A new methodology for velocity estimation in sheet and rilled overland flow using modified Manning's roughness coefficient

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Title A new methodology for velocity estimation in sheet and rilled overland flow using modified Manning's roughness coefficient
Author Rouhipour, H.; Ghadiri, Hossein; Rose, Calvin Wyatt; Yu, Bofu
Publication Title Soil and Water Conservation, Climate Change and Environmental Sensitivity
Year Published 2008
Place of publication Budapest, Hungary
Abstract Manning's roughness coefficient for flow over bare soil is needed in order to determine other hydraulic parameters such as flow depth and velocity in overland flow, parameters needed to calculate streampower and shear stress in erosion process studies. A modified equation of Manning's n was developed to estimate flow velocity in shallow overland flow in experiments undertaken in a 5.8 by 1 m flume of the Griffith University Tilting flume Simulated Rainfall facility and adopted data from the literature. Even with the flow of water over a soil surface in which roughness elements are well inundated, and in less erosive situations where erosional bed forms are not pronounced, the magnitude of resistance coefficients in equations such as those of Manning, Darcy-Weisbach or Chezy vary with flow velocity (at least). Using both original laboratory and field data, and data from the literature, the paper examines this question of the apparent variation of resistance coefficients in relation to flow velocity, even in the absence of interaction between hydraulics and resulting erosional bed forms. Resistance equations are first assessed as to their ability to describe overland flow velocity when tested against these data sources. The result is that Manning's equation received stronger support than the Darcy-Weisbach or Chezy equations, though all equations were useful. The second question addressed is how best to estimate velocity of overland flow from measurements of slope and unit discharge, recognizing that the apparent flow velocity variation in resistance coefficients is probably a result of shortcomings in all of the listed resistance equations. A new methodology is illustrated which gives good agreement between estimated and measured flow velocity for both well-inundated sheet and rill flow. Comments are given on the predictive use of this methodology.
Peer Reviewed No
Published Yes
Publisher URI http://www.tucson.ars.ag.gov/isco/
Alternative URI http://tucson.ars.ag.gov/isco/isco15/MS.htm
Copyright Statement Copyright remains with the authors 2008. The attached file is posted here with permission of the copyright owners for your personal use only. No further distribution permitted. For information about this conference please refer to the publisher's website or contact the authors.
Conference name 15th International Soil Conservation Conference
Location Budapest, Hungary
Date From 2008-05-19
Date To 2008-05-23
URI http://hdl.handle.net/10072/24085
Date Accessioned 2009-04-14
Language en_AU
Research Centre Environmental Futures Research Institute
Faculty Faculty of Science, Environment, Engineering and Technology
Subject PRE2009-Land Capability and Soil Degradation
Publication Type Conference Publications (Full Written Paper - Non-Refereed)
Publication Type Code e2

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