Xバンドレーダを用いた天竜川河口域の出水による地形変化の観測

摘要

天竜川河口のある遠州灘の各海岸の多くは侵食傾向にある. 河川からの土砂供給を促進し，これを沿岸に波及させる検討がされており，そのーつがダム再編事業である. 河川からの土砂は河口を経て海域に移動するので河ロ域の流動, 土砂移動などを知ることが沿岸域への効率的な土砂供給を図る上で必要になる.%Morphological changes during a flood event in July 2010 at the mouth of Tenryu River were observed with X-band marine radar. Extent of the observation is approximately 2 km from the shoreline to river channel. Hourly radar images were collected from the beginning of the flood for more than 72 hours. The changes of the area were interpreted from the radar images: An isolated river dune was washed away by the flood; Eroded and accreted areas along the river channel were identified; Width of the river mouth increased gradually. Image analysis on the radar images was applied to estimate the migration speeds of the brightness pattern, which should be a proxy of bottom undulation. The speeds were substituted to existing formula to estimate the amount of sediment discharge.