Journal of the Japan Society of Erosion Control Engineering, Vol.58,No.3,2005
Restoration process of pools filled up with sediment in step]pool bed form
Masaharu FUJITA Takahisa MIZUYAMA Toyoaki SAWADA Shinei NIIHARA
Abstract
Natural mountainous rivers with step]pool bed form provide good habitats for fish.
However, once too much sediment is naturally or artificially supplied there, the
habitats must be damaged by the severe sediment deposition. The following clear
water flow tries to restore the habitat, but the impact could continue until the
bed condition is back to the previous situation. Important information on impact
evaluation of the sediment movement is the deposition volume in pools, the erosion
volume and the time necessary to be thoroughly restored. The aim of this paper
is to make the restoration process from a fully sediment deposition clear. Firstly,
a field experiment on artificial sediment flushing from a check dam was carried
out in the Hiru]dani torrent. The restoration process from fully sediment deposition
in the pools was monitored over one year. As a result, the pools had the different
restoration rate and some pools did not return to the previous situation. This
is because restoration process depends on the experienced water discharges. Then,
a restoration process was analyzed with a focus on the bottom velocity in pools
and a method for evaluating the restoration rate was presented. The method could
explain the restoration process in the Hiru]dani torrent.
Key words:restoration, step]pool, sediment deposit, sediment flushing, habitat,
mountainous rivers
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