Introduction

This web page provides diverse perspectives on what is meant by the term “Ecohydraulics”.  Read through them and reflect on what you find value in among the different ideas. Viewpoints are presented in alphabetical order.

If you would like to add your viewpoint to this page, please email Greg Pasternack at UC Davis and he will add it.

Prof. Takashi Asaeda
Saitama University

(Grammatical editing by Prof. Pasternack, [] are added by Prof. Pasternack to aid translation)

I am wondering a little how we can cope with neighboring fields from now on, such as Ecohydrology (Journal of Ecohydrology), River Science (River Research and Applications), etc.. Key to ecohydraulics and where ecohydraulics plays an important role are the topics of species-habitat relationships, biota movements, e-flows, and mitigation measures / river restoration – including infrastructure related matters.

Considering the background of ecohydraulics emerging from IAHR, ecohydraulics roles should be the intermediate field between hydraulics/fluid mechanics and biology/ecology. For instance, it is a little hard for people from other fields to come to addressing the problem of species-habitat relationships, particularly related to the physical processes and e-flows as an application as well as considering biota movement. The reason is that these functions are more or less based on hydraulics/fluid mechanics, which is not well understood by biologists [presumably because of their lack of formal education in physics and hydraulics in many curricula]. Thus, ecohydraulics can be of major relevance to these topics. But unfortunately they are more or less small-scale matters.

An important large phenomenon treated in IAHR as a major topic is, I suppose, fluvial dynamics and resulting engineering. Recent increasing floods are making it more and more important. The way ecohydraulics comes into play here is its coverage of biota, riparian vegetation, particularly woody species. These are very important because in many regular rivers the lack of natural disturbance means vegetation abundance is increasing all over the world. As a result, ecohydraulics and its coverage of vegetation-hydraulics linkages makes it very important in the management of flood protection, too. Of course it is one of the species-habitat relationships, but if we say “species-habitat relationship” we normally consider smaller-scale phenomena, not large patches of vegetation. Looking at even larger scales, phenomena related to global warming will become more important, and thus we should add such topics to ecohydraulics. For instance, floods are increasing and affecting habitat or biota more seriously year by year.

River Science is also treating ecohydraulic matters, however, from geomorphological point of view, and thus not much related to management. Still, there are the largest number of people involved in ecohydraulics from this direction compared with other societies. Why don’ t you add this kind of topic as a key issue? It is better to make a special issue to get advantage, too.
Of course they are not excluded in the scope, but not positively added. Looking at neighbouring journals, for instance, these submissions are increasing, but not necessarily particularly described in the journals. If we add such key words, we can get advantage probably.

Prof. Sung-Uk Choi
Yonsei University

Ecohydraulics is a study that attempts to understand ecosystem structure and functions using physical methods.

Prof. Peter Goodwin
University of Maryland Center for Environmental Science

During the Anthropocene, where climate and the environment is primarily influenced by human activity, the field of ecohydraulics studies the interface between these human activities (examples include: infrastructure, climate, land use change, water supply, water quality, wildfire) with the changing dynamics in the aquatic environment (examples include: flood, droughts, habitat, species behavior, population dynamics, food webs) and includes innovative strategies such as nature-based solutions and removal or modification of historic infrastructure that has contributed to the demise of a healthy ecosystem.

Dr. Chris Katopodis
Katopodis Ecohydrualics Ltd

Ecohydraulics is the inter- and trans-disciplinary field broadly characterized by the ecohydraulic trilogy: (1) movements, abilities and passage of aquatic organisms; (2) e-flows, by which I mean environmental, ecological or instream flow regimes for aquatic flora and fauna; and (3) restoration of aquatic habitats and ecosystems.

I outlined the ecohydraulic trilogy concept at ISE 2014 in Trondheim when I was asked to make some remarks on 20 years of Ecohydraulics. The concept was expanded at a Special Session I organized at ISE 2016 in Melbourne. It is also incorporated in the scope and topics for the J. of Ecohydraulics.

