in May 2008. 

Seining was conducted with seine nets that were either 9 m or 4.5 m long by 1.2 m high with a 

3-mm mesh. All backwaters that were present at the observed discharge and were larger than about 2 m2

were sampled. 

Summary statistics of the fish captures (intended only to portray presence or absence of fish at a 

specific time) were assembled to provide an overview of the fish community present during the months 

that followed the 2008 HFE, the first growing season available to fish following the experiment. 

Sampling was delayed until after the spring equinox so that backwaters were exposed to some solar 

radiation, allowing them to warm and thereby providing one of the hypothesized primary benefits to 

fish. The summary statistics presented in this report characterize the numbers and species captured; a 

more synthetic analysis has been initiated that incorporates backwater capture data from previous years 

as well as additional physical habitat information. 

Results 

Sandbar Surveys 

Processes of Sandbar Morphologic Change that Affect Backwater Habitat 

Changes in bar morphology that affect the size and location of the return channel and backwater 

habitats depend on the specific pattern of sand deposition and erosion within the eddy. The morphology 

of the potential backwater habitats are most directly dependent on whether there is deposition or erosion 

on the reattachment bar platform and whether there is scour or fill in the return channel. The frequency 

of each of these processes during the 2008 HFE and the period between the March 2008 HFE and 

October 2008, is shown in table 3, along with information about whether the habitat changes were 

associated with an increase, decrease, or no measurable change in backwater area and volume. The most 

common responses during the 2008 HFE were reattachment bar deposition and return channel scour that 

resulted in increases in backwater area and volume. 

Additional changes in sandbar topography occurred between April and October 2008. During 

this period, deposition on reattachment bars continued to cause increases in backwater area, although 

this deposition occurred at lower elevations than deposition during the 2008 HFE. Return channel scour 

during summer 2008 was much less common than during the March HFE. In addition, the processes that 

13
caused increases in backwater area and volume in that period were accompanied by processes of 

reattachment bar erosion and return channel fill that resulted in a net decrease in backwater volume. 

Table 3. Processes of observed sandbar morphologic response associated with changes in return channel volume 

Process Number of sites 

Feb.-Apr. Apr.-Oct. 

Responses associated with an increase in return channel volume 

Deposition on reattachment bar1 44 37 

Erosion in return channel 36 19 

Responses associated with a decrease in return channel volume 

Erosion of reattachment bar2 21 37 

Deposition in return channel 9 25 

Responses associated with little or no change in return channel volume 

Deposition on reattachment bar1 18 10 

Erosion in return channel 11 

Total number of sites evaluated3 78 78 

1

 Deposition was above the elevation associated with the 340 m3/s stage between February and April and below that stage 

thereafter. 

2

 Erosion was below the elevation associated with the 340 m3/s stage between February and April and above that stage 

thereafter. 

3

 Responses are not mutually exclusive and, therefore, do not sum to equal the number of sites evaluated. 

At many of the study sites, the combination of deposition on the reattachment bar and scour in 

the return channel during the HFE resulted in the formation of large sandbars and distinct return 

channels. This type of response is illustrated at RM 45 on the left, looking downstream (figs. 1, 5). In 

this case deposition that occurred during the 2008 HFE (S.A. Wright, U.S. Geological Survey, written 

commun., 2009) resulted in a large reattachment bar that extended into the eddy (fig. 4). The return 

channel was also scoured during the HFE and, following flow recession, a large backwater was present 

(fig. 4). These changes are illustrated by relations between calculated backwater size (area and volume) 

and discharge for each of the survey trips (fig. 6). In February, before the HFE, there was no backwater 

present at any discharge, which is indicated by zero values for both backwater area and volume. In 

April, following the HFE, a backwater was present at all discharges modeled, and both backwater area 

and volume were largest at flows of about 450 m3

/s. The erosion of the sandbar caused both backwater 

area and volume to decrease in such a pattern that the area and volume of habitat was similar across the 

range of discharges modeled. This is an example of a backwater for which the size of the habitat was 

moderately sensitive to changes in flow immediately following the HFE and insensitive to changes in 

flow by May. In each of the post-HFE surveys through October 2008, backwater habitat was 

continuously present across the range of flows considered. 

14
A March 4, 2008, 7:56 a.m. 

B March 11, 2008, 3:56 p.m. 

C April 11, 2008, 3:56 p.m. 

D May 11, 2008, 3:56 p.m. 

Figure 4. Matching oblique views photographed by remote camera looking from the right shore across to the 

sandbar and backwater at RM 45 left. Flow is from left to right. A, The eddy before the March 2008 HFE on 

March 4, 2008, 7:56 a.m. B, The sandbar and newly created backwater on March 11, 2008, 3:56 p.m. C, The 

eddy on April 11, 2008, 3:56 p.m., showing sandbar erosion and decreasing backwater size. D, The eddy on 

May 11, 2008, 3:56 p.m. following additional sandbar erosion. 

15
Reattachment bar deposition and return channel scour did not result in bar morphology that 

created backwaters at every site where those processes occurred (table 3). At 21 of the study sites, 

reattachment bars eroded, resulting in loss of return channel morphology and decrease in backwater area 

and volume. The sandbars that eroded were typically low-elevation deposits emergent at elevations 

associated with discharges of 340 m3/s or lower. This type of response was evident at the RM 3 left 

study site, where erosion of a low-elevation reattachment bar during the HFE resulted in the elimination 

of most of the bar platform and the loss of the return channel morphology and backwater habitat (fig. 7). 

This is an example of a site where backwater habitat size was extremely sensitive to changes in 

discharge. Both backwater area and volume were highest at relatively low discharges and nonexistent at 

relatively high discharges before the HFE (fig. 8). Between discharges of about 350 m3/s and 450 m3/s, 

the reattachment bar would be inundated and backwater habitat would no longer be present. At this 

upstream study site, a low-discharge backwater habitat returned in October 2008, when a new lowelevation reattachment bar was present (fig. 8). 

16
Figure 5. Maps of study site RM 45 left showing 1-m resolution DEMs derived from topographic and bathymetric 

mapping occurring from February to October 2008. Arrows indicate locations where erosional or depositional 

processes resulted in changes to the backwater. A, DEM of surface elevations in February 2008. B, DEM of 

surface elevations in April 2008. C, DEM of surface elevations in May 2008. D, DEM of surface elevations in 

October 2008. Dates of survey and discharge at time of measurement are listed in appendix B. E, Erosiondeposition map, calculated as the difference between DEMs comparing the February and April surveys. F, 

Erosion-deposition map comparing the April and May surveys. G, Erosion-deposition map comparing the May 

and October surveys. 

17
Figure 5. Maps of study site RM 45 left showing 1-m resolution DEMs derived from topographic and bathymetric 

mapping occurring from February to October 2008. Arrows indicate locations where erosional or depositional 

processes resulted in changes to the backwater. A, DEM of surface elevations in February 2008. B, DEM of 

surface elevations in April 2008. C, DEM of surface elevations in May 2008. D, DEM of surface elevations in 

October 2008. Dates of survey and discharge at time of measurement are listed in appendix B. E, Erosiondeposition map, calculated as the difference between DEMs comparing the February and April surveys. F, 

Erosion-deposition map comparing the April and May surveys. G, Erosion-deposition map comparing the May 

and October surveys.—Continued. 

18
0

200

400

600

800

1,000

1,200

1,400

200 250 300 350 400 450 500 550 600

RM 45 left

Feb.

Apr.

May

Oct.

 BACKWATER AREA, IN SQUARE METERS

DISCHARGE, IN CUBIC METERS PER SECOND A

0

500

1,000

1,500

2,000

2,500

3,000

3,500

200 250 300 350 400 450 500 550 600

Feb.

Apr.

May

Oct.

 BACKWATER VOLUME, IN CUBIC METERS

DISCHARGE, IN CUBIC METERS PER SECOND B

RM 45 left

Figure 6. Relations between backwater size and discharge for RM 45 left during 2008. A, Measured backwater 

area plotted as a function of discharge. B, Measured backwater volume plotted as a function of discharge. 

19
Figure 7. Maps of study site RM 3 left showing 1-m resolution DEMs derived from topographic and bathymetric 

mapping between February and April, 2008. Arrows indicate locations where erosional processes resulted in 

changes to the backwater. A, DEM of surface elevations in February 2008. B, DEM of surface elevations in 

April 2008. Dates of survey and discharge at time of measurement are listed in appendix B. C, Erosiondeposition map, calculated as the difference between DEMs comparing the two surveys. 

20
0

100

200

300

400

500

600

200 250 300 350 400 450 500 550 600

RM 3 left

Feb.

Apr.

May

Oct.

 BACKWATER AREA, IN SQUARE METERS

DISCHARGE, IN CUBIC METERS PER SECOND A

0

100

200

300

400

500

600

200 250 300 350 400 450 500 550 600

RM 3 left

Feb.

Apr.

May

Oct.

 BACKWATER VOLUME, IN CUBIC METERS

DISCHARGE, IN CUBIC METERS PER SECOND B

Figure 8. Relations between backwater size and discharge for RM 3 left during 2008. A, Measured backwater 

area plotted as a function of discharge. B, Measured backwater volume plotted as a function of discharge. 

21
Substantial fluvial reworking of the 2008 HFE sandbars occurred in the 2 to 3 months following 

the return to diurnal fluctuating flow operations at the Glen Canyon Dam hydropower plant, particularly 

in response to higher dam releases in mid April (fig. 3) associated with a shift to wetter hydrology in the 

upper Colorado River Basin and requirements to equalize water storage between Lakes Powell and 

Mead (fig. 1); these sandbar responses are described by Hazel and others (2010). At many sites, newly 

rebuilt sandbars eroded, resulting in smaller return channels and reduced area and volume of backwater 

habitat. This response is illustrated at RM 45 left, where erosion following the HFE occurred between 

March and May and continued thereafter to October (fig. 5). By October 2008, the remaining backwater 

was small, yet still larger than the size present in February 2008, before the HFE. At other sites, 

backwater area decreased owing to sandbar reworking and filling of the return channel. This process 

occurred at RM 172 left, where reattachment bar deposition and return channel scour resulted in 

increases in backwater area and volume (fig. 9). Following the March HFE, between the April and 

October measurements, deposition in the return channel resulted in decreases in backwater area and 

volume (fig. 10). This also occurred at RM 65 left, where deposition near the mouth of the return 

channel can be seen in repeat, time-lapse photographs (fig. 11). 

The relations between backwater area and volume for RM 172 left provide an illustration of how 

backwater habitat can change in response to changes in morphology that occur over time, and to 

changes in discharge for any given morphology. In February, there was a backwater present at low 

discharge and high discharge, but not at intermediate discharges (fig. 10). This often occurs when there 

are distinct low-elevation and high-elevation parts of the sandbar. Low-elevation habitat is first lost as 

discharge increases and stage rises, then new high-elevation habitat is gained as yet higher stages 

inundate the return channel associated with the higher part of the sandbar. Deposition during the HFE 

resulted in a sandbar morphology that provided backwater habitat across the full range of discharges, 

with greatest area and volume at low to intermediate discharges (fig. 10). 

22
Figure 9. Maps of study site RM 172 left showing 1-m resolution DEMs derived from topographic and bathymetric 

mapping between February and April, 2008. Arrows indicate locations where depositional processes resulted in 

changes to the backwater. A, DEM of surface elevations in February 2008. B, DEM of surface elevations in 

April 2008. C, DEM of surface elevations in October 2008. Dates of survey and discharge at time of 

measurement are listed in appendix B. D, Erosion-deposition map, calculated as the difference between DEMs 

comparing the February and April surveys. E, Erosion-deposition map comparing the April and October 

surveys. 

23
Figure 9. Maps of study site RM 172 left showing 1-m resolution DEMs derived from topographic and bathymetric 

mapping between February and April, 2008. Arrows indicate locations where depositional processes resulted in 

changes to the backwater. A, DEM of surface elevations in February 2008. B, DEM of surface elevations in April 

2008. C, DEM of surface elevations in October 2008. Dates of survey and discharge at time of measurement 

are listed in appendix B. D, Erosion-deposition map, calculated as the difference between DEMs comparing the 

February and April surveys. E, Erosion-deposition map comparing the April and October surveys.—Continued. 

24
0

50

100

150

200

250

200 250 300 350 400 450 500 550 600

RM 172 left

Feb.

Apr.

May

Oct.

 BACKWATER AREA, IN SQUARE METERS

DISCHARGE, IN CUBIC METERS PER SECOND A

0

10

20

30

40

50

60

200 250 300 350 400 450 500 550 600

RM 172 left

Feb.

Apr.

May

Oct.

 BACKWATER VOLUME, IN CUBIC METERS

DISCHARGE, IN CUBIC METERS PER SECOND B

Figure 10. Relations between backwater size and discharge for RM 172 left during 2008. A, Measured backwater 

area plotted as a function of discharge. B, Measured backwater volume plotted as a function of discharge. 

25
A April 13, 2008, 11:56 a.m. 

B October 25, 2008, 1:44 p.m. 

Figure 11. Two matching oblique views photographed by remote camera looking across the Colorado River to the 

RM 65 left study site. Flow is from left to right. A, Image taken on April 13, 2008, at 11:56 a.m. B, Image taken 

on October 25, 2008, at 1:44 p.m. 

In some cases, sandbar reworking resulted in increases in backwater area and volume between 

April and October 2008. This typically occurred by deposition forming a new reattachment bar 

emergent at discharges below the range of fluctuating hydroelectric powerplant discharges, which 

peaked at 527 m3

/s in July 2008, during FR 3 (fig. 3). At the RM 55 right study site, the March 2008 

HFE did not produce a sandbar that supported a large return channel and backwater. However, 

reworking and deposition between April and October did result in a new low-elevation bar and 

backwater (fig. 12) that was largest at flows of 227 m3

/s (fig. 13). This also occurred at the RM 65 left 

study site, where repeat, time-lapse photographs taken by the remote camera showed the formation of a 

low-elevation bar and associated backwater during the higher fluctuating flow operations during the 

month of August (fig. 11). 

26
Figure 12. Maps of study site RM 55 right showing 1-m resolution DEMs derived from topographic and bathymetric 

mapping between February and April, 2008. Arrows indicate locations where depositional processes resulted in 

changes to the backwater. A, DEM of surface elevations in April 2008. B, DEM of surface elevations in October 

2008. Dates of survey and discharge at time of measurement are listed in appendix B. C, Erosion-deposition 

map, calculated as the difference between DEMs comparing the two surveys. 

27
0

100

200

300

400

500

600

700

200 250 300 350 400 450 500 550 600

RM 55 right Feb.

Apr.

May

Oct.

 BACKWATER AREA, IN SQUARE METERS

DISCHARGE, IN CUBIC METERS PER SECOND A

0

100

200

300

400

500

200 250 300 350 400 450 500 550 600

RM 55 right

Feb.

Apr.

May

Oct.

 BACKWATER VOLUME, IN CUBIC METERS

DISCHARGE, IN CUBIC METERS PER SECOND B

Figure 13. Relations between backwater size and discharge for RM 55 right during 2008. A, Measured backwater 

area plotted as a function of discharge. B, Measured backwater volume plotted as a function of discharge. 

28
Systemwide Changes in the Abundance and Size of Backwater Habitat 

The above descriptions of responses at specific study sites illustrate the dependence of 

backwater habitat on sandbar morphology and flow regime. These examples also demonstrate how 

processes of sandbar erosion and deposition that are associated with sandbar building and subsequent 

dam operations result in changes to backwater habitat over relatively short time periods. Relations 

between habitat and flow regime were developed for a total of 135 backwater locations at 97 study sites 

where detailed topographic surveys were made in 2008. The wide range of backwater sizes and the large 

number of zero values (sites where no backwater was present at a given discharge) creates difficulty 

with quantification of average response. For these reasons, we begin with an analysis of the number of 

backwaters present among the study sites, which is not size dependent. Next, we present all of the data 

for backwater area and volume, which illustrate the range of backwater sizes, followed by a summary by 

total habitat area and volume. Finally, we present an analysis that quantifies the habitat abundance for 

particular diurnally fluctuating and steady flow operations associated with Glen Canyon Dam. 

