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.
Considering definitions provided by Statzner, et al. 1988 and Rice, et al. 2010, ecohydraulics is a mechanistic, interdisciplinary reenvisioning of several previously segregated disciplines now brought together in service of solving the various manifestations of the crisis of river ecosystem collapse. Maddock, et al. 2013 demonstrates that applied fluvial ecohydraulics includes a wide variety of techniques applied to solve problems stemming from physical alteration of rivers, loss of vegetation and wood, and regulation of flow an sediment supply. Broadly similar tools are being developed all over the world aiming at general applicability, but they are often customized to regional settings thus far. The global adoption of ecohydraulics in river management is evident in the diversity of regional synthesis articles and reports, such as those of Yoshimura, et al. 2005; James and King 2010; Pompeu, et al. 2012; and Wang, et al. 2013. Applied ecohydraulics often focuses on fish, but Gore, et al. 2001 and, more recently, Kim and Choi 2018, demonstrate the importance of considering macroinvertebrates. Other aquatic and riparian species require more basic investigation and then application in river management. In considering the diversity of species and holistic ecosystem functioning, there is also the need to get beyond the local scale of a stream reach to effectively characterize and predict ecohydraulics at catchment and regional scales, which is no small feat if one aims to preserve mechanistic realism. Remote sensing, environmental informatics, and numerical modeling technologies are quickly developing to meet this challenge. That means that ecohydraulicists must continue to move beyond previous frameworks and mindsets to use these products in new tools and frameworks. Wheaton, et al. 2018 lays out a visionary, advanced framework and case study for such holistic evaluation at larger scales without sacrificing too much in the details.
Gore, J. A., J. B. Layzer, and J. Mead. 2001. Macroinvertebrate instream flow studies after 20 years: A role in stream management and restoration. Regulated Rivers: Research and Management 17:527–542.
Ecohydraulics is about more than just fish. This article argues that responsible environmental stewardship requires a broader assessment of biotic phenomena. The article illustrates this point by presenting a thorough accounting of ecohydraulics for aquatic macroinvertebrates.
James, C. S., and J. M. King. 2010. Ecohydraulics for South African rivers: A review and guide. WRC Report No. TT 453/10. Pretoria: Water Research Commission..
This technical report may be viewed as an introductory textbook on ecohydraulics, as it presents the major concepts in basic and applied ecohydraulics. The examples and references include many case studies from South African rivers. One small element that stands out is the useful glossary, the need for which has been discussed by early career ecohydraulicists.
Kim, S. K., and S. U. Choi. 2018. Prediction of suitable feeding habitat for fishes in a stream using physical habitat simulations. Ecological Modelling 385:65–77.
This study theorizes that fish habitat will be predicted more accurately if it addresses not only direct fish microhabitat but also locations with favorable fish feeding condition. Hydraulic modeling was performed with River2D. Habitat suitability curves were developed for three target fishes and four macroinvertebrates those fish eat. Individual species habitat indices were computed with the geometric mean and then an integrated index among all species was made by multiplication.
Maddock, I., A. Harby, P. Kemp, and P. Wood. 2013. Ecohydraulics: An integrated approach. Malden, MA: Wiley Blackwell.
This book spans natural and applied fluvial ecohydraulics research but especially has many cases of new methods and management applications. All of the topics addressed in this article are covered in the book. Few of the individual book chapters are used in this article to save space for a diversity of authors, but all are highly recommended for reading as part of understanding ecohydraulics.
Pompeu, P. S., A. A. Agostinho, and F. M. Pelicice. 2012. Existing and future challenges: The concept of successful fish passage in South America. River Research and Applications 28:504–512.
This synthesis article presents the migratory fishes of South America’s large rivers, the history of impacts on them due to dams, and progress toward enabling efficient fish passage. The article presents a novel concept for moving beyond traditional passage metrics to considering whether passage in fact serves the larger goal of enabling a viable population for any given species. This is a more challenging target that integrates diverse ecohydraulic issues.
Rice, S. P., S. Little, P. J. Wood, H. J. Moir, and D. Vericat. 2010. The relative contributions of ecology and hydraulics to ecohydraulics. River Research and Applications 26:1–4.
This article is an editorial synthesis of a special issue of the journal River Research and Applications devoted to ecohydraulics. The article identifies ecohydraulics as an emerging discipline, analyzes where ecohydraulics research is being published, and reports survey results from questions posed to conference attendees.
Statzner, B., J. A. Gore, and V. H. Resh. 1988. Hydraulic stream ecology: Observed patterns and potential applications. Journal of the North American Benthological Society 7:307–360.
Foundational scientific article envisioning what we now call “ecohydraulics.” Most importantly, it identifies that mechanisms ought to be the focus of scientific inquiry in aquatic ecology. The article comprehensively spans a wide range of mechanisms in which fluid mechanics influences biotic phenomena.
Wang Z., J. H. W. Lee, and M. Xu. 2013. Eco-hydraulics and eco-sedimentation studies in China. Journal of Hydraulic Research 51:19–32.
This article reviews and synthesizes applied ecohydraulic research in China, with an emphasis on regulated rivers. China has a diversity of environmental settings necessitating significant investment in basic and applied research to manage river ecosystems. Organizations such as the China Institute of Water Resources and Hydropower Research play an important role in national and international ecohydraulic science and engineering.
Wheaton, J. M., N. Bouwes, P. Mchugh, et al. 2018. Upscaling site-scale ecohydraulic models to inform salmonid population-level life cycle modeling and restoration actions – lessons from the Columbia River Basin. Earth Surface Processes and Landforms 43:21–44.
This article is unprecedented in its depth, breadth, vision (see Figure 11), and results. If ecohydraulics needed a champion to justify its existence and future potential, this is the article that should be put forward to make the case. This is what a mid-21st-century framework for watershed science and management founded on mechanistic abiotic-biotic linkages looks like, and it arrived a decade or two ahead of its time.
Yoshimura, C., T. Omura, H. Furumai, and K. Tockner. 2005. Present state of rivers and streams in Japan. River Research and Applications 21:93–112.
This article reviews and synthesizes knowledge about rivers in Japan, including many elements of ecohydraulics, such as the physical and biodiversity characterizations of rivers as well as anthropogenically derived physical, chemical, and ecological problems. The article also presents examples of river restoration. Japan’s intense physiographic relief and short, narrow valleys present an interesting case study compared to other regions.
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