Environmental assessment method for a small-river restoration plan

Although more than 23,000 river restoration projects have been conducted during the past 15 years in Japan, reliable environmental assessment methods have not yet been identified. The environment of the Kamisaigo River is assessed before restoration. The river had been canalized with concrete revetments, reducing its biological function. In 2007, the Fukutsu City Government initiated a program to restore the environmental quality of the river. The aim of this paper was to determine the best method of assessing the river environment. The fish and the physical environment to assess the environmental condition of the river are surveyed. A fish index developed by Kyushu University adequately represented characteristics of river health and was used to determine which sites warranted restoration, rehabilitation priorities, and appropriate methods. The authors calculated 14 regionally developed indices using the ecological features of the fish at several river sites. The environmental quality of the river varied substantially across seven sampling sites. Using these assessment results, the authors determined the specific weaknesses that affected the condition of each site. A restoration and improvement program based on these findings accomplished several goals, including restoring the floodplain, incorporating a variety of flow rates, and enhancing vegetation for fish spawning.