There were approximately 60 to 70 backwaters present, among the 135 backwater locations that 

were monitored, at discharges in the range of 227 m3

/s to 283 m3/s at all surveys (fig. 14). At flows of 

340 m3

/s and greater, there were more backwaters in April following the HFE than there were at other 

times. Thus, the reattachment bar deposition and return channel scour associated with the March HFE 

caused an increase in the number of backwaters present at higher flows (typically associated with 

summer fluctuating flow dam operations) while maintaining the number of backwaters present at lower 

flows (more typically associated with monthly release volumes from Glen Canyon Dam typical of 

spring and fall seasons in years with below-average upper Colorado River Basin hydrology). Water year 

2008 was below average in terms of annual release volume from Lake Powell, but it was slightly higher 

than a minimum release year of 8.23 million acre feet, owing to requirements that year to equalize 

storage between Lakes Powell and Mead after April 1. Between April and May, there was a decrease in 

the number of backwaters at those same flows of 340 m3/s and greater. By October, the pattern of the 

relationship between backwater abundance and discharge was very similar to the pattern that existed in 

February before the HFE, but with 5 to 14 percent more backwaters present in October than in February. 

0

10

20

30

40

50

60

70

80

0 100 200 300 400 500 600

Feb.

Apr.

May

Oct.

NUMBER OF BACKWATERS 

AT INDICATED DISCHARGE

DISCHARGE, IN CUBIC METERS PER SECOND

135 locations at 97survey sites

Figure 14. The number of backwaters present among the study sites for each survey period in 2008 as a function 

of discharge. 

29
The changes in backwater area and volume from February through October are consistent with 

the changes in backwater abundance, but they show the extremely wide range in size of backwater 

habitats (fig. 15). There were backwaters as small as 2 m2

 in area (the minimum mapping size) and 0.1 

m3

 in volume. The largest backwaters mapped were more than 2,000 m2 in area and 3,000 m3 in volume 

(fig. 15). Despite this wide range in size, there was a clear shift up in both area and volume between 

February and April, followed by downward shifts between April and May and again between May and 

October. 

The changes in habitat size are summarized by relations between discharge and total backwater 

area and volume (fig. 16). These plots show the same pattern of response shown by the changes in 

backwater abundance (fig. 14). There were measurable increases in habitat area and volume between 

February and April, especially at the higher discharges, followed by decreases in habitat size in the 

subsequent time intervals. By October 2008, total backwater habitat area and volume were very similar 

to the condition prior to the 2008 HFE. 

Figure 15. Plots showing calculated backwater volume and area for each of the five discharges analyzed in 2008. 

Horizontal lines are the median of non-zero values. A, Backwater volume for 227 m3/s. B, Backwater area for 

227 m3/s. C, Backwater volume for 283 m3/s. D, Backwater area for 283 m3/s. E, Backwater volume for 340 

m3/s. F, Backwater area for 340 m3/s. G, Backwater volume for 453 m3/s. H, Backwater area for 453 m3/s. I, 

Backwater volume for 566 m3/s. J, Backwater area for 566 m3/s. 

30
Figure 15. Plots showing calculated backwater volume and area for each of the five discharges analyzed in 

2008. Horizontal lines are the median of non-zero values. A, Backwater volume for 227 m3/s. B, Backwater 

area for 227 m3/s. C, Backwater volume for 283 m3/s. D, Backwater area for 283 m3/s. E, Backwater volume for 

340 m3/s. F, Backwater area for 340 m3/s. G, Backwater volume for 453 m3/s. H, Backwater area for 453 m3/s. 

I, Backwater volume for 566 m3/s. J, Backwater area for 566 m3/s.—Continued. 

31
Figure 15. Plots showing calculated backwater volume and area for each of the five discharges analyzed in 

2008. Horizontal lines are the median of non-zero values. A, Backwater volume for 227 m3/s. B, Backwater area 

for 227 m3/s. C, Backwater volume for 283 m3/s. D, Backwater area for 283 m3/s. E, Backwater volume for 340 

m3/s. F, Backwater area for 340 m3/s. G, Backwater volume for 453 m3/s. H, Backwater area for 453 m3/s. I, 

Backwater volume for 566 m3/s. J, Backwater area for 566 m3/s.—Continued. 

32
0

4,000

8,000

12,000

16,000

0 100 200 300 400 500 600

Feb

Apr

May

Oct

TOTAL BACKWATER AREA AT INDICATED 

DISCHARGE, IN SQUARE METERS

DISCHARGE, IN CUBIC METERS PER SECOND A

0

4,000

8,000

12,000

16,000

0 100 200 300 400 500 600

Feb

Apr

May

Oct

TOTAL BACKWATER VOLUME AT INDICATED 

DISCHARGE, IN CUBIC METERS

DISCHARGE, IN CUBIC METERS PER SECOND

B

Figure 16. Plots showing total habitat area and volume for all study sites as functions of discharge in 2008. A, The 

sum of backwater area as a function of discharge for all study sites that were surveyed four times in 2008 

during the study. B, The sum of backwater volume as a function of discharge for the same sites. 

Although the data presented above summarize the gross changes in backwater habitat abundance 

and size, further analysis is required to evaluate the presence of habitat associated with a particular dam 

operating flow regime. The simple summary relationship for total habitat availability (fig. 16) hides the 

complexity that arises from the many different relations between backwater size and discharge (for 

33
example, figs. 6, 8, 10, and 13), which result from differences in sandbar morphology. These 

complexities are evaluated in the context of post-HFE flow regime by a calculation of the fraction of 

time each site has a backwater present for any particular diurnally fluctuating or steady dam operating 

flow regime. These results are presented as cumulative probability distributions (fig. 17), which show, 

for each of the four different flow regimes that occurred following the 2008 HFE, comparisons of 

backwater habitat availability for each of the four measurement periods (fig. 3). 

For each of the topographic measurement periods (February, April, May, and October), the fall 

steady flow regime (FR 4) was associated with the highest percentage of emergent sandbars with 

backwaters present continuously. For the October topography, the experimental steady dam releases of 

approximately 351 m3/s (FR 4) resulted in about 40 percent of the sites having backwaters present 100 

percent of the time, while FR3 for the same topography would have resulted in only about 10 percent of 

the sites having backwaters present 100 percent of the time. However, because during a steady flow 

regime backwaters are either continuously present or continuously absent (that is, there are no 

backwaters that are intermittently present as flow rises and falls), the 2008 experimental steady flow 

regime was also associated with the highest percentage of sites with no backwaters present (fig. 17). For 

the October topography, about 60 percent of the sites had no backwater present during the steady flows, 

whereas for FR3 only about 35 percent of the sites had no backwater present. Thus, the fluctuating flow 

dam operation associated with the FR3 period would have resulted in 55 percent of the sites having 

intermittently present backwaters if those flows occurred in October 2008. 

For the 351-m3/s steady flow operating regime that occurred in September and October, the 

fraction of sites with continuously present backwaters was greatest for sandbar topography that existed 

in April (before the onset of higher monthly volume fluctuating operations) and least for the topography 

that existed in May (following the abrupt shift to higher monthly volume fluctuating operations 

associated with reservoir storage equalization), with February and October approximately equal. Among 

the fluctuating flow regimes, FR1 (fluctuations between 198 and 340 m3/s) was associated with a greater 

percentage of sites having backwaters present for a greater fraction of time. This occurred in the period 

of springtime lower fluctuations following the HFE, but before higher diurnal fluctuating dam 

operations that were released starting in mid April for purposes of equalizing water storage between 

Lakes Powell and Mead. These data show that if the habitat requirements for juvenile native fish in the 

mainstem Colorado River require continuous backwater availability for enhanced growth and survival, 

then the steady flow regime provides more habitat availability and provides it most consistently. If, 

however, intermittently present backwater habitat is deemed to be adequate for promoting juvenile 

native fish growth and survival (meaning, enough added benefit to reduce overwinter mortality), then 

the fluctuating flow operation may result in approximately equal amounts of backwater habitat, 

depending on the accompanying upper Colorado River Basin hydrology, the annual flow regime, and 

sandbar morphology. 

A further comparison was made to illustrate the effect of higher monthly volume fluctuating 

flows than occurred in 2008. Results from an analysis of habitat availability using the same 2008 

sandbar-morphology data used in fig. 17, but evaluated for the relatively higher monthly volume, 

experimental fluctuating flows (a daily peak of 566 m3

/s, with a fluctuating range of 424 m3/s versus the 

currently allowed range of 226 m3/s) that occurred between January 3 and April 9, 2005, following the 

November 2004 HFE (fig 18). The relative position of each of the curves, with April providing the most 

abundant backwater habitat and February providing the least, is the same as shown in fig. 17B and C. 

All of the curves are, however, shifted upward and to the left for backwaters present about 50 percent of 

the time or more; and the curves are similar or shifted downward and to the right for backwaters present 

about 50 percent of the time or less. The above analysis indicates that higher monthly release volumes, 

34
when also associated with a wider daily allowable fluctuating flow regime (that also results in high daily 

peak discharges)—such as the operation tested in the winters of 2003 through 2005—tend to result in 

fewer backwaters that are available 50 percent of the time or more and a similar or greater number of 

backwaters that are present intermittently. It is important to point out that this analysis only considers 

the effect of the different flow regimes on given sandbar morphology (those that were measured during 

2008); it does not include consideration of how the different dam operating regimes might result in 

different rates of sandbar erosion and therefore changing sandbar morphology. 

35
Figure 17. Cumulative frequency distributions showing the fraction of study sites as a function of the fraction of 

time a backwater is present for each of the four flow regimes associated with dam operations that followed the 

2008 HFE (see fig. 3). A, Frequency distribution for each survey based on FR 1. B, Frequency distribution for 

each survey based on FR 2. C, Frequency distribution for each survey based on FR 3. D, Frequency 

distribution for each survey based on FR 4. 

36
0 0.2 0.4 0.6 0.8 1

0

20

40

60

80

100

FR5: 146 to 581 m3

/s fluctuating flow

Feb.

Apr.

May

Oct.

FRACTION OF TIME BACKWATER PRESENT AT SITE

PERCENT OF SITES WITH BACKWATER PRESENT 

INDICATED FRACTION OF TIME OR LESS

Figure 18. Cumulative frequency distributions showing the fraction of study sites as a function of the fraction of 

time a backwater is present for the experimental fluctuating flows that occurred from January 3 to April 9, 2005, 

following the November 2004 HFE. 

Backwater Inventory 

The inventory of sandbar-created backwaters (appendix A) indicated that backwaters were more 

abundant in October 2008 than in February 2008 (table 4), which is consistent with the findings made 

on the basis of analyses of the study sites (fig. 15). However, the inventory also indicated far fewer 

backwaters were present in April and May, which is not consistent with the findings made on the basis 

of field surveys. This results from the fact that the inventory is simply a record of all backwaters 

observed in the field and is, therefore, subject to the biases imposed by the flow regime during the 

particular trip. 

Thus, discrepancies between the inventory and the results from the analysis of the survey data 

may result from poor water clarity during the inventory conducted in April and from the higher volume 

flows that occurred during the May inventory. Both of these factors limit the ability to observe the 

presence of backwaters at the low range of flows (< 283 m3

/s). A comparison between results from the 

backwater inventory and the surveyed backwaters for all of the study sites (table 5) shows that there was 

agreement in responses at between about 57 and 74 percent of the study sites. Where there were 

differences in responses between the inventory and the survey, it was usually the result of identification 

of a backwater in the survey data where one had not been identified in the field during the inventory. 

Again, the consistent underprediction of the number of backwaters by the inventory most likely results 

from the limitations imposed when making field observations at one particular discharge in this river 

ecosystem, particularly when studies are conducted during unsteady flows associated with the 

fluctuating flow operations at Glen Canyon Dam. 

37
Table 4. Summary of backwater inventory results. 

Observation Feb. Apr. May July Sept.1 

Flow regime 244–382 

m3

/s 

198–340 

m3/s 

283–453 

m3/s 

311–538 

m3/s 

351 m3

/s 

Water visibility good poor good good good 

Number of study sites 

No backwater present 524 679 653 701 464 

Backwater present only at low range of 

operations 

168 26 130 144 76, 252 

Backwater present only at upper range of 

operations 

81 49 33 24 3, 38 

Backwater present across range of operations 107 126 64 11 22 

Subtotal of backwater present at any discharge 

within range of operations 

356 201 227 179 391 

Total number of sites visited 880 880 880 880 855 

1

Where two values are listed the first value is the number of backwaters present at the time of observations and the second 

value indicates the number of backwaters expected to occur at higher or lower flow. 

Table 5. Comparison between backwater inventory and surveys. 

Observation Feb. Apr. May Oct. 

Number of sites 

Backwater absent in survey and inventory 16 18 12 8 

Backwater present in survey and absent in inventory 21 22 27 28 

Backwater absent in survey and present in inventory 3 3 4 5 

Backwater present in survey and inventory 53 49 42 35 

Total number of backwaters identified in survey 74 71 69 63 

Total number of backwaters identified in inventory 56 52 46 40 

Total number of sites compared 93 92 85 76 

Percent of sites 

Percent of sites with agreement 74 73 64 57 

Longitudinal Distribution of Backwater Habitats 

The changes in backwater habitat were not distributed uniformly in the downstream direction, 

but were generally greatest in reaches where known backwater habitat locations are most abundant. In 

some cases, increases in backwater volume coincided with reaches of known humpback chub 

aggregations. We evaluated the backwater volumes for each of the five discharges analyzed based on 

the February, April, and October survey data after these data were plotted by distance downstream from 

Lees Ferry (fig. 19). As described above, the sandbar topography in April resulted in the greatest 

amount of backwater habitat at all discharges. At a discharge of 227 m3/s, the February topography 

resulted in greater backwater habitat volume than October in all reaches. However, for most reaches, 

and at all discharges greater than 227 m3

/s, the October sandbar topography resulted in greater 

backwater habitat volume than February. The increases in backwater habitat volume were concentrated 

in three segments of the river: RM 25 to RM 70, RM 120 to RM 125, and RM 175 to RM 215. Within 

these reaches are some, but not all, of the known humpback chub aggregation areas (table 2). 

38
0

100

200

300

400

500

1,500

3,000

0

10

20

30

40

50

60

0 50 100 150 200

Backwater volume in Feb.

Backwater volume in Apr.

Backwater volume in Oct.

Number of backwater locations

BACKWATER VOLUME AT 227 CUBIC METERS PER 

SECOND FOR EACH STUDY SITE

NUMBER OF BACKWATER LOCATIONS 

PER 10 KM SEGMENT

DISTANCE DOWNSTREAM FROM LEES FERRY, IN RIVER MILES A

0

100

200

300

400

500

1,500

3,000

0

10

20

30

40

50

60

0 50 100 150 200

Backwater volume in Feb.

Backwater volume in Apr.

Backwater volume in Oct.

Number of backwater locations

BACKWATER VOLUME AT 283 CUBIC METERS PER 

SECOND FOR EACH STUDY SITE

NUMBER OF BACKWATER LOCATIONS 

PER 10 KM SEGMENT

DISTANCE DOWNSTREAM FROM LEES FERRY, IN RIVER MILES B

 

Figure 19. Downstream distributions of backwater habitat at differing discharges during 2008. Each plot shows 

backwater habitat volume for each site at the indicated discharge. Each plot also shows the number of 

backwater habitat locations per 10 km river segment based on the complete backwater inventory (appendix A). 

The locations of known humpback chub aggregations (table 2) are shown by the thick green lines. Note the 

break in scale on the left axis to improve readability. A, Backwater volume by distance downstream for a 

discharge of 227 m3/s. B, Backwater volume by distance downstream for a discharge of 283 m3/s. C, 

Backwater volume by distance downstream for a discharge of 340 m3/s. D, Backwater volume by distance 

downstream for a discharge of 453 m3/s. E, Backwater volume by distance downstream for a discharge of 566 

m3/s. 

39
0

100

200

300

400

500

1,500

3,000

0

10

20

30

40

50

60

0 50 100 150 200

Backwater volume in Feb.

Backwater volume in Apr.

Backwater volume in Oct.

Number of backwater locations

BACKWATER VOLUME AT 340 CUBIC METERS PER 

SECOND FOR EACH STUDY SITE

NUMBER OF BACKWATER LOCATIONS 

PER 10 KM SEGMENT

DISTANCE DOWNSTREAM FROM LEES FERRY, IN RIVER MILES C

0

100

200

300

400

500

1,500

3,000

0

10

20

30

40

50

60

0 50 100 150 200

Backwater volume in Feb.

Backwater volume in Apr.

Backwater volume in Oct.

