A legislative framework for environmental flow implementation: 30‐years operation in Japan

The Japanese environmental flow (e‐flow) concept and framework are outlined in the current study. We first review the natural and historical background related to the establishment and implementation of the e‐flow framework in Japan. We then summarize the national guidelines used to assess e‐flows. Finally, we discuss a river for which the guidelines have been applied to set e‐flow requirements. It is legally mandated that flows be established to maintain the riverine environments of class A rivers managed by the national government. These correspond to e‐flows, which are referred to as maintenance flows in Japan. A Guideline established in 1997 provides detailed instructions on how to assess e‐flows, and the e‐flow framework has been implemented for 100 class A rivers according to the guidelines. E‐flow objectives in Japan are intended to benefit ecosystems through the protection of river habitats and fisheries and the protection and maintenance of water quality, groundwater levels, riverine scenery, and navigable waterways. E‐flow objectives also address cultural and social needs, such as the prevention of salt damage and estuary clogging, and the protection of wooden infrastructure management facilities. Although Japanese rivers are characterized by large fluctuations and sudden peaks in flow, there has been little discussion about e‐flow evaluation methods that take flow variability into consideration. This is because dams on Japanese river basins control only a small percentage of total runoff volume. This is one reason why the guidelines for setting e‐flows focus only on the minimum flows required to prevent extreme low‐flow conditions.