Study on the destruction of riparian trees in a gravel-bed river caused by flood disturbance

洪水扰动对砾石河道河岸树木破坏的研究

基本信息

批准号：
14550508
负责人：
SHIMIZU Yoshihiko
金额：
$ 2.37万
依托单位：
Gunma University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2003
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-14550508/
关键词：
Riparian trees expansion Robinia pseudo-acacia gravel-bed river flood disturbance degradation maximum size of movable gravels destruction of riparian trees 樹木の破壊・撹乱平面流解析

项目摘要

Recently, bed degradation has been generated in many gravel-bed rivers. As the result, flooding areas exist only around the low-water channel and on the other hand, non-submerged areas or the regions affected by the weak flood disturbance occur in the river channel. Furthermore, riparian trees in the course of gravel bed-river have extremely increased and enlarged their covered-area over bars and flood plain.Such a situation causes the degeneration of the dynamic river system and that of inherent habitat environment in gravel-bed rivers, which brings about problems of river management for the environmental aspects as well as the safety of rivers against flood. In this paper, the magnitude of recent flood disturbance, the fall down process and the destruction mechanism of the riparian trees caused under the degeneration of river channel characteristics were examined through the field investigation in the segment-I reach of Watarase River. Based on the field study and numerical calculation with 2D-flow model, the destruction of the plant was classified into next four types : a)Yield of the tree due to the hydrodynamic force by the increase in the project area of trees to the flow because of trapping of flowing things, b)the disturbance of physical ground in stands, c)the disappearance of trees due to the erosion of the river bed/bank. As an index as such situation occurs, the maximum size of movable gravels and the local bed-degradation to be a key index of the scale of flood disturbance and results showed that the destruction mechanism of the riparian trees is caused by the disturbance of movable bed.

近年来，许多砾石河床河流出现河床退化。因此，洪水区仅存在于低水位河道周围，而河道内则存在非淹没区或受弱洪水扰动影响的区域。此外，砾石河床河道中的河岸树木极大地增加和扩大了它们在坝和河漫滩上的覆盖面积。这种情况导致了砾石河床河流动力系统和固有生境环境的退化。这带来了河流管理的环境问题以及河流防洪安全问题。本文通过对渡良濑川Ⅰ段河段的实地调查，探讨了近期洪水扰动的强度、河道特性退化引起的河岸树木倒伏过程和破坏机制。基于现场研究和二维流模型数值计算，植物的破坏分为以下四种类型： a) 由于水动力而导致树木屈服，因为树木对水流的投影面积增加，因为流动物体的滞留，b）对林分中物理地面的干扰，c）由于河床/河岸的侵蚀而导致树木消失。作为这种情况发生的指标，可移动砾石的最大尺寸和局部河床退化成为洪水扰动规模的关键指标，结果表明，河岸树木的破坏机制是由可移动河床的扰动造成的。。