Session3: Environmental Hydraulics
Title: COARSE SEDIMENT MOVEMENT AROUND U-SHAPED VEGETATION ZONE ON GRAVEL BAR WITH TWO MEANDERING CHANNELS
Hirokazu Ikeda, Kosuke Iimura, Yuka Soeta, Chie Kawashima, Satoshi Komura
Vegetation transition was investigated on a large-gravel bar with two meandering channels in Kinugawa River, where the restoration had just been implemented. It is shown that a U-shaped vegetation zone, open to the upstream side, was formed along the main channel and the second channel. This U-shaped zone was mainly composed of Poaceae. The endemic species for gravel bar, such as Aster kantoensis Kitam and Anaphalis margaritacea subsp. yedoensis, and the alien species, such as Eragrostis curvula, seemed to inhabit according to the coarse sediment size deposited in/around the U-shaped zone. Based on the field investigation, Numerical experiments were performed to examin the effect of the U-shaped zone (and its partial clearing) on flow field and coarse sediment movement. The topography of the gravel bar for the numerical analyses was introduced based on a laboratory experiment, and movement of coarse sediment which is smaller than the materials of the gravel bar was investigated. It is suggested that fine sand for Eragrostis curvula can be deposited on the internal or downstream area of the U-shaped zone, and that gravel for the endemic species can appear in the outer edge of the U-shaped zone. It was also shown that the partial removal of the “bottom” part of the U-shape will be most effective for suppression of fine sand deposition, which can be one of the powerful options for effective vegetation management.