FLOW VELOCITY CALCULATED FROM UPROOTED TREES AT THE AUGUST 2003 FLOOD OF SARU RIVER

Typhoon No.10, which struck Hokkaido Prefecture in August 2003, caused serious flood damage on the Saru River, which is in the easternmost part of the Iburi district. Driftwood washed into the river in great quantity. In this research, the flow velocity during the flood on the Saru River was estimated by measuring the critical turning moment at which trees are uprooted and applying it to partly uprooted trees. We also investigated how the influence of the tree crown on water flow depends on the tree crown form, and the relationship between the tree height and the bending arc. Although the calculated flow velocities did not closely correlate with values obtained from measurements, the calculated values can still serve as commonsense values that represent the flow conditions during the flood to some degree.