• (概要)

    本研究は、産学官連携による技術研究開発を促進することを目的とした国土交通省 河川砂防技術開発公募研究 河川生態部門(地域課題分野)令和2年度 一般研究に採択され、狩野川を管理する沼津河川国道事務所と連携し進めている。

    (背景・課題)

    放水路を有する河川は全国に数多く存在するものの,その開閉が河川や沿岸の生態系機能にどのように影響を与えているのかについての知見は極めて乏しい。年間降水量が2000mmを越える伊豆半島を流れる狩野川で、放水路によるピークカットが50余年を経て下流生態系にどのような影響を与えたか。また近年多発する豪雨イベントに伴う放水路の開閉が河川環境や生物群へどの程度の影響を与えるのか、また河川の流量調節が沿岸生態系へどのような影響を与えているかを押さえることが、水災害の多発に認められるように今日の気候変動下にある河川管理の上でも喫緊の課題となろう。日本有数の多雨地帯にある狩野川は、一方、富士山麓から多量の湧水が供給されることから地表水の動きを地下水との連動で水循環を考える格好の場である。これらを踏まえ、水系全体で陸域と海域の連続性を確保し、水辺環境や生態系へ配慮した流況の実現に向けた知見を提出することが統合的な河川管理に求められていよう。

    (研究目的)

    大規模出水への対応として年間平均2、3回行われる放水路によるピークカットが、狩野川の河川生態系や狩野川本川が流出する沼津港から放水路の出口となる江浦湾に至る駿河湾東北部沿岸にどのような影響を与えているかを考察する。具体的には放水路による流量調節が行われる豪雨イベントの前後と、それには至らない程度の降雨イベントがもたらす水位変動を対象に、河川水質、河床形態、底生動物群集、魚類(アユ)、河畔林植生や沿岸の一次生産の変化や応答についての知見を集積し、これをもとに河川管理者との合同作業で生物多様性の観点から生態系保全にも配慮した放水路の運用やあり方について提案する。

  • 準備中・・・・・

    準備中・・・・・

    (Summary)

    This research was adopted as a general research project in FY2020 by the Ministry of Land, Infrastructure, Transport and Tourism, in the category of river ecology, which aims to promote technological research and development through cooperation between industry, academia, and government.

    (Background and Issues)

    Although there are many rivers in Japan that have spillways, there is very little knowledge on how the opening and closing of these spillways affects the ecological functions of rivers and coastal areas. In the Kano River, which flows through the Izu Peninsula with an annual precipitation of over 2000 mm, how has the peak cutoff by the spillway affected the downstream ecosystem over a period of more than 50 years? What impact has the peak cutoff by the spillway had on the downstream ecosystem over the past 50 years? The impact of the opening and closing of the spillway in conjunction with recent heavy rainfall events on the river environment and its biological communities, as well as the impact of river flow regulation on coastal ecosystems, are urgent issues for river management under the current climate change, as evidenced by the high frequency of water-related disasters. The Kano River, located in one of the rainiest areas in Japan, is a good place to consider the water cycle by linking the movement of surface water with groundwater, as the river receives a large amount of spring water from the foot of Mt. Based on these considerations, integrated river management is required to ensure continuity between land and sea areas in the entire water system and to submit findings to realize a flow regime that takes the riparian environment and ecosystem into consideration.

    (Purpose of the study)

    To examine how the Kano River ecosystem and the northeastern coast of Suruga Bay from Numazu Port, where the main Kano River flows out, to Eura Bay, the outlet of the spillway, are affected by the peak cut-offs by the spillway, which occur on average two or three times a year as a response to large-scale flooding. The study will examine the impact on the northeastern coast of Suruga Bay. Specifically, we will accumulate knowledge on changes in and responses to river water quality, riverbed morphology, benthic fauna, fish (ayu), riparian forest vegetation, and coastal primary production before and after heavy rainfall events that regulate flow through the spillway, as well as during rainfall events that do not reach such levels. Based on this knowledge, we will propose the operation of the drainage canal and the way it should be in consideration of ecosystem conservation from the viewpoint of biodiversity through joint work with the river administrator.

 

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