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応用生態工学 10(2), 131-139, 2007

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原著論文 ORIGINAL PAPER

ECEロゴマーク

森林小河川における落葉堆積形態の分類と機構特性

中嶋 崇志・浅枝 隆・藤野 毅・アウン ナンダ

埼玉大学大学院理工学研究科 〒338-8570 埼玉県さいたま市桜区下大久保255

Takashi NAKAJIMA, Takashi ASAEDA, Takeshi FUJINO and Aung NANDA: Leaf pack distribution and accumulation mechanism in a second-order stream. Ecol. Civil. Eng. 10(2), 131-139, 2007.

Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama-shi, Saitama 338-8570, Japan

Abstract: Leaf pack distribution was investigated in 270-m interval of a second-order forest stream, the Yanase River. The dominant tree type was Keyaki (Zelkova serrata). Leaf pack sampling was conducted in pools and riffles. At the first, the leaf pack distribution area was estimated, and then sample was taken by hand and fishing net in the pools. In the riffles, 1.0-m-x-1.0-m quadrates were located first, and then the leaf pack was sampled. All leaf pack was sorted into leaves and branches. At the time of leaf pack sampling, physical stream variables were also measured. The variables were water depth and current velocity. In the riffles, stone width, stone height and stone distance were measured. The collected leaf pack was categorized by their accumulation types: LS (Leaf retained by Stone), SLP (Settled Leaf in Pool), SLPi (Settled Leaf in Pool at inner bend), SLPo (Settled Leaf in Pool at outer bend) and DD (Debris Dam). The accumulated leaf pack amounts at each leaf pack type were compared with the measured physical stream variables, and their correlation was tested. From the results, for leaf pack accumulation in riffles, stones projecting above water surface and their arrangements influence to entrap or release leaf litters in transport. In pools, leaf pack accumulation is assumed to occur at high stream flow where there are sufficient pool spaces. At stream meandering points, leaf pack accumulation is influenced by production of a secondary flow, and the leaf pack has a tendency to be pushed over to the inner side of the bend. Finally, debris dams contribute greatly to accumulate leaf packs even when the number of the dam is few. LS was the largest in leaf pack density and the stones in the riffles were the most retentive structures.

Key words: forest stream, leaf pack distribution, pool, riffle, stone, stream floor type

摘要

 森林を流れる2次河川,柳瀬川の270m区間を対象に落葉堆積分布量の調査と河川物理量の測定を行った. 河川物理量は堆積落葉採取地点の水深と流速,瀬の礫の礫高,礫幅,礫間距離を測定した. 結果を用いて落葉堆積量と河川物理量との相関を比較し落葉堆積機構に関する検証を行った. 瀬における落葉堆積は礫による捕捉効果とそれらの配置が重要であった.淵の落葉堆積は高流量時に瀬に堆積した落葉 が再輸送され,十分のスペースがある淵に定着することによって起こると考えられた.蛇行点における落葉堆積は, そこで発生する2次流によって蛇行点の外側から内側へ輸送され,河床へ定着すると考えられた. 倒木による落葉堆積は,倒木によって形成されるダムの数が重要で,それらには地域性がある.

line 2006年4月14日受付,2006年10月30日受理
* e-mail: t.nakajima@asahi-kg.co.jp line
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