U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2009-1147

Prepared in cooperation with the Platte River Whooping Crane Maintenance Trust

Channel Morphology and Bed Sediment Characteristics 

Before and After Habitat Enhancement Activities in the 

Uridil Property, Platte River, Nebraska, Water Years 

2005–2008

Channel Morphology and Bed Sediment 

Characteristics Before and After Habitat 

Enhancement Activities in the Uridil 

Property, Platte River, Nebraska, Water 

Years 2005–2008

By Paul J. Kinzel

Prepared in cooperation with the Platte River Whooping Crane Maintenance Trust

Open-File Report 2009-1147

U.S. Department of the Interior

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

KEN SALAZAR, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2009

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Suggested citation: Kinzel, P.J., 2009, Channel morphology and bed sediment characteristics before and after

habitat enhancement activities in the Uridil Property, Platte River, Nebraska, water years 2005–2008: 

U.S. Geological Survey Open-File Report 2009-1147, 23 p.
iii

Contents

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

Introduction.....................................................................................................................................................1

Purpose and Scope .......................................................................................................................................3

Acknowledgments.........................................................................................................................................3

Study Area.......................................................................................................................................................3

Geomorphology.....................................................................................................................................3

Hydrology ...............................................................................................................................................7

Management Activities........................................................................................................................8

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

Channel Morphology............................................................................................................................9

Island and Bed Sediment Sampling.................................................................................................10

Statistical Analysis .............................................................................................................................10

Ground Photography ..........................................................................................................................11

Analysis of Channel Morphology ..............................................................................................................12

Analysis of Bed Sediment Characteristics..............................................................................................18

Inferences from Habitat Enhancement Activities ..................................................................................21

Summary and Conclusions.........................................................................................................................21

References Cited..........................................................................................................................................22

Appendixes

1. Transect elevation graphs............................................................................................Online

2. Bed sediment data tables.............................................................................................Online

3. Ground photography......................................................................................................Online

Figures

1. Map showing the location of the Uridil Property study site along the central 

Platte River, Nebr.....................................................................................................................4

2. Map of the Uridil Property study site showing the location of monitoring 

transects and locations of sediment removal and addition.............................................4

3A. Map created by the General Land Office circa 1867 using surveys from 

1859 to 1867...............................................................................................................................5

3B. Black and white aerial photograph of the Uridil Property taken October 24, 

1938 by the Soil Conservation Service. Distortion in image is a result of 

warping the image during the georeferencing process...................................................5

3C. Black and white aerial photograph of the Uridil Property taken 

April 27, 1951.............................................................................................................................6
iv

3D. Natural color photograph of the Uridil Property taken between July 16 

to July 23, 2006.........................................................................................................................7

4. Hydrograph showing the mean daily streamflow during the study and 

the mean of the mean daily flows between 1941 to 2008 at USGS 06770500, 

Platte River near Grand Island, Nebr., the mean daily stage during the study 

at USGS 06770375, Platte River near Prosser, Nebr., and the dates of 

geomorphic data collection and island management in the study reach .....................8

5. Topographic surveys collected along transect 14 before (2005) and after 

(2006) island management .....................................................................................................9

6. Panoramic images created from ground photographs taken from the right 

bank near transect 13. The photographs were taken looking upstream at 

islands 1 and 2 (A) Before the management activities on July 26, 2005 (B) 

and following the management activities on May 20, 2006............................................11

7. Longitudinal mean bed elevation upstream from, within, and downstream 

from the management area prior to (2005) and following the management 

(2006 to 2008) for (A) the entire channel, (B) the managed islands, and (C) 

the south channel..................................................................................................................12

8. Net change in area between annual transect surveys (A) entire channel, 

(B) managed islands, and (C) south channel ....................................................................14

9. Interpolated median grain size (D50) surface generated from river bed 

samples (A) collected July 2005 and (B) May 2006, and (C) interpolated 

difference in bed sediment median grain size (D50) between samples 

collected in 2005 and those collected in 2006. The 2005 sample results 

were subtracted from the 2006 sample results; therefore a negative value 

indicates the area sampled became finer from 2005 to 2006 and a positive 

value indicates the area sampled became coarser........................................................18

10. Grain-size distribution of sediment samples collected along transect 11 in 

the Uridil Property in 2005....................................................................................................20

Tables

1. Results of Wilcoxon signed-rank test for annual transect surveys..............................16

2. Results of Wilcoxon signed-rank test for the size parameters in 

the 2005 and 2006 sediment samples..................................................................................20
v

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)

 cubic yard (yd3

) 0.7646 cubic meter (m3)

 Flow rate

 cubic foot per second (ft3

/s) 0.02832 cubic meter per second (m3/s)

 Mass

 ton, short (2,000 lb) 0.9072 megagram (Mg)

 ton, long (2,240 lb) 1.016 megagram (Mg)

 Density

 pound per cubic foot (lb/ft3

) 16.02 kilogram per cubic meter (kg/m3)

[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)

 Mass

 megagram (Mg) 1.102 ton, short (2,000 lb)

 Density

 kilogram per cubic meter (kg/m3

) 0.06242 pound per cubic foot (lb/ft3) 

 Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

 (NAVD 88)

 Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83)

Abstract

Fluvial geomorphic data were collected by the United 

States Geological Survey from July 2005 to June 2008 (a time 

period within water years 2005 to 2008) to monitor the effects 

of habitat enhancement activities conducted in the Platte River 

Whooping Crane Maintenance Trust’s Uridil Property, located 

along the Platte River, Nebraska. The activities involved the 

removal of vegetation and sand from the tops of high permanent islands and the placement of the sand into the active river 

channel. This strategy was intended to enhance habitat for 

migratory water birds by lowering the elevations of the high 

islands, thereby eliminating a visual obstruction for roosting 

birds. It was also thought that the bare sand on the lowered 

island surfaces could serve as potential habitat for nesting 

water birds. Lastly, the project supplied a local source of sediment to the river to test the hypothesis that this material could 

contribute to the formation of lower sandbars and potential 

nesting sites downstream. Topographic surveys on the islands 

and along river transects were used to quantify the volume 

of removed sand and track the storage and movement of the 

introduced sand downstream. Sediment samples were also 

collected to map the spatial distribution of river bed sediment 

sizes before and after the management activities. While the 

project lowered the elevation of high islands, observations of 

the sand addition indicated the relatively fine-grained sand that 

was placed in the active river channel was rapidly transported 

by the flowing water. Topographic measurements made 3 

months after the sand addition along transects in the area of 

sediment addition showed net aggradation over measurements 

made in 2005. In the year following the sand addition, 2007, 

elevated river flows from local rain events generally were 

accompanied by net degradation along transects within the 

area of sediment addition. In the spring of 2008, a large magnitude flow event of approximately 360 cubic meters per second occurred in the study reach and was accompanied by net 

aggradation in the managed area. These observations illustrate 

the high sediment transport capacity of the river channel both 

at lower flows, when the sand was added, and during higher 

flow events. This field experiment also serves as a practical 

example of the dynamic response of a Platte River channel 

to a relatively small-scale sand augmentation project directed 

toward enhancing in-channel habitat for avian species.

