Stream Bank Stability in Eastern Nebraska

This report describes a study to analyze bank stability at selected sites in eastern Nebraska and develop a simplified method for estimating the stability of banks at future study sites. Bank cross sections along straight reaches of channel and geotechnical data were collected at approximately 150 sites. The sites were categorized into three groups based on mapped soil permeability. With increasing permeability of the soil groups, the median cohesion values decreased and the median friction angles increased. Three analytical methods (Culmann, Agricultural Research Service and an indirect method) were used to determine if banks were stable, at risk, or unstable. The maximum angle from horizontal at which the bank would be stable for the given soil and bank height conditions also was computed with the indirect method. A comparison of the expected stable bank angles for saturated conditions and the surveyed bank angles indicated that many of the surveyed bank angles were considerably less than the maximum expected stable bank angles despite the banks being classified as at risk or unstable. For severely degraded channels along straight reaches this was not expected. Several possible explanations are discussed. At least for some bank sections, it appears that the summary results of bank stability for this study are overly optimistic. Although some individual bank sections may be accurately portrayed, it is not known which or how many bank sections are accurately classified without more extensive data to determine variability in soil shear strength. If the variability of soil parameters, especially cohesion, can be determined for a site, and if the variability is small so that average or weakest values can be used to represent the banks, any of the methods demonstrated in this report can be used to make preliminary assessments of channel bank stability at future study sites. An electronic spreadsheet has been developed to make preliminary assessments of existing bank stability or to assess future bank stability. The spreadsheet also can automatically compute the maximum uniform angle at which a bank section would be expected to be stable.

[1]  Yang H. Huang,et al.  Stability analysis of earth slopes , 1983 .

[2]  Colin R. Thorne,et al.  Stream Channel Stability. Appendix D. Bank Stability and Bank Material Properties in the Bluffline Streams of Northwest Mississippi , 1981 .

[3]  David L. Rus,et al.  Trends in channel gradation in Nebraska streams, 1913-95 , 1999 .

[4]  K. Van Wilson,et al.  Channel and bank stability of Standing Pine Creek at State Highway 488 near Freeny, Leake County, Mississippi , 1992 .

[5]  A. Bishop.  The use of the Slip Circle in the Stability Analysis of Slopes , 1955 .

[6]  V. Drnevich,et al.  Suggested Method for Performing the Borehole Shear Test , 1987 .

[7]  D. Phil Turnipseed,et al.  Channel and bank stability of Bakers Creek at State Highway 547 near Port Gibson, Claiborne County, Mississippi , 1992 .

[8]  J. W. Emerson.  Channelization: A Case Study , 1971, Science.

[9]  A. Simon.  A model of channel response in disturbed alluvial channels , 1989 .

[10]  A. Simon,et al.  Pore Pressure and Bank Stability: The Influence of Matric Suction , 1998 .

[11]  N. M. Fenneman,et al.  Physical divisions of the United States , 1946 .

[12]  S. V. Chitale,et al.  River Width Adjustment. I: Processes and Mechanisms , 2000 .

[13]  Ronald L. Iman,et al.  A Modern Approach To Statistics , 1983 .

[14]  Donald P. Coduto,et al.  Geotechnical Engineering: Principles and Practices , 1998 .

[15]  Andrew Simon,et al.  Man-induced channel adjustment in Tennessee streams , 1982 .

[16]  A. Simon.  THE DISCHARGE OF SEDIMENT IN CHANNELIZED ALLUVIAL STREAMS , 1989 .

[17]  R A Lohnes,et al.  Slope Angles in Friable Loess , 1968, The Journal of Geology.

[18]  M. E. Austin.  Land resource regions and major land resource areas of the United States (exclusive of Alaska and Hawaii) , 1965 .

[19]  A. Simon,et al.  CHANNEL INSTABILITY IN THE LOESS AREA OF THE MIDWESTERN UNITED STATES 1 , 2000 .

[20]  Benjamin J. Dietsch,et al.  Streambed Adjustment and Channel Widening in Eastern Nebraska , 2003 .

[21]  T. Lambe.  Soil testing for engineers. , 1951 .

[22]  G. R. Olson.  Direct shear and consolidation tests of undisturbed loess , 1958 .

[23]  N. Casagli,et al.  Pore water pressure and streambank stability: results from a monitoring site on the Sieve River, Italy , 1999 .

[24]  J. Brice.  Erosion and deposition in the loess-mantled Great Plains, Medicine Creek drainage basin, Nebraska , 1966 .

[25]  W. Perry,et al.  Low-flow characteristics of streams in the Mississippi embayment in Tennessee, Kentucky, and Illinois, with a section on quality of the water , 1965 .

[26]  Alan J. Lutenegger,et al.  Borehole Shear Test in Geotechnical Investigations , 1981 .

[27]  K. V. Wilson.  Changes in channel characteristics, 1938-74, of the Homochitto River and tributaries, Mississippi , 1979 .

[28]  Andrew Simon,et al.  Gradation processes and channel evolution in modified West Tennessee streams; process, response, and form , 1994 .

[29]  D. Fredlund,et al.  Soil Mechanics for Unsaturated Soils , 1993 .

[30]  D. G. Fredlund,et al.  Slope stability analysis incorporating the effect of soil suction , 1987 .

[31]  A. Lutenegger,et al.  Borehole Shear Test for Stiff Soil , 1978 .

[32]  Irving S. Dunn,et al.  Fundamentals of Geotechnical Analysis , 1980 .

[33]  C. Hupp,et al.  Geomorphic and Vegetative Recovery Processes Along Modified Stream Channels of West Tennessee , 1992 .

[34]  E. W. Lane.  The Importance of Fluvial Morphology in Hydraulic Engineering , 1955 .