STUDY ON COMMON REED(PHRAGMITES AUSTRALIS) OVERGROWTH CONTROL BY SUNLIGHT COVER IN A SMALL RIVER

Abstract

 In small and medium-sized rivers, deterioration of landscape and water flow capacity due to overgrowth of vegetation such as reeds are problems. Vegetation control by hydraulic factors is not easy. In this study, we focused on the solar radiation as a factor of controlling overgrowth. According to the solar shading experiment on a reed overgrowing sandbar in a small river, the higher the shading ratio is, the smaller the total length of the reeds is. When the shading ratio exceeds 76%, the reeds density became smaller. When 60% shading, the reeds fell more easily during flooding, and at 94% shading, almost all reeds fell. From the reed coverage survey and solar radiation analysis of the river, it was found that most of the reed coverage can be explained by open sky ratio caused by trees and direct solar radiation ratio determined by topographical factors. From these results, it was shown that the solar radiation may limit the growth of reeds even in actual rivers. Thus the possibility of controlling the overgrowth of reeds by solar shading was demonstrated.