Introduction

The Platte River in central Nebraska is a prime ecological 

resource for migratory bird species. Both wading and nesting 

birds gather among the mix of shallow channels and emergent sandbars. These riverine habitats are also used by three 

federally listed avian species: the endangered whooping crane 

(Grus Americana) (U.S. Fish and Wildlife Service, 1967), 

interior least tern (Sterna antillarum), and the threatened 

piping plover (Charadrius melodus) (U.S. Fish and Wildlife 

Service, 1985a,b). In the last century, habitats for the listed 

species along the central Platte River have been negatively 

impacted as upstream dams and diversions for agriculture have 

altered the flow regime in the central Platte River (National 

Research Council, 2004; U.S. Department of the Interior, 

2006). A reduction in the frequency and magnitude of flows 

necessary for mobilizing and preventing vegetative succession 

on sandbars has been accompanied by profound changes in the 

channel morphology. In the 20th century, the river narrowed 

significantly in response to the altered flow regime (Williams, 

1978; Eschner and others, 1983; Johnson, 1997). Narrower 

river channels are believed to be less suitable with regard to 

the roosting habitat requirements of the whooping crane (U.S. 

Department of the Interior, 2006). Similarly, the absence of 

large magnitude flows and reduction in upstream sediment 

supply has impaired the creation of high-elevation emergent 

sandbars in the river channel, effecting the nesting habitat of 

the interior least tern and piping plover (U.S. Department of 

the Interior, 2006).

Habitat enhancement and preservation activities for 

the listed species along the central Platte River have been 

Channel Morphology and Bed Sediment Characteristics 

Before and After Habitat Enhancement Activities in the 

Uridil Property, Platte River, Nebraska, Water Years 

2005–2008

By Paul J. Kinzel
2 Channel Morphology and Bed Sediment Characteristics, Uridil Property, Platte River, Nebraska 

underway for some time. Vegetation clearing, conducted since 

the 1980s, has attempted to control vegetation succession on 

emergent sandbar areas and islands as a means to enhance 

river roosting habitat for cranes (Currier, 1991). Clearing 

strategies have included the application of herbicides, burning, 

mowing, and mechanically discing vegetated surfaces. Discing 

typically involves using a tractor to pull a trailer with rows of 

steel discs over a vegetated surface. The intent of the discing 

process is to disturb the vegetation root system and decrease 

its stabilizing effects on the sand substrate. These clearing 

strategies have typically not attempted to deliberately alter the 

topography of sandbars and islands or intentionally redistribute sand into the active channel.

There has been increasing interest by river managers 

in implementing strategies to augment the sand supplied to 

Platte River channels to enhance habitat for the listed avian 

species. This interest was prompted in part by the findings of 

the Platte River Final Environmental Impact Statement (U.S. 

Department of the Interior, 2006). Specifically a temporal 

analysis of topographic river transects by Murphy and Randle 

(2001) pointed out the linkage between clear water inputs 

to the Platte River from hydropower operations and recent 

(post-1989) scouring of the river bed. Aside from this work, 

Kinzel and others (1999) showed that the bed sediments of the 

Platte River were coarser in 1998 than in 1931 and hypothesized that upstream regulation and reduced sediment supplies 

were responsible for winnowing fine material from the river 

bed. Taken together, observations of degrading channels and 

coarser, less mobile, bed materials suggest that the present 

sediment supply may be influencing the Platte River channel 

morphology. 

Potential strategies to restore river channel habitat for the 

endangered and threatened species were identified in the Final 

Environmental Impact Statement prepared for the Platte River. 

These strategies included: “vegetation clearing and discing on 

banks and islands to improve sight distance across and along 

the river and to create roosting and nesting opportunities,” 

“island leveling—lowering elevation of vegetated islands and 

river banks to improve sight distance and create sandbars,” 

and “moving river sand from islands or banks back into the 

active river channel to offset ongoing erosion of the channel 

and support formation of new sandbars” (U.S. Department of 

the Interior, 2006). Similar strategies were identified in the 

Adaptive Management Plan component of the Platte River 

Recovery Implementation Program Document, hereinafter 

referred to as the Program, as actions that could be undertaken 

to improve habitat and offset or ameliorate imbalances in the 

sediment budget (Governance Committee, 2006). The “FlowSediment-Mechanical Strategy” also referred to as the “Clear/

Level/Pulse” strategy mentioned in the Program document 

describes a process by which islands are first cleared of vegetation, then leveled to a lower elevation through mechanical 

means. The material removed by the leveling process would 

be placed into the active channel for a managed flow release, 

or pulsed-flow event, to transport downstream. The overarching hypothesis of this approach is that it will “...generate 

detectable changes in the channel morphology of the Platte 

River, and habitats for whooping crane, least tern, piping plover, pallid sturgeon, and other species of concern.”

Despite the advocacy in these habitat enhancement 

strategies, no comprehensive large-scale examples of their 

application along the Platte River were available when the 

Program document was written. For this reason, as the Platte 

River Recovery Implementation Program moves forward, pilot 

investigations and experiments are necessary to determine 

how best to undertake and monitor a large-scale management program, of which sand augmentation is a component, 

to ensure that the treatment produces the desired effects both 

from a physical and biological perspective while at the same 

time keeping with the Program’s goal of avoiding negative 

third-party effects. The importance of monitoring habitatmanagement sites was also identified by the National Research 

Council (NRC) in their review of the needs of the endangered 

and threatened species in the Platte River basin. The NRC 

noted that “as with most habitat-management strategies in the 

central Platte River, there has been no specific monitoring to 

assess the success of clearing. Unintended effects remain to be 

investigated.” (National Research Council, 2004).

Although not a comprehensive or large-scale example 

of the “Flow-Sediment-Mechanical” approach, the vegetation clearing habitat enhancement project conducted by the 

Nebraska Public Power District (NPPD) in their Cottonwood 

Ranch Property from 2002 to 2004 has some similar components. The project lowered the elevation of several islands and 

introduced bank and island material into the active channel. 

The volume of bank material directly introduced to the river 

in this phase of the Cottonwood Ranch project was estimated 

by Kinzel and others (2006a) to be approximately 250 cubic 

meters (m3

). Additional material was indirectly introduced as a 

consequence of island leveling activities conducted by NPPD. 

These activities involved pushing island sand to its periphery, 

increasing the area of the island but lowering its overall elevation. The process made accounting for any sand introduced 

to the channel more difficult to estimate, but approximately 

1,500 to 3,000 m3

 of material was estimated to have been 

made available for river flows to transport downstream (Kinzel 

and others, 2006a). Despite these direct and indirect sediment 

additions, Kinzel and others (2006a) found no statistically 

significant evidence of greater incidences of increased mean 

channel elevations downstream compared to upstream from 

the managed area. 

