This page publishes the research themes of the River Restoration Team of the Public Works Research Institute (PWRI).

Recently, terrible disasters due to climate change increase the importance of flood control. Maintenance of good river environments is also important. Although flood control and river environments are reciprocal, the results of research on river environments have clarified moderate flood disturbance maintenance diversity of river environments (river ecosystems). River managers can conserve and restore river environments using river excavation projects for flood control.

Many biotic communities, including important species inhabit rivers. However, the details of its life histories and habitats have not been sufficiently clarified. Then, we conducted the conservation of birds and amphibians according to precious data, such as national censuses on river environments and field survey results.

River ecosystems can be considered as “interactive systems between physical environments and biotic communities in rivers.” Biotic communities, such as algae, amphibians, vegetation, fish, and mammals live and reproduce by utilizing flows, morphologies, food, and resources (e.g., organic matter), implying that deep relationships between physical environments and biotic communities exist. Research on river ecosystem modeling is formalizing and understanding the relationships between the physical environments and biotic communities. RRTs believe that we can predict how river ecosystems change after the accuracy of river ecosystem modeling has increased. We will predict how a river ecosystem will change according to river environmental management and research river environmental management methods that maintain river ecosystems in good conditions by minimizing costs.

Although different fish species inhabiting rivers and lakes move and utilize various water environments needed for their life history, their migration abilities and life stages are different. The conservation of various biota inhabiting rivers, the objective evaluation of migration conditions in aquatic systems, and the conservation of migration environments corresponding to the migration ability of each biotic factor are important. Previous studies have indicated the objective evaluation method applying gene information to the migration conditions of native fish species.

To increase the application of this evaluation method, this study considers the application of new technologies, such as environmental DNA and backscattering of ADCP for the observation of juvenile sweet fish. In addition, we have developed simple improvement methods based on observational data of fish behavioral data such as using a high-speed camera.

Various animals inhabit rivers and lakes. Floating DNA originating from tissue slices (scales, droppings, etc.) of these biotas are called, “Environmental DNA.” In later years, research using Environmental DNA have focused on obtaining information about biota inhabiting aquatic areas. Needs for environmental DNA survey are only "water" in the water area. Environmental DNA is a very simple survey as compared with traditional biotic surveys, such as capture surveys using fishing equipment. Environmental DNA is expected to improve the biotic information quality, as well as decrease research time and costs. However, environmental DNA has many technical issues. The extent of change in environmental DNA is influenced by biotic species, the body sizes and life stages of biotic species, seasons, decomposition, and sediment process of flow down, influenced dilution due to groundwater inflowing, its dynamics, and characteristics, etc. Therefore, this research aims to demonstrate research planning methods that apply environmental DNA in actual river environmental management.

Riverfronts are connecting bases where humans have access to rivers. Waterfront areas have many attractive characteristics, such as open landscapes, biotic communities, water sounds, through the wind on the water surface. Recently, to create amazing space fusions, such as KAWAMACHIDUKURI, of cities and waterfronts, the coupling of river management and city planning is promoted. However, because planning and design methods have not been clarified, water space where use and application do not progress occurred even if developed. Therefore, this study conducts a survey of good development cases of water spaces and aims to establish design methods for water spaces.

Various wastes from vegetation occur in river and lake management. Examples are wood for keeping flooding capacity, aquatic vegetation overgrowth for preventing obstacle of fisheries activity, etc.

A trial method (Nagaeturuno-geitou) that does not dispose of aquatic vegetation but was applied to agricultural resources was conducted in Inba-numa Lake in Chiba Prefecture. Applications of this vegetation not only reduces the cost of disposing the river manager but also increase the interests and activities of local community estranged from rivers and lakes.