Developaent of a successive flow monitoring system to elucidate the relationship of erosion, transportation and deposition of gravel controlled by flow-depth and velocity, and observation by the system.

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1.With a view to reveal the relationship between the relationship of erosion, transportation and deposition of gravel and the flow-depth and the flow-velocity, and to get continuous flow-data, we developed the River monitoring system by Nortec AS EasyQ doppler-type two dimensional monitoring stream, and made a continuous monitoring at the Midaregawa River in the Yamagata Basin, Northeast Japan.2.There were a several flooding during July to November in 2002 and we corrected the data of flooding. At the largest flooding in July 10 to 11, caused by Typhoon 6Lh, when the velocity of the stream exceeded 2m/s, pebbles on the river bed began to move, and deposited on the monitoring system which was located along the side of the river margin when the velocity reached to 2. Sm/s. The maximum speed of the flow was estimated to be more than 3.5m/s. The gravels seemed to move with saltation and with elongating parallel to the flow direction, according from the fabric of gravels on the river floor. The monitoring system had malfuncitoned during high flooding stage (velocity was more than 2. Sm/a), and then evened out at waning stage of flooding. This means that the flow begins to incise the gravel river bed and deposit the gravels on the river margin when the velocity of the stream exceeds 2.5m/s, and is incising and depositing continuously during maximum flooding stage, then begins to erode laterally river margin at the stage of waning stage.