Streambed Adjustment and Channel Widening in Eastern NebraskaBy David L. Rus, Benjamin J. Dietsch, U.S. Geological Survey, and Andrew Simon, National Sedimentation LaboratoryAvailable 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. This document also is available in pdf format:
WRIR 03-4003.pdf (5.5 MB) AbstractIn 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 ContentsAbstract 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
|
|
USGS | Biology | Geology | Geography | Water | WRI Reports | Water Related Reports |
AccessibilityFOIAPrivacyPolicies and Notices | |