Hydrolink 1/2023. IAHR and the Water-Related Sustainable Development Goals

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International Association for Hydro-Environment Engineering and Research (IAHR) (Hg.)

Hydrolink 1/2023. IAHR and the Water-Related Sustainable Development Goals


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International Association for Hydro-Environment Engineering and Research (IAHR)

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International Association for Hydro-Environment Engineering and Research (IAHR) (Hg.) (2023): Hydrolink 1/2023. IAHR and the Water-Related Sustainable Development Goals.

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International Association for Hydro-Environment Engineering and Research

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IAHR and the Sustainable Development Goals

This year marks the midpoint of the Water Action Decade (2018- 2028) aimed at mobilizing and supporting efforts to achieve inter- nationally agreed water-related goals and targets, including those contained in the 2030 Agenda for Sustainable Development. On this occasion, the United Nations is organizing a midterm review during the 2023 Water Conference in New York. Recognizing that progress towards achieving the water-related Sustainable Develop- ment Goals (SDGs) is not on track, the Water Conference aims at producing a Water Action Agenda, calling on pledges to action from governments, water professionals and all stakeholders to accelerate work on the SDGs. The 2023 Water Conference is only the second time in almost fifty years that the United Nations has convened the world’s countries on the topic of water. As such it is viewed as one of the most significant events since the 1977 Mar del Plata Con- ference that produced the first action plan on water and sanitation.

IAHR, as a partner of the UN-Water platform is contributing to the effort to reach specific targets of the SDGs through the work of its technical committees on different relevant aspects of hydro- environment engineering and research. The nature of this work reflects the significant changes in water engineering over the last sixty years or so, from the time that the design of water infrastructure was based on strictly technical and economic criteria to today’s very different philosophy of planning and design. In contrast to past approaches, today’s engineering is (and must be) much more holistic and inclusive. It considers potential environmental impacts, has embraced the principles of sustainable development and explores and implements nature-based solutions. In addition, engineers are making progress towards accounting for social, gender equity, envi- ronmental justice issues, increasing the engagement of engineers with all stakeholders, including other sectors such as health, education or via the Water-Food-Energy nexus, and improving the ways they can work more effectively with policy makers and financing orga- nizations. In this issue of Hydrolink dedicated to the water-related SDG’s, we warmly welcome the views of Federico Properzi, Chief Technical Advisor of UN-Water, who in a short interview explains the challenges and his hopes for the 2023 Conference on Water, and highlights how engineers and scientists can contribute to achieving the SDG’s.

This issue of Hydrolink includes articles from the leadership of four IAHR Technical Committees (TCs) that discuss the contributions of their work to the SDGs. The first of these articles by the TC on Hydraulic Structures, one of the most traditional subjects of hydraulic engineering and research, calls for a science-based understanding of the interaction of hydraulic structures with the environment, and the need to manage and correct problems inherited from the past and to improve the development of sustainable hydraulic structures in the future. The article makes the point that the development of


hydraulic structures must balance the societal, environmental, and economic goals of each project and presents examples in six thema- tic application areas relevant to several SDGs.

The second article in this issue by the TC on Flood Risk Manage- ment discusses the direct and indirect effects of floods on sustainable development and the effort to achieve several SDGs, and stresses the need for Integrated Flood Risk Management (IFRM) which in- cludes working in different time frames and spatial scales, addressing the different components of flood risk, adopting the best mix of structural and non-structural mitigation strategies, and ensuring public participation at all levels of decision-making. It then discusses different modeling tools that have been used to support IFRM projects around the world, some of which included stakeholder engagement.

The third article by the TC on Ecohydraulics, an emerging trans- disciplinary field studying the intertwined abiotic-biotic phenomena in aquatic and riparian inland and coastal zones across a wide range of scales, discusses the tools and methods for quantifying the im- pact of climate change on inland and coastal ecosystems and eva- luating climate change adaptation scenarios. This includes numerical models and different remote sensing methods for data collection, such as satellites, aerial vehicles and underwater technologies.

An interesting question posed in this article in the context of climate change mitigation and adaptation strategies, is whether existing aquatic communities should be helped to survive under new adverse climate scenarios or find a balance with new communities that are able to thrive under future conditions.

