Many kinds of development have been so violently increased in upstreams of forested watersheds that natural own characteristics of watersheds have been changed and natural disasters have been frequently generated. Man induced destruction of nature has climbed up to upstreams of watersheds by road construction, water reservoirs, mining, agriculture, grazing, wood production and others. Therefore, the necessity of watershed conservation is strongly requied for effective land use.
In undeveloped areas as Tohoku and Hokkaido, developments have been carried out in forested area of upstreams and changed natural characteristics as well as hydrological and erosional ones.
Especially, the affects of wash load in the lower reaches of the river became a serious problem on applied hydrology. The managements of forested areas occupied the major portion of the river basin have an important role on the control of the wash load. The purpose of this paper is to clear up characteristics of forested watersheds related to water and soil conservation. Relationships of hydrological factors to erosion phenomena as surface erosion, landslides and debris movement were discussed from the previous results.
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