特集: 河川環境の保全と復元
FEATURE: Conservation and restoration of river environment
総説 REVIEW

日本における河川環境の保全・復元の取り組みと今後の課題

池内幸司^*・ 金尾健司

国土交通省河川局　〒100-8918　東京都千代田区霞が関2-1-3

Koji IKEUCHI^* and Kenji KANAO: The approach and the issue to conservation and restoration for river environment in Japan Ecol. Civil. Eng. 5(2), 205-216, 2003.

River Bureau, Ministry of Land, Infrastructure and Transport, 2-1-3, Kasumigaseki, Chiyoda-ku, Tokyo 100-8918, Japan

Abstract:In Japan, river training projects designed for efficient flood control, have turned meandering rivers into straight and monotonous concrete-lined channels. Although these measures have been effective to mitigating flood damage, they have had considerable adverse effects on the natural environments of rivers. In its 1981 report, the River Council, an advisory council for the Minister of Construction (now the Minister of Land, Infrastructure and Transport), stressed the importance of managing the river environment so that the flood control, water utilization and river environment goals can be achieved harmoniously. In 1990, a government notification concerning the "nature-oriented river works" was issued, and "nature-oriented river works" measures designed to "conserve or create scenic natural landscapes" were taken on a pilot project basis in many parts of the country, taking natural riverine habitat requirements into consideration. In 1997, the River Law was amended, and "improvement and conservation of river environment" was incorporated as one of the goals of the law. Under this amendment, efforts to conserve and restore river environments were upgraded, and measures such as full-scale implementation of "nature-oriented river works" projects, amendment of related standards and the establishment of Aqua Restoration Research Center have been taken. Most of the conventional "nature-oriented river works" projects had focused only on limited aspects of channel protection or improvement, such as the conservation and restoration of riparian zones, conservation and restoration of channel forms in certain river sections, conservation and restoration of streamside woods and the reduction of the environmental impact of river improvement works. This paper introduces two pioneering river plans (the Kitagawa River in Miyazaki Prefecture and the Otogawa River in Aichi Prefecture) drawn up from the viewpoint of the conservation of the natural river environment. This paper also describes the concept and scope of "nature restoration projects" (instituted in fiscal 2002) designed primarily to restore the natural environments of rivers, lakes and ponds, and wetlands lost as a consequence of human activities. Finally, the paper discusses the roles that have been played by "nature-oriented river works" projects, as well as the next challenges to be addressed in connection with the conservation and restoration of natural river environments.

Key words: conservation, mitigation, Nature-oriented river works, restoration, river environment

摘要

頻発する水害に効率的に対応するために,河道の直線化,定規断面化,河道の固定化,コンクリート護岸の整備等が進められ,治水上の観点からは一定の効果は上がったものの,その代償として河川環境や景観に大きな影響を与えてきた.このような状況に対して,1981年の河川審議会の答申において,治水,利水,河川環境が全体として調和がとれるよう河川環境管理を行うことの重要性が謳われた.1990年には,「多自然型川づくり」の推進について通達が出され,「河川が本来有している生物の良好な成育環境に配慮し,あわせて美しい自然景観を保全あるいは創出」する「多自然型川づくり」がパイロット的に実施され,全国各地で様々な試みがなされた.1997年には,河川法が改正され,法の目的に「河川環境の整備と保全」が位置付けられた.これを受けて,「多自然型川づくり」の本格的な実施,各種基準の改定,自然共生研究センターの設立など,河川環境の保全・復元に関する施策がより一層積極的に推進されている.
これまで行われてきた多自然型川づくりの事例は,河岸城の保全・復元,限られた区間の河道形態の保全・復元,河畔林の保全・復元,地先の河川改修工事を行う際の環境影響の軽減など,河道の限られた部分に視点を置いた事例が非常に多かった.河川全体の自然環境保全の視点から策定された河川計画の先駆的な事例(北川(宮崎県),乙川(愛知県))を紹介した.
既往の人為的な影響で損なわれてしまった河川・湖沼・湿地等の自然環境を再生することを主目的とした自然再生事業(2002年度制度創設)の考え方とその内容について述べた.
多自然型川づくりの果たしてきた役割について考察を行うとともに,河川環境の保全・復元に関する今後の課題について論じた.

2001年10月23日受付，2002年7月10日受理
* e-mail: ikeuchi-k2hq@mlit.go.jp