Finally, an article by two members of the TC on Water Resources Management addresses the role of information and communication in the formulation of adaptation policies in support of the water- related SDGs. The article stresses the need to present policy makers with multiple scenarios to account for the uncertainty in future conditions and incorporate equity and social justice criteria in the evaluation of scenario outcomes and future pathways. The article also draws lessons from the water crisis in parts of Brazil between 2012 and 2018.

As can be seen in the contents of these articles, but also in se- veral articles in past issues of Hydrolink that present examples of the contribution of other IAHR TCs to the SDGs, hydraulic engineering and research are key elements of sustainable development. They underpin and impact almost every aspect of water policy and finan- cial, physical, social and environmental solutions. The contributions of hydraulic engineering to sustainability will continue beyond 2030, the target year for the SDGs, as many of the threats to water security will remain beyond that year. Climate change affecting water re- sources and water hazards, population growth in parts of the world such as sub-Saharan Africa, and urbanization around the world will remain as water challenges well beyond 2030. IAHR is promising to help overcome these challenges.

Hydrolink Editor Executive Director



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Angelos Findikakis

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Joe Shuttleworth Cardiff Univerisity Editorial Assistant Estíbaliz Serrano

IAHR Publications Manager | publications@iahr.org

Hydrolink Advisory Board Luis Balairon

CEDEX | Ministry Public Works, Spain Jean Paul Chabard

EDF Research&Development, France Jaap C.J. Kwadijk

Deltares, Netherlands Henrik Madsen DHI, Denmark Sean Mulligan

VorTech Water Solutions and National University of Ireland, Galway, Ireland

Yasuo Nihei

Tokyo University of Science, Japan Jing Peng

China Institute of Water Resources and Hydropower Research, China

Olivier Bertrand

Artelia Eau&Environnement, France James Sutherland

HR Wallingford, UK Karla González Novion

Instituto Nacional de Hidráulica, Chile

Cover picture: IAHR and the Water-Related Sustainable Development Goals


ISSN: 1388-3445


IAHR.org International Association

for Hydro-Environment Engineering and Research Hosted by Spain Water and IWHR, China



Interview with UN-Water Federico Properzi


IAHR Events Calendar 2023/2024


Hydraulic Structures At the Heart of 21st Century Global Sustainable Development

By S. Mulligan, S. Felder, E. Pummer, D. Valero, V. Heller, S. Erpicum, M. Oertel, F. Bombardelli and B. Crookston

05 10 14 19 22 27 30

Integrated flood risk management as a tool to achieve UN Sustainable Development Goals

By D. Molinari, B. Dewals, S. Haun, K. Abderrezzak, R. Vitthal and Flood Risk Management Technical Committee of IAHR

Climate Change Prediction and Adaptation in Ecohydraulics

By G. B. Pasternack, D. Tonina, R. Casas-Mulet, A. Adeva-Bustos, D. Vanzo, A, John and R. Tinoco

Accelerating change towards the SDGs: The role of information and communication

By Elpida Kolokytha and Carlos de Oliveira Galvão


Environmental Engineering:

‘Connecting to Nature’ with Virtual Reality

By Jörg Imberger IN DEPTH

Digital Water and Climate and its relation with AI

By Vladan Babovic



Federico Properzi

Chief Technical Adviser of UN-Water. He has more than twenty years of experience working in the United Nations system in different agen- cies at country and headquarters levels.

In 2020 the United Nations launched the SDG 6 Global Acceleration Framework to mobilize UN agencies, governments, civil society, private sector, and other stakeholders around five accelerators, Financing, Data and information, Capacity development, Innovation and Governance. How has this accelerator initiative worked so far, and what more must be done?

The SDG 6 Global Acceleration Framework was launched in 2020, just a few months into the COVID-19 pandemic. Its aim was, and still is, to unify and speed up the global effort to achieve the goal of universal access to safely managed water and sanitation by 2030.

