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An Experimental Investigation on Hydraulic Resistance in Vegetative Open Channel Flows

Author(s): Dong Sop Rhee; Hyoseop Woo

Linked Author(s): Hyoseop Woo

Keywords: Flow resistance; Open channel; Resistance coefficient; Vegetation

Abstract: Vegetation in rivers is an important factor for improving and restoring river environment. Vegetation usually used for levee protection and revetments has high aesthetic values as well as environment-friendliness. In view of open channel hydraulics, however, vegetation in the channel usually causes changes in flow resistance and thus causes increases in flood stage. Researches have been conducted on the flow resistance of vegetation in open channel, both experimentally and numerically. Those researches, however, are based on the vegetation found frequently in the regions where the researchers themselves locate, causing a locality problem. In this study, three Korean natural plants, Zoysia matrella (Korean Golden Zoysia), Pennisetum alopecuroides (L. ) Spreng. (Korean Pennisetum), and Phragmites communis Trin. (Reed) were used for flume tests on the effect of vegetation in the channel on flow resistance. The “n-VR” retardance curves have been developed for each grass. All these grasses were tested under un-mown conditions. Zoysia matrella was tested under fully submerged conditions and the other two were tested under both submerged and un-submerged conditions. Resistance coefficients, expressed as Manning’s n for Zoysia matrella is converged to about 0. 03 as VR increases. The resistance coefficients for other plants are affected by the state of plants, i. e., “green” or “dormant.” Generally, the resistance coefficients are rather large when plant state is “green” rather than “dormant.” Also, it is larger when the flow is affected by the leaf-part of vegetation rather than by only the stem-part of vegetation. Interaction of the bending-part of vegetation and water surface tends to increase magnitude of the resistance coefficient. Resistance coefficients for Zoysia matrella and Pennisetum alopecuroides (L. ) Spreng., however, are less affected by water depth than Phragmites communis Trin.


Year: 2007

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