Number of backwater locations

BACKWATER VOLUME AT 453 CUBIC METERS PER 

SECOND FOR EACH STUDY SITE

NUMBER OF BACKWATER LOCATIONS 

PER 10 KM SEGMENT

DISTANCE DOWNSTREAM FROM LEES FERRY, IN RIVER MILES D

 

Figure 19. Downstream distributions of backwater habitat at differing discharges during 2008. Each plot shows 

backwater habitat volume for each site at the indicated discharge. Each plot also shows the number of 

backwater habitat locations per 10 km river segment based on the complete backwater inventory (appendix A). 

The locations of known humpback chub aggregations (table 2) are shown by the thick green lines. Note the 

break in scale on the left axis to improve readability. A, Backwater volume by distance downstream for a 

discharge of 227 m3/s. B, Backwater volume by distance downstream for a discharge of 283 m3/s. C, Backwater 

volume by distance downstream for a discharge of 340 m3/s. D, Backwater volume by distance downstream for 

a discharge of 453 m3/s. E, Backwater volume by distance downstream for a discharge of 566 m3/s.—

Continued. 

40
0

100

200

300

400

500

1,500

3,000

0

10

20

30

40

50

60

0 50 100 150 200

Backwater volume in Feb.

Backwater volume in Apr.

Backwater volume in Oct.

Number of backwater locations

BACKWATER VOLUME AT 566 CUBIC METERS PER 

SECOND FOR EACH STUDY SITE

NUMBER OF BACKWATER LOCATIONS 

PER 10 KM SEGMENT

DISTANCE DOWNSTREAM FROM LEES FERRY, IN RIVER MILES E

Figure 19. Downstream distributions of backwater habitat at differing discharges during 2008. Each plot shows 

backwater habitat volume for each site at the indicated discharge. Each plot also shows the number of 

backwater habitat locations per 10 km river segment based on the complete backwater inventory (appendix A). 

The locations of known humpback chub aggregations (table 2) are shown by the thick green lines. Note the 

break in scale on the left axis to improve readability. A, Backwater volume by distance downstream for a 

discharge of 227 m3/s. B, Backwater volume by distance downstream for a discharge of 283 m3/s. C, Backwater 

volume by distance downstream for a discharge of 340 m3/s. D, Backwater volume by distance downstream for 

a discharge of 453 m3/s. E, Backwater volume by distance downstream for a discharge of 566 m3/s.—

Continued. 

Observations of Fish in Backwater Habitats 

A total of 16,070 fish were captured during the four fish-sampling trips. The supplemental trip in 

April 2008 only sampled sites downstream of Diamond Creek (RM 225), accounting for 180 of the total 

number of fish captured. Over the course of the four trips, 185 different backwaters were seined, 

including backwaters occurring at 60 of the SBM and BWM study sites. Fish were captured at 44 out of 

the study sites that were seined. Native fish, especially speckled dace (Rhinichthys osculus), were 

captured more frequently than nonnative fish. Captures of bluehead sucker (Catostomus discobolus) and 

flannelmouth sucker (Catostomus latipinnis) were high, but humpback chub captures were rare. Among 

nonnative fish, the most numerous were fathead minnow (Pimephales promelas). Most fish were found 

in backwaters in September, when 7,402 fish and 11 different fish species were captured. The species 

were: common carp (Cyprinus carpio), fathead minnow, red shiner (Cyprinella lutrensis), speckled 

dace, humpback chub, bluehead sucker, flannelmouth sucker, rainbow trout (Oncorhynchus mykiss), 

brown trout (Salmo trutta), plains killifish (Fundulus zebrinus), and black bullhead (Ameiurus melas). 

Of these, speckled dace, humpback chub, bluehead sucker, and flannelmouth sucker are the only species 

native to Grand Canyon (fig. 20). The capture data from the supplemental sampling trips accounted for 

smaller numbers of fish but were generally consistent for the number of species captured (data not 

shown). 

41
0

1,000

2,000

3,000

4,000

CRP FHM RSH SPD HBC BHS FMS RBT BNT PKF BBH

NUMBER OF INDIVIDUALS CAPTURED

SPECIES CAPTURED

September sampling

May sampling

Figure 20. Captures of fish species for the May (under fluctuating flows) and September (under experimental 

steady flows of 354 m3/s) backwater sampling periods in 2008. Speckled dace and flannelmouth sucker were 

the most common native fish captured in the backwaters. Fathead minnow were the most common nonnative 

fish species captured in the backwaters. Key to species abbreviations: CRP, common carp (Cyprinus carpio); 

FHM, fathead minnow (Pimephales promelas); RSH, red shiner (Cyprinella lutrensis); SPD, speckled dace 

(Rhinichthys osculus); HBC, humpback chub (Gila cypha); BHS, bluehead sucker (Catostomus discobolus); 

FMS, flannelmouth sucker (Catostomus latipinnis); RBT, rainbow trout (Oncorhynchus mykiss); BNT, brown 

trout (Salmo trutta); PKF, plains killifish (Fundulus zebrinus); and BBH, black bullhead (Ameiurus melas). 

Conclusions and Management Implications 

Topographic and bathymetric surveys conducted at 97 study sites before and after the March 

2008 HFE show that the experimental release from Glen Canyon Dam resulted in sand deposition on 

reattachment sandbars and scour in return channels that more than doubled the total backwater area and 

volume at the study sites. The 97 study sites represent about 20 percent of the total number of these 

habitats in Grand Canyon National Park between Lees Ferry and Diamond Creek. The HFE also 

resulted in the loss of some backwaters where low-elevation reattachment bars scoured or return 

channels filled with HFE-deposited sand. 

In the 6-month period between the March HFE and the October measurements, reattachment 

bars were eroded and there was deposition in return channels. These processes resulted in loss of 

backwater habitat created by the 2008 HFE. However, during this period there was also formation of 

new low-elevation reattachment bars and creation of new backwater habitats. The net result from the 

sandbar reworking that occurred in response to the fluctuating flow operation at the dam was a return to 

a number of backwaters and total area and volume of backwater habitat for selected flows that was 

similar to the condition measured before the March 2008 HFE. However, some lasting effect of the HFE 

was evident in the availability of backwater habitats across the range of flows associated with the dam’s 

normal fluctuating flow regime (termed the Modified Low Fluctuating Flow; see U.S. Department of the 

Interior, 1995, 1996). For each of the flow regimes that were released in 2008, following the HFE, the 

42
October topography associated with the experimental steady flow of 351 m3

/s was consistently 

associated with a greater number of sites with backwaters present 50 percent of the time or greater 

compared to the February topography. Thus, while the most dramatic effects of the HFE on backwater 

habitat persisted only for a month or two, a small (up to 14 percent) increase in habitat availability 

persisted through October 2008. 

The availability of continuously present backwater habitats was maximized by steady flows 

compared to fluctuating flows, regardless of sandbar morphology. The precise steady flow that would 

maximize habitat, depends, of course, on the sandbar morphology and varied throughout the year. In 

April, habitat would have been maximized by a steady flow of about 453 m3

/s. However, the amount of 

habitat that would have been available at lower steady flows was also relatively high. In October, the 

greatest area and volume of habitat would have been achieved with a lower steady flow of 227 m3

/s. 

Thus, based on the limited data collected over the 6-month period for this study, low steady flows 

appear to provide as much or more habitat when compared to higher flows, except immediately 

following a HFE. 

Among the four fluctuating flow regimes analyzed, the relatively lower monthly volume 

fluctuating flows (FR1) were consistently associated with higher backwater availability than the higher 

monthly volume fluctuating flows, such as those that occurred mid-April through August (FR 2 and FR 

3), or the higher monthly volume, experimental fluctuating flows that occurred during January through 

March 2003 through 2005. Compared to steady flows of 351 m3

/s, the relatively lower monthly volume 

fluctuating flows associated with March to mid April 2008, had a greater number of intermittently 

available backwaters across the range of daily dam operations, but fewer backwaters that were 

continuously available. Annual release volumes at Glen Canyon Dam are associated with variability in 

upper Colorado River Basin hydrology and are determined by a variety of laws and the Colorado River 

Compact, whereas variability of seasonal to monthly release volumes is associated with development of 

the annual operating plan for the Colorado River. In addition to affecting the characteristics of 

backwater habitat available to native fish, the relative proportion of continuously available versus 

intermittently available backwaters may have implications for other aspects of the ecosystem, such as 

the degree of warming and primary production. 

The results from the backwater inventory indicate that there are as many as 880 potential 

backwater locations between Lees Ferry and Diamond Creek, of which 569 are sand-bounded 

backwaters of the type included among the study sites where topographic data were collected. These 

estimates of the total population of backwaters may be used in conjunction with the results from the 

detailed surveys to estimate total habitat abundance by reach. However, because the results of the 

inventory are biased by factors such as the discharge at time of observation and water clarity, the 

inventory results are not appropriate for monitoring trends in backwater habitat abundance. 

The fish-sampling data provided for use in this study support the hypothesis that small-bodied 

fish, whether small adults or juveniles, native or otherwise, in the Colorado River can be found in 

backwaters, which in most cases are of lower velocity and higher temperatures (at least during spring 

through early fall months) than the mainstem river. Fish captures within backwaters along the main 

channel of the Colorado River increase downstream from its confluence with the Little Colorado River 

at approximately RM 60. While fish were captured in backwaters during all flow regimes sampled, the 

highest captures were during the experimental fall steady flows of 2008, when dam releases were at 351 

m3

/s. Although this season precedes the period when water release temperatures from Glen Canyon 

Dam are highest, it follows the period of greatest solar warming to the river in Grand Canyon. Owing to 

reduced solar radiation after fall months, the relatively shallow backwater habitats along the shorelines 

become colder relative to the water of the main channel, perhaps making them a less advantageous area 

43
44

for juvenile fish attempting to survive the overwintering period. While these data confirm that native 

fish utilize backwater habitat in Grand Canyon National Park, the data are not conclusive with respect to 

linking the recruitment success of native juvenile fish in the main channel of the river to the abundance 

and distribution of backwater habitats or their continuous or intermittent use of such habitats below the 

dam. Further studies that evaluate utilization of all available habitats by native fish are required to 

address this question. 

Acknowledgements 

This work was made possible by the efforts of many individuals. Coordination of survey efforts 

and geodetic control for the study sites was provided by Keith Kohl. Field surveys were led by Paul 

Rauss and Matt Kaplinski, with the assistance of many support surveyors, including Milada Majerova, 

Aaron Borling, and Meagan Polino. James Androwski and Rob Ross tirelessly analyzed the survey data 

with assistance from Bob Tusso and Tom Gushue. The backwater inventory was led by Randy Van 

Haverbeke and Angela Abel. Carol Fritzinger organized the fish seining, and Paul Alley and Michael 

Dodrill provided assistance with analyzing the fish seining data. Rian Bogle designed and constructed 

the digital remote cameras. Logistical and additional field support was provided by Scott Perry, Steve 

Jones, Lynn Roeder, Emily Perry, Brent Burger, and others. The clarity and presentation of this report 

was aided by reviews provided by Joe Hazel, Ted Melis, and two anonymous reviewers. A special 

acknowledgement is given to the late Frank Protiva, who was instrumental in getting the field data 

collection effort off the ground. 

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eds., The controlled flood in Grand Canyon: American Geophysical Union, Geophysical Monograph, 

v. 110, p. 329-341. 

Schmidt, J.C., and Brim-Box, J.B., 2004, Application of a dynamic model to assess controls on age-0 

Colorado Pikeminnow distribution in the middle Green River, Colorado and Utah: Annals of the 

Association of American Geographers, v. 94, no. 3, p. 458-476. 

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

1986, Colorado River, Grand Canyon National Park, Arizona: U. S. Geological Survey Professional 

Paper 1493, 74 p. 

Schmidt, J.C., and Rubin, D.M., 1995, Regulated streamflow, fine-grained deposits, and effective 

discharge in canyons with abundant debris fans, in Costa, J.E., Miller, A.J., Potter, K.W., and 

Wilcock, P.R., eds., Natural and anthropogenic influences in fluvial geomorphology: American 

Geophysical Union, v. 89, p. 177-195. 

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

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

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

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

Schmidt, J.C., Marzolf, G.R, and Valdez, R.A., eds., The controlled flood in Grand Canyon: 

American Geophysical Union, Geophysical Monograph, v. 110, p. 185-203. 

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

Colorado River March development in the Grand Canyon, Arizona: Ecological Applications, v. 5, no. 

4, p. 1025-1039. 

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

grain-size evolution and sediment depletion during Colorado River floods, in Webb, R.H., Schmidt, 

J.C., Marzolf, G.R., and Valdez, R.A., eds., The 1996 controlled flood in Grand Canyon: American 

Geophysical Union, Geophysical Monograph, v. 110, p. 71-98. 

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

sediment supply limitation and the influence of Glen Canyon Dam: Water Resources Research, v. 36, 

no. 2, p. 515-542. 

Topping, D.J., Schmidt, J.C., and Vierra, L.E., Jr., 2003, Computation and analysis of the instantaneousdischarge record for the Colorado River at Lees Ferry, Arizona, May 8, 1921, through September 30, 

2000: U.S. Geological Survey Professional Paper 1677, 118 p. 

Topping, D.J., Rubin, D.M., Schmidt, J.C., Hazel, J.E., Jr., Melis, T.S., Wright, S.A., Kaplinski, M., 

Draut, A.E., and Breedlove, M.J., 2006, Comparison of sediment-transport and bar-response results 

from the 1996 and 2004 controlled-flood experiments on the Colorado River in Grand Canyon, in 

45
Federal Inter-Agency Sedimentation Conference, 8th, Reno, Nevada, 2006, CD-ROM Proceedings 

(ISBN 0-9779007-1-1). 

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

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

U.S. Department of the Interior, 1996, Record of Decision, operation of Glen Canyon Dam: 

Washington, D.C., Office of the Secretary of the Interior, 13 p. 

Valdez, R.A., and Clemmer, G.C., 1982, Life history and prospects for recovery of the humpback chub 

and bonytail chub, in Miller, W.H., Tyus, H.M., and Carlson, C.A., eds., Fishes of the upper Colorado 

River system—present and future: Bethesda, Md., Western Division, American Fisheries Society, p. 

109-119. 

Valdez, R.A., and Ryel, R.J., 1995, Characterization of the life history and ecology of the humpback 

chub (Gila cypha) in the Colorado River, Grand Canyon, Arizona: Final Report to Bureau of 

Reclamation, Salt Lake City, Utah, contract no. 0 -CS-40 -09110, BIO:WEST Report No. TR-250-08, 

286 p. 

Valdez, R.A., Holden, P.B., and Hardy, T.B., 1990, Habitat suitability curves for humpback chub of the 

upper Colorado River basin: Rivers, v. 1, no. 1, p. 31-42. 

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

flood on fishes of the Colorado River in Grand Canyon, Arizona: Ecological Applications, v. 11, no. 

3, p. 686-700. 

Webb, R.H., 1996, Grand Canyon, a century of change—rephotography of the 1889–1890 Stanton 

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

Webb, R.H., Schmidt, J.C., Valdez, R.A., and Marzolf, G.R., eds., 1999, The controlled flood in Grand 

Canyon: American Geophysical Union, Geophysical Monograph, v. 110, 367 p. 

Wiele, S.M., and Griffin, E.R., 1997, Modification to a one-dimensional model of unsteady flow in the 

Colorado River through the Grand Canyon, Arizona: U.S. Geological Survey Water-Resources 

Investigations Report 97-4046, 17 p. 

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

operations on downstream sand resources of the Colorado River in Grand Canyon, in Gloss, S.P., 

Lovich, J.E., and Melis, T.S., eds., The state of the Colorado River ecosystem in Grand Canyon: U.S. 

Geological Survey Circular 1282, p. 17-31. 

