Influence of Large-Scale Flood given to Material Transportation

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  • 物質輸送に与える大規模洪水の影響
  • ブッシツ ユソウ ニ アタエル ダイキボ コウズイ ノ エイキョウ

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Transport of Materials ( suspended solids (SS) and nutrient salt ) increases during floods. Nutrient salts transported in river water are important in terms of river ecosystems. Understanding of nutrient salt behavior in the river environment is important in the maintenance and management of the rivers. To better understand the influence of flooding on the river environment, this study aims to clarify the influence that a large-scale flood gives to the material transportation, and to estimate the amount of SS and nutrient salts deposited on the flood plain as a result of flood. The study area was the Saru River basin, and the study was conducted in three steps. First, toward understanding the differences in material transport in four floods (two rainfall floods and two snowmelt floods) observation data were examined. Second, equations were derived from the observation data in order to estimate the amounts of SS and nutrient salts deposited on the flood plain as a result of flooding events. Third, calculation for unsteady flow in a compound cross-section was performed to clarify how the amounts of nutrient salts deposited in the high-water channel differ by the flood scale. The following were found: 1) The volume of material supplied from the channel relates to the discharge, and we could hypothesize that when the discharge reaches a certain threshold, the material being transported reaches a saturation concentration. Moreover, in the snowmelt flood before and behind the Large-scale flood, the thing that the density of the material in the stream rises has been understood. 2) From the estimation equation that we derived for nutrient salts, we found a close correlation between the amount of silt deposition and the amount of water quality components in particulate form. 3) The calculations revealed that the influence of floods of different scale on the river environment varies by location.

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