Future Design of Small and Medium Sized Rivers Under Population Decline

Abstract

　This article has summarized the problems faced by small and medium-sized rivers in regions with rapid population decline and considered solutions. The length of rivers that must be managed by local governments is long, and it is difficult to immediately develop all small and medium-sized rivers. Additionally, there are significant constraints on the human resources available for river management. We showed several examples of river problems caused by these and population decline. Analysis on population change data showed that the length of rivers with no population in the Tohoku region is accelerating. There are many prefectures with many rivers with no population in the Tohoku, Chugoku-Shikoku, and Kyushu regions. Given these circumstances, we proposed “Kawa-jimai” (in Japanese), which involves renouncement of river management, and divided the timing and method into three categories, and discussed kawa-jimai for each category, focusing on costs. To promote kawa-jimai, the government should allocate areas that are managed or not managed for basins or rivers, develop human resources who can comprehensively design rivers suitable for the region, and improve flood control and water circulation to make use of limited human resources, and develop water experts who cover flood management, water resources, water environment, etc. In addition, it is necessary to develop policies with co-benefit in terms of both hardware and software, and to this end, collaboration across departments, industry, government, academia, and NGOs is desired.