Most of research in river hydraulics has supported hydraulic design of river projects particularly related to flood protection, and recently its role has expanded toward conservation of river environment, particularly eco-system conservation. Since the River Act Japan revised in 1997 and the river environment enhancement became one of major purposes of river management as well as flood risk mitigation and water resources utilization, research activities for required knowledge and techniques supporting assessment, restoration and enhancement of river environment have been vigorous. However, it includes knowledge and techniques out side of our familiar fields, which are biology limnology and ecology. Ecohydraulics is a newly developed field, and several research groups have already started activities internationally. In Japan, the river ecological research groups have begun the cooperative studies in multidisciplinary fields by targeting several special rivers. Before 1999, they have started in the Tama as a regulated gravel river, the Chikuma as a less-regulated gravel river, and the Kizu as a sandy river. Needless to say, the river ecosystem is formed as a system composed of various species of organism on a dynamic system in a river. Without any collaboration of various fields of science, who can understand the dynamism of the ecosystem, and who can find the mitigation way after various human activities degrades the river ecosystem? Or with whom can the river managers or administrators consult for mitigation or restoration of degraded ecosystem? The cooperative research and its output are absolutely necessary.
The basic concept is firstly “habitat”, which support the life cycles of various organisms. Most of organisms rely on their habitats on the hydro- and geo- dynamics of rivers as well as vegetation there. We have to understand the physical dynamics of rivers, and the dynamic system of various organisms on it with interaction among various organisms' activities. Sometimes we have to know the feedback between hydro- geo dynamics and biological activities.