人的利用が河川高水敷の地被状態変化に及ぼす影響の定量的把握方法とその考察

抄録

The purpose of this paper is to examine the trend of the riparian land-cover changes over the past 100 years quantitatively. We have analyzed the land-cover and the height of plants within riparian area in the year of 1890, 1947, 1961, 1974 and 1990 by using maps and aerial photos in the downstream part of Kokai river.
The ratio of land-cover and the height of plants did not change significantly until 1970's, suggesting that riparian environment was in equilibrium. However, the area of the forest increased by 18% and the height of trees increased up to 15-20m from 1970's to 1990's. This can be attributed to the decline of the human disturbance. We have characterized three typical processes which lead to the growth of forest in riparian area in Kokai river, as follows.
1) Reed area was transformed to forest area. 2) Trees in forest area have been no longer cut and used as fuel. 3) Cultivation activity has been lowered in riparian area. Above three processes seem to have been accelerated due to the change of the life style of people in the vicinity of the river.