Applied Fluvial Ecohydraulics

All over the world rivers and the fluvial ecosystem are systemically collapsing in response to cumulative historic and modern anthropogenic impacts. Scientists, engineers, and managers from diverse backgrounds have come together in local to international groups to diagnose problems and implement solutions that restore responsible environmental stewardship. Unfortunately, many river science ideas have proven too general, idealistic, and uncertain, precluding their use for precise, accurate engineering and management. The necessity of developing better scientific ideas and engineering solutions has led to the emergence of a new branch of basic and applied science called “ecohydraulics.” Ecohydraulics is the study of the mechanisms that explain hierarchically nested aquatic and riparian biotic phenomena. Biotic phenomena consist of individual-, population-, and community-level conditions, behaviors, and interactions. Hierarchical nesting means that phenomena are present across a wide range of spatial scales- from the smallest fluid continuum scale to the scale of the entire Earth. Because it focuses on mechanisms, ecohydraulics is well positioned to make new discoveries about nature without relying on spurious correlations, thereby enabling more reliable environmental stewardship. This article addresses the ways in which ecohydraulics has generated new ideas, methods, and solutions for managing rivers. It builds on the Oxford Bibliographies article Natural Fluvial Ecohydraulics that covers ecohydraulics’ basic scientific foundations. It differs by focusing in the first half on practical methods and in the second half on four major river management applications of applied ecohydraulics. River assessment addressing the status of intertwined abiotic-biotic mechanisms could involve a wide variety of specific physical, chemical, and biological studies, plus studies investigating interactions among them. Yet on a practical level, river management is often going to come down to one of four actions: re-regulating flows, modifying river corridor topography, adding/removing in-stream structures, and/or catchment management. Therefore, applied ecohydraulics primarily provides results useful for driving one or more of these actions. Such results require development of practical technologies for observing river-corridor landforms, habitats, and biota as well as numerical models for predicting future abiotic-biotic interactions under different management scenarios. Thus, these tool topics are presented before going into management applications. This article covers well-established 20th-century approaches to applied fluvial ecohydraulics and the extensive criticisms of those approaches. It also illustrates the most novel and important approaches emerging in the 21st century. Overall, applied fluvial ecohydraulics is about creative people from all walks of science and engineering doing their best to envision solutions to real-world environmental problems. Established ideas have laid important foundations, but ecohydraulics’ energized youth spurs a rapid pace of creative development. Applied ecohydraulics is growing in importance for environmental stewardship, but the community must remain humble and open to new ideas, because the discipline has a long way to go to reach the goal of preventing ecological collapse.