杉浦 未希子

Water scarcity is a social and relative concept that necessitates considering the social and technological factors that determine the quantity and quality of water demand and supply. Thus, institutional responses to water scarcity are diverse and dynamic, reflecting climatic and geographical conditions. In the case of Japan, located in monsoon Asia and experiencing irregular rainfall and drought with a certain probability, a water use order has been formed based on the river-water use for irrigation as a stable source. In terms of increasing supply, modern advances in engineering technology has made it possible to augment river flows by releasing water stored in multipurpose dams, which has enabled the establishment and operation of the modern permitted water rights system, and a new water use order and its adjustment. The "drought coordination" (Kassui-chōsei) is an example of such a system, which was institutionalized in anticipation of voluntary coordination among water users due to the functions of multipurpose dams and the existence of river administrators. Although river water is "public water" and not subject to trade along with water rights, the implementation of various administrative strategies to create new water rights have also contributed to alleviating conflicts caused by social water shortages. In terms of reducing demand, field-based irrigation commons still play an essential role. Block rotational irrigation efficiently reduces demand as part of the nesting structure implemented by LID, a traditional mura-based Water Users Association. It implements a determined rate of water conservation through effective and efficient water management as part of the structure.

Watarease-yusuichi, a man-made retarding basin, which has functioned as a flood control for about 100 years, entered a new phase in 2012 as a registered site under the Ramsar Convention. Through diversification of wetland use, despite the complexity of the root of the Convention’s “wise use,” Watarase-yusuichi represents a unique perspective on sustainable development so that wetlands can continue creating new value for human society. The emerging ecological function as the habitat for endangered fauna and flora exemplifies not only the universal paradigm shift in human involvement in the wetland’s use, but also the importance of the integration of stakeholders regarding the issues of wetland management as IRBM (the Integrated River Basin Management), which gives us more holistic perspective on a participatory and comprehensive approach to planning and management. Regarding the integration of stakeholders, despite the significant differences in original ideas on wetland management, it should be noted that five major types of stakeholders, including the local and scholarly communities, collaborated to device a future plan for Watarase-yusuichi through lengthy discussions.

統合的流域管理の文脈では、分水嶺で定義された集水域を原初形態としつつ、河川水資源供給圏とその使用を通じて拡大する使用圏を合わせて理解・把握する必要性がある。この視点から、利根川関係流域をみると、三段階に分けて捉えることができる。 特に重要なのは、水資源の「開発から管理へ」の遷移を、河川水資源の多目的との調整という課題に対応しつつ実践した、いわば統合的流域管理の理念型といえることである。

いわゆる環境用水水利権とは, 他の水利権のような河道外での排他的使用を想定しない, 河川以外の水路等への導水による特殊水利権であり, その本質は河川法が及ばない水環境を利用した, 河川管理者による河川低水管理である．河川水に対する思潮の大きな変化を受けて登場し, 生物多様性の保全と持続可能性に価値を置く新奇性と, 豊水時に限り取水が可能であり, 3年更新で最劣後の水利権である等の特異性がある．既存の土地改良管理施設（農業用用排水路）を利用した最初期の環境用水水利権では, 水質改善（希釈）を主目的とした．同施設の管理に関する知識と経験を持つ土地改良区が, なんらかの対価を受け取りつつ関与していくことは, 初期投資や管理コストを抑えながら本来の意義を発揮させうるという意味で, 水利権者である地方自治体にとっても魅力のある選択肢のひとつとなるだろう．

資源節約は21世紀の世界的課題となっており, 灌漑においても効率的水利用による「節水」が求められている．本稿では, 水田灌漑において節水効果が期待されている従量制による水利費賦課方式について, 三重用水地区を対象に実態を分析し, その節水効果を検討した．結果として, 平水時は従量制によって水源（元圦）からの取水量が節水されるが, 従量制の節水効果がもっとも期待される渇水時には取水量が増加し, 従量制の節水効果は認められないことが確認された．また, 渇水時において従量制が直ちに節水効果に結びつかなかった理由として, 1）基本料金制でかつ超過取水に対する料金が安く, 水利費の徴収単位期間が1年間と長いという料金体系によること, 2）加えて本地区の場合, 補給灌漑地区であるという用水事情があることを明らかにした．

In Japan, a developed country in Asia, the Land Improvement Act systems have worked as a measure of social capital accumulation as well as an adjective law in implementing irrigation projects since 1949. This paper illustrates the status and problems in applying the concept of social capital to agricultural and rural development policy systems in developing countries, EU and Japan. The results obtained are summarized as follows: (1) it is desirable that governments formulate public policies that are appropriate for correcting inefficiencies in resource distribution for accumulating social capital, so that the governments play a significant role in developing and supporting social capital; (2) the effect of policies in the areas, where government-supported land improvement projects have been implemented, has been improved, subsequent to which the efficient use of the national budget allocated for the projects has been improved, while the projects significantly contribute to the national land conservation and social stability by continuously promoting minimum social capital accumulation nationwide. In addition, Japan and countries in the Asian monsoon region, which hold the five elements in common that constitute the characteristics of rice field irrigation in humid climates, should take over the advantages of the land improvement project system while learning from the success achieved by the LEADER+ programme in Europe, where society precedes Asian countries concerning the problems of decline in the birth rate, and expansion of an aging society.

香川県木田郡旧下高岡村では、「地主水」と呼ばれる水利慣行が存在した。地主水とは、本来土地所有権と堅固に結びついているはずの水利権が、例外的に土地から切り離されて(本稿ではこれを属人性とする)売買された慣行水利権である。現在では売買自体は行われていないが、その売買を側面から支えた配水システム、番組(配水)の合意形成プロセス、および水利費課金方法などは現在まで残っている。本稿は、先行研究から得られる地主水の特徴の整理と、現地調査によって得られた現在の水利状況から、地主水を成り立たせていた要因を考察し考えられる4点を指摘した上で、現代の稀少性にかかわる議論(私的財・経済財)への示唆を読み取る。