The management activities in the Cottonwood Ranch 

Property provided some empirical data necessary to evaluate the response of the river channel to habitat enhancement 

activities, specifically riparian vegetation clearing and sediment additions. A key difference between the management 

at the Cottonwood Ranch and that proposed by the Program 

is that although a pulse-flow release was considered by the 

U.S. Fish and Wildlife Service (USFWS), the agency which 

manages the environmental water account for the Platte River, 

a pulse flow was not released during the time period of the 

management activities and monitoring in the Cottonwood 
Study Area 3

Ranch Property. The study described herein, conducted by the 

U.S. Geological Survey (USGS) in cooperation with the Platte 

River Whooping Crane Maintenance Trust (PRWCMT), is the 

result of an effort to build upon the observations collected and 

the monitoring methodology developed for the Cottonwood 

Ranch Property by directly adding a larger quantity of sand 

to the river at the Uridil Property and monitoring the fate and 

transport of that material downstream. Although a pulsed-flow 

event was not released during the management and monitoring activities at the Uridil Property, naturally elevated river 

flows from local rain events occurred in the final 2 years of the 

study. These elevated flows provided an opportunity to monitor the effects of higher magnitude discharges on the channel 

morphology of a recently managed river reach.

Purpose and Scope

 This report presents an analysis of channel morphology and bed sediment characteristics based on data collected 

in the PRWCMT Uridil Property during water years 2005 to 

2008. The report is intended to provide the data necessary to 

detect the physical response of the river channel to a management strategy designed to enhance in-channel habitat for 

migratory water birds. This strategy also includes components 

of an approach suggested in the Platte River Environmental 

Impact Statement document and in the Platte River Recovery Implementation Program document intended to enhance 

habitat for endangered and threatened species in the Platte 

River basin. This report also addresses a primary objective of 

the USGS Platte River Priority Ecosystem Program: Evaluating the effects of management strategies on individual species 

and their habitats. The data used in the analysis provided in 

this report are provided in the appendixes and include transect plots, tables of bed sediment grain-size distributions, and 

ground photographs.

Acknowledgments

This study was supported through a the proposal written 

by the PRWCMT to the Nebraska Environmental Trust (NET). 

The NET project proposal was developed by Robert Henszey 

formerly of the PRWCMT. Kenny Dinan, Jeff Runge, and 

Kirk Schroeder (USFWS, Grand Island, Nebr.) provided technical assistance in the project design and execution phases. 

Assistance with field data collection was provided by Ashley 

Heckman, Brandy Logan, Richard McDonald, Jonathan Nelson, Francisco Simões, and Andrew Wilcox (USGS, Golden, 

Colo.), and Jason Alexander, Brent Hall, Brian Imig, and Matt 

Moser (USGS, Lincoln, Nebr.). Ashley Heckman (USGS, 

Golden, Colo.) provided laboratory analysis of the bed sediment samples. The recording stage gage on the site, USGS station 06770375 Platte River at Prosser, Nebr., and the upstream 

and downstream streamflow-gaging stations: USGS stations 

06770200 Platte River at Kearney, Nebr. and 06770500 Platte 

River at Grand Island, Nebr. were maintained by the USGS 

office in North Platte, Nebr. The author would like to thank 

Sharon Gloe and Barbara and Jarron Suck for kindly providing access to the portions of the Platte River located on their 

properties. 

Study Area

The PRWCMT’s Uridil Property is located in Hall 

County, Nebraska. The Uridil Property lies along a reach of 

the Platte River between the town of Shelton to the west and 

the Wood River to the east (fig. 1). The Platte River through 

this area includes three braids or channels (north, middle, and 

south channels). This property and others adjacent to it along 

the middle channel of the Platte River are popular locations 

for water birds to congregate. Each spring thousands of sandhill cranes can be observed roosting in this reach (Kinzel and 

others, 2006b). This is due, in part, to the habitat management 

activities which have maintained a wide channel through discing operations on the sandbars. The slope of the river valley 

through the reach, determined from USGS topographic maps 

produced in 1962 and revised in 1993, is 0.0014.

Geomorphology

Two complete islands and the upstream part of a third 

island in the PRWCMT’s Uridil Property were selected for 

clearing and leveling. The islands are numbered 1 to 3 from 

upstream to downstream (fig. 2). The history of island development in the study reach was established by examining 1867 

General Land Office (GLO) Cadastral Surveys and serial 

aerial photography from 1938, 1951, and 2006. The cadastral 

surveys by the General Land Office (GLO) were used to create maps of Platte River channels in this area. The managed 

islands were not delineated in the plat map made from surveys 

conducted between 1859 to 1867 of Township 9 North and 12 

West (fig. 3A). However, GLO plat maps should be interpreted cautiously because the spatial extent of the managed 

islands may have been deemed insufficient by the surveyor 

for cartographic purposes and therefore were omitted from the 

map. Johnson and Boettcher (1999) thought that some islands 

were not surveyed by the GLO because the islands had little 

agricultural value, they were too time consuming to survey, 

and they were only documented when surveyors crossed the 

river. Examination of the GLO plat map does, however, show 

the location of the meander corners or the river banks along 

the reach. 

The managed islands are identifiable in an aerial photograph taken by the Soil Conservation Service on October 

24, 1938 (fig. 3B). In this photograph, portions of the managed islands are present and appear to have trees similar in 

size to those on the river banks. It could be inferred that if 

the islands were inundated in the years leading up to when 
4 Channel Morphology and Bed Sediment Characteristics, Uridil Property, Platte River, Nebraska 

Figure 1. Map 

showing the location of 

the Uridil Property study 

site along the central 

Platte River, Nebr.

Figure 2. Map of the 

Uridil Property study 

site showing the 

location of monitoring 

transects and locations of sediment 

removal and addition. 

Flow is from lower left 

to upper right.
Study Area 5

Figure 3A. Map created 

by the General Land Office 

circa 1867 using surveys 

from 1859 to 1867. 

Figure 3B. Black and 

white aerial photograph of 

the Uridil Property taken 

October 24, 1938 by the 

Soil Conservation Service. 

Distortion in image is a result 

of warping the image during 

the georeferencing process. 
6 Channel Morphology and Bed Sediment Characteristics, Uridil Property, Platte River, Nebraska 

the 1938 photograph was taken, these flows did not prevent 

vegetative succession on the islands. The shape and position of 

the south bank of the middle river channel in 1938 is similar 

to that delineated by the GLO surveys, suggesting that the 

islands were not connected to the river bank in 1867, although 

this does not rule out the possibility that they were connected 

sometime before this.

