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ARS Home » Southeast Area » Oxford, Mississippi » National Sedimentation Laboratory » Watershed Physical Processes Research » Research » Publications at this Location » Publication #103637
Title: RIVER WIDTH ADJUSTMENT. I: PROCESSES AND MECHANISMS

Author
item THORNE, COLIN - UNIV NOTTINGHAM, UK
item Alonso, Carlos
item BORAH, DEVA - IL STATE WATER SURVEY
item DARBY, STEPHEN - UNIV SOUTHAMPTON, UK
item DIPLAS, PANOS - VA POLYTH UNIVERSITY
item JULIEN, PIERRE - CO STATE UNIVERSITY
item KNIGHT, DONALD - UNIV BIRMINGHAM, UK
item PIZZUTO, JIM - UNIV DELAWARE
item QUICK, MICHAEL - UNIV BRITISH COLUMBIA
item Simon, Andrew

Submitted to: American Society of Civil Engineers Journal of Hydraulic Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: Erosion of unstable stream channels is a principle means of land loss in agricultural watersheds. Sediment from eroding streambanks contributes at least 75% of the material emanating from unstable alluvial channels and poses a significant threat to flood plain resources and agricultural activities through land loss, long-term availability of water resources through reservoir sedimentation, and to downstream habitat and water quality. Stream bank erosion is usually associated with channel deepening and stream meandering. This paper presents a state-of the-art review conducted by an ASCE Task Committee established to evaluate (1) our existing knowledge of channel widening processes and temporal evolution of eroding streams, (2) important knowledge gaps in this area, and (3) engineering methods developed to assess the stability of alluvial streams. The conclusions presented in the paper will be very useful to engineers and geologists working on the development of effective rehabilitation technology to reduce land loss and problems associated with eroding channels.

Technical Abstract: In 1993 a Task Committee (TC) of the ASCE was established to study the hydraulics, bank mechanics, and modeling of width adjustment in alluvial channels. The work of the TC in reviewing width adjustment processes and mechanisms is reported in this paper. A companion paper presents the findings of the TC with regard to width adjustment modeling. This paper first establishes the geomorphic context within which width adjustments occur, and it demonstrates that width adjustment may take place over a wide range of scales in time and space. In the past engineering analyses of channel width have tended to concentrate on prediction of the equilibrium width for stable channels. Most commonly the regime, extremal hypothesis, and rational (mechanistic) approaches are used, and these are reviewed herein. More recently, attention has switched to watershed land use, river regulation, or channel engineering. Characterizing and explaining the time-dependent behavior of width in such channels requires an understanding of the fluvial hydraulics of unstable channels, especially in the near-bank regions. Existing knowledge is reviewed, useful engineering tools are presented, and gaps requiring further field and laboratory research are identified. Finally, this paper considers the mechanics of bank retreat due to flow erosion and mass failure under gravity, and bank advance due to sedimentation and berm building.