46
Appendixes 

Appendix A. Data from Backwater Inventories Conducted Between February and 

September 2008 

[River miles are downstream from Lees Ferry. River sites as viewed when looking downstream. Source indicates backwaters 

identified in seining trips conducted from 2003 through 2007 (S), analysis of aerial images (I), identified by both sources (S,

I), or during field observations in 2008 (indicated by month). The class is the geomorphic classification described in table 1 

of the text. Study site indicates sites selected for detailed topographic surveys (appendix B). The categories for backwater 

status in February, April, May and July are (0) no backwater present for any discharge within the range of flow fluctuations 

at time of observation; (1) backwater present only for the lower 50 percent of the range of flow fluctuations at time of 

observation; (2) backwater present only for the upper 50 percent of the range of flow fluctuations at time of observation; and 

(3) backwater present across the full range of flow fluctuations at time of observation. The additional categories for 

backwater status in September include a letter indicating whether a backwater was present (P) or absent (A) at the time of 

observation and a numerical code that indicates whether a backwater would be present (1) at flows lower than the steady 

discharge, (2) at flows greater than the steady discharge, or (3) at flows both lower and greater than the steady discharge. A 

double dash (--) indicates backwaters that were not visited in the September inventory.] 

River mile River side Source Class Site1 Status in backwater inventory 

Feb.-08 Apr.-08 May-08 July-08 Sept.-08 

1.10 right S sb 1.2R 0 0 0 0 0 

1.17 right I rb 1.2R 0 0 0 0 0 

1.27 right Feb. rb 1.2R 3 0 0 0 0 

1.38 left S cm 0 1 0 0 A1 

1.58 right S bank 0 0 0 0 0 

1.69 left S bank 3 3 1 0 P1 

1.74 left S sb 0 0 0 0 0 

1.83 right S, I rb 2 0 2 0 P1 

2.41 left S cm 3 0 0 0 0 

2.54 left S, I rb 2.5L 3 1 0 0 A1 

2.69 left S rb 3 2 0 0 A1 

3.13 left Apr. gb 0 1 3 0 A1 

3.18 left Apr. sb 0 2 2 0 A1 

3.22 left S, I rb-gb 3 3 0 0 A1 

3.35 left S, I rb 3.37L 3 2 2 0 A2 

3.47 left S rb 0 0 0 0 P1 

3.53 left S rb 3 2 0 0 P1 

3.73 left S, I rb 0 0 2 0 A2 

3.77 left Feb. rb 3 2 2 0 A2 

4.04 left S sb 3 0 0 0 0 

4.10 left Apr. rb 0 3 3 0 P3 

4.16 left I sb 1 0 0 0 0 

4.18 left I rb 0 0 0 0 0 

4.20 right I rb 2 0 0 0 0 

4.39 left S, I rb 3 0 3 2 P1 

4.50 left S bank 0 3 3 2 0 

4.54 left Feb. cm 1 3 1 0 0 

4.70 left Feb. sb 2 3 3 2 P2 

4.96 left I cm 0 0 0 0 0 

5.21 left Feb. rb 3 0 0 0 0 

47
Appendix A. Data from backwater inventories conducted between February and September 2008.--Continued 

River mile River side Source Class Site1 Status in backwater inventory 

Feb.-08 Apr.-08 May-08 July-08 Sept.-08 

5.50 right S cm 0 0 0 0 0 

5.88 right I bank 1 0 0 0 0 

6.07 left S, I rb 6.07L 3 0 0 0 0 

6.29 right July cm 0 0 0 2 0 

6.70 right I cm 2 0 0 0 0 

7.21 left S cm 2 0 2 0 A2 

7.42 left S rb 2 0 2 2 A2 

8.49 left I gb 0 0 0 0 0 

8.85 left S, I rb 8.9L 3 3 3 2 P1 

9.36 right S, I cm 0 0 0 2 0 

9.49 right Feb. cm 0 0 0 2 A2 

9.66 left Feb. cm 3 0 0 0 A1 

9.84 left S cm 0 0 0 0 A1 

9.86 right S, I rb 0 0 0 0 0 

9.93 left S, I rb 9.93L 3 0 0 1 A1 

10.14 right I rb 3 0 0 1 0 

10.20 right S, I cm 0 0 1 1 0 

10.31 left S cm 2 0 1 1 A1 

10.32 left Feb. cm 2 0 1 1 A1 

10.46 left Feb. rb 3 0 0 1 P1 

10.67 left Feb. rb 3 2 0 1 0 

10.72 left Feb. cm 2 0 0 1 P1 

10.79 left Feb. cm 3 0 0 1 P1 

10.97 left S rb 0 0 0 1 P1 

11.07 left S rb 2 0 0 1 0 

11.24 left S cm 0 0 0 0 0 

11.30 right I bank 0 0 0 1 0 

12.43 left S sb 0 0 0 0 0 

13.22 left I up 3 0 0 0 A1 

14.42 right S bank 2 0 0 1 A1 

15.18 right S bank 0 0 0 0 0 

15.50 right S, I rb 0 1 0 0 A1 

15.61 left S rb 0 0 0 1 0 

15.64 right Feb. bank 2 0 0 1 0 

16.00 right Apr. bank 0 3 3 0 0 

16.01 left S bank 0 0 0 0 0 

16.01 right Apr. bank 0 3 3 0 0 

16.11 left S bank 0 1 1 1 P1 

16.65 left S sb 16.6L 0 0 0 0 0 

17.60 right S rb 17.6R 1 3 2 2 A1 

18.28 right July rb 0 0 0 1 A1 

18.59 left S cm 3 0 0 0 0 

18.86 left Apr. bank 0 1 1 1 P1 

19.37 right S rb 0 0 0 0 0 

19.42 left May up 0 0 3 0 A1 

19.47 left S sb 3 3 3 0 0 

19.60 left S, I rb 1 0 0 2 0 

19.61 right S, I rb 19.61R 3 0 1 1 A1 

19.67 right Feb. cm 1 0 0 0 0 

19.69 right S sb 0 0 0 0 0 

19.71 left S, I rb 1 0 0 0 0 

48
Appendix A. Data from backwater inventories conducted between February and September 2008.--Continued 

River mile River side Source Class Site1 Status in backwater inventory 

Feb.-08 Apr.-08 May-08 July-08 Sept.-08 

19.72 right I rb 0 0 0 0 0 

20.10 right May bank 0 0 1 0 0 

20.13 left S up 2 0 0 2 A2 

20.56 right Feb. cm 1 0 0 0 A1 

21.74 left Feb. sb 0 0 0 0 0 

22.03 right S, I rb 22R 1 3 3 0 P3 

22.16 right S rb 0 0 0 0 A1 

22.26 right Feb. cm 1 0 0 0 A2 

22.29 right Feb. cm 1 0 0 0 0 

22.47 left I cm 0 0 1 0 0 

23.06 left S, I rb 1 3 1 0 P1 

23.09 right S, I rb 0 3 3 0 A1 

23.39 right S, I rb 0 0 1 0 A1 

25.07 left S up 0 0 0 0 0 

25.31 right I rb-br 0 0 0 0 0 

25.61 right S cm 0 0 0 0 0 

25.97 right I up 1 0 0 1 0 

26.08 right May cm 0 0 3 0 0 

26.26 right I rb 0 0 0 1 0 

26.56 left S, I sb 3 0 1 1 0 

26.57 left I rb 0 0 1 1 0 

26.76 left S cm 0 0 0 0 0 

27.03 right I bank 0 0 0 0 0 

27.61 right Apr. up 0 1 0 0 0 

27.75 left S rb 0 3 3 1 P1 

27.84 right Feb. rb 1 2 0 0 0 

27.88 right Feb. up 1 0 0 0 0 

28.19 right S up 0 0 0 0 0 

28.30 right S, I rb 0 0 1 0 A1 

28.85 left S sb 1 0 0 1 A1 

29.19 right Feb. up 1 0 0 1 0 

29.27 right S, I rb 29.28R 0 3 3 0 P3 

29.81 right S sb 1 0 0 1 A2 

30.41 right I st 0 0 0 0 0 

30.51 right S up 0 0 0 0 0 

30.74 right S, I rb 30.7R 1 3 3 0 A3 

30.79 right S rb-ext 30.7R 0 0 0 0 0 

30.97 right S cm 0 0 0 0 0 

31.04 left I bank 0 0 0 0 0 

31.07 right I rb 0 0 0 0 A1 

31.17 right Feb. cm 2 0 0 0 A1 

31.33 right S sb 0 0 0 0 0 

31.48 right Feb. up 3 0 0 0 0 

31.50 left S rb-br 3 0 0 0 P1 

31.57 right Feb. cm 2 0 0 0 0 

31.71 right I up 3 0 0 0 0 

32.09 right Feb. st 2 0 0 0 0 

32.35 right S, I sb 0 0 0 0 0 

32.46 left I bank 0 0 0 0 0 

32.56 left S cm 0 0 0 0 A1 

49
Appendix A. Data from backwater inventories conducted between February and September 2008.--Continued 

River mile River side Source Class Site1 Status of backwater inventory 

Feb.-08 Apr.-08 May-08 July-08 Sept.-08 

32.84 right Feb. cm 3 0 0 0 0 

33.14 left S sb 2 0 0 0 0 

33.22 left S rb 2 0 0 0 P3 

33.30 right S, I rb-br 1 0 0 1 P2 

33.32 left S cm 33.3L 1 0 0 0 0 

33.45 left May bank 0 0 1 0 A1 

33.49 left S cm 0 3 0 0 A1 

33.51 left Feb. cm 1 0 0 0 0 

33.58 left Apr. cm 0 3 0 0 0 

33.64 left Apr. sb 0 3 0 0 A1 

33.67 right S cm 0 0 1 1 A1 

33.77 left Feb. up 2 0 0 0 0 

33.90 right S gb 0 0 0 0 0 

33.93 left May bank 0 0 1 0 0 

34.40 right S bank 0 0 0 0 0 

34.50 right S sb 0 0 0 0 0 

34.88 right Apr. bank 0 1 0 0 0 

35.17 right S st 0 0 0 0 0 

35.20 left S cm 0 0 0 0 0 

35.30 right S cm 0 0 0 1 0 

35.41 right S bank 0 0 0 0 0 

35.47 right S cm 0 0 0 1 A2 

35.63 right S, I rb 35.63R 1 0 0 0 P1 

35.96 left S, I sb 3 3 0 1 A1 

36.20 right S, I rb-br 1 0 0 0 A1 

36.26 left S cm 2 0 0 1 0 

36.52 right S cm 0 0 0 0 0 

37.02 right May st 0 0 2 0 0 

37.05 right S, I sb 0 0 0 2 A1 

37.23 right S st 2 0 0 0 0 

37.31 left S, I rb-br 1 0 0 0 P1 

37.55 right Feb. sb 0 0 0 0 0 

37.57 right S, I rb 37.55R 0 0 0 0 A1 

37.80 left S rb 0 0 0 1 P1 

37.89 right S up 3 0 0 0 A1 

37.92 left S up 3 0 0 0 0 

37.99 left Feb. rb 3 0 0 0 0 

38.02 left S rb 3 0 0 0 A2 

38.09 right S, I rb 0 3 3 0 A1 

38.49 left Feb. cm 3 0 0 0 A1 

38.68 left Feb. cm 2 0 0 0 0 

38.83 left Feb. cm 2 0 1 0 0 

38.88 left S, I cm 1 0 0 0 0 

38.93 right S cm 2 0 0 0 0 

38.99 left Apr. cm 0 3 0 0 0 

39.48 right Feb. cm 2 0 0 0 0 

39.49 right S cm 1 0 0 0 0 

39.57 left Feb. cm 2 0 0 0 0 

39.58 right S cm 2 0 1 1 A2 

50
Appendix A. Data from backwater inventories conducted between February and September 2008.--Continued 

River mile River side Source Class Site1 Status in backwater inventory 

Feb.-08 Apr.-08 May-08 July-08 Sept.-08 

39.60 right Feb. cm 1 0 0 0 0 

39.67 left S, I rb 1 0 0 0 P1 

39.92 left Feb. cm 2 0 0 0 0 

40.16 left S, I rb 1 3 1 0 A1 

40.28 left Feb. cm 2 0 0 0 0 

40.32 right S cm 1 0 0 0 0 

40.38 left S cm 2 0 0 0 0 

40.42 left Feb. bank 3 0 0 0 0 

40.81 right Feb. cm 2 0 0 0 0 

41.03 left I cm 1 0 0 0 0 

41.12 right S, I up 0 0 0 0 0 

41.26 right S st 2 3 0 2 0 

41.40 right S, I rb 41.3R 2 2 2 3 P3 

41.85 right Feb. st 2 0 0 0 A2 

42.04 right S cm 2 0 0 0 A2 

42.74 right S bank 0 0 0 0 0 

42.76 left Apr. bank 0 3 0 0 0 

43.42 left S up 43.4L 0 0 0 0 A1 

43.81 left S, I sb 3 0 0 0 A1 

43.84 left S rb 0 0 0 0 0 

43.86 left May rb-ext 0 0 2 0 0 

43.88 left S sb 1 3 0 1 0 

44.17 right S cm 1 0 0 0 0 

44.57 left Feb. rb 44.5L 1 3 3 0 0 

44.59 left S, I rb 44.5L 1 3 3 3 P3 

45.00 left S, I rb 45L 0 0 2 2 P3 

45.28 left S, I rb 2 2 0 2 0 

45.50 left S rb 0 0 0 0 0 

45.66 left S, I rb 3 0 1 0 P1 

45.89 right S cm 3 1 0 1 0 

45.89 left S, I rb 1 0 0 0 A1 

45.93 right S, I rb 45.93R 1 1 1 1 A1 

45.99 right S rb 1 0 1 1 A1 

46.14 left I sb 0 1 0 1 0 

46.28 right Feb. rb 0 0 0 0 0 

46.39 left S, I rb 46.39L 0 3 1 1 P1 

46.79 left S cm 0 0 0 0 0 

46.82 right S, I cm 0 0 0 0 0 

46.83 left Apr. cm 0 3 0 0 0 

46.88 right I up 1 0 0 0 A1 

47.04 right S, I rb 1 0 0 0 A1 

47.63 right S, I rb 47.6R 2 3 0 1 A1 

47.76 right S cm 0 0 0 0 0 

47.81 left S sb 0 0 0 1 0 

47.84 right S rb 0 0 0 0 0 

47.86 left S cm 0 0 0 1 0 

47.98 left S, I rb 1 3 3 1 A1 

48.14 right S cm 0 0 0 0 0 

48.25 left Feb. sb 2 0 0 0 0 

51
Appendix A. Data from backwater inventories conducted between February and September 2008.--Continued 

River mile River side Source Class Site1 Status in backwater inventory 

Feb.-08 Apr.-08 May-08 July-08 Sept.-08 

48.34 right S gb 0 0 0 1 0 

48.47 left S cm 0 0 0 2 0 

48.65 right S, I up 1 3 3 3 A1 

48.78 right S, I rb 48.79R 1 3 3 0 A3 

48.91 right I sb 1 0 0 1 0 

48.92 left S, I rb 48.91L 2 0 0 1 A1 

49.11 left S cm 0 0 0 0 0 

49.31 right S up 2 0 0 1 P1 

49.36 right Feb. rb 2 0 0 0 P1 

49.38 left S gb 3 0 0 0 A2 

49.52 right I up 1 2 2 0 A2 

49.55 left S bank 0 0 0 0 A1 

49.84 right Apr. bank 0 2 0 0 0 

49.98 right S, I up 3 2 2 0 A1 