On the one hand, the global context at that time was extremely challenging, but on the other, the COVID-19 crisis was laying bare the public health consequences of chronic underinvestment in water and sanitation, which added impetus to our efforts to accelerate change. With the express backing of the UN Secretary-General and Executive Heads of many of UN entities, the Framework has unified cross sectoral support for SDG 6 and helped to create unprecedented political consensus around water as a central pillar of sustainable development.

We always say that “water is everyone’s business” because there is not a single actor in any sector for whom a well-functioning water cycle is not absolutely fundamental. Yes, the latest data show that governments must work on average four times faster to meet SDG 6 on time, but crisis cannot be solved by governments alone. Public sector, private sector, the UN system, academia, civil society – we all have a vital role to play and the Framework directs our efforts.

Nearly three years on, as we focus on the UN 2023 Water Con- ference, we can be proud of the role the Framework has played in structuring the conversations and deliberations that have paved the way to this meeting. The Conference co-hosts, the Republic of Tajikistan and the Kingdom of the Netherlands, and the United Na- tions Department of Economic and Social Affairs that serves as the Conference Secretariat with UN-Water’s support, have used the Framework as the basis for the five interactive dialogues that will focus minds and generate transformative action plans. Going forward, the international community will use the SDG 6 Global Acceleration Framework as the basis for its support for the implementation and scaling up of the voluntary commitments in the Water Action Agenda, a main outcome of the Conference.

What are your hopes for the 2023 UN-Water Conference and espe- cially for any actions that would follow it?

I would say that “hopes” must be replaced by expectations and accountability. We know what we need to do and how to do it. What we need now is rapid, transformative action, led by governments, with the support of the UN system, and backed by strong, cross sectoral multi-stakeholder partnerships.

Solving the water and sanitation challenges is absolutely critical to building resilience and supporting progress towards all of the other SDGs, including on climate change, environment, gender, health, education, social justice and livelihoods. This is why the UN 2023 Water Conference must be a turning point in the water story. The blueprint for the coming years, up until the end of the 2030 Agenda and beyond, is the Water Action Agenda, a growing collection of vo- luntary commitments from governments, organizations and institu- tions, as well as community groups and members of the public.

This inclusivity will be vital. Just as the fight against climate change is as much a personal, cultural and social movement as it is a political and technical endeavour, so the fight to solve the water and sanitation crisis must capture the hearts of the public as well as the minds of decision-makers. The Water Action Agenda belongs to all of us and it is in all of our interests that it delivers transforma- tional change for those people and sections of the economy that need it most.

IAHR is an Association of engineers and scientists working on hydro- environment problems in engineering companies and research and academic institutions. What message would you have for the IAHR community on how to contribute to the SDGs?

My message would begin with a heartfelt “thank you”! The vital work of engineers, scientists, researchers and academics in the field of water and sanitation is what drives the services, solutions and inno- vations that change lives and transform economies. From the point of view of how and where to make interventions that will help achieve the SDGs, I would say, please follow the data. Explore UN-Water’s SDG 6 Data Portal to see the gaps that need to be bridged and fully investigate the needs you are trying to meet so that technical solu- tions are fit for purpose, affordable and sustainable for the long term.

I would also ask the IAHR community to leverage its existing partnerships – and make new ones – to coordinate efforts to impact as many SDGs at once as you can. The architecture of the 17 Goals that make up the 2030 Agenda was designed to be mutually support- ing, so please help to break down “silo thinking” and to integrate considerations of water and sanitation across your work in all sectors.

Lastly, I would encourage you and your organization to take action by contributing to the Water Action Agenda. As an individual, you can choose to commit to small-scale water actions in your daily life, such as taking shorter showers, eating local produce with a low water footprint or creating raingardens in your area. At the same time, with your work colleagues, you can commit your company or institution to take larger-scale action across your operations.

Small or big, as a single person or in a group, your commitments to taking water actions can be added to the Water Action Agenda that will drive progress throughout society.