Below is a more detailed list of ecohydraulic topics:

Ecohydraulic trilogy – at the heart of the inter- and trans-disciplinary field of Ecohydraulics

1. Movements, abilities and passage of aquatic organisms
   • Migratory behaviour, life cycle requirements in fresh, brackish & saline waters
   • Upstream and downstream passage systems
   • Biomechanics (behaviour, swimming abilities, bioenergetics, modeling)
2. E-flow regimes (environmental, ecological or instream flows)
   • Hydraulic and habitat quantification & modeling involving aquatic flora and fauna
   • Ecohydrology, thermal & water quality aspects
   • Population dynamics and ecological modeling
3. Restoration of aquatic habitats and ecosystems
   • Morphodynamics, sediment transport, ice dynamics
   • Riparian vegetation dynamics and modeling
   • Habitat & ecosystem restoration, dam removal

Prof. Paul Kemp
University of Southampton

When posed the question, What is Ecohydraulics?, my immediate, almost instinctive, response is to recite a definition. There have of course been lots of previous attempts to do this, including by John Nestler and other in 2008, Steven Rice and others in 2010, and Ian Maddock and others in 2013. Indeed, Vlad Nikora raised this question at a really interesting presentation given at a workshop held in Loughborough over a decade ago. Based on these discussions, Chris Katapodis and I provided a definition in the editorial of the first issue of the Journal of Ecohydraulics in 2016. That is:

“Ecohydraulics is the synthesis of ecology and hydraulics, and as a discipline exists at the interface of the two. This definition can be broadened more generally to include other disciplines that are related to aquatic biology (such as physiology, population dynamics, and evolution), engineering (e.g. fluid mechanics and hydrodynamics), and other physical sciences (e.g. geomorphology and hydrology)”.

Since that time, however, I have often questioned just how useful such a definition is. Not that this is necessarily a bad definition, as definitions go, but really I wonder whether we should get too “hung-up” on definitions in the first place. What I have found really impressive about the International Symposia on Ecohydraulics, the first experience of which I had was at the Fourth Symposium held in Cape Town in 2002, is the mix of people, disciplines, cultures, and topics presented and discussed. Whether some of the presentations truly fit into the definition provided might be questionable, but the ethos of the conference is that topics that range from fundamental first principles to very applied challenges are welcomed, provided they are of sufficient quality to be accepted during a review process, judged by the organising committees. There is a recognition that the subject is innately interdisciplinary, and that the boundaries are somewhat fuzzy and dynamic, and may change over time. I often wonder whether the aspiration to develop ecohydraulics as a new transdisciplinary subject is the right one, and whether we should continue to embrace interdisciplinarity and the joining of people from different core disciplines to unite in face of common questions and challenges is actually the best approach to adopt if innovation and creativity is the intended destination. In other words, is there a danger that ecohydraulics may one day become its own disciplinary silo, in which people known as ecohydraulicists (or some other derivation, such a ecohydraulicians, or less formally –ecohydraulicies), seek shelter under a new disciplinary refuge, and the beautiful interchange of interdisciplinary ideas are eroded or even lost? So my question is this: in a world where the global challenges we face are invariably complex, and often reduced to component parts that are placed in boxes by humans who find it easier to understand them when they do so, should we really worry too much about the significance of a definition? Perhaps we should “let it ride” a bit, and be prepared to go with the flow and see where we end up; it most certainly will be more exciting that way, and perhaps more productive!!

Prof. Markus Noack
Hochschule Karlsruhe – Technik und Wirtschaft

From my perspective ecohydraulics is a term that developed over time. In the beginning the focus was purely on the coupling of hydraulics with biota (the first interdisciplinary research and the first attempts to bridge the gaps between engineers and biologists/ecologist). However, nowadays, the term “ecohydraulics” is used as a synonym including all interactions between abiotics and biota in fluvial systems, including many, many different sub-disciplines.

As a scientist working on the interactions between hydraulics, sediments and ecological responses with focus on the dynamic interactions between these three disciplines the term ‘ecohydraulics’ in its original meaning might be too narrow for the wide interdisciplinary research field that is covered by the ‘ecohydraulic community’. But to me, the term ‘ecohydraulics’ stands for linking different disciplines to achieve a common goal: conservation and sustainable development of vital river and riparian systems.