50.19 right S, I rb 50.1R 0 0 1 0 A1 

50.24 right I rb-ext 0 0 0 0 0 

50.29 left S, I rb 50.28L 3 0 0 0 A1 

50.34 right S rb 2 3 0 0 A1 

50.48 left Feb. cm 2 0 0 0 0 

50.65 left S, I rb 50.64L 1 3 0 0 P1 

50.73 left S rb-ext 50.64L 1 0 1 0 0 

50.81 left S cm 3 1 0 0 A1 

50.84 right Feb. cm 1 0 0 0 A2 

50.88 right Feb. cm 2 0 0 0 0 

50.90 left S, I rb 50.91L 0 0 0 0 A1 

50.92 right Apr. bank 0 3 0 0 0 

50.95 left S, I rb 50.91L 0 0 0 1 P2 

51.04 left S rb 0 0 0 0 0 

51.11 right I rb 1 3 0 1 A1 

51.40 left S, I rb 51.5L 0 0 0 0 A1 

51.43 left Feb. rb 51.5L 2 0 0 0 0 

51.46 left S rb-ext 51.5L 0 3 0 0 A1 

51.49 right I rb 1 3 0 1 A1 

51.53 right Feb. cm 2 0 0 0 0 

51.67 left S, I sb 0 0 0 0 0 

51.68 left I rb 0 0 0 0 P1 

51.75 right I cm 0 0 0 0 0 

51.76 right I cm 0 0 0 0 0 

51.88 right I rb 0 0 0 0 0 

52.07 right I up 0 0 0 0 A1 

52.13 left May cm 0 0 3 0 0 

53.14 right Apr. rb-gb 0 3 3 0 0 

53.29 right S rb-gb 1 0 3 3 P3 

53.30 right S, I rb-gb 1 3 3 1 A2 

53.54 right S sb 0 0 2 0 0 

53.95 right I rb 0 0 0 1 P1 

53.95 left Apr. rb 0 3 0 0 0 

54.28 right May sb 0 0 1 0 0 

54.45 right I up 2 0 2 1 0 

52
Appendix A. Data from backwater inventories conducted between February and September 2008.--Continued 

River mile River side Source Class Site1 Status in backwater inventory 

Feb.-08 Apr.-08 May-08 July-08 Sept.-08 

54.54 right S, I rb 54.6R 1 0 1 1 P1 

54.60 right Feb. rb-ext 54.6R 3 0 0 0 A2 

54.61 left S, I rb 0 0 1 0 0 

54.66 left S rb-ext 0 0 0 0 A1 

54.82 right S, I cm 1 0 0 0 A1 

54.85 left S, I rb 3 3 1 1 P1 

54.91 left I rb 1 0 1 1 A1 

55.02 right S rb 55.02R 3 2 0 1 A1 

55.52 left S, I rb 0 0 0 0 A1 

55.53 right S rb 0 0 0 0 A1 

55.74 left S rb 3 3 1 0 A1 

55.87 right S, I rb 55.9R 2 0 0 0 A1 

55.92 right Feb. rb-ext 55.9R 2 0 0 0 A1 

55.95 left S cm 2 0 0 0 A1 

56.54 right S sb 56.6R 1 1 0 0 0 

56.54 right S sb 56.6R 1 1 0 0 0 

57.13 right I sb 0 0 0 0 0 

57.31 right S sb 0 0 3 0 A1 

57.32 right S, I sb 1 0 3 0 A2 

57.53 left S, I rb 1 3 3 1 A1 

57.55 left Apr. cm 0 3 0 0 0 

57.75 left S, I rb 57.75L 0 0 0 1 A1 

58.08 left I rb 58.1L 0 3 3 1 0 

58.18 right Feb. sb 0 0 0 0 0 

58.30 left S, I rb-gb 0 0 0 0 A1 

58.63 right I rb 0 2 0 1 0 

58.74 right S, I rb 58.72R 1 0 2 0 A3 

58.80 left S, I cm 0 0 2 0 0 

59.05 left S cm 0 0 0 0 0 

59.18 left S, I rb 59.19L 1 0 0 1 A1 

59.29 left S rb-ext 1 0 0 0 A1 

59.33 right S cm 3 0 0 1 0 

59.38 left I up 0 0 0 0 0 

59.43 left Feb. st 2 0 0 0 0 

59.48 left S, I rb 59.48L 2 3 1 0 A1 

59.57 right Sept. cm 0 0 0 0 P1 

59.64 right I rb 0 0 0 0 P1 

59.79 left Feb. up 1 3 0 0 A1 

59.86 left S, I rb 1 0 1 1 0 

59.90 right S cm 1 0 0 0 0 

59.98 left S cm 0 0 0 0 0 

60.56 right S, I rb 0 0 0 1 A1 

60.61 left I rb 0 3 0 0 0 

60.88 left S, I rb 0 0 0 0 A1 

60.93 left I rb-ext 0 1 0 0 A1 

61.19 right S, I rb 0 3 3 1 A1 

61.27 left S, I rb 3 0 0 3 0 

61.30 left S rb-ext 0 3 3 0 0 

61.43 right S rb 1 0 0 0 0 

53
Appendix A. Data from backwater inventories conducted between February and September 2008.--Continued 

River mile River side Source Class Site1 Status in backwater inventory 

Feb.-08 Apr.-08 May-08 July-08 Sept.-08 

61.44 right Feb. rb-ext 1 0 0 0 P1 

61.62 right I st 0 0 0 0 0 

61.66 left S cm 0 0 0 0 0 

61.95 left S gb 0 0 0 0 0 

61.97 right I gb 0 0 0 0 0 

62.30 left S, I rb 62.3L 0 0 0 0 A1 

62.32 left Feb. rb 62.3L 1 0 0 0 A1 

62.34 left Feb. rb 62.3L 3 0 0 0 A1 

62.49 right S up 0 0 0 0 P1 

62.69 right I rb 0 0 0 0 0 

63.04 right S, I st 0 2 1 0 A2 

63.07 left S, I rb 1 3 3 0 0 

63.09 right S rb 1 0 3 2 A3 

63.59 left I rb 63.6L 0 0 3 0 0 

63.62 left Apr. rb-ext 63.6L 0 3 2 0 A2 

63.74 left S sb 0 3 0 0 0 

63.90 left I up 0 3 0 0 0 

64.13 right S sb 0 0 0 0 0 

64.23 left S, I up 0 0 1 0 A1 

64.34 left S, I rb 64.36L 0 3 3 0 0 

64.51 left I rb-ext 64.5L 1 3 0 0 A2 

64.59 left May bank 0 0 3 0 0 

64.63 left S, I sb 0 3 0 0 0 

64.71 left I rb 0 3 0 0 P3 

64.93 left S, I rb 64.93L 0 0 0 0 P1 

64.97 right I cm 0 0 0 0 0 

65.07 right S st 0 0 0 0 A2 

65.18 right I rb 65.1R 0 3 3 3 0 

65.31 left S, I rb 0 0 0 0 P1 

65.77 left S, I rb 65.8L 0 3 3 3 0 

65.83 right S rb-br 3 0 0 0 A2 

66.15 left S, I rb 66.11L 3 0 3 0 A2 

66.64 left S gb 0 0 2 0 0 

66.83 left Apr. gb 0 2 0 0 A1 

67.43 left S, I rb 67.43L 3 3 1 0 A1 

68.15 left I cm 0 0 0 0 0 

68.52 left S, I rb 68.49L 3 0 1 0 A1 

68.81 right S rb-gb 68.8R 3 3 0 0 A1 

69.79 right S, I rb 0 0 0 0 P1 

69.79 left Apr. cm 0 2 0 0 0 

69.84 right I rb-ext 0 0 0 0 0 

69.94 right S cm 0 3 0 0 0 

70.40 left S cm 0 0 0 0 0 

71.01 right S rb-gb 0 0 0 0 A1 

71.07 left S rb 3 0 0 0 P1 

71.17 left S cm 2 0 0 0 A1 

71.32 left S cm 0 2 0 0 0 

71.44 left S cm 0 0 0 0 0 

71.67 left I rb 71.67L 1 0 0 0 A1 

54
Appendix A. Data from backwater inventories conducted between February and September 2008.--Continued 

River mile River side Source Class Site1 Status in backwater inventory 

Feb.-08 Apr.-08 May-08 July-08 Sept.-08 

71.68 right S cm 1 0 0 0 P1 

71.78 right S cm 0 0 0 0 0 

71.83 right S st 0 0 0 0 0 

72.42 right S, I rb 2 0 0 0 A1 

72.54 right S rb 72.54R 0 0 0 0 0 

72.71 left S rb-gb 0 0 1 0 A2 

72.82 right S st 0 0 0 0 0 

74.03 right I gb 0 0 0 0 0 

74.16 right I gb 0 0 0 0 0 

74.19 right S, I gb 0 0 0 0 0 

74.51 right S sb 0 0 0 0 A1 

74.95 right S, I rb 0 0 0 0 A1 

75.54 left I cm 0 0 0 0 0 

76.34 right S rb 0 0 0 0 A1 

76.40 left S cm 0 0 0 0 0 

76.58 left S rb 0 3 3 0 A1 

76.63 left S, I rb-ext 0 0 1 0 0 

76.97 right I cm 3 0 0 0 A1 

76.99 right I cm 0 0 0 0 0 

77.02 right I cm 0 0 0 0 0 

77.12 left I up 1 0 0 0 A1 

78.00 right I rb 0 0 0 0 0 

78.01 right S, I rb-br 1 0 0 0 0 

78.04 left Sept. up 0 0 0 0 P1 

78.60 right S st 0 0 0 0 0 

78.74 left S bank 0 0 0 0 0 

84.42 left S bank 0 0 0 0 0 

84.54 right S up 84.6R 0 0 0 0 0 

84.57 right Feb. up 84.6R 0 0 0 0 P1 

87.03 left S rb 0 0 0 0 A1 

87.51 right Feb. rb-br 3 0 0 0 0 

87.57 right Feb. bank 2 0 0 0 0 

87.58 left May up 87.6L 0 0 1 0 0 

87.61 right I rb-br 0 3 3 0 P1 

87.89 left S, I rb-br 87.87L 0 0 0 1 

88.06 right S up 88.1R 3 3 0 0 

88.09 right Feb. up 88.1R 2 0 0 0 

89.13 right Feb. gb 0 0 0 0 

90.66 right I rb-br 0 0 0 0 

90.66 left I rb-br 1 0 0 0 

92.22 left S rb-br 0 0 0 0 

92.22 right Apr. bank 0 2 0 0 

92.36 left Apr. cm 0 2 1 0 

92.82 left I sb 0 0 0 0 

93.07 left Feb. up 3 0 0 0 

93.32 left I cm 0 0 0 0 

93.78 left S, I rb-br 93.8L 0 0 3 1 

93.79 right Feb. rb-br 3 3 0 0 

93.81 right Feb. rb-br 1 0 0 0 

55
Appendix A. Data from backwater inventories conducted between February and September 2008.--Continued 

River mile River side Source Class Site1 Status in backwater inventory 

Feb.-08 Apr.-08 May-08 July-08 Sept.-08 

94.11 right S gb 1 0 0 0 

94.24 right S gb 1 0 0 0 

94.81 left Apr. bank 0 3 0 0 

95.03 right S rb 0 0 0 0 

95.93 right S rb-br 0 0 0 0 

96.04 left S bank 2 0 0 0 

96.13 right S bank 0 0 0 0 

96.37 right S, I rb-br 0 0 0 0 

96.46 left S bank 0 0 0 0 

96.57 right I rb-br 0 0 0 0 

97.48 right I bank 3 0 0 0 A1 

97.49 right S, I bank 0 0 3 0 A1 

97.54 right I rb-br 3 3 0 0 P1 

97.72 right Feb. cm 1 0 0 0 A1 

97.80 left S cm 0 0 0 0 0 

98.34 left S cm 0 0 0 1 0 

98.45 right I rb-br 0 0 0 1 P1 

99.63 left I rb 0 1 0 0 P1 

100.00 right I up 0 2 0 0 A1 

101.63 right S rb-br 0 0 0 0 0 

103.05 right S, I rb-br 0 0 0 1 0 

104.42 right I up 104.4R 0 0 0 0 0 

105.84 right S cm 0 0 0 0 0 

112.56 right S, I rb 3 0 0 1 A1 

113.94 right Feb. up 3 0 0 0 0 

114.08 left S bank 3 0 0 0 0 

114.10 right Sept. cm 0 0 0 0 A2 

114.39 left S bank 0 0 0 1 0 

114.46 left S bank 0 0 0 1 0 

114.68 left S, I rb-br 3 3 0 0 0 

114.73 left Feb. bank 3 0 0 0 0 

115.04 left S st 2 0 0 0 0 

115.08 right S st 0 0 0 0 0 

115.49 left S st 2 0 0 0 0 

115.70 left S rb-gb 0 0 0 0 0 

115.72 left S bank 0 0 0 0 0 

115.89 left S, I rb-br 0 0 0 0 A1 

115.94 left S, I rb 0 0 0 1 A1 

116.21 right Feb. sb 3 0 1 0 0 

116.31 right May up 0 0 1 0 0 

116.45 right Apr. rb 0 3 0 0 0 

116.48 left S rb 116.5L 0 0 0 0 A1 

116.86 right Feb. rb-br 1 0 1 0 0 

117.16 left S up 0 0 0 0 0 

118.08 left I rb-br 0 0 0 0 0 

118.29 right S, I rb-br 2 0 1 0 A1 

118.40 right Feb. st 0 0 0 0 0 

118.58 right S cm 1 0 0 0 0 

118.76 right S rb 0 0 0 0 0 

56
Appendix A. Data from backwater inventories conducted between February and September 2008.--Continued 

River mile River side Source Class Site1 Status in backwater inventory 

Feb.-08 Apr.-08 May-08 July-08 Sept.-08 

118.78 left I rb 0 0 1 0 0 

118.79 left May cm 0 0 1 0 0 

119.04 right S, I rb 119R 1 2 0 0 A1 

119.40 right S rb 119.4R 0 0 3 0 0 

119.60 left May cm 0 0 1 0 0 

119.74 right S, I rb 119.8R 1 3 1 1 A1 

119.91 left S, I rb 119.9L 0 3 1 0 A1 

119.96 left S rb-ext 0 0 0 0 A1 

120.13 left I rb 120.1L 0 3 0 1 A1 

120.14 right May rb 0 0 0 0 0 

120.32 left S, I sb 0 0 0 0 A3 

120.48 left Apr. cm 0 2 0 0 0 

120.50 right S, I rb 120.5R 1 3 0 0 0 

120.78 right S sb 0 3 0 0 0 

120.98 left July gb 0 0 0 2 A2 

121.10 left S, I up 0 2 2 1 A1 

121.13 left Apr. up 0 3 1 0 0 

121.34 right S, I rb 0 0 0 0 0 

121.50 left S, I rb 121.6L 1 1 0 0 0 

121.55 left Apr. rb-ext 121.6L 0 2 1 0 0 

121.81 right S bank 0 1 0 0 0 

121.85 left S, I rb 121.9L 0 3 3 3 P1 

121.87 left Apr. rb-ext 121.9L 0 2 3 3 A1 

122.70 right S, I rb 122.7R 1 3 3 1 P3 

122.93 left S, I rb 122.93L 0 3 3 2 A1 

122.96 left Feb. rb 122.93L 3 0 0 0 0 

123.23 left S, I rb 123.3L 1 1 1 1 P1 

123.56 right S up 0 0 0 0 A2 

123.71 right July rb-gb 0 0 0 3 P3 

123.83 left S cm 0 0 0 0 0 

123.86 left Feb. bank 1 0 0 0 0 

123.89 right S cm 0 0 0 0 0 

123.90 left May up 0 0 1 0 0 

124.08 left I up 0 0 0 0 0 

124.35 right S rb 0 0 1 1 0 

125.18 right S cm 0 0 0 0 0 

125.22 left I cm 0 0 0 0 0 

126.21 right Sept. rb 0 0 0 0 A1 

126.23 right Apr. st 0 2 1 0 P3 

126.29 left Feb. cm 1 0 0 0 0 

126.38 left S cm 3 0 1 0 0 

126.83 left I rb 126.9L 0 0 0 0 A1 

126.86 right S, I rb 126.9R 2 0 1 1 P1 

127.00 right July up 0 0 0 2 A2 

127.29 right S rb 127.3R 0 1 0 1 A1 

127.44 right I up 0 0 0 0 0 

127.46 right S, I up 0 0 0 0 A1 

127.86 right S bank 0 0 0 0 0 

127.96 right Feb. bank 1 0 0 0 0 

57
Appendix A. Data from backwater inventories conducted between February and September 2008.--Continued 

River mile River side Source Class Site1 Status in backwater inventory 

