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

In response to the increasing severity of rainfall disasters, attributed to climate change, river improvement projects aimed at flood control are being accelerated across Japan. It is equally important to maintain and enhance a healthy river ecosystem and to promote river development that benefits nature. Moderate outflow disturbance plays a pivotal role in fostering a favorable river environment; thus, river channel modifications, including excavation, should be leveraged as opportunities to preserve and restore the habitats, growth, and reproductive environments of aquatic life.

Our Watershed Restoration Research Team is developing river environment monitoring techniques using cutting-edge technologies such as Airborne LiDAR Bathymetry and artificial intelligence. This research includes the development of water use analysis methods that consider vegetation growth, aiming to achieve river improvements that effectively balance flood control with environmental considerations.

Fish and other aquatic species navigate through various water environments crucial to their life cycles. Localized areas of low water temperature serve as critical refuges for cold-water fishes and are vital for preserving biodiversity within the watershed. Concerns are growing that climate change, driven by global warming, is impacting these cool-water refuges. Therefore, maintaining the diversity of river ecosystems necessitates river management strategies that focus on preserving these habitats.

Our Watershed Restoration Research Team is investigating the locations of these low-temperature areas in rivers, such as springs and inflowing tributaries, and their impact on the biodiversity of rivers, including cold-water fishes and other species. From the findings of these studies, we are developing river management techniques aimed at preserving the habitats of these aquatic species.

Various animals and plants inhabit rivers and lakes, releasing DNA from tissue fragments such as scales and droppings. This DNA is known as environmental DNA (eDNA). In recent years, research focusing on eDNA has been instrumental in gathering information about the biota in aquatic areas. The requirements for conducting an eDNA survey are minimal, needing only water samples from the area of study. Compared with traditional biotic surveys, which may involve capture methods using fishing equipment, eDNA surveys are simpler, potentially enhancing the quality of biotic information while reducing both the time and costs associated with research.

Our Watershed Restoration Research Team has identified that the concentration of eDNA varies with several factors, including the type and size of organisms, their growth stages, seasons, and tidal movements. Furthermore, we have explored its dynamics and characteristics—such as dilution due to water inflow—through basic experiments and field verification in experimental rivers. Currently, as part of developing environmental monitoring technologies that utilize eDNA, our efforts include advancing flow observation technologies using eDNA tracers, improving eDNA water sampling methods that consider water flow, and enhancing invasive species monitoring technologies.

Riverfronts are pivotal areas where people interact with rivers. These locations offer numerous attractions, including expansive views, green spaces, diverse flora and fauna, the sounds of water, and breezes over the water. Recently, there has been a concerted effort to integrate river development and urban planning, exemplified by initiatives like “Kawamachidukuri,” which strive to harmonize urban spaces with the waterside.

Our Watershed Restoration Research Team is committed to developing sustainable waterfront spaces by collaborating with various stakeholders. This approach is informed by global trends such as partnerships with private enterprises and green infrastructure that supports watershed management. Our team is exploring advanced domestic cases and developing spatial design methods tailored to specific formation schemes and regional characteristics, with the goal of crafting high-quality waterfront spaces.

In Japan, approximately 30% of aquatic plant species found in rivers are rare, and their communities provide essential habitats and feeding grounds for aquatic insects and birds. However, aquatic plants growing along the water’s edge are particularly vulnerable to river maintenance activities and are declining nationwide. Consequently, conserving these plants is a crucial aspect of river management, aiming to balance flood control with environmental preservation.

Our Watershed Restoration Research Team employs eDNA analysis, satellite imagery, and aerial photography to determine the distribution of aquatic plants and identify environments conducive to their growth. Our research focuses on establishing optimal conservation practices tailored to the characteristics of each species.