Journal of Natural Disaster Science

MEASUREMENT OF WIND DRAG FORCES ON TREES

Hiroyoshi SHI-IGAI
Professor, Institute of Engineering Mechanics, University of Tsukuba, Tsukuba
and
Tohru MARUYAMA
Engineer, Nissei Jushi Kogyo, Nagano

(Received 6 October, 1988 and revised form 12 January, 1989)

Abstract

Trees have a lot of effects on soil conservation at mountainous regions. However, they often trigger land slides or mud avalanches if they cannot resist against strong winds, since the fallen trees may dam up mud and water and that natural dam eventually collapses, which triggers landslides. We developed a technique to estimate the total mass of trees in vivo and evaluated the wind force which acts on trees under natural conditions. The evaluated wind drag coefficients of trees whose height is about four meters showed much greater values than the shorter trees obtained in several wind tunnels. We propose several reasons of this unusual phenomenon.

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