Feb.-08 Apr.-08 May-08 July-08 Sept.-08 

133.81 right S, I cm 1 0 0 0 0 

133.84 right I cm 1 0 0 0 A1 

134.27 right S rb-br 0 0 0 1 A1 

134.91 right S st 0 0 0 0 0 

134.93 right S st 0 0 0 0 0 

136.43 left S rb-br 0 0 0 0 0 

136.52 left S rb-br 1 0 0 0 0 

137.32 left I cm 0 0 0 0 0 

137.56 right S cm 0 0 0 0 A1 

137.59 right S rb 0 0 0 0 A1 

137.66 left S, I rb 137.7L 3 3 1 1 P1 

137.76 left S, I rb 2 0 0 0 0 

138.00 right S, I rb 0 3 0 0 0 

138.23 left Feb. rb 3 0 0 0 A2 

138.97 left S rb 3 2 1 0 A1 

139.14 left S, I up 3 3 1 1 A1 

139.34 right S sb 0 0 0 0 0 

139.59 right I up 139.6R 1 0 1 1 0 

140.01 right S bank 0 0 0 0 0 

140.35 left S, I up 0 0 0 1 A1 

141.41 left S rb 0 0 1 1 0 

141.50 left I rb 1 0 0 0 0 

141.65 left Feb. cm 3 0 0 0 0 

142.18 right S rb 0 0 1 1 A1 

143.06 right S rb 1 2 0 0 0 

143.86 left S st 0 0 1 1 A1 

145.38 left S cm 0 0 0 0 0 

145.71 left S rb 0 0 0 0 0 

145.84 left S rb 145.9L 3 0 1 1 0 

146.42 right I rb 0 0 0 0 A1 

146.72 left Feb. bank 3 0 0 0 0 

146.88 left May sb 0 0 1 0 0 

148.21 right S bank 3 0 1 0 A1 

148.40 left S st 0 0 0 0 0 

148.75 left S st 0 0 0 0 0 

151.31 right S rb 0 0 3 0 A1 

151.48 left S up 0 0 0 0 0 

151.96 right Feb. bank 3 0 0 0 0 

151.97 left Feb. bank 1 0 0 0 A1 

152.20 left S rb 0 0 1 0 0 

155.71 right S st 0 0 1 0 0 

155.72 right Feb. sb 3 0 0 0 0 

155.84 right S rb 0 0 0 0 0 

157.22 right I rb-br 1 0 0 0 0 

159.70 left S st 3 0 0 1 A2 

159.91 right S cm 0 0 0 1 A1 

160.11 right S cm 0 0 0 0 0 

160.63 right S rb 0 0 0 1 A1 

160.67 right S rb 0 0 1 0 0 

58
Appendix A. Data from backwater inventories conducted between February and September 2008.--Continued 

River mile River side Source Class Site1 Status in backwater inventory 

Feb.-08 Apr.-08 May-08 July-08 Sept.-08 

161.25 left S cm 3 0 1 1 P1 

161.25 right S up 1 0 0 1 A1 

161.48 right S rb 0 0 0 0 0 

161.49 left S bank 0 2 0 1 A1 

161.55 right S up 1 0 0 1 A1 

161.59 left S bank 0 0 0 0 A1 

161.67 right S rb 3 0 0 0 A1 

161.83 right S sb 2 0 0 0 0 

161.93 left S sb 0 0 0 2 A1 

162.00 right S, I sb 0 0 0 0 0 

162.10 left S, I up 0 0 0 0 0 

162.15 left S, I rb 3 2 0 0 A1 

162.26 left S up 2 0 0 0 A2 

162.83 right S cm 0 0 0 0 0 

163.29 right I up 0 3 0 0 0 

163.56 right I rb 1 0 0 0 0 

164.34 left I cm 0 0 0 0 0 

164.43 left S, I st 3 0 1 1 P1 

164.49 left Feb. sb 1 0 1 1 0 

164.96 right S, I up 2 0 0 1 A1 

165.30 left S, I rb 165.3L 0 3 1 1 A1 

165.33 left Apr. rb-ext 165.3L 0 3 1 1 0 

165.45 left S, I rb 0 0 0 0 0 

165.50 left May rb 0 0 1 0 0 

165.65 right S, I rb 165.7R 2 0 0 2 A1 

165.80 right S, I rb 0 0 0 1 0 

165.91 left S rb 1 0 0 0 P1 

165.97 right S, I rb 1 0 1 1 0 

166.08 right S rb 0 2 0 0 0 

166.26 left I rb 0 0 0 0 0 

166.30 right I up 0 0 0 0 0 

166.38 right I rb 2 0 0 0 0 

166.53 right S cm 0 0 0 0 0 

166.66 right May bank 0 0 1 0 0 

166.88 left S up 3 0 1 2 P3 

167.35 right S cm 0 0 0 0 0 

167.42 right S gb 1 0 1 0 0 

167.47 right Feb. cm 1 0 0 1 A1 

167.50 right S, I rb 1 0 0 0 P1 

167.67 right Feb. cm 3 0 0 1 P1 

167.75 left Feb. st 2 0 0 0 0 

167.80 left S rb 3 0 1 1 0 

167.85 right S, I rb 0 0 1 1 A1 

168.04 right S, I rb 168.1R 1 0 0 1 A1 

168.06 left S, I rb 1 0 0 1 P1 

168.14 right S bank 1 0 0 1 A1 

168.17 right S, I rb 0 0 0 0 A1 

168.25 right I rb 0 0 0 0 A1 

168.32 right S, I rb 1 0 0 1 P1 

59
Appendix A. Data from backwater inventories conducted between February and September 2008.--Continued 

River mile River side Source Class Site1 Status in backwater inventory 

Feb.-08 Apr.-08 May-08 July-08 Sept.-08 

168.44 right S, I up 1 0 0 0 A1 

168.49 right S st 1 0 0 0 0 

168.75 left S, I rb-br 0 0 1 0 0 

168.76 right S, I rb 0 0 1 0 A1 

168.86 left S rb 0 0 0 0 0 

168.94 left S cm 1 0 0 0 0 

169.06 left S cm 0 0 0 0 A1 

169.18 left S, I rb 3 3 0 0 A1 

169.22 right S rb 1 3 0 1 A1 

169.30 left S bank 1 0 0 0 A1 

169.35 left S cm 0 0 0 0 P1 

170.23 left S cm 0 0 0 0 P1 

170.60 right S, I rb 0 0 0 0 0 

170.75 right I sb 0 0 0 0 0 

170.89 left S, I rb 1 0 0 0 A1 

171.06 left Feb. rb 1 0 0 0 A1 

171.25 left May rb 0 0 1 0 0 

171.70 right S, I rb 1 0 0 0 0 

171.78 left S, I up 1 2 0 1 A1 

172.13 left I rb 0 2 1 0 A1 

172.22 left S rb-ext 0 0 0 0 0 

172.55 left S, I rb 172.6L 2 3 3 1 A1 

172.70 left S rb 172.7L 1 3 1 1 P1 

172.92 left Feb. rb 1 0 0 0 0 

173.07 right S rb 0 0 1 1 A1 

173.09 left S rb 1 0 0 1 0 

173.28 left I up 0 0 0 0 A1 

173.29 right I rb 0 0 2 0 0 

173.48 right S, I rb 0 0 1 1 A1 

173.51 right Apr. rb-ext 0 3 0 0 0 

173.65 right I up 0 0 0 0 0 

173.81 right I rb 1 0 0 0 A1 

173.91 right I cm 0 0 0 0 0 

174.21 right S up 0 0 0 0 0 

174.34 left S, I rb 3 0 0 1 A1 

174.47 right I rb 0 0 0 0 A1 

174.60 left Feb. gb 0 0 0 0 0 

174.70 left I rb 0 0 0 0 0 

175.14 left S sb 0 0 0 0 0 

175.39 right S, I rb 175.4R 0 0 0 1 P3 

175.68 right I rb 0 0 0 0 0 

176.04 right S, I rb 176.1R 0 3 3 1 A1 

176.11 right Apr rb-ext 176.1R 0 3 3 0 A1 

176.39 right S rb 1 0 0 0 A1 

176.58 right S cm 0 0 0 0 0 

176.67 left I cm 0 0 0 0 A1 

176.94 right S, I rb 0 3 3 1 A1 

177.04 right I up 1 0 0 1 0 

177.06 left S rb 1 0 1 0 0 

60
Appendix A. Data from backwater inventories conducted between February and September 2008.--Continued 

River mile River side Source Class Site1 Status in backwater inventory 

Feb.-08 Apr.-08 May-08 July-08 Sept.-08 

177.38 left I rb 0 0 0 0 A1 

177.48 left S, I rb 1 2 0 1 A1 

177.60 left May st 0 0 1 0 0 

177.76 left I rb 0 0 0 0 0 

177.93 S gb 3 0 0 0 A1 

178.04 left S cm 2 0 0 0 A2 

178.18 right S rb 0 3 1 0 A1 

178.26 right S, I rb 0 0 1 0 A1 

178.41 right S, I rb 1 0 1 1 P1 

178.63 left Feb. rb 1 3 0 0 0 

178.68 right I rb 0 0 0 0 0 

178.79 left S, I rb 0 0 1 0 0 

178.98 left S, I rb 0 0 1 0 A1 

179.06 right S rb 0 0 0 0 0 

179.28 right S, I rb 179.3R 3 0 0 0 A1 

180.50 left S gb 0 0 1 0 A1 

181.21 left S, I rb 0 2 0 0 0 

181.37 right S, I rb 181.4R 1 1 0 1 P1 

181.58 left S, I up 3 0 0 0 0 

181.64 left Feb. rb 1 0 0 0 0 

181.68 left S, I rb 1 0 0 0 A1 

181.80 right S, I rb 0 0 0 0 A1 

181.93 left S cm 0 0 0 0 0 

182.12 right Sept. sb 0 0 0 0 P1 

182.18 left S, I rb 0 0 0 0 P1 

182.33 left S up 0 3 0 0 A1 

182.39 right S up 0 0 0 0 0 

182.61 right S gb 0 0 0 0 0 

182.78 right S, I rb 0 3 0 0 A1 

182.94 right S, I sb 1 0 2 0 A1 

183.29 right S, I rb 183.3R 0 2 1 0 P1 

183.73 left S cm 1 0 0 0 0 

183.85 left S rb 0 0 0 0 0 

184.47 right I rb-gb 0 0 0 0 0 

184.53 right Apr. rb-gb 0 1 1 0 0 

184.77 right S cm 1 0 0 0 0 

184.80 right Feb. cm 0 0 0 0 A1 

184.82 left Apr. cm 0 2 0 0 0 

184.93 left S, I rb 1 0 2 0 A1 

185.50 left S, I up 0 0 0 1 0 

185.53 left S up 2 0 0 0 0 

185.82 right S, I rb 0 1 0 0 0 

186.00 left S, I rb 1 0 0 1 A1 

186.03 right Feb. up 1 0 0 0 0 

186.38 right S, I rb 3 3 2 1 0 

186.58 left S, I up 0 0 0 1 0 

186.74 left I rb 0 3 0 0 0 

186.77 left S, I rb-ext 0 0 0 0 0 

186.77 right I rb 0 0 0 0 A1 

61
Appendix A. Data from backwater inventories conducted between February and September 2008.--Continued 

River mile River side Source Class Site1 Status in backwater inventory 

Feb.-08 Apr.-08 May-08 July-08 Sept.-08 

186.87 left I rb 0 0 0 0 A1 

187.04 right S rb 0 0 0 0 0 

187.10 left S, I rb 1 0 0 1 A1 

187.15 left S rb-ext 0 0 0 0 A1 

187.27 right S, I cm 0 0 0 0 0 

187.85 right Apr. cm 0 2 0 0 0 

187.95 right S, I rb 188R 0 3 1 0 A1 

187.99 right S rb 188R 1 0 0 0 A1 

188.48 right Feb. st 2 0 0 0 0 

189.82 right S, I gb 0 0 0 0 A1 

190.03 left Feb. up 2 0 0 0 0 

190.22 left I bank 0 0 0 0 0 

190.24 left I bank 0 0 0 0 0 

190.39 right I gb 0 2 0 0 0 

190.41 right Apr. gb 0 3 1 0 A1 

190.50 left S, I bank 2 0 0 0 A1 

190.53 left S bank 3 0 0 0 A1 

190.69 left S, I up 0 0 0 0 A1 

190.83 left S, I rb 0 0 1 0 0 

191.52 right Sept. gb 0 0 0 0 P1 

191.80 right S, I rb 0 0 1 0 A1 

191.91 left S, I rb 0 0 0 0 A1 

191.95 right S, I rb 1 0 0 0 0 

192.09 S gb 0 0 1 0 A1 

192.14 left S cm 0 0 0 0 0 

192.24 left S rb 2 0 0 0 A1 

192.40 right S gb 0 0 0 1 A1 

192.42 left I rb 0 0 0 0 A1 

192.50 right S gb 0 0 0 0 A1 

192.78 right S, I rb-gb 0 0 0 0 A1 

193.37 left I rb 0 0 0 0 0 

193.83 right I cm 0 0 0 0 0 

194.03 left I rb-br 0 0 0 0 0 

194.53 right S, I rb 1 0 1 1 A1 

194.56 left S, I rb 194.6L 1 3 0 2 P1 

194.60 right S rb-ext 2 0 0 0 0 

195.55 right S, I cm 0 0 0 0 0 

196.05 right S, I rb 196.1R 1 2 1 0 A1 

196.19 left S gb 0 0 0 0 A1 

196.31 right Feb. sb 196.4R 1 0 0 0 0 

196.35 right Feb. rb 196.4R 1 0 0 0 0 

196.37 right S, I rb 196.4R 2 0 0 1 A1 

197.07 left S rb 0 0 0 0 0 

197.20 left May cm 0 0 1 0 0 

197.28 right S rb 0 0 1 0 P1 

197.89 right S, I rb 197.9R 1 0 1 0 0 

198.00 left S, I sb 0 1 1 1 P1 

198.02 right Feb. rb 3 3 3 0 0 

198.06 left Feb. rb 0 0 0 0 0 

62
Appendix A. Data from backwater inventories conducted between February and September 2008.--Continued 

River mile River side Source Class Site1 Status in backwater inventory 

Feb.-08 Apr.-08 May-08 July-08 Sept.-08 

198.15 left S up 0 0 1 0 0 

198.20 right I sb 0 0 0 0 0 

198.25 left S, I rb 0 3 0 0 A1 

198.37 right S, I rb 0 0 1 0 0 

198.90 right S st 3 0 0 0 P3 

199.28 right Apr. gb 0 1 0 0 A2 

199.51 left S, I rb 199.5L 1 0 2 0 P1 

199.53 right S rb 199.5R 0 3 3 0 A1 

199.86 left May gb 0 0 2 0 0 

200.32 left S, I rb 1 0 0 0 A1 

200.50 right S, I sb 1 0 1 0 0 

200.54 left S rb 0 0 1 0 A1 

200.64 left S, I cm 0 0 0 0 A1 

200.89 left I rb 0 0 0 1 P1 

200.95 right S, I rb 0 3 3 0 A1 

200.96 left I rb-ext 0 0 0 0 0 

201.28 right S, I rb 0 2 0 0 P1 

201.31 right S rb-ext 0 2 0 0 0 

201.65 right S, I rb 201.7R 1 3 3 1 A3 

201.72 right Feb. bank 1 0 0 0 A1 

201.80 right Sept. cm 0 0 0 0 P1 

202.64 right Feb. cm 0 0 0 0 0 

202.77 right S rb 0 0 0 0 A1 

202.86 right S, I rb 1 0 1 0 A1 

203.14 left Apr. cm 0 2 1 0 0 

203.22 left I gb 0 0 0 0 0 

203.35 left May gb 0 0 3 0 A1 

203.43 right I rb 1 0 1 0 0 

203.51 left S, I rb 0 0 0 0 0 

203.55 left I rb-ext 0 0 0 0 A1 

203.81 left S, I rb 0 3 0 0 0 

204.17 right S, I rb 0 0 0 0 A1 

204.36 right S, I rb 204.4R 0 3 3 1 A1 

204.42 right S rb-ext 0 0 3 0 0 

204.60 left I rb 1 0 1 0 A1 

204.66 right Feb. sb 3 0 0 0 0 

204.66 left S rb 0 0 2 0 A1 

204.67 right S sb 3 0 0 0 0 

204.69 left S rb 0 0 0 0 0 

