Hydraulic resistance of some selected vegetation in open channel Flows

Abstract

Vegetation in rivers has important roles in improving and restoring river environment. Other than it adds high aesthetic value to revetments, that it can be used as a levee protection in environmental friendly way. In open channel hydraulics, vegetation often causes changes in the flow resistance, usually resulting in the increase of flood stage. Both experimental and numerical researches have been conducted on flow resistance of vegetation in open channels, however, the researches were based mostly on the vegetation found in the region where the researches were conducted, and this restricts the generality of the results. In this study, three Korean natural vegetations, Zoysia matrella (Korean zoysia), Pennisetum alopecuroides (L.) Spreng. (Korean native vegetation) and Phragmites communis Trin. (Korean reed) were used in flume tests on the effect of vegetation in the channel on flow resistance. ‘n‐VR’ retardance curves were developed for each grass. All the grasses were tested under unmown conditions. Z. matrella was tested under fully submerged condition and other two were tested under both submerged and un‐submerged conditions. Resistance coefficient, expressed as Manning's n, converged to about 0.027 (total roughness) for Z. matrella as VR increased. Resistance coefficients for other plants were found affected by the states of the plants, that is, whether they were ‘green’ or ‘dormant’. Generally, resistance coefficients are higher when plants are ‘green’ than when they are ‘dormant’. This is because the resistance coefficient is influenced by the leaf elements of vegetation on the river flow in addition to the stem of vegetation. The interaction between the bending part of vegetation and the water surface can also increase the resistance coefficient. In terms of water depth, P. communis Trin were found more affected on the resistance coefficients compared to Z. matrella and P. alopecuroides (L.) Spreng. Copyright © 2008 John Wiley & Sons, Ltd.

Evaluation on Flow Discharge of Grassed Swale in Lowland Area

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Experimental Study on Wetland Hydraulic Characteristics of Vegetated Drainage Ditches

“…(1) In traditional flume experiments, Rhee et al [30] determined a roughness coefficient that was 0.029-0.195 using the combination of flume and real grass. Research made by Abood et al [31] suggested that roughness coefficient was 0.01~0.23, and that roughness coefficient turned to the largest at a minimum water velocity or water depth.…”

Spatial distribution and environmental determinants of denitrification enzyme activity in reed-dominated raised fields

“…4). Moreover, a high level of rhizome biomass was observed in the slope of raised fields because of the requirement of extensive root systems to keep P. australis growing normally (Rhee et al, 2008).…”