Hydraulic Structures

At the Heart of 21 st Century Global Sustainable Development

By Sean Mulligan, Stefan Felder, Elena Pummer, Daniel Valero, Valentin Heller, Sebastien Erpicum, Mario Oertel, Fabian Bombardelli and Brian Crookston

Let’s envisage a world where all hydraulic structures and associated services were suddenly erased from existence. Most households would not have clean drinking water. The absence of sewage infrastructure would manifest in critical sanitation problems and serious public health issues. Local environments and ecosystems would be in major flux with undesirable impacts from pollution, flooding, droughts, and sediment transport. The absence of hydroelectric power would significantly decrease renewable energy production and hence impact energy prices and greenhouse gas emissions, whereas coastal erosion and flooding would threaten shoreline and estuarine communities.

Thankfully, the reality is that many hydraulic structures have provided security in water related services that lies at the very heart of global sustainable development1, 2. Hydraulic services underpin societal development and economic wealth2, 3, whether they function deep beneath the ground as drainage or storage systems or operate remotely to convey water for purposes.

For millennia, societal progress, health and prosperous economic growth has been closely linked to development of water infrastructure. Now in the 21


century, humankind faces some immense challenges including increasing and migrating populations, water and food security, damaged ecosystems, and a growing energy crisis, all coupled with the effects of climate change. Considering these challenges, future hydraulic structures must play a grander role in sustainable development through balanced preservation of societal, environmental, and economic goals collectively. This article showcases the positive contribution of hydraulic structures on these three pillars of global sustainable development through six newly defined thematic impact areas.

Figure 1 | The Great Salt Lake railroad causeway disrupts natural lake currents between northern and southern sections. Lowering of lake levels in recent times due to climate change and consumption is intensifying salt concentrations in the southern section to critical levels, creating a serious threat to the ecosystems and the economies that depend on it. This is an exemplary case of how hydraulic structures interact with societal, environmental, and the economic goals collectively in the face of climate change. Now, hydraulic engineering research groups at Utah State University are providing insights into the complex flows through the breach to inform management during drought periods6. Photo courtesy of Brian Crookston.

Unseen to the public eye and not fully appreciated until there is a problem, essential water infrastructure ensures continuous water supply, waste removal and energy and food security amongst many other benefits to society1, 3, 4.

Nonetheless, there is still a growing need for sustainable hydraulic structures, with requirements for water infrastructure accounting for more than half of the budget required for all glo- bal infrastructure by 20305. In the face of 21st century societal, environmental, and economic pressures of population growth, energy and food consumption, damaged ecosystems due to natu- ral and human disturbances all coupled with intensifying climate change effects, the hydraulic structures community is now at a crossroads towards the sustainable development goals (SDGs)1. There is a call for a renewed scientific understanding of how hydraulic structures interact with the environment to man- age and repair problems inherited from prior generations and to better plan for future sustainable hydraulic structures development.


To address 21st century challenges, concrete action is required in (1) adaptation, (2) mitigation, and (3) enhanced resilience through hydraulic structures development. However, robust sustainable development can only be achieved by preserving a good balance between societal, environmental, and economic goals of a project collectively (Figure 2).

To support this strategy, six newly defined thematic application areas have been identified. Each theme is described below with highlights of exemplary activity, impacts and challenges in each area with reference to the SDGs.

Water, Energy and Food Security

Figure 2 | Hydraulic structures thematic application areas underpin 21st century sustainable development pillars: society, environment, and the economy.

Dams and reservoirs have provided an essential security belt around the world in ensuring water, energy, and food supply2. Hydropower plays a role in climate change mitigation, yielding circa 16% of the world’s generated electricity as a low-carbon energy source2, 7. Large hydropower reservoirs have been essen- tial for providing flexibility and storage in large quantities and over periods from hours to years to facilitate fast response to demand along with black start possibility. Dams and reservoirs are also critical for water storage and conveyance to satisfy irrigation and food production for growing populations. It is reported that one third of the world is still undernourished, and a large population is threatened by famine. This risk can be lessened by irrigation of arid regions by hydraulic structures3. An example is the development of the Kaleshwaram Lift Irri- gation project in India with a capacity to pump 56 million m3/day to provide water for irrigation, consumption and industrial use across drought prone regions using flood waters. In terms of adaptation, dams and reservoirs also act as a buffer to water resource changes. Following learnings in the past, careful atten- tion to avoid or mitigate negative impacts is a necessity in future developments through a balanced approach in assessing environ- mental and social costs of the project during planning stages1. Significant investments are also being made in the management and refurbishment of existing dams to add capacity, reduce maintenance, and extend lifespan. In this context, reservoir sedimentation is also a critical problem for management agendas, where 0.5–1% of the world water storage capacity is lost annually to sedimentation8.