Dr. Valerie Ouellet
University of Birmingham

Ecohydraulics aims to unravel the links between stream/river ecology (e.g. fish physiology and habitat in my case) and the hydrodynamics or related abiotic factor (e.g. water temperature). To do so, we also need to look at other variables like the influence of stream geomorphology, local and regional climate, anthropic activities, riparian vegetation, etc. so it is truly an interdisciplinary science!

Dr. Xiaodong QU
China Institute of Water Resources and Hydropower Research

Ecohydraulics still is not a well-known discipline in China, although it had been used to reduce effects of the dam construction, control the movements of contaminants in the water, and manipulate the habitat restoration of aquatic organisms for the purposes of ecosystems protection and restoration.

According to different study aims, the scientists named the discipline as “environmental hydraulics” and “ecohydraulics”. The former focused on the studies of contaminant movement in the water and their relationships with hydraulics. And the later focused on the inter-correlations between aquatic organisms and hydraulics. Meanwhile, the “eco-environmental hydraulics” was also used due to the study aims may include both aquatic organisms and contaminants in the water. During the past decades, the ecohydraulics has been dominated and replaced the environmental hydraulics gradually.

The earliest study of ecohydaulics started around 1980s in China. The agencies and authorities of environmental protections of China used the models of environmental hydraulics to calculate the concentration and movement of contaminants from the point pollutions for the purposes of water quality control. The studies started around 1990s, Dr. Li researched the flow field characteristics of Oncomelania hupensis Gredler in the stream for the purpose of controlling the disease of schistosomiasis (Li 1990). Since then now, the researches of the flow filed characteristics of fish in streams dominated. Almost all the ecohydraulics scientists originated from hydraulics or hydrology and had very weak background of stream ecology in China. So from my personal options, we need to expand the basic knowledge of stream ecology to ecohydraulics scientist using the words simply they could accept and can be translated into the ecohydraulic models. And most important thing, we should attract the young student with the background of ecology to study the ecohydraulics.

I cited the most widely used definition of ecohydraulics in China and try to conclude several quotes from them.

1. The ecohydrology mostly focused on the studies of flow regime at the macroscopic perspective, and ecohydraulics focused on the studies of flow speed, fluidic characteristics, water depth, water temperature, water quality (contaminant, nutrients, pH, dissolved oxygen, etc) and sediment (concentration of sediment, substrates) etc (Peng and Liao, 2006).

2. The ecohydraulics studied the relationships among the hydraulic characteristics, flow, river (stream) and ecosystems for the purposes of restorations of rivers and wetlands (Jiang et al., 2003).

3. Ecohydraulics is the interdiscipline between ecology and hydraulics. The ecohydraulics studies the relations between flow and aquatic community in the stream, it described the living environment of aquatic organisms and flow condition which could support the living environments. So ecohydraulics should include two aspects, 1) the effects of different flow conditions on aquatic organism, 2) the variations of flow conditions originated from the changes of growth situation of aquatic organism (Yu and Wang, 2003). They also compared the differences between environmental hydraulics and ecohydraulics. The environmental hydraulics studied about the movement of contaminants in the water. The ecohydralics studies the inter-correlations between the flow and the ecosystem and its environments. The ecohydrology studies the hydrological mechanisms in ecosystem patterns and process (Yu and Wang, 2003).

4. Eco-fluvial dynamics is a science to study the relationships between sediment movement and its river bed morphology and biochemical process of rivers. This science focused mainly on the surface characteristics and movement rules of sediments and their effects on the river ecosystems (Fang et al., 2019).

5. Ecohydraulics is a developing and new interdiscipline science to study the inner-relationships between hydraulics and aquatic ecosystems dynamics. Ecohydraulics studies the effects of variations of hydraulics on the balance of aquatic ecosystems and biodiversity. Meanwhile, ecohydraulics also studies the effects of ecosystems successions on hydraulic regimes (Chen and Ouyang, 2003).

6. Ecohydraulics is a developing and new interdiscipline science recently, including hydromechanics, biology, ecology, environmental sciences and engineering sciences. Ecohydraulics studies the movement rules of aquatic organisms in the water, and their controlling techniques related with mechanics (Fu and Bing, 2012).