In the aerial photograph taken of the study site on April 

27, 1951, the higher portions of the islands vegetated in 1938 

are also vegetated in 1951 (fig. 3C). However, many sandbars 

that appeared bare and unvegetated in the 1938 photography 

are vegetated in the 1951 photography. This is especially true 

along the north side of the channel where these vegetated 

sandbars have begun to accrete to the river bank. The size of 

island 3 in particular appears to have increased from 1938 

to 1951 as a sandbar accreted to the downstream end of the 

island. 

Aerial imagery collected between July 16 to 23, 2006 

shows the extent of lateral accretion and channel narrowing 

in this reach since 1938 (fig. 3D). A sandbar that was present along the south bank in 1938 and 1951 between islands 2 

and 3 forms the south bank of the river in 2006. The distance 

between high banks in the study reach has been reduced by 

approximately 50 percent from 1938 to 2006, approximately 

880 m to 426 m respectively. Most of the bank to bank width 

in the 1938 photograph was relatively unvegetated, indicating that few islands were present and most of the channel 

was likely made up of low elevation sandbars that would be 

expected to be mobile or active if inundated. Even though the 

2006 photograph was taken after the islands in this study were 

cleared of vegetation and the sediment removed, the channel is 

obstructed in other parts of the reach by the presence of high 

and stable vegetated islands. These islands surfaces would 

be inundated and mobilized only under high magnitude flow 

events. Successive years of low magnitude flows leading up to 

the 2006 photograph accentuated the low elevation channels in 

this reach, providing preferential flow paths to route water and 

sediment at these flows. 

Figure 3C. Black and white aerial photograph of the Uridil Property taken April 27, 1951. 
Study Area 7

Hydrology

Upstream from the study site, flow in the Platte River 

is regulated by upstream diversions and impoundments 

(Williams, 1978; National Research Council, 2004; U.S. 

Department of the Interior, 2006). The study site is located 

between two USGS streamflow-gaging stations. The USGS 

streamflow gaging station 06770200 Platte River near 

Kearney, Nebr. (contributing drainage area 136,078 km2

) is 

located approximately 39 km upstream from the study area 

and USGS streamflow-gaging station 06770500 Platte River 

near Grand Island, Nebr. (contributing drainage area 137,114 

km2

) is located approximately 34 km downstream (fig. 1). 

The mean daily streamflows from the Grand Island gage 

over the period of the study and the mean of the daily mean 

discharge at the Grand Island gage from 1941 to 2008 (http://

waterdata.usgs.gov/ne/nwis/dv/?site_no=06770500&agency_

cd=USGS&referred_module=sw) are shown in figure 4. 

In addition to the streamflow-gaging stations a recording stage 

gage (USGS station 06770375 Platte River at Prosser, Nebr.) 

is located at the upstream end of the study reach (figs. 1, 2). 

Mean daily stage values recorded at this gage during the study 

are shown in figure 4.

In the first year of the study, July 1, 2005 to June 30, 

2006, the total annual flow was approximately 22 percent of 

the average total annual flow from 1941 to 2008 and no major 

peak flows occurred. From July 1, 2006 to June 30, 2007 two 

major peak flows occurred, February 23, 2007 at 206 m3

/s and 

April 26, 2007 at 183 m3

/s. These magnitudes fall between 

peak discharges with a 2 and 5 year reoccurrence interval 

(Soenksen and others, 1999). The total annual flow in this year 

was 57 percent of the average total annual flow. In the final 

year of the study, 2007 to 2008, a flow of a larger magnitude 

than those observed in 2007 occurred in the study reach (fig. 

4). These elevated flows were caused by rain events (Kinzel, 

2008). The maximum provisional flow measured at the Grand 

Island gage was approximately 360 m3

/s. This magnitude falls 

between peak discharges with a 5 and 10-year reoccurrence 

interval, 306 and 391 m3

/s, respectively (Soenksen and others, 

1999). The total annual flow from July 1, 2007 to June 30, 

2008 was 76 percent of the average total annual flow.

Figure 3D. Natural color photograph of the Uridil Property taken between July 16 to July 23, 2006.
8 Channel Morphology and Bed Sediment Characteristics, Uridil Property, Platte River, Nebraska 

Management Activities

The elevations of the managed islands were designed so 

that the islands would both remain above the water surface 

(emergent) at a flow of 34 m3

/s, an anticipated high flow during the tern and plover nesting season, and would be below the 

water surface at a flow of 85 m3

/s, an anticipated high spring 

peak flow. It was thought that a peak flow of this magnitude, 

either from a high natural spring flow or an artificial pulsedflow event, would overtop and have the potential to scour vegetation seedlings on the island surfaces. The scouring action 

and erosion provided by these higher events was thought to be 

capable of maintaining the island surfaces free from vegetation and preserving them as suitable tern and plover nesting 

habitat. The volume of sediment removed from the islands 

was estimated in the project proposal (Platte River Whooping 

Crane Maintenance Trust, 2003) by taking the individual areas 

of the three islands and multiplying by an estimated elevation that each island was to be lowered. It was estimated that 

27,378 m3

 of sediment was to be removed from the islands.

On February 3, 2004 a permit application was submitted by the PRWCMT to the U.S. Army Corps of Engineers to 

discharge sediment under Section 404 of the Clean Water Act 

and concurrently to the Nebraska Department of Environmental Quality for a Water Quality Certification under Section 401 

of the Clean Water Act. Approval to proceed with the project 

was given on April 23, 2004. However, changes in the scope 

and personnel involved in the project delayed selection of a 

contractor and initiation of work until February 1, 2006. The 

contractor began the process of clearing the vegetation on 

the three islands in February of 2006 (fig. 2). The vegetation 

was removed using a bulldozer to scrape the vegetation and 

top soil from the islands. The contractor then proceeded from 

upstream to downstream using a bulldozer (see cover photograph) to scrape the majority of the sand from the island tops 

south into the adjacent river channel. This part of the study 

reach is referred to as the south channel (fig. 2) and should not 

be confused with the south channel of the Platte River which 

is a separate braid of the river. The island sand was spread 

evenly into the flowing water to avoid damming the channel 

and to permit the water to mobilize the sediment. Observations 

made by the author during this process indicated that even in 

relatively small depths of flowing water (less than one-half 

meter) sand mounds deposited in the channel by the bulldozer 

were easily eroded by the flowing water and the material was 

transported downstream in a matter of a few minutes. The 

contractor completed work on March 6, 2006 and submitted 

an invoice that indicated that 14 days (119.5 hours) were spent 

clearing, leveling, and reshaping the islands (Kenny Dinan, 

USFWS, written communication, January 20, 2009). In the 

time period following the management and up to the final 

topographic survey completed for this report (March 2006 

to June 2008), the managed islands were not disced (Kenny 

Dinan, USFWS, written communication, January 20, 2009). 

