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Scientific Investigations Report 2013–5035

Erosional and Depositional Changes Wrought by the Flood of May 1978 in the Channels of Powder River, Southeastern Montana

By Robert H. Meade and John A. Moody

Thumbnail of and link to report PDF (16.4 MB)Abstract

Powder River’s second largest flood of record (1919–2012) moved through northeastern Wyoming and southeastern Montana during May 1978. Within a ninety-kilometer reach of the channel in southeastern Montana, the most prominent planform effects of the flood were the growth of meander bends by bank erosion (this was most intense just downriver of bend apexes, causing 1–2 channel widths of lateral displacement) and the erosion of new cutoff channels through the necks of two large and two small meanders. Surveys of cross sections, made before and after the flood, show the responses of the channel to the flood waters, which ranged from minimal (bedrock control) to large (maximum channel curvature in unconsolidated bank and terrace deposits). Geomorphic work done during two weeks of extreme flooding in May 1978, as measured by cross-channel erosion and new sediment deposition, was approximately equal in magnitude to the work done during the two decades (1978–1998) that followed the flood.

First posted December 16, 2013

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Director, Branch of Regional Research
U.S. Geological Survey
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Denver, CO 80225
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Suggested citation:

Meade, R.H., and Moody, J.A., 2013, Erosional and depositional changes wrought by the flood of May 1978 in the channels of Powder River, southeastern Montana: U.S. Geological Survey Scientific Investigations Report 2013–5035, 29 p., and 1 map plate, http://dx.doi.org/10.3133/sir20135035.

ISSN 2328-0328 (online)



Contents

Abstract

Introduction

Powder River and the Flood of May 1978

Effects of the Flood of 1978 on River Channels

Effects of the Flood of 1978 Compared with the Cumulative Effects of Subsequent

Flows of Less Magnitude

Recollections of the Flood of 1923

Summary

Acknowledgments

References Cited


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