多雪山地源流域における流出土砂量の経時変化

概要

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Temporal changes in sediment yield were monitored at three forested watersheds (Nos. 1-3) at Kamabuchi Experimental Watershed, which is located in a heavy snow region of Northern Japan. Monitoring has been performed since autumn 1997 at Nos. 1 and 2 and since autumn 2002 at No. 3. The observation results up to autumn 2007, showed that sediments flowed out of each experimental watershed due to a few floods caused by downpours from the end of July to August, whereas, sediments hardly flowed out during the snowmelting period. Comparing the annual mean sediment yield per unit area from each experimental watershed, the sediment yield from No. 3 was the largest, and that from No. 2 was the smallest. In No. 3, much sediment has accumulated in the channel from August of 2002 when a bank failed fairly close to the gauging weir. Thus, it is suggested that the increase in sediment yield from No. 3 was due to the bank failure. In No. 2, some fallen trees dammed up the sediment near the gauging weir, which is thought to have controlled the sediment yield from No. 2. In No. 1, the sediment was dammed up in some places by small fallen trees in the channel. If these fallen trees are moved by a flood, the sediment yield increases as in No. 3, but if these trees aren't moved, the sediment yield decreases as in No. 2. Thus, in No. 1, it is suggested that the movement of fallen trees by flood is important for sediment yield.
2010-04-25