The world’s big rivers and their floodplains were central to development of civilization and are now home to c. 2.7 billion people. They are economically vital whilst also constituting some of the most diverse habitats on Earth. However, a number of anthropogenic stressors, including large-scale damming, hydrological change, pollution, introduction of non-native species and sediment mining, challenge their integrity and future, as never before. The rapidity and extent of such change is so great that large-scale, and potentially irreparable, transformations may ensue in periods of years to decades, with ecosystem collapse being possible in some big rivers. Prioritizing the fate of the world’s great river corridors on an international political stage is imperative. Future sustainable management, and establishment of environmental flow requirements for the world’s big rivers, must be supported through co-ordinated international funding, and trans-continental political agreement to monitor these rivers, finance their continual upkeep and help ameliorate increasing anthropogenic pressures. To have any effect, all of these must be set within an inclusive governance framework across scales, organizations and local populace. Stressors such as large-scale damming, hydrological change, pollution, the introduction of non-native species and sediment mining are challenging the integrity and future of large rivers, according to a synthesis of the literature on the 32 biggest rivers.

Anthropogenic stresses on the world’s big rivers

Much effort has been devoted to developing, constructing and refining fish passage facilities to enable target species to pass barriers on fluvial systems, and yet, fishway science, engineering and practice remain imperfect. In this review, 17 experts from different fish passage research fields (i.e., biology, ecology, physiology, ecohydraulics, engineering) and from different continents (i.e., North and South America, Europe, Africa, Australia) identified knowledge gaps and provided a roadmap for research priorities and technical developments. Once dominated by an engineering-focused approach, fishway science today involves a wide range of disciplines from fish behaviour to socioeconomics to complex modelling of passage prioritization options in river networks. River barrier impacts on fish migration and dispersal are currently better understood than historically, but basic ecological knowledge underpinning the need for effective fish passage in many regions of the world, including in biodiversity hotspots (e.g., equatorial Africa, South-East Asia), remains largely unknown. Designing efficient fishways, with minimal passage delay and post-passage impacts, requires adaptive management and continued innovation. While the use of fishways in river restoration demands a transition towards fish passage at the community scale, advances in selective fishways are also needed to manage invasive fish colonization. Because of the erroneous view in some literature and communities of practice that fish passage is largely a proven technology, improved international collaboration, information sharing, method standardization and multidisciplinary training are needed. Further development of regional expertise is needed in South America, Asia and Africa where hydropower dams are currently being planned and constructed.

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The future of fish passage science, engineering, and practice

The term restoration is used in many ways; however, it normally implies return to an original state. In ecological restoration, it should be thought of as applying to whole ecosystems. It must be remembered that options, such as rehabilitation or replacement, exist that may be more practicable than restoration. The components of restoration are the chemical and physical aspects of the habitat and the species themselves. Each of these may require specific treatment, but natural restorative processes should be used wherever possible; in fact, natural processes may be sufficient once the degrading influences have been removed. Because the process of restoration is progressive, the criteria of success are not easy to define. The most important point is that ecosystem development should be on an unrestricted upward path. From this, it follows that successful restoration is a serious test of our ecological understanding. Resume : Le terme restauration est utilise dans plusieurs sens, mais il suppose normalement un retour a l'etat initial. Dans le domaine de l'ecologie, il faut voir la restauration comme s'appliquant a des ecosystemes complets et se souvenir que d'autres solutions, comme la rehabilitation et le remplacement, peuvent etre plus realistes. La restauration vise a la fois les aspects chimiques et physiques de l'habitat et les especes elles-memes; chacun de ces volets peut exiger des mesures particulieres, mais il faut autant que possible se fier aux mecanismes naturels de restauration. En fait, si on a elimine les sources de degradation, ces mecanismes sont souvent suffisants. Comme la restauration est un processus progressif, il peut etre difficile de fixer des criteres de reussite. Il faut avant tout se rappeler que l'ecosysteme doit se developper sans entrave dans le sens d'une amelioration. La reussite d'une telle operation met a rude epreuve notre comprehension de l'ecologie. (Traduit par la Redaction)

Underlying principles of restoration

Urbanization and climate change implications in flood risk management: Developing an efficient decision support system for flood susceptibility mapping.

Assessing channel changes of the Ganges-Padma River system in Bangladesh using Landsat and hydrological data

Riverbank migration and island dynamics of the braided Jamuna River of the Ganges–Brahmaputra basin using multi-temporal Landsat images

The hydraulics of a vertical slot fishway: A case study on the multi-species Vianney-Legendre fishway in Quebec, Canada

Field and numerical assessment of turning pool hydraulics in a vertical slot fishway

Detailed mean flow characteristics generated by a staggered arrangement of boulders in a rock-ramp-type naturelike fish pass were investigated experimentally at three different channel slopes (5%, 3%, and 1.5%). The results showed that this type of fish pass can produce adequate water depth and favorable flow velocity suitable for fish passage. Three different characteristic velocity regions were identified, namely, downstream of boulders (wake region), intermediate region, and upstream of boulders. Some general correlations were developed for predicting the flow depth and velocity in a rock-ramp fish pass as a function of normalized discharge. Moreover, a flow-resistance analysis based on basic concepts for wake-interference flow regime in this fish pass has resulted in a general equation for the average velocity. This study improves the understanding of the complex flow characteristics in a rock-ramp fish pass.

Abul Basar M. Baki

Papers

Riverbank migration and island dynamics of the braided Jamuna River of the Ganges–Brahmaputra basin using multi-temporal Landsat images

The hydraulics of a vertical slot fishway: A case study on the multi-species Vianney-Legendre fishway in Quebec, Canada

Field and numerical assessment of turning pool hydraulics in a vertical slot fishway

Mean Flow Characteristics in a Rock-Ramp-Type Fish Pass

Assessing morphological changes of the Ganges River using satellite images