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United States Department of Agriculture

Agricultural Research Service

Title: Estimating Manning's Roughness Coefficient for Shallow Overland Flow in Non-Submerged Vegetative Filter Strips

Authors
item Jin, Chang-Xing - MISSISSIPPI STATE UNIV
item Romkens, Mathias
item Griffioen, F - WAGENINGEN AG UNIV

Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 18, 2000
Publication Date: N/A

Interpretive Summary: An important constituent process in soil erosion is sediment transport by overland flow on upland areas. The ability of flow to carry rainfall detached soil particles or soil particles detached by shear forces of overland flow is determined by the flow rate, flow velocity, and the nature of the detached soil material. During most of the year, upland areas are covered in part or in full with vegetation, crop residue, or surface mulch. The ability of flow to transport soil particles is to a large degree determined by the resistance that is afforded by the vegetative or residue cover on the soil surface. This resistance is usually referred to as Manning's coefficient. This paper examines how Manning's coefficient varies for different flow conditions (flow rate, flow velocity/slope steepness) and vegetative cover. It recognizes that Manning's coefficient is made up of two components - one due to the soil surface itself, the other due to the vegetative elements. The results show that Manning's coefficient for non-submerged vegetative filter strips is a function of flow velocity, slope steepness, and flow depth. This information will be very helpful in understanding and calculating sediment transport in shallow overland flow situations such as on grass filter strips.

Technical Abstract: Results of experimental study showed that overland flow in non-submerged vegetative filter strips can be described by Manning's formula with a variable roughness coefficient. The roughness coefficient is made up of the shear stress caused by the boundary roughness and the drag force caused by vegetation. Resistance due to vegetation was related to vegetation density and flow depth. For small flow rates, the shear stress at the boundary played the major role. As the flow rate increased, the drag force due to vegetation became dominant. The model can be used in design of vegetative filter strips, irrigation channels and other vegetated waterways.

Last Modified: 7/31/2014
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