Author
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Temple, Darrel |
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Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 2/1/1999 Publication Date: N/A Citation: N/A Interpretive Summary: The flow resistance offered by the boundary of a water conveyance channel determines the size that the channel must be to carry a given volume of water. When grass is used on the upper banks of the channel to protect them from erosion, the grass interacts with high flows, causing the flow resistance to vary with the amount of water in the channel. A procedure is presented for use in determining the amount of flow resistance generated b a partially vegetated channel so that the channel may be dimensioned to carry the desired quantity of water. The ability to confidently determine the channel dimensions required for this condition will encourage the use of vegetation rather than more costly or less environmentally desirable bank protection measures. Technical Abstract: Grass channel linings interact with the flow in such a way as to make the flow resistance vary with flow conditions. For uniformly vegetated channels such as grassed waterways, the traditional approach managing this variation in computations has been to express Manning's n for the channel as a function of product of mean velocity and hydraulic radius (n-VR) or Reynold's number. The extent to which this approach could be applied to th computation of composite roughness in channels only partially lined with vegetation, or where vegetal conditions vary sharply within the cross-section, has not been clear. Therefore, tests were conducted to determine the appropriate procedure for computing the composite roughness of these channels. It was found that the traditional n-VR curves could be applied consistently in combination with linear averaging of the wetted perimeter weighted roughness within the cross-section for this purpose. |
