Effects of Riparian Forest on Disaster Prevention andPreservation of Natural Environments

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We have investigated about 5 subjects, targeting the riparian forest where plays an important role to the environment fromation of mountainous region. A general outline of each study is explained in the following.(1) Flow resistance in woody vegetated channels with low forestCharacteristics of flow resistance in woody vegetated channels was studies by hydraulic model experiments. With the vegetated roughness concentration, the ratio of flow depth increased in an exponentially manner, wheras the ratio of glow velocity decreased in a similar manner. Flow velocity uniformity was established in cases of high roughness cocentration. Equations for calculating friction factor were proposed.(2) Bed-load sediment transport in woody vegetated channelsBed-load sediment transport rate in woody vegetated channels was studied by hydraulic model experiments. As the roughness concentration of trees in channels increased, the bed-load sediment transport rate decreased. Then, the necessity of taking add … More ount of effective tractive force was recongnized. Eqations for calculation effective tractive force were proposed.(3) Effect of density of trees on drag exerted on trees in river channelsDrag exerted on trees with defferent tree densty along straight channels was measured using by hydraulic experiments. Test results indicated that the drag varies greatly with the dencity of trees × flow depth and they were correlated with te drag coefficient of velocity. Equations were obtained for deriving the drag coefficient.(4) Characteristics of stream bank erosion in woody vegetated channelsCharacteristics of stream bank erosion in woody vegetated channels was studies by hydraulic model experiments. While erosion rate of stream bed decreased, erosion rate of stream bank did not always decrease in woody vegetated channels. Especially, at the edge of water, increasing of erosion rate was found according to circumstances.(5) Actual conditions of promoting deposition of debris caused by debris avalanches by forest zonesA number of debris avalanches occurred in southern Fukushima Prefecture in August 1998 was studiesd for the purpose of examining the functionality of forest zones for promoting deposition of debris caused by debris avalanches using aerial photo interpretation and topographic analysis. The functionality of forest zones for promoting debris deposition was confirmed. Less