204.84 right Feb. rb 1 0 2 0 A2 

204.89 right S, I rb-ext 0 0 0 0 0 

205.21 right S, I rb 3 0 0 0 0 

205.22 left S rb 205.2L 0 3 3 3 A3 

205.23 right S, I rb 3 0 0 0 A1 

205.73 left Feb. sb 2 0 0 0 0 

206.66 right S, I rb 206.7R 0 3 3 0 A2 

207.08 right Apr. bank 0 3 0 0 0 

207.45 right S cm 0 0 0 0 0 

207.72 right S gb 0 0 0 1 A1 

63
Appendix A. Data from backwater inventories conducted between February and September 2008.--Continued 

River mile River side Source Class Site1 Status in backwater inventory 

Feb.-08 Apr.-08 May-08 July-08 Sept.-08 

207.94 left S, I rb-gb 1 3 0 0 0 

207.97 right S sb 0 0 0 0 0 

208.11 right Feb. cm 1 0 0 0 0 

208.40 left S, I rb 1 0 0 0 A1 

208.56 right S cm 0 0 1 0 0 

208.61 left I rb-br 0 0 0 0 0 

209.00 right Feb. st 3 0 2 0 0 

209.62 left S gb 3 3 0 0 A1 

210.64 right S cm 0 0 0 0 0 

210.77 right S rb 1 0 0 0 A1 

211.01 right Feb. cm 3 0 0 0 0 

211.12 right S rb 0 0 0 0 A1 

211.37 left S, I rb 211.4L 0 0 0 0 A1 

211.62 left S, I rb 1 3 1 0 P1 

211.83 right S, I rb-gb 211.8R 3 0 0 0 P1 

211.86 right I rb-ext 211.8R 0 0 0 0 A1 

212.85 left S cm 0 0 0 0 0 

213.01 right S, I rb 213R 0 1 1 0 A1 

213.27 left S up 213.3L 0 0 0 0 0 

213.27 right I rb 0 0 0 0 0 

214.44 right S rb 214.5R 0 0 1 0 P1 

214.55 left I rb 0 0 0 0 A1 

214.55 right May sb 0 0 2 0 0 

214.67 left S bank 0 0 0 0 0 

214.85 right I cm 0 0 0 0 0 

214.89 right S, I cm 0 0 0 0 0 

214.94 left I cm 0 0 0 0 0 

215.30 left I rb 3 0 1 0 0 

215.51 left S rb 1 0 0 0 0 

215.83 left I rb 0 0 0 0 0 

215.95 right I cm 0 0 0 0 0 

216.37 left Apr. up 0 2 0 0 A1 

216.64 right S, I rb 216.6R 0 2 0 0 0 

216.67 right Apr. rb-ext 216.6R 0 3 0 0 0 

217.08 left I up 0 3 0 0 0 

217.09 left Apr. up 0 3 0 0 0 

217.45 left I rb 2 0 0 0 A1 

218.03 left Apr. sb 0 2 2 0 0 

218.54 right I bank 0 0 0 0 0 

219.38 left S rb 2 0 0 0 0 

219.47 right I sb 0 0 0 0 0 

219.80 right I sb 0 0 0 0 0 

220.05 right S cm 0 0 0 0 A1 

220.14 right S up 220.1R 0 0 0 0 0 

220.14 left Apr. rb-ext 0 2 3 0 0 

220.38 right S, I cm 0 0 0 0 A1 

220.40 left Sept. rb 0 0 0 0 P1 

220.49 right S cm 0 0 0 0 P1 

220.59 left I rb-br 0 0 1 0 0 

64
Appendix A. Data from backwater inventories conducted between February and September 2008.--Continued 

River mile River side Source Class Site1 Status in backwater inventory 

Feb.-08 Apr.-08 May-08 July-08 Sept.-08 

221.43 left Apr. bank 0 3 0 0 A1 

221.54 right S, I rb 1 0 0 0 A1 

221.69 left S, I rb 0 0 0 0 A1 

222.14 right S sb 0 2 0 0 0 

222.34 left S rb 222.3L 2 0 1 0 0 

222.46 left S, I rb 0 0 1 0 A1 

222.63 left S, I gb 1 0 0 0 A1 

222.85 left S rb 0 0 0 0 A1 

223.15 left Apr. rb 0 3 0 0 0 

223.36 left I rb 1 3 2 0 P1 

223.73 left I cm 0 0 0 0 A1 

225.45 left May cm 0 0 1 0 0 

225.48 right I rb 225.5R 0 0 0 0 0 

225.71 right S sb 0 0 0 0 0 

228.09 left Feb. rb 228.1L 0 0 0 0 -- 

228.75 left Feb. bank 1 0 1 0 -- 

229.64 right Feb. up 0 0 0 0 -- 

233.10 right Feb. bank 0 0 0 0 -- 

233.89 left Feb. bank 3 0 0 0 -- 

234.38 right Feb. bank 1 0 0 0 -- 

234.41 right Feb. bank 1 0 0 0 -- 

235.23 left Apr. up 0 1 0 0 -- 

237.82 right Apr. bank 0 3 0 0 -- 

238.54 left Apr. rb-br 0 3 0 0 -- 

238.74 left Feb. rb 0 0 0 0 -- 

238.79 right Apr. rb-br 0 3 1 0 -- 

238.81 right Apr. rb-br 0 3 1 0 -- 

239.39 left Apr. rb-br 0 3 0 0 -- 

239.55 right Apr. rb 239.6R 0 0 0 0 -- 

239.81 right Apr. st 0 3 3 0 -- 

240.53 left Apr. bank 0 0 0 0 -- 

240.56 right Feb. bank 3 0 3 0 -- 

240.60 left Feb. up 2 3 3 0 -- 

240.62 left Feb. up 3 0 0 0 -- 

240.65 left Apr. rb 0 3 0 0 -- 

241.45 right Apr. bank 0 1 0 0 -- 

241.49 right Feb. rb-br 0 1 0 0 -- 

241.76 left Apr. bank 0 1 0 0 -- 

242.17 right Apr. bank 0 1 0 0 -- 

242.29 right Apr. bank 0 1 0 0 -- 

242.49 left Apr. bank 0 3 0 0 -- 

242.79 left Feb. bank 1 0 0 0 -- 

242.94 right Feb. rb-br 242.9R 3 0 0 0 -- 

243.65 right Apr. bank 0 3 0 0 -- 

243.66 left Apr. cm 0 3 2 0 -- 

244.15 left Apr. bank 0 3 0 0 -- 

244.20 left Feb. bank 1 0 0 0 -- 

244.33 left Apr. bank 0 1 0 0 -- 

245.05 left Apr. bank 0 1 0 0 -- 

65
Appendix A. Data from backwater inventories conducted between February and September 2008.--Continued 

River mile River side Source Class Site1 Status in backwater inventory 

Feb.-08 Apr.-08 May-08 July-08 Sept.-08 

247.81 left Apr. bank 0 3 0 0 -- 

248.27 left Feb. cm 1 0 0 0 -- 

248.80 right Feb. cm 0 3 0 0 -- 

248.83 right Apr. cm 0 0 3 0 -- 

249.56 right Feb. bank 1 0 0 0 -- 

250.01 right Apr. cm 0 0 1 0 -- 

250.06 left Feb. rb-br 3 1 0 0 -- 

250.53 right Feb. rb-br 1 0 0 0 -- 

253.26 right Feb. rb 1 0 0 0 -- 

256.76 right Feb. bank 1 0 0 0 -- 

257.00 right Feb. bank 1 0 0 0 -- 

257.57 left Feb. rb 3 0 0 0 -- 

257.96 right Apr. cm 0 3 3 0 -- 

1

A study site may appear in multiple lines in the inventory because several study sites have multiple backwater locations. 

66
Appendix B. List of Sandbar Monitoring and Backwater Monitoring Study Sites, 

the Date and Time of Each Survey, and the Discharge at Time of Survey 

[Site location is in river mile (downstream from Lees Ferry), with left (L) and right (R) side of river when looking 

downstream indicated. Site code is the label used to identify each site in the backwater processing files, and indicating 

whether data were used in analyses presented in text: Y indicates data were used in analyses; Z indicates no backwaters were 

present during study period and site was included with zero values; N indicates site was not included in analyses] 

Location Site code Site type1 Date of survey2 Discharge at time of survey (m3/s)2

Feb.-08 Apr.-08 May-08 Oct.-08 Feb.-

08 

Apr.-

08 

May08 Oct.-

08 

1.2 R 1R Y SBM 2-Feb. 28-Mar. 17-May 11-Oct. 285 278 232 355 

2.5 L 3L Y SBM* 2-Feb. 28-Mar. 17-May 11-Oct. 322 352 318 394 

3.37 L 3_4L Y BWM** 2-Feb. 29-Mar. 17-May 20-Sept. 292 268 289 351 

6.07 L 6L Y BWM 3-Feb. 29-Mar. 17-May 20-Sept. 266 283 339 351 

8.9 L 9L Y SBM 3-Feb. 29-Mar. 17-May 12-Oct. 252 300 369 358 

9.93 L 10L Y BWM 3-Feb. 29-Mar. 17-May 20-Sept. 289 270 375 351 

16.6 L 16L Y SBM* 3-Feb. 29-Mar. 12-Oct. 282 279 384 

17.6 R 17R Y BWM 3-Feb. 30-Mar. 18-May 21-Sept. 295 219 272 351 

19.61 R 19R Y BWM 4-Feb. 30-Mar. 17-May 21-Sept. 264 219 270 

22 R 22R Y SBM** 3-Feb. 29-Mar. 17-May 12-Oct. 284 267 265 366 

29.28 R 29R Y BWM 4-Feb. 30-Mar. 17-May 22-Sept. 259 217 276 349 

30.7 R 30R Y SBM** 4-Feb. 30-Mar. 19-May 13-Oct. 266 257 336 365 

33.3 L 33L Y SBM 5-Feb. 30-Mar. 13-Oct. 264 220 347 

35.63 R 36R Y BWM 4-Feb. 30-Mar. 19-May 23-Sept. 269 226 341 

37.55 R 37R N BWM 4-Feb. 31-Mar. 23-Sept. 266 255 

41.3 R 41R Y SBM* 5-Feb. 31-Mar. 19-May 14-Oct. 303 316 294 357 

43.4 L 43L Z SBM 6-Feb. 31-Mar. 19-May 14-Oct. 282 273 301 368 

44.5 L 44L Y SBM* 6-Feb. 31-Mar. 19-May 14-Oct. 270 237 345 

45 L 45L Y SBM** 7-Feb. 31-Mar. 20-May 15-Oct. 320 227 385 358 

45.93 R 46R Y BWM 5-Feb. 31-Mar. 20-May 24-Sept. 330 313 377 356 

46.39 L 46L N BWM 5-Feb. 31-Mar. 

47.6 R 47R Y SBM* 7-Feb. 31-Mar. 20-May 15-Oct. 339 307 343 361 

48.79 R 49R Y SBM 5-Feb. 31-Mar. 20-May 24-Sept. 286 269 394 346 

48.91 L 49L Y SBM 5-Feb. 31-Mar. 20-May 24-Sept. 301 273 

50.1 R 50R Y SBM* 1-Apr. 20-May 15-Oct. 292 309 360 

50.28 L 50L Y BWM 5-Feb. 1-Apr. 20-May 24-Sept. 275 319 313 355 

50.64 L 50_6L N BWM 6-Feb. 1-Apr. 342 307 

50.91 L 50_9L Y BWM 6-Feb. 1-Apr. 21-May 24-Sept. 342 284 394 355 

51.5 L 51L Y SBM** 8-Feb. 2-Apr. 21-May 15-Oct. 335 328 414 358 

54.6 R 54R Y SBM 6-Feb. 1-Apr. 21-May 16-Oct. 334 287 358 

67
Appendix B. List of sandbar monitoring and backwater monitoring study sites.--Continued 

Location Site code Site type1 Date of survey2 Discharge at time of survey (m3/s)2

Feb.-08 Apr.-08 May-08 Oct.-08 Feb.-

08 

Apr.-

08 

May08 Oct.-

08 

55.02 R 55_0R Y BWM 6-Feb. 1-Apr. 21-May 25-Sept. 319 310 333 356 

55.9 R 55R Y SBM* 8-Feb. 2-Apr. 21-May 16-Oct. 318 275 328 348 

56.6 R 56R Z SBM 2-Apr. 21-May 16-Oct. 252 303 372 

57.75 L 57L N BWM 7-Feb. 1-Apr. 

58.1 L 58L Y SBM 8-Feb. 3-Apr. 23-May 17-Oct. 307 337 511 368 

58.72 R 59R N BWM 7-Feb. 2-Apr. 313 322 

59.19 L 59L Y BWM 7-Feb. 2-Apr. 23-May 25-Sept. 340 321 418 356 

59.48 L 60L Y BWM 7-Feb. 2-Apr. 23-May 25-Sept. 329 342 433 355 

62.3 L 62L Y BWM 8-Feb. 2-Apr. 23-May 308 385 334 

63.6 L 63L Y SBM 9-Feb. 3-Apr. 24-May 17-Oct. 337 340 397 340 

64.36 L 64L Y BWM** 8-Feb. 2-Apr. 24-May 25-Sept. 306 369 

64.5 L 64L Y BWM 8-Feb. 2-Apr. 24-May 25-Sept. 

64.93 L 64_9L Y BWM 8-Feb. 2-Apr. 24-May 17-Oct. 344 363 439 364 

65.1 R 65R Y SBM 9-Feb. 4-Apr. 24-May 17-Oct. 372 332 410 387 

65.8 L 65L Y SBM** 8-Feb. 3-Apr. 24-May 17-Oct. 375 347 424 368 

66.11 L 66L Y SBM 9-Feb. 3-Apr. 24-May 18-Oct. 296 315 353 363 

67.43 L 67L Y BWM 9-Feb. 3-Apr. 24-May 26-Sept. 295 384 305 

68.49 L 68L Y BWM 9-Feb. 3-Apr. 25-May 26-Sept. 351 381 439 

68.8 R 69R Y SBM* 10-Feb. 5-Apr. 25-May 18-Oct. 279 341 420 344 

71.67 L 72L Y BWM 9-Feb. 4-Apr. 25-May 18-Oct. 347 358 438 365 

72.54 R 73R N BWM 9-Feb. 4-Apr. 351 355 

84.6 R 84R Y SBM 11-Feb. 6-Apr. 27-Sept. 309 279 353 

87.6 L 87L Z SBM* 11-Feb. 6-Apr. 19-Oct. 334 329 368 

87.87 L 87_8L N BWM 10-Feb. 5-Apr. 27-Sept. 279 306 

88.1 R 88R Y SBM 11-Feb. 6-Apr. 19-Oct. 327 300 337 

93.8 L 93L Y SBM* 12-Feb. 7-Apr. 20-Oct. 322 276 360 

104.42 R 104R Y SBM* 12-Feb. 7-Apr. 20-Oct. 323 303 360 

116.46 L 116L Y BWM 11-Feb. 5-Apr. 28-Sept. 285 356 

119.03 R 119R Y BWM 11-Feb. 6-Apr. 27-May 29-Sept. 290 288 322 

119.4 R 119_4R Y SBM* 12-Feb. 8-Apr. 21-Oct. 319 299 372 

119.8 R 119_8R Y SBM** 12-Feb. 8-Apr. 27-May 21-Oct. 317 318 386 368 

119.91 L 119_9L Y BWM 11-Feb. 6-Apr. 27-May 29-Sept. 294 280 346 361 

120.1 L 120L Y BWM 11-Feb. 6-Apr. 27-May 21-Oct. 297 297 372 363 

120.5 R 120R Y BWM 11-Feb. 6-Apr. 27-May 21-Oct. 297 302 407 363 

121.55 L 121L Y BWM 12-Feb. 6-Apr. 27-May 21-Oct. 325 303 363 

121.85 L 122L Y BWM 12-Feb. 7-Apr. 27-May 21-Oct. 342 267 372 

122.71 R 122R Y SBM* 12-Feb. 8-Apr. 27-May 21-Oct. 343 337 411 363 

122.88 L 122_9L Y BWM 12-Feb. 7-Apr. 28-May 21-Oct. 323 269 332 366 

123.25 L 123L Y SBM** 13-Feb. 8-Apr. 28-May 21-Oct. 358 286 360 376 

126.85 R 126R Y BWM 12-Feb. 7-Apr. 28-May 29-Sept. 292 266 347 361 

68
Appendix B. List of sandbar monitoring and backwater monitoring study sites.--Continued 

Location Site code Site type1 Date of survey2 Discharge at time of survey (m3/s)2

Feb.-08 Apr.-08 May-08 Oct.-08 Feb.-

08 

Apr.-

08 

May08 Oct.-

08 

126.85 L 126L Y BWM 12-Feb. 7-Apr. 28-May 29-Sept. 292 266 347 361 

127.29 R 127R Y BWM 12-Feb. 7-Apr. 28-May 29-Sept. 345 265 

137.7 L 137L Y SBM* 13-Feb. 9-Apr. 22-Oct. 336 284 362 

139.6 R 140R Y SBM* 13-Feb. 9-Apr. 22-Oct. 346 299 380 

145.85 L 145L Y SBM* 13-Feb. 9-Apr. 29-May 22-Oct. 346 327 327 365 

165.3 L 165L Y BWM 13-Feb. 7-Apr. 29-May 30-Sept. 348 328 343 

165.65 R 166R Y SBM 13-Feb. 10-Apr. 29-May 30-Sept. 359 338 347 340 

168.06 R 168R Y BWM 13-Feb. 8-Apr. 30-May 1-Oct. 335 300 384 360 

172.6 L 172L Y SBM** 14-Feb. 10-Apr. 30-May 23-Oct. 344 297 362 346 

172.7 L 173L N BWM 14-Feb. 9-Apr. 30-May 1-Oct. 377 363 381 360 

175.39 R 175R Y BWM 14-Feb. 9-Apr. 30-May 1-Oct. 383 365 365 360 

176.05 R 176R Y BWM 14-Feb. 9-Apr. 30-May 1-Oct. 366 332 355 360 

179.3 R 179R Y BWM 14-Feb. 9-Apr. 30-May 2-Oct. 365 344 

181.37 R 181R Y BWM 15-Feb. 10-Apr. 31-May 2-Oct. 391 363 432 

183.3 R 183R Y SBM* 15-Feb. 11-Apr. 31-May 24-Oct. 386 363 417 369 

187.95 R 188R Y BWM 15-Feb. 10-Apr. 31-May 2-Oct. 384 363 420 

194.6 L 194L Y SBM* 15-Feb. 11-Apr. 31-May 24-Oct. 376 349 377 363 

196.1 R 196R Y BWM 16-Feb. 10-Apr. 31-May 25-Oct. 383 352 391 

196.37 R 197R Y BWM 16-Feb. 10-Apr. 31-May 

197.9 R 198R Y BWM 16-Feb. 11-Apr. 31-May 25-Oct. 390 354 372 

199.5 L 200L Y BWM 16-Feb. 11-Apr. 11- June 25-Oct. 357 296 448 

199.5 R 200R Y BWM** 16-Feb. 11-Apr. 11- June 25-Oct. 357 296 462 

201.65 R 201R Y SBM 10-Feb. 11-Apr. 1-June 25-Oct. 350 353 405 369 

204.35 R 204R Y BWM 17-Feb. 12-Apr. 1- June 3-Oct. 345 342 421 

205.22 L 205L Y BWM 17-Feb. 12-Apr. 1-June 3-Oct. 346 341 402 

206.66 R 207R Y BWM 17-Feb. 12-Apr. 1-June 364 348 

211.37 L 211L Y BWM 17-Feb. 12-Apr. 2-June 4-Oct. 357 357 460 

211.83 R 212R Y BWM 17-Feb. 12-Apr. 2-June 4-Oct. 378 356 460 

213.01 R 213R Y BWM 17-Feb. 13-Apr. 2-June 4-Oct. 376 340 442 

213.27 L 213L Z SBM* 17-Feb. 12-Apr. 2-June 26-Oct. 344 338 433 362 

214.5 R 214R Y SBM 17-Feb. 12-Apr. 2-June 26-Oct. 363 343 453 374 

216.58 R 217R Y BWM 18-Feb. 13-Apr. 3-June 4-Oct. 343 337 

220.1 R 220R Z SBM 17-Feb. 12-Apr. 26-Oct. 449 415 438 

222.34 L 222L N BWM 18-Feb. 13-Apr. 348 330 

225.5 R 225R Y SBM** 18-Feb. 13-Apr. 3-June 26-Oct. 372 328 391 364 

228.12 L 228L N BWM 18-Feb. 13-Apr. 

239.55 R 239R N BWM 19-Feb. 14-Apr. 

242.93 R 243L N BWM 19-Feb. 

1

SBM is for sandbar monitoring site and BWM is for backwater monitoring site. Sites with * have a remote film camera and 

sites with ** have a remote digital camera. 

2

Blank cells indicate site was not surveyed at that time. 

69
Appendix C. Relations Between Water Surface Elevation and Discharge for 

Study Sites 

[Site code is the label used to identify each site (see appendix B). Y, data were used in analyses; 0, no backwaters were 

present during study period and site was included with zero values; N, site was not included in analyses. The number of stage 

observations is the number of independent observations. Each observation consists of one or many measurements of water 

surface elevation that were averaged. Z, elevation in meters; Q, discharge in cubic meters per second. Stage-discharge 

relations for SBM sites were determined by Hazel and others (2006a) where additional information is available. Relations are 

only valid for the range of flows observed, which is from about 227 to 1,274 m3

/s] 

Site code Site 

type1

Number of 

observations of 

stage 

Equation R2 

1R SBM Y -- Z = 9.20E+02 + 1.64E-04Q - 1.51E-09Q2 -- 

3L SBM Y -- Z = 9.20E+02 + 1.70E-04Q - 1.41E-09Q2 -- 

3_4L BWM Y 11 Z = 9.17E+02 + 9.35E-03Q - 3.90E-06Q2 0.98 

6L BWM Y 7 Z = 8.20E+02 + 9.12E+01Q1.36E-02 0.88 

9L SBM Y -- Z = 9.09E+02 + 2.34E-04Q - 2.23E-09Q2 -- 

10L BWM Y 9 Z = 9.09E+02 + 5.91E-03Q - 1.23E-06Q2 0.99 

16L SBM Y -- Z = 8.95E+02 + 1.47E-04Q - 1.14E-09Q2 -- 

17R BWM Y 9 Z = 8.90E+02 + 8.44E-03Q -3.02E-06Q2 1.00 

19R BWM Y 10 Z = 7.94E+02 + 8.49E+01Q1.96E-02 0.99 

22R SBM Y -- Z = 8.78E+02 + 2.91E-04Q - 2.45E-09Q2 -- 

29R BWM Y 11 Z = 8.59E+02 + 4.57E-03Q - 5.43E-07Q2 0.98 

30R SBM Y -- Z = 8.54E+02 + 2.41E-04Q - 1.89E-09Q2 -- 

33L SBM Y -- Z = 8.49E+02 + 1.83E-04Q - 8.87E-10Q2 -- 

36R BWM Y 8 Z = 7.52E+02 + 8.73E+01Q1.68E-02 0.94 

37R BWM N na na na 

41R SBM Y -- Z = 8.40E+02 + 1.67E-04Q - 9.15E-10Q2 -- 

43L SBM 0 -- Z = 8.38E+02 + 7.16E-03Q - 1.95E-06Q2 

44L SBM Y -- Z = 8.36E+02 + 1.86E-04Q - 1.34E-09Q2 -- 

45L SBM Y -- Z = 8.35E+02 + 1.44E-04Q - 5.59E-10Q2 -- 

46R BWM N 8 Z = 8.35E+02 + 3.65E-03Q - 2.69E-07Q2 0.99 

46L BWM N na na na 

47R SBM Y -- Z = 8.33E+02 + 1.66E-04Q - 1.26E-09Q2 -- 

49R SBM Y -- Z = 8.32E+02 + 1.01E-04Q - 1.59E-11Q2 -- 

49L SBM Y -- Z = 8.32E+02 + 1.00E-04Q + 4.21E-11Q2 -- 

50R SBM Y -- Z = 8.29E+02 + 1.78E-04Q - 1.24E-09Q2 -- 

50L BWM Y 9 Z = 8.29E+02 + 7.86E-03Q - 3.40E-06Q2 0.99 

70
Appendix C. Relations between water surface elevation and discharge for study sites.--Continued 

Site Code Site 

Type1

Number of 

observations of 

stage 

Equation R2 

50_6L BWM N na na na 

50_9L BWM Y 10 Z = 8.29E+02 + 5.54E-03Q - 4.43E-07Q2 1.00 

51L SBM Y -- Z = 8.29E+02 + 1.73E-04Q - 1.41E-09Q2 -- 

54R SBM Y -- Z = 8.20E+02 + 1.44E-04Q - 9.20E-10Q2 -- 

55_0R BWM N 9 Z = 8.20E+02 + 5.61E-03Q - 1.78E-06Q2 1.00 

55R SBM Y -- Z = 8.19E+02 + 1.24E-04Q - 1.02E-09Q2 -- 

57R SBM 0 -- -- -- 

57L BWM N na na na 

58L SBM Y -- Z = 8.10E+02 + 1.79E-04Q - 1.47E-09Q2 -- 

59R BWM N na na na 

59L BWM Y 11 Z = 8.08E+02 + 4.91E-03Q - 1.03E-06Q2 1.00 

60L BWM Y 9 Z = 8.08E+02 + 4.70E-03Q - 9.09E-07Q2 1.00 

62L BWM N 9 Z = 7.92E+02Q2.40E-03 0.93 

63L SBM Y -- Z = 7.98E+02 + 2.38E-04Q - 2.43E-09Q2 -- 

64L BWM Y 8 Z = 7.96E+02 + 6.02E-03Q- 1.57E-06Q2 1.00 

64_5L BWM Y na na na 

64_9L BWM Y 9 Z = 7.97E+02 + 2.44E-03Q+ 3.59E-07Q2 1.00 

65R SBM Y -- Z = 7.96E+02 + 1.22E-04Q - 7.79E-10Q2 -- 

65L SBM Y -- Z = 7.96E+02 + 1.23E-04Q - 1.01E-09Q2 -- 

66L SBM Y -- Z = 7.94E+02 + 5.04E-05Q - 8.69E-11Q2 -- 

67L BWM Y 7 Z = 7.89E+02 + 6.05E-03Q - 1.63E-06Q2 1.00 

68L BWM Y 8 Z = 7.86E+02 + 3.46E-03Q - 5.72E-07Q2 1.00 

69R SBM Y -- Z = 7.76E+02 + 1.17E-04Q - 9.36E-10Q2 -- 

72L BWM Y 8 Z = 7.77E+02 + 3.22E-03Q - 7.80E-07Q2 1.00 

73R BWM N na na na 

84R SBM Y -- Z = 7.25E+02 + 1.76E-04Q - 9.49E-10Q2 -- 

87L SBM 0 -- Z = 7.16E+02 + 2.13E-04Q - 2.01E-09Q2 -- 

87_8L BWM N na na na 

88R SBM Y -- Z = 7.16E+02 + 1.66E-04Q - 1.34E-09Q2 -- 

94L SBM Y -- Z = 6.97E+02 + 1.61E-04Q - 1.51E-09Q2 -- 

104R SBM Y -- Z = 6.58E+02 + 1.87E-04Q - 1.49E-09Q2 -- 

116L BWM Y 8 Z = 6.19E+02 + 6.97E-03Q - 1.53E-06Q2 1.00 

119R BWM Y 11 Z = 6.16E+02 + 3.46E-03Q + 4.69E-07Q2 0.99 

119_4R SBM Y -- Z = 6.14E+02 + 2.04E-04Q - 1.42E-09Q2 -- 

119_8R SBM Y -- Z = 6.13E+02 + 2.00E-04Q - 1.39E-09Q2 -- 

119_9L BWM Y 13 Z = 6.14E+02 + 6.05E-03Q - 1.29E-06Q2 0.99 

120L BWM Y 9 Z = 6.12E+02 + 1.06E-02Q - 4.19E-06Q2 0.99 

120R BWM Y 9 Z = 6.14E+02+8.02E-04Q + 1.88E-06Q2 1.00 

121L BWM Y 13 Z = 6.10E+02 + 8.81E-03Q - 2.99E-06Q2 0.99 

71
Appendix C. Relations between water surface elevation and discharge for study sites.--Continued 

Site Code Site 

Type1

Number of 

observations of 

stage 

Equation R2 

122L BWM Y 9 Z = 6.10E+02 + 7.14E-03Q - 2.10E-06Q2 0.98 

122R SBM Y -- Z = 6.08E+02 + 2.08E-04Q - 1.72E-09Q2 -- 

122_9L BWM Y 11 Z = 6.08E+02 + 6.44E-03Q - 1.73E-06Q2 0.99 

123L SBM Y -- Z = 6.07E+02 + 2.21E-04Q - 2.06E-09Q2 -- 

126R BWM Y 12 Z = 5.94E+02 + 7.75E-03Q - 2.78E-06Q2 1.00 

126L BWM Y 7 Z = 5.94E+02 + 8.38E-03Q - 2.85E-06Q2 1.00 

127R BWM N 9 Z = 5.92E+02 + 9.58E-03Q - 3.23E-06Q2 1.00 

137L SBM Y -- Z = 5.62E+02 + 1.98E-04Q - 1.45E-09Q2 -- 

140R SBM Y -- Z = 5.57E+02 + 2.12E-04Q - 1.61E-09Q2 -- 

145L SBM Y -- Z = 5.40E+02 + 2.35E-04Q - 1.78E-09Q2 -- 

165L BWM N 10 Z = 5.92E+02 + 4.42E-03Q - 1.06E-07Q2 0.99 

166R SBM Y -- Z = 5.05E+02 + 3.22E-04Q - 3.72E-09Q2 -- 

168R BWM N 10 Z = 5.06E+02 + 4.22E-03Q - 3.98E-07Q2 0.99 

172L SBM Y -- Z = 4.97E+02 + 1.71E-04Q - 1.15E-09Q2 -- 

173L BWM N 8 Z = 4.97E+02 + 5.38E-03Q - 1.07E-06Q2 1.00 

175R BWM Y 9 Z = 4.93E+02 + 3.10E-03Q + 6.81E-07Q2 0.99 

176R BWM Y 9 Z = 4.91E+02 + 3.30E-03Q - 4.65E-08Q2 1.00 

179R BWM N 8 Z = 4.86E+02 + 6.21E-03Q - 1.65E-06Q2 1.00 

181R BWM Y 10 Z = 4.75E+02 + 4.98E-03Q - 1.01E-06Q2 1.00 

183R SBM Y -- Z = 4.70E+02 + 1.96E-04Q - 1.50E-09Q2 -- 

188R BWM N 7 Z = 4.62E+02 + 4.86E-03Q - 1.21E-06Q2 1.00 

194L SBM Y -- Z = 4.47E+02 + 1.82E-04Q - 1.41E-09Q2 -- 

196R BWM Y 12 Z = 4.43E+02 + 6.24E-03Q - 1.93E-06Q2 0.99 

197R BWM N 7 Z = 9.73E+01 + 3.10E-03Q - 5.07E-08Q2 0.98 

198R BWM Y 8 Z = 4.40E+02 + 4.06E-03Q - 6.60E-07Q2 1.00 

200L BWM Y 8 Z = 4.37E+02 + 4.99E-03Q - 1.27E-06Q2 0.99 

200R BWM Y 6 Z = 4.37E+02 + 4.03E-03Q - 6.73E-07Q2 1.00 

201R SBM Y -- Z = 4.30E+02 + 4.78E-04Q - 6.50E-09Q2 -- 

204R BWM Y 9 Z = 4.30E+02 + 4.08E-03Q - 6.59E-07Q2 0.99 

205L BWM Y 8 Z = 4.29E+02 + 4.53E-03Q - 1.09E-06Q2 0.98 

207R BWM N 10 Z = 4.22E+02 + 4.33E-03Q - 1.04E-06Q2 1.00 

211L BWM Y 7 Z = 4.09E+02 + 5.78E-03Q - 7.82E-07Q2 1.00 

212R BWM Y 7 Z = 4.09E+02 + 3.39E-03Q + 7.89E-07Q2 1.00 

213R BWM N 9 Z = 4.04E+02 + 7.20E-03Q - 1.12E-06Q2 1.00 

213L SBM 0 -- Z = 4.04E+02 + 9.56E-03Q - 2.51E-06Q2 -- 

214R SBM Y -- Z = 4.29E+02 + 1.11E-04Q - 1.62E-11Q2 -- 

217R BWM Y 12 Z = 4.01E+02 + 4.09E-03Q - 1.38E-07Q2 0.98 

220R SBM 0 -- Z = 3.94E+02 + 3.88E-03Q - 5.323E-07Q2 -- 

222L BWM N na na na 

225R SBM Y -- Z = 3.81E+02 + 1.85E-04Q - 1.97E-09Q2 -- 

72
73

Appendix C. Relations between water surface elevation and discharge for study sites.--Continued 

Site Code Site 

Type1

Number of 

observations of 

stage 

Equation R2 

228L BWM N na na na 

239R BWM N na na na 

243L BWM N na na na 
Grams and others—2008 High-Flow Experiment at Glen Canyon Dam—Morphologic Response of Eddy-Deposited Sandbars and Associated Aquatic Backwater 

Habitats along the Colorado River in Grand Canyon National Park—Open–File Report 2010–1032