Changes in the Topography and Vegetation on the Upstream Side After Check Dam Construction

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  • 治山堰堤建設に伴う後背地の地形と植生の変化
  • チサン エンテイ ケンセツ ニ トモナウ コウハイチ ノ チケイ ト ショクセイ ノ ヘンカ

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Changes in topography and vegetation over the past 23 years were surveyed on the upstream side of a check dam. The target dam was constructed in 1981 on the Yunosawa River, a branch of the Matsukawa River that flows in Hachimantai City, Iwate Prefecture, Japan. The dam is located at an eastern longitude of 140°54′37″and a northern latitude of 39°52′21″. It's altitude is about 900m. The examination method involved aerophotograph decipherment, a topographic survey, and a vegetation survey.<br>The results showed that the maximum width of the floodplain in the study area expanded from 10m prior to the dam's construction to 60m after the dam's construction. In the survey area before the dam's construction, the relative height between the passage and floodplain was large. In addition, the survey area was stable, allowing a growth area for many trees 60 years or older. However, the survey area has been transformed into an unstable environment covered with flood sedimentation caused by rainfall that had been generated by an occurrence probability once in two years. Currently, in the survey area, several grown trees (Betula ermaii Cham, Fagus Crenata Blume, and Abies mariesii Masters, and other species) that had been healthy prior to the check dam construction have weakened or withered. However, Betula ermaii Cham, and Salix which have a comparatively short longevity, have invaded and are growing on the new topographic surface formed after dam construction. In the future, Betula ermaii Cham and other trees with comparatively short longevity will occupy the greater part of this area, if these trees can adjust to the present environment.

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