7. Ecohydraulics is an interdisciplines including hydraulics, biology, and ecology. Ecohydraulics mainly studies related mechanisms of effects of hydraulic condition on aquatic ecosystems and hydraulic controlling techniques for the purposes of sustaining the aquatic ecosystem health. Ecohydraulics studies the effects of variations of hydraulic condition on the biogeochemical processes and community composition, habitat distribution and ecosystem functions. Meanwhile, Ecohydraulics studies the effects of succession of ecosystem on hydraulic regimes (Chen, 2010; Chen 2016).

Quotes and conclusions of ecohydraulics in China:

1) The ecohydraulics is a developing and new interdiscipline. The ecohydraulics mainly included hydraulics, hydrology, limnology, freshwater biology, and environmental sciences, and it also related with river dynamics, mechanics (fluvial mechanics, soil mechanics, etc), sedimentation, and engineering sciences, etc.

2) The biological targets of ecohydraulics researches mostly considered fish, invertebrate (mostly mussels), vegetation at the individual and population levels, the targets should also include the community structure and succession, ecosystems processes and functions, and all the related physio-chemical environment.

3) The differences between ecohydraulics and ecohydrology were not clearly identified current, and at least two of my student could not clearly explain the differences. I imagined it may not only cause the confusions in my lab, but also for the others.

The definition: The ecohydraulics studies the relationships between hydraulics and aquatic ecosystem, which includes not only the ecosystem structures and functions, but also the environments supporting the process and succession of ecosystems.

References
1. Chen QW, Ouyang ZY. 2005. Integrated ecohydraulics model and the application. Journal of hydraulic engineering, 36(11): 1273-1279.
2. Chen QW. 2010. River eco-hydraulics: Reservoir dam downstream river ecology and eco-friendly scheduling. Science Press, Beijing.
3. Chen QW. 2016. Discipline of ecohydraulics and the application to modeling and mitigating eco-environmental effects of hydraulic works. Journal of hydraulic engineering, 47(3): 413-423.
4. Fang HW, He GJ, H L. et al., 2019. Progresses and challenges in the study of Eco-fluvial dynamics. Journal of hydraulic engineering, 50(1): 75-87.
5. Fu XL, Bing LL. 2012. The ecological characteristics research of limnoperna fortune. China rural water and hydropower, 37(1): 18-24.
6. Jiang YL, Wang MJ, Li R, Luo L. 2003. Application of eco-hydraulics principle in protection and rehabilitation of urban river. Journal of hydraulic engineering, 34(08), 75-78.
7. Li DM. 2006. Ecohydraulics. Science press, Beijing.
8. Peng QD, Liao WG. 2006. The ecohydraulics reviews of dams effects on fish. The seventh national environmental hydraulics symposium report, pp: 548-553.
9. Yu YL, Wang DH. 2003. The several questions about ecohydraulics. The first national hydraulics and hydroinformatics symposium report, pp: 129-134.

Professor Gregory Pasternack
University of California at Davis

I developed a definition for my pair of ecohydraulics annotated bibliographies published by Oxford Press in 2019, so I’ll quote from those: Ecohydraulics is the study of the mechanisms that explain hierarchically nested aquatic and riparian biotic phenomena. Mechanisms are sequential actions that can be physical, biological, or an interaction between the two. 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. Many ecohydraulic studies prominently address scaling. Under this definitional framework and given the widespread occurrence of water on Earth, ecohydraulics is the “proximal” science mediating the influence of “distal” landscape drivers (e.g., climate, geology, and topography). A key missing element of this definition is chemistry, as thus far few ecohydraulicists integrate chemical reactions, but clearly this is relevant. Further, while social science has a nexus with ecohydraulics in light of river degradation and management having many drivers associated with environmental injustice, I’m not sure it should be integrated into the definition explicitly. I’m sure others would argue it should be integrated into the definition, and I respect that.

Prof. Rafael O. Tinoco
University of Illinois at Urbana-Champaign

Ecohydraulics is a rapidly developing interdisciplinary field which examines the interactions and feedbacks between hydrodynamic, ecological, and geomorphic processes in natural and altered waters, in order to develop better approaches to monitor, manage, and restore the functions of aquatic ecosystems.