Environmental Restoration and Protection

A specific theme for the environment has been introduced where hydraulic structures will play a vital role in both restoration and protection against natural and human disturbance in the

future. In terms of natural impacts, examples are protection of habitats and ecosystems against erosion, sea level rise, floods etc; however, any indirect or cumulative effects of protection structures (e.g., sediment transport) should be understood in detail and mitigated where practical ahead of design. More importantly, impacts on the environment due to human activity and infrastructure development are inherent, where many current challenges have been inherited from development of prior generations. Ongoing and future hydrau- lic structures practice will require collaboration with other professionals and specialists in the field to manage existing challenges3, 6, restore natural environments and to innovate infrastructure development and management strategies to minimise impact on the environment.

For example, the field of eco/etho-hydraulics is maturing to understand and better integrate hydraulic structures and ecosystems (Figure 3(b)). Another example is combined sewer overflows which continue to be a pollution source across the world; however, large-scale interception structures are being constructed in many key locations to help mitigate discharges and restore natural waterways and habitats.

Flood and Coastal Defence

The growing frequency of significant flooding disasters instils great urgency to adapt flood and coastal protection measures to the compounding effects of climate change and increased urbanisation. Such strategies should consider holistically the system and corresponding behaviours, including the cause or source, for solutions to be effective and proactive whilst ensuring environmental goals are being preserved. For example, shoreline management plans are increasingly integrating a range of green- gray solutions such as artificial structures with ecological fea- tures, like vertipools or habitat tiles (Figure 3(c)). To mitigate flooding risk, sustainable planning and upgrades are being developed across cities such as more effective levee networks and, where possible, deep sewer conveyance systems, storm storage, and pumping systems.


Clean Water and Sanitation

Hydraulic structures play a pivotal role in the provision of water supply for clean water consumption, industrial use, and irrigation along with sanitation across the world. Before and after treatment, water is primarily collected and stored in reservoirs and distri- buted through extensive canal and pipeline systems. Sanitation systems include sewers, culverts, drop structures, and pumping stations, which safely transport wastewater away from society towards treatment infrastructure for efficient cleaning prior to environmental discharge. There are also recent strides towards the circular economy in this regard, where for example pollution abatement projects in India are adopting a “use, treat and reuse”

approach in wastewater management where hydraulic infras- tructure is fundamental to its success9 (Figure 3(d)). However, with some 46% of the world still having no access to safely managed sanitation, there remains a lot of work to be done.

The hydraulic structures engineer will continue to play a key role in this context in collaboration with environmental and process engineers and scientists.

Transport, Recreation and Heritage

Most of the world’s most valuable transport systems are via the sea and inland waterways which will also be the case for the future3. Many of these transportation routes have been enabled by pioneering hydraulic designs (Figure 3(e)). An exem- plary project is the Panama Canal that was constructed over

100 years ago. Over 1 million vessels have transited the canal since it opened. Economic dependence on such structures was ominously exhibited by the Suez Canal blockage accident in 2021, which had caused major disruption to global commerce.

Hydraulic structures such as harbours, canals, bridges, locks, and waterway promenades also represent important historic areas of recreation and heritage amongst society where efforts for preservation must be incorporated in project development strategies. For example, Thames Tideway launched a heritage interpretation strategy ahead of construction of their £5 Bn super sewer, which set out the historic and cultural themes to inspire the design and delivery of the project to align with local recreation and heritage10.

