USGS

Streambed Adjustment and Channel Widening in Eastern Nebraska

By David L. Rus, Benjamin J. Dietsch, U.S. Geological Survey, and Andrew Simon, National Sedimentation Laboratory

Available from the U.S. Geological Survey, Branch of Information Services, Box 25286, Denver Federal Center, Denver, CO 80225, USGS Water-Resources Investigations Report 03-4003, 63 p., 34 figs.

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Abstract

In eastern Nebraska, stream straightening and dredging efforts since the 1890s have disturbed the natural equilibrium of stream channels and have led to streambed adjustment by degradation and subsequent channel widening. This report describes a study to evaluate the effect these disturbances have had on stream channels in eastern Nebraska.

Two sets of survey data were collected approximately 2 years apart during 199699 at 151 primary sites. Additionally, historical streambed-elevation data (dating back to the 1890s) were compiled from several sources for the primary sites and 45 supplemental sites, and relevant disturbances were identified for each of eight basin groupings. Streambed-elevation data sets were used to estimate the amount of change to the streambed at the sites over the time period of the data. Recent channel widening was documented for 73 of the primary sites by comparing the two survey sets.

The majority of observed streambed-gradation responses appear to be related to the various straightening efforts and to the effects of grade-control structures in the study area. Channel responses were complicated by the presence of multiple disturbances. However, in many cases, the streambed-elevation data sets provide a reliable representation of the past streambed gradation, with some sites showing 6 to 7 meters of degradation since they were straightened. Many sites that had been straightened showed considerable degradation following the disturbance. This indicates that eastern Nebraska stream channels can regain equilibrium mainly through the slope adjustment process of head-ward-progressing degradation.

Bank failures were documented at sites in all eight of the basin groupings analyzed, and widening rates were computed at 64 of 73 sites. Observed bank widening in the Big Blue River Basin, a relatively unstraightened basin, indicates that other disturbances besides stream-channel straightening may be causing channel responses in the basin and possibly in the entire study area.


Table of Contents

Abstract

Introduction

Purpose and Scope

Description of Study Area

Attributes Associated with Channel Adjustment in Eastern Nebraska

Acknowledgments

Methods

Site Selection

Data Collection

Topographic Data

First-Round Survey

Second-Round Survey

Reference to National Geodetic Vertical Datum of 1929

Streambed Particle-Size Analyses

Characterization of Streambed Adjustment

Streambed Elevation History

Influences on the Streambed

Disturbances

Knickpoints

Grade-Control Structures

Characterization of Recent Channel Widening

Contouring First-Round Survey Data

Overlay of Second-Round Survey Data

Characterization of Individual Top-of-Bank Failures

Computation of Widening Rates

Streambed Adjustment

Potential Study-Area-Wide disturbances

Changes to the Median Water-Surface Elevation of the Missouri River

Agricultural Development in Nebraska

Missouri River Tributary Basins

Documented Disturbances, Knickpoints, and Grade-Control Structures

Streambed Summaries

Papillion Creek Basin

Documented Disturbances, Knickpoints, and Grade-Control Structures

Original Straightening

Urbanization

Flood-Control Channel Modifications Since the 1960s

Degradation of the Missouri River

Streambed Summaries

Platte River Tributary Basins

Documented Disturbances, Knickpoints, and Grade-Control Structures

Straightening in the Platte River Flood Plain

Basinwide Straightening

Straightening at PRT-3

Streambed Summaries

Elkhorn River Basin

Documented Disturbances, Knickpoints, and Grade-Control Structures

Straightening of the Elkhorn River

Straightening of Logan Creek

Straightening of Maple Creek

Straightening of Other Elkhorn River Tributaries

Streambed Summaries

Salt Creek Basin

Documented Disturbances, Knickpoints, and Grade-Control Structures

Original Channelization of Salt Creek

Individual Tributary Modifications

Urbanization and Flood Control Modifications in the Lincoln Area

Streambed Summaries

Little Nemaha River Basin

Documented Disturbances, Knickpoints, and Grade-Control Structures

Original Straightening

Channelization in the South Fork Little Nemaha River and Muddy Creek Subbasins

Streambed Summaries

Big Nemaha River Basin

Documented Disturbances, Knickpoints, and Grade-Control Structures

Streambed Summaries

Big Blue River Basin

Documented Disturbances, Knickpoints, and Grade-Control Structures

Streambed Summaries

Channel Widening

Summary and Conclusions

References

 

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