Figure 4. Hydrograph showing the mean daily streamflow during the study and the mean of the mean daily flows between 1941 to 

2008 at USGS 06770500, Platte River near Grand Island, Nebr., the mean daily stage during the study at USGS 06770375, Platte River 

near Prosser, Nebr., and the dates of geomorphic data collection and island management in the study reach.
Methods 9

Methods 

Channel Morphology

Thirty transects spanning the entire width of the middle 

channel of the Platte River (fig. 2) were established in the 

study reach in 2005. The transects were spaced approximately 

every 55 m and were distributed to obtain measurements of 

channel morphology upstream from, within, and downstream 

from the area where island clearing and leveling activities were to occur. Ten transects were placed immediately 

upstream from the islands, 10 across the islands, and 10 immediately downstream (fig. 2). The horizontal coordinates of the 

transect end points, Universal Transverse Mercator (UTM) 

coordinate system in the North American Datum of 1983, were 

defined in the office using a digital aerial orthophotograph of 

the study area. The horizontal coordinates were then uploaded 

into global positioning system (GPS) data controllers for use 

in the field. 

A survey-grade global positioning system (GPS) was 

operated in real-time kinematic mode (RTK) to transmit corrections from a fixed GPS receiver (base station) located over 

an established concrete benchmark to roving GPS receivers. 

The manufacturer reported precisions of an RTK GPS measurement are described as centimeter (cm) level (Trimble 

Navigation Ltd, 1998). In practice the precisions of RTK 

measurements were found to be approximately +/- 2 cm in 

the horizontal and +/- 3 cm in the vertical based on periodic 

checks against fixed monuments during the surveys. The base 

station for the topographic surveys used coordinate values 

obtained from a survey collected in 1998 as part of a contract 

to the United States Bureau of Reclamation (Druyvestein, 

Johnson & Anderson, 1998). Surveyors operating the roving 

GPS receivers in RTK mode could precisely navigate to the 

location of the transect end points using output from a handheld data collector. After a transect endpoint was located on 

one bank, surveyors could then follow and position themselves 

interactively along an imaginary line connecting that transect 

endpoint to the corresponding endpoint of the transect on the 

other bank. While traversing the transect lines, surveyors were 

instructed to measure a topographic point every few meters 

in addition to the locations of major changes in elevation 

gradient (for example, the top and bottom of a river bank), 

and locations where the water surface intersected a landform 

(river bank, sandbar, or island). Ellipsoidal heights measured 

with the GPS were converted to orthometric heights relative to 

the North American Vertical Datum of 1988 (NAVD88) using 

GEOID 99 (Smith and Roman, 2001). In addition to points 

collected along the transects crossing the islands, topographic 

points were also collected in distributed locations on the island 

surfaces before and after the management activities. Taken 

together these points helped to estimate the quantity of material removed from these surfaces. River channel topographic 

surveys were not conducted downstream from transect 18 

(fig. 2) in 2008 due to a change in landowner permissions for 

survey access.

In the office, survey data from the data collectors were 

downloaded to an office computer and the locations of the 

points surveyed along a transect were related to the horizontal 

coordinates of the left bank transect endpoint using a Euclidian 

distance equation (the left bank of the river is defined as the 

bank on the left side of an observer facing down river). The 

surveyed elevations were then linearly interpolated to obtain a 

set of points for each transect spaced at 1-m increments. This 

procedure is identical to that described by Kinzel and others 

(2006a). Figure 5 illustrates the elevations along transect 14 

surveyed before and after the management activities. Graphs 

that include surveys along all of the transects collected during 

all of the site visits are included in Appendix 1. 

Figure 5. Topographic surveys collected along transect 14 before (2005) and after (2006) island management.
10 Channel Morphology and Bed Sediment Characteristics, Uridil Property, Platte River, Nebraska 

The interpolated transect elevations were used to compute a mean elevation for segments along the transects, including the entire transect (left bank to right bank), the managed 

islands, and the south channel. For example, two points on 

the interpolated transect were used to define the extent of the 

island surface. The mean elevation was computed by taking 

the average of the interpolated points that were between those 

two points. Similarly, points were identified along the interpolated transects that defined the entire active channel (left 

to right bank) and the south channel, a segment between the 

islands that were managed and the right bank of the river.

Annual area changes between segments on the transects 

were computed by subtracting the elevation at each interpolated 1-m position from its corresponding position in a 

subsequent year. If the elevation value for the subsequent 

measurement was greater than the previous year’s measurement an increase in elevation was recorded, and if it was less 

than the previous year a decrease in elevation was recorded. A 

net change in area was approximated for each transect by multiplying the net change in elevation at each point by the 1-m 

distance between the mid-points and summing the changes 

between all of the points along the transect segment. 

Detailed topographic surveys were conducted along channel transects before and after the island leveling (fig. 2). These 

transects were supplemented with additional points collected 

along the island surfaces and were used in the ArcGISTM software (ESRI Redlands, Calif.) to create surfaces for each survey. The software estimated the volume of sediment removed 

from the islands by differencing these surfaces. 

Island and Bed Sediment Sampling

Sediment was sampled from the islands in the channel 

and from the bed of the river before and after the management 

activities to document the variability and spatial distribution of sediment grain sizes in the study reach. Sediment was 

sampled at regular intervals in 2005, approximately every 22 

m, along every other river transect using a ‘can on a stick’ 

bed sediment-sampling device (Edwards and Glysson, 1999). 

The location of the sediment samples were recorded with the 

GPS surveying equipment. In 2006 a subset, 173, of the 250 

locations where sediment samples were obtained in 2005 were 

resampled. The samples collected in 2006 were obtained in 

the lower elevation areas of the transects as opposed to the 

samples collected in 2005 which also included samples on 

higher elevation island surfaces along the transects. Because 

these higher islands surfaces were not overtopped by water 

and subjected to fluvial processes or to management activities 

in the intervening period, they were not expected to provide 

additional information and thus were not resampled in 2006.

Sediment was sampled by plunging the bed-sediment 

sampler into the river bed, exposed sandbar, or high island surface and removing the top 5 centimeters of sand. If vegetation 

and top soil were present on the high islands, the top few centimeters of this material was removed before the sediment was 

sampled at those locations. Each sediment sample was placed 

in a separate sample bag and labeled with the date, time, transect number, and sample number. The sediment samples were 

numbered in increasing order from the right to the left bank 

The samples were processed at the USGS Geomorphology and 

Sediment Transport Laboratory (Golden, Colo.) to determine 

their grain-size distribution. Grain-size analysis involved 

mechanically agitating the sample through a series of sieve 

stacks at 1⁄2 phi intervals (a phi unit is defined as the negative 

base 2 logarithm of the grain diameter in millimeters). The 

cumulative mass of the sample was noted at each interval 

and plotted as a cumulative size-distribution curve. The sizes 

for which 16, 50, and 84 percent of the sample by mass were 

finer than were computed by interpolation of the cumulative 

size-distribution curves. These parameters are denoted as D16, 

D50, and D84 respectively. The size parameters of each sample 

and their sampling locations within the channel are provided 

in Appendix 2. 