Technology, Research and Innovation

Technological advancement and innovation will continue to be important for the sustainable development of hydraulic struc- tures. Some examples of impactful research include the use of Acoustic Doppler Current Profilers for determining the efficiency of sediment bypass tunnels, application of phase-detection intrusive instrumentation in full scale high Reynolds number flows11, enhancements of 3D printing for rapid physical model development (Figure 3(f)12) and advancements in multiphase modelling for predicting behaviours of complex flows in hydraulic structures13. These strides in research are providing exciting opportunities in the development of hydraulic structures, yet field data is greatly needed in many applications including hydromachinery, treatment, sedimentology, nature-based solutions, and digitalisation of water management systems14.


Figure 3 | The six thematic application areas of sustainable hydraulic structures engineering, by image example (a) Energy and Food–Kaleshwaram Lift Irrigation project (https://bhoopalapally.telangana.gov.in/), (b) Environmental Restoration and Protection–Fish bypass tunnel and rack physical model (photo courtesy of Elena Pummer), (c) Flood and Coastal Protection–Environmentally friendly seawall at Carss Bush Park, NSW, Australia (photo courtesy of James Carley, UNSW Water Research Laboratory),(c) Water Supply and Sanitation-Effluent discharge downstream of a sewerage treatment plant for water re-use purposes (photo courtesy of Sean Mulligan),(e) Transport and Recreation-Sart canal bridge in Belgium on the Center canal (photo MET-D.434) and (f) Technology Research and Innovation-3D printed physical models of non-linear weirs (photo courtesy of Mario Oertel).




There is a need for water engineers (practitioners and researchers) to be aware of how the SDGs relate to their work, to better pro- gress and promote their activity2. The purpose of the discussion of the six thematic application areas is to raise awareness amongst the community about the role of hydraulic engineering in sustainable development. It is important to also note that each application area is not independent and overlaps broadly with other application areas. For example, environmental res- toration and protection overlaps with impacts and objectives in dams, flood/coastal defence, sanitation etc., whereas techno- logical development overlaps with all themes. However, it must be appreciated that elements of society, environment, and economy are present across all thematic areas with goals which can vary widely. Therefore, to enact strong sustainable development, these goals should be well understood to ensure that an inclusive and practical balance of the three pillars is maintained in future projects.

The success of the hydraulic structures field depends on a shared vision for sustainability where dissemination and knowledge sharing has been, and must continue to be, at the heart of the community’s activity. For example, the International Junior Researcher and Engineer Workshop on Hydraulic Struc- tures (IJREWHS) 2021 and the International Symposium on Hydraulic Structures (ISHS) held in Roorkee, India in 2022 brought together junior and senior hydraulic professionals from around the world to present and discuss research and projects, reflecting the ever-growing and diverse interest in the hydraulic structures engineering field. In addition, a working group in the EU COST Action has recently been founded to promote

“Sustainable hydropower and its adaptation to climate change”

(PEN@Hydropower) and a masterclass on hydraulic structures engineering will also be launched at the IAHR World Congress in Vienna in 2023.

However, key challenges still exist which should be continually addressed to accelerate progress. Some key examples are:

•There is a growing need for diverse, interdisciplinary part- nerships in addressing the challenges, particularly those between policy makers, utilities/contractors, and academia.

•It is predicted that natural and climate related disasters will continue to rise. Given experience that spans hydrology, data analysis, fluid dynamics and construction, the hydraulics structures community have a lot to offer in advancing solu- tions to address these critical challenges in future years through adaptation, mitigation, and resiliency measures.

•The hydraulic structures community can advance its role further towards global decarbonisation efforts. For example, the remaining feasible hydropower projects can significantly replace electricity sourced from fossil fuels2. Such projects should however undergo a screening process to holistically assess and quantify impacts on the environment and socie- ty to determine if the benefits sufficiently outweigh any such negative impacts1. Energy efficiency of hydraulic in- frastructure can provide a significant contribution also, along with integration of low carbon materials and construc- tion methods in future developments.

It is not an over exaggeration to state that hydraulic structures will be fundamental in future development3(e.g., water, energy, and food security). However, in many cases, there will still be inherent competing interests between societal, environmental, and economic goals. The future sustainability challenge will be for the community, comprising a host of multidisciplinary stakeholders, to fully appreciate these goals collectively on a project-by-project basis, in order to nurture a better balance between them, from policy development and design all the way to construction and long-term management.


