Field surveys have been conducted on the floodplain at the Honmura district in the Kita River after the severe flood damage by Typhoon No.19 in 1997. The process of changes in topographical feature and vegetation luxuriance corresponding to the flow scale has been quantitatively explained through the analysis of the aerial photographs by authors.
In the paper, a vegetation factor VF, which expresses the degree of luxuriance of vegetation, is introduced to quantitatively analyze the relation between vegetation luxuriance situations and flow scale. The factor is assumed to be a linear function of the maximum discharge in the year, and function parameters are determined from the trial and error method. From the simulated results, it is shown that the history of destruction and restoration of vegetation on the floodplain at the Honmura district in the last 36 years can be quantitatively inferred from the scale of flood by using the introduced vegetation factor. Moreover, it is found that the destruction and restoration of vegetation has been repeated roughly every six years under the critical discharge of 2, 300 m3/s.