Effect of Density of Trees on Drag Exerted on Trees in River Channels

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概要

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• Recently, riparian forests have attracted attention as they are effective for ecological preservation and landscape enhancement. Usesof such forests in flood prevention, sediment control, and erosion control works have been actively promoted. This study aims toclarify the effect of density of riparian trees on drag exerted on trees along river channels under the regime of bed load transport.Hydraulic model experiments were performed using a straight channel, and the methods to calculate the drag coefficient necessaryfor deriving drag exerted on trees were studied. Previous studies have stated that the drag coefficient of a cylinder is fairly constantwhen Reynolds number, Re, is between 10^3 and 10^5 (e.g., Schlichting, 1979). This study clarified, however, that in cases of relativelydense arrangements of model trees (cylinders), the drag coefficient varies greatly with the density of the trees. As such, correlationbetween the drag coefficient and Reynolds number was found to be slight. Test results indicated that the drag coefficient of trees,C_d, correlates strongly with the coefficient of velocity, U'/U_*', friction factor of the channel bed, f', and roughness concentrationof trees X flow depth, aH' or ratio of the area occupied by trees, λ. Furthermore, the drag coefficient, C_d. was also found to be slightly correlated with the gradient of the channel bed, l. Equations using either of the following parameters were obtained for deriving the drag coefficient, C_d, based on the experiment results:aH';λ; U'/U_*'; and Froude number, F_r. These equations allow fairly accurate calculation of drag exerted on trees.

• 日本森林学会の論文
• 2000-11-16

著者

• Ishikawa Yoshiharu

  Department Of Forest Science Faculty Of Agriculture Kyoto Prefectural University

• Ishikawa Y

  Institute Of Information Sciences And Electronics University Of Tsukuba

• Mizuhara Kunio

  Department of Forest Science, Faculty of Agriculture, Kyoto Prefectural University

• Ashida Shinnya

  Forest Conservation Division, Private Forest Department, Forestry Agency

• Mizuhara Kunio

  Department Of Forest Science Faculty Of Agriculture Kyoto Prefectural University

• Mizuhara Kunio

  Department Of Agriculture And Forestry Nara Prefectural Government

• Ashida Shinnya

  Forest Conservation Division Private Forest Department Forestry Agency

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• Requirement Specification and Derivation of ECA Rules for Integrating Multiple Dissemination-Based Information Sources
• Effect of Density of Trees on Drag Exerted on Trees in River Channels
• Effect of density of riparian vegetation on effective tractive force
• Flood-deposition characteristics of debris flows and runoff sediment volume on coastal alluvial fans (Debris flow disasters in the Province of Vargas, Republic of Venezuela in 1999)

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