1 | Felder, S., Erpicum, S., Mulligan, S., Valero, D., Zhu, D. and Crookston, B., 2021. Hydraulic structures at a crossroads towards the SDGs. IAHR White Paper.

2 | Schleiss, A., 2017. Better water infrastructures for a better world–The important role of water associations. Hydrolink, 3(Article), pp.86-87.

3 | Schleiss, A., 2000. The importance of hydraulic schemes for sustainable development in the 21st century. Hydropower & Dams, 7(Article), pp.19-24.

4 | Burkett, M.H., 2020. Silent and unseen: Stewardship of water infrastructural heritage. Adaptive Strategies for Water Heritage, p.21.

5 | Pörtner, H.O., Roberts, D.C., Adams, H., Adler, C., Aldunce, P., Ali, E., Begum, R.A., Betts, R., Kerr, R.B., Biesbroek, R. and Birkmann, J., 2022. Climate change

2022: Impacts, adaptation and vulnerability. IPCC Sixth Assessment Report, pp.37-118.

6 | Rasmussen, M., Dutta, S., Neilson, B.T. and Crookston, B.M., 2021. CFD Model of the density-driven bidirectional flows through the west crack breach in the

Great Salt Lake causeway. Water, 13(17), p.2423.

7 | Berga, L., 2016. The role of hydropower in climate change mitigation and adaptation: a review. Engineering, 2(3), pp.313-318.

8 | Schleiss, A.J., Franca, M.J., Juez, C. and De Cesare, G., 2016. Reservoir sedimentation. Journal of Hydraulic Research, 54(6), pp.595-614.

9 | Breitenmoser, L., Quesada, G.C., Anshuman, N., Bassi, N., Dkhar, N.B., Phukan, M., Kumar, S., Babu, A.N., Kierstein, A., Campling, P. and Hooijmans, C.M., 2022.

Perceived drivers and barriers in the governance of wastewater treatment and reuse in India: Insights from a two-round Delphi study. Resources, Conservation and Recycling, 182, p.106285.

10 | Stride, M.P., 2019. The Thames tideway tunnel: Preventing another great stink. The History Press.

11 | Hohermuth, B., Boes, R.M. and Felder, S., 2021. High-velocity air–water flow measurements in a prototype tunnel chute: Scaling of void fraction and interfacial velocity. Journal of Hydraulic Engineering, 147(11), p.04021044.

12 | Oertel, M. and Shen, X., 2022. 3D printing technique for experimental modeling of hydraulic structures: Exemplary scaled weir models. Water, 14(14), p.2153.

13 | Catucci, D., Briganti, R. and Heller, V. 2021. Numerical validation of novel scaling laws for air entrainment in water. Proceeding of the Royal Society, A 477(2255)

14 | Erpicum, S., Crookston, B.M., Bombardelli, F., Bung, D.B., Felder, S., Mulligan, S., Oertel, M. and Palermo, M., 2021. Hydraulic structures engineering: An evolving

science in a changing world. Wiley Interdisciplinary Reviews: Water, 8(2), p.e1505.


Stefan Felder

Associate Professor Stefan Felder is leading the hydraulic engineering research at the Water Research Laboratory at UNSW Sydney. He uses advanced experimental methods in the laboratory and at full-scale, to resolve applied and fundamental research challenges in hydraulic engineering including flow conveyance, fish passage and environmental flows. He is pas- sionate to step-change the profession’s traditions towards the sustainable development goals.

Elena Pummer

Dr.-Ing. Elena Pummer is Associate Professor in the Hydraulic Engineering Group at NTNU. Her research focuses on hydraulic modelling, including sediments and ethohydraulics, to solve fundamental hydraulic questions and develop sustainable designs. For this, she uses CFD simulations, physical modelling and field measurements.

Daniel Valero

Dr Daniel Valero is working as research Associate at KIT (Germany) and as Sr. Lecturer at IHE Delft (the Netherlands).

His work focuses on multiphase flows occurring in hydraulic structures and rivers.

Valentin Heller

Valentin Heller is an Associate Professor in Hydraulics in the Department of Civil Engineering at the University of Nottingham, UK. He is active in Experimental