Surveyed GPS coordinates for each of the 173 bed-sediment sample locations were used to map the spatial distribution of in-channel bed sediment characteristics before (2005) 

and after (2006) the management treatment. A geographic 

information system (GIS) layer delineating the river channel and islands developed from the 1998 imagery (Bureau of 

Reclamation, 2000) was used to define the boundary of an 

inverse-distance weighted spatial interpolation of the sample 

parameters. Maps were created showing the D50 of samples 

collected from the river bed in 2005 were subtracted from the 

D50 of samples collected from the river bed in 2006.

Statistical Analysis

A non-parametric technique (the Wilcoxon signed-rank 

test) was used to detect the significance of pair-wise differences between the interpolated elevations from the annual 

topographic surveys along various transect segments. This 

technique was also used to detect the significance of pairwise differences between the 2005 and 2006 bed-sediment 

samples. The Wilcoxon signed-rank test is often used as an 

alternative to the paired student’s t-test because it does not 

require assumptions about the distribution of the measurements (TIBCO Software Inc., 2008). The test evaluates if the 

null hypothesis, that the samples follow the same distribution, 

can be rejected provided a given level of significance. If the p 

value computed by the test is less than the significance level 

(alpha), the alternative hypothesis, that the samples follow 

different distributions, can be accepted. The tests used a significance level of 5 percent or 0.05. The Spotfire S+ statistical 

software package version 8.1 for WindowsTM (TIBCO Sofware 

Inc.) was used to conduct the Wilcoxon signed-rank testing.
Methods 11

Ground Photography

To document changes in the managed islands and the 

adjacent river channel, ground photographs were taken along 

the right bank of the river with either a 35-mm single action 

reflex camera and slide film or a 3.3-megapixel digital camera. 

Three photographs were taken near each end point, one with 

the photographer facing upstream, one facing across the channel along the transect, and the third facing downstream. The 

slide film was developed onto slides that were scanned into 

digital images at a resolution of 200 dots per inch. Panorama 

photographs were taken from the right bank at transect 13 

looking upstream at two of the three managed islands in 2005 

before the management activities and in 2006 following the 

management activities (figs. 6A,B). The collection of ground 

photographs taken during the study period are provided in 

Appendix 3. The file name of each photograph indicates the 

year, transect number, and direction the photograph was taken. 

Photographs taken upstream are identified (us), along transects 

(xs), and downstream (ds).

Figure 6. Panoramic images created from ground photographs taken from the right bank near transect 13. The photographs were 

taken looking upstream at islands 1 and 2. (A) Before the management activities on July 26, 2005 and (B) following the management 

activities on May 20, 2006.

A

B
Islands

12 Channel Morphology and Bed Sediment Characteristics, Uridil Property, Platte River, Nebraska 

Analysis of Channel Morphology

As the islands prior to leveling were not of uniform 

height, and the heights used in the preliminary volume computation represented a maximum height on the island, the volume 

identified for removal in the project proposal (Platte River 

Whooping Crane Maintenance Trust, 2003) was an overestimate. The ArcGISTM software calculated the volume of material removed from the islands to be closer to 14,100 m3

, almost 

half the volume identified in the project proposal. Assuming 

a bulk density of sand of 1.59 g/cm3

 this volume represents a 

mass of 22,400 Mg.

Plots of mean elevations along various segments of the 

transects were made to illustrate the mean-bed elevations for 

the annual surveys and their standard deviations (fig. 7). For 

the annual site visits (2005 to 2008) all of the points surveyed 

between the left and right banks along transects 1 and 30 

were used to compute a mean elevation for the transects in 

this reach (entire channel) (fig. 7A). In the reach of the river 

between transects 11 and 20, the mean elevations on the managed islands are plotted for 2005 to 2008 (fig. 7B). The mean 

elevation of the points surveyed between the island and the 

right bank (south channel) along transects 11 through 30 are 

also plotted (fig. 7C). Figure 7A shows that the reach upstream 

of the islands (transects 1 to 10) has relatively small standard 

deviations and as the transects transition downstream and 

across the managed islands, the standard deviations increase 

in magnitude. The profiles shown in figure 7B indicate the 

change in the mean elevations on the islands as a result of the 

management activities. The mean elevation at transect 11 on 

the island decreased over 1 m from the management. However, it is the only transect with a post-management mean that 

falls outside the standard deviations of the pre-management 

measurements. The majority of transects between 11 and 23 in 

the south channel (13 out of 20) showed an increase in mean 

elevation in the surveys conducted from 2005 to 2006 (fig. 

7C), which coincide with the time period of sediment addition, 

but these changes also fall within the standard deviations of 

the measurements. 

599.5

600

600.5

601

601.5

602

602.5

603

0 5 10 15 20 25 30 35

TRANSECT

ELEVATION, IN METERS

MEAN BED ELEVATION 2005

MEAN BED ELEVATION 2006

MEAN BED ELEVATION 2007

MEAN BED ELEVATION 2008

1 STANDARD DEVIATION

Figure 7. Longitudinal mean bed elevation upstream from, within, and downstream from the management area prior 

to (2005) and following the management (2006 to 2008) for (A) the entire channel, (B) the managed islands, and (C) the 

south channel.

A
Islands

Analysis of Channel Morphology 13

599.5

600

600.5

601

601.5

602

602.5

603

603.5

604

604.5

0 5 10 15 20 25

TRANSECT

ELEVATION, IN METERS

MEAN BED ELEVATION 2005

MEAN BED ELEVATION 2006

MEAN BED ELEVATION 2007

MEAN BED ELEVATION 2008

1 STANDARD DEVIATION

B

599.5

600

600.5

601

601.5

602

602.5

603

0 5 10 15 20 25 30 35

TRANSECT

ELEVATION, IN METERS

MEAN BED ELEVATION 2005

MEAN BED ELEVATION 2006

MEAN BED ELEVATION 2007

MEAN BED ELEVATION 2008

1 STANDARD DEVIATION

C
Islands

14 Channel Morphology and Bed Sediment Characteristics, Uridil Property, Platte River, Nebraska 

Because of the large variation in elevations surveyed 

across the islands and the channels compared to the magnitude 

of change caused by the management activities, using the 

standard deviation alone to determine statistical significance 

is not particularly diagnostic. The interpolated transects along 

the study area were also examined to compute the net changes 

in area (aggradation plus degradation) between the transects 

along the entire channel, the islands, and the south channel 

(fig. 8). Figure 8A shows the net change in channel area for 

the entire channel. In the year between 2005 and 2006 along 

the area where island management activities were performed 

(transects 11 to 18) net degradation was measured as the 

material on the island surfaces was removed and the elevation reduced. In the same time period, a waterfowl pond was 

excavated in an island along transect 17 (independent of this 

project) by a downstream landowner. Net degradation along 

transect 17 was detected from the excavation and net aggradation was measured along transect 18 where the excavated 

material was deposited. A majority of the transects surveyed 

across the entire channel showed net degradation from 2006 

to 2007. A continuous interval of net aggradation was detected 

from transect 7 to 16 from 2007 to 2008 which overlaps the 

area where the island management activities were previously 

performed and includes the time period with the highest peak 

flow measured during the study, 360 m3

/s. The profiles in 

figure 8B traverse the island channel segment. As in figure 8A, 

the island management reduced the mean channel elevation 

from 2005 to 2006. From 2006 to 2007 magnitudes of aggradation and degradation are nearly balanced across the island 

and from 2007 to 2008 some net aggradation was measured 

at the upstream end of the islands. Figure 8C shows the net 

gradation profiles computed in the south channel. From 2005 

to 2006 a small quantity of aggradation was measured in the 

area of sediment addition (transects 12 to 19) which extends 

downstream to transect 22. In the year between 2006 to 2007 a 

majority of the transects in the south channel underwent degradation while from 2007 to 2008 a small amount of aggradation was detected from transects 11 to 15. 

While figures 7 and 8 allow the magnitude of large 

changes in channel elevation to be visualized, the statistical 

significance of these and smaller magnitude changes are not 

readily apparent. The Wilcoxon signed-rank test was used to 

test the statistical significance of the changes that were identified in figures 7 and 8 (table 1). Of special interest is a determination if the net aggradation along transects near the area 

of sediment addition in figure 8C is statistically significant. 

The Wilcoxon signed-rank test indicated that the distributions 

along transects 13 to 16 were significantly different from 2005 

and 2006 as were the transects 19, 21, and 22.

-60

-40

-20

0

20

40

60

0 5 10 15 20 25 30

TRANSECT

NET CHANGE IN CHANNEL AREA, IN SQUARE METERS .

2006-2005

2007-2006

2008-2007

Figure 8. Net change in area between annual transect surveys (A) entire channel, (B) managed islands, and 

(C) south channel.

A
Islands

Analysis of Channel Morphology15

-60

-40

-200

20

40

60

05 10 15 20 25 30

TRANSECT

NET CHANGE IN ISLAND AREA, IN SQUARE METERS .

2006-2005

2007-2006

2008-2007

-60

-40

-200

20

40

60

05 10 15 20 25 30

TRANSECT

NET CHANGE IN CHANNEL AREA, IN SQUARE METERS .

2006-2005

2007-2006

2008-2007

BC
16 Channel Morphology and Bed Sediment Characteristics, Uridil Property, Platte River, Nebraska 

Entire Channel p-values by year

Transect 2005–2006 2006–2007 2007–2008

 1 0.32 0.01 0.01

 2 0.12 0.02 0.01

 3 0.00 0.00 0.28

 4 0.60 0.00 0.00

 5 0.24 0.00 0.01

 6 0.01 0.00 0.02

 7 0.78 0.00 0.02

 8 0.41 0.08 0.00

 9 0.50 0.34 0.02

10 0.58 0.00 0.03

11 0.00 0.01 0.00

12 0.00 0.00 0.00

13 0.00 0.00 0.00

14 0.00 0.59 0.00

15 0.00 0.00 0.00

16 0.00 0.00 0.00

17 0.00 0.05 0.40

18 0.00 0.42 0.00

19 0.00 0.00 NA

20 0.67 0.99 NA

21 0.00 0.00 NA

22 0.00 0.65 NA

23 0.14 0.01 NA

24 0.00 0.00 NA

25 0.00 0.32 NA

26 0.00 0.03 NA

27 0.00 0.01 NA

28 0.00 0.00 NA

29 0.46 0.06 NA

30 0.02 0.99 NA

Table 1. Results of Wilcoxon signed-rank test for annual transect surveys. Significant p-values 

are less than 0.05. [NA, not applicable]
Analysis of Channel Morphology 17

Managed p-values by year Islands

Transect 2005–2006 2006–2007 2007–2008

11 0.00 0.00 0.00

12 0.00 0.00 0.00

13 0.00 0.04 0.00

14 0.00 0.21 0.00

15 0.00 0.14 0.01

16 0.00 0.88 0.02

17 0.00 0.01 0.00

18 0.00 0.00 0.00

19 0.05 0.01 NA

20 0.39 0.95 NA

South

Channel p-values by year

Transect 2005–2006 2006–2007 2007–2008

11 0.00 0.02 0.36

12 0.18 0.91 0.62

13 0.00 0.00 0.11

14 0.00 0.00 0.01

15 0.02 0.89 0.90

16 0.00 0.05 0.30

17 0.07 0.00 0.85

18 0.78 0.51 0.56

19 0.00 0.00 NA

20 0.00 0.00 NA

21 0.00 0.00 NA

22 0.00 0.03 NA

23 0.66 0.08 NA

24 0.42 0.00 NA

25 0.05 0.00 NA

26 0.73 0.00 NA

27 0.17 0.01 NA

28 0.57 0.00 NA

29 0.64 0.00 NA

30 0.97 0.21 NA

Table 1. Results of Wilcoxon signed-rank test for annual transect surveys. Significant p-values 

are less than 0.05. [NA, not applicable].—Continued
18 Channel Morphology and Bed Sediment Characteristics, Uridil Property, Platte River, Nebraska 

Analysis of Bed Sediment 

Characteristics

 Examination of the maps of bed-sediment median grain 

size, D50, illustrate that there was a large range in the D50

parameter throughout the reach (figs. 9a and b). The mean 

D50 in 2005 across the reach was 0.69 mm with a standard 

deviation of 0.37 mm; those collected in 2006 had a mean 

of 0.68 mm with a standard deviation of 0.59 mm. Figure 

9C illustrates the spatially interpolated differences. A small 

amount of fining is seen near the areas of sediment addition 

(fig. 2). However, other areas in the study reach away from the 

augmentation underwent similar or even greater magnitudes 

of fining (fig. 9C). The samples collected on all the islands 

in the reach prior to the management (2005) had an average 

D50 of 0.34 mm and a standard deviation of 0.15 mm, while 

the samples collected on the islands that were leveled had an 

average D50 of 0.32 mm and a standard deviation of 0.12 mm. 

The percentage of silt and clay in the island samples ranged 

between 0.17 percent of the total by mass to 16.63 percent 

with an average of 4.58 percent and a standard deviation of 

5.22 percent. 

Figure 9. Interpolated median grain size (D50) surface generated from river bed samples (A) 

collected July 2005 and (B) May 2006, and (C) interpolated difference in bed sediment median grain 

size (D50) between samples collected in 2005 and those collected in 2006. The 2005 sample results 

were subtracted from the 2006 sample results; therefore a negative value indicates the area sampled 

became finer from 2005 to 2006 and a positive value indicates the area sampled became coarser.

A
Analysis of Bed Sediment Characteristics 19

B

C
20 Channel Morphology and Bed Sediment Characteristics, Uridil Property, Platte River, Nebraska 

Samples collected along transect 11 were used to illustrate the variability in grain sizes across a transect and on a 

managed island. Figure 10 shows the grain-size distribution of 

samples collected along transect 11 in 2005. The size distributions of the 13 samples obtained in the river channel were 

averaged to compute a mean grain-size distribution. The D50

of this average distribution was 0.49 mm compared with a 

maximum D50 of 1.5 mm and minimum D50 of 0.25 mm. The 

D50 of the sample obtained from the island along transect 11 

was 0.22 mm. 

The Wilcoxon signed-rank test was also used to determine if the size parameters computed for sediment samples 

collected in 2005 followed the same distribution as those 

collected in 2006. Table 2 shows the results of the analysis 

for 3 size parameters collected in different areas of the study 

reach. Samples collected in the entire reach, input, managed, 

and output reaches, and the reach along the south channel 

were tested. The D16 of the samples collected in the entire 

reach in 2006 were determined to be of a different distribution 

that was finer than that sampled in 2005. The D16 and D50 sizes 

of the input reach samples collected in 2005 were also finer 

than those measured in 2006 and determined to be statistically 

significant. The managed or output reaches did not show significant changes in the sediment sizes considered. The south 

channel indicated that the D84 showed a significant increase 

from 2005 to 2006 (table 2). 

Stratification D16

p-values by parameter

D50 D84

n

All samples 0.03 0.16 0.70 173

Input 0.03 0.04 0.18 57

Managed 0.96 0.99 0.58 79

Output 0.06 0.65 1.00 37

S. channel 0.12 0.11 0.04 24

Table 2. Results of Wilcoxon signed-rank test for the size parameters in the 2005 and 2006 sediment samples. [D16 , size for which 16 

percent of the sample by mass is finer; D50 , size for which 50 percent of the sample by mass is finer; D84 , size for which 84 percent of the 

sample by mass is finer]

Figure 10. Grain-size distribution of sediment samples collected along transect 11 in the Uridil Property in 2005.
Summary and Conclusions 21

Inferences from Habitat Enhancement 

Activities 

The grain-size distribution of island sediment sampled 

in the study reach was finer that that which was present on 

the river bed. When introduced to the river, these relatively 

fine-grained sands were easily transported down river by 

suspension while the coarser fraction was made available to 

contribute to the elevation of the river bed. Statistical analysis 

of bed elevations in the area of sediment addition provided 

evidence that elevated bed levels were significantly raised and 

aggradation occurred in the time period of the management 

activities, providing a causal linkage. However, it does not 

eliminate the possibility that the changes in mean bed elevation measured in the south channel in this time period were the 

result of natural fluvial processes. Elevated river flows in the 

final 2 years of the study also occurred over the same period 

of statistically significant but opposite changes. Net degradation along the majority of transects in the entire reach segment 

occurred in 2007 while in 2008 net aggradation was observed 

in the majority of the transects surveyed. These differential 

responses could be attributed to the variation in flow magnitudes and (or) the magnitude of upstream sediment supply.

Bed elevation adjustments in natural river channels 

are forced by the supply rate and caliber of sediment loads 

imposed on them. Adjustments are also influenced by the 

effects of flow regime (magnitude, duration, and rate of 

change) which interacts with the sediment supply influencing 

the resultant sediment storage or evacuation in a natural channel. Controlled experiments in laboratory channels have been 

used to examine the effects of sediment supply on channel elevation (Soni and others, 1980; Germanoski and Shumm, 1993; 

Madej and others, 2009). These approaches are instructive but 

simplify the effect of reach-scale hydraulics which are driven 

by topographic complexity. Flume studies also have difficulty 

simulating long time scales over which natural flow regimes 

influence sediment storage. Acquiring this insight from field 

data sets also is problematic given the inability to either accurately measure or manipulate key variables. However, because 

some level of topographic monitoring will be required at 

sediment augmentation sites for permitting purposes, standardizing the monitoring methodology and analysis techniques will 

facilitate inter-comparison of the empirical results. Results 

from the study described in this report should stimulate efforts 

toward this objective.

More temporal intensive sediment monitoring which 

would include both bed-load, bed-sediment, and suspendedsediment sampling during an augmentation experiment 

would provide more detailed information and perhaps a better 

estimate of sediment residence time. These data could contribute toward a better understanding of the effect of shear stress 

on local bed-load and suspended-load transport and how the 

addition of fine-grained sand influences the caliber of bed 

sediment in the channel over shorter time scales furthering 

the development of computer models that simulate these 

processes. 

If island sediment is to be used to augment natural supplies and alter channel elevations, an understanding of the size 

distribution of the added material is essential. The deposition 

history, fluvial or eolian, can produce varying size distributions which influence both the persistence of added material 

and potential for bed armoring. In addition, the supplies of 

island sediment are finite and may be locally exhausted during a multi-year sediment-augmentation program; therefore, 

sustained addition of sediment is needed if the goal.

The U.S. Fish and Wildlife Service’s spring 2006, 2007, 

and 2008 airboat surveys did not observe tern and plover 

nests on any of the islands modified as part of this project 

(Jeff Runge, USFWS, oral communication, 2008). Growth of 

phragmites (common reed) on the islands following clearing 

required subsequent management in 2008 using both herbicides 

and mechanical discing. The addition of coarser substrate to 

the islands has also been identified as a means that could be 

used in the future to provide suitable nesting habitat for terns 

and plovers (Kenny Dinan, USFWS, written communication, 

2008).

Summary and Conclusions

This report presents an analysis of channel morphology 

and bed sediment characteristics based on data collected in the 

Platte River Whooping Crane Maintenance Trust (PRWCMT) 

Uridil Property during water years 2005 to 2008. The report 

is intended to provide the data necessary to detect the physical response of the river channel to a management strategy 

designed to enhance in-channel habitat for migratory water 

birds. This strategy also includes components of an approach 

outlined by the Platte River Final Environmental Impact Statement and the Platte River Recovery Implementation Program 

intended to benefit endangered and threatened species in the 

Platte River basin.

Repeat topographic surveys along the study reach 

indicate that the sand that was mechanically introduced into 

the south channel as a result of this project had a relatively 

short residence time. Increases in mean-bed elevation and net 

aggradation detected 3 months after sediment addition were 

not observed 15 months later. The changes in bed elevation 

in the south channel from natural flows were of comparable 

magnitude to the changes in bed elevation that could be 

attributed to the effect of the mechanical sediment addition. 

This fact highlights the need for sustained addition of sediment to channels if the goal of sediment addition is to raise 

and maintain bed elevations. Subtraction of median grain sizes 

from samples collected in 2005 from those collected in 2006 

indicate a subtle fining of bed sediment near the sedimentaddition site. However, fining of bed-sediment samples during 

this time period was not found to be unique to the areas of 

sediment addition or statistically significant.
22 Channel Morphology and Bed Sediment Characteristics, Uridil Property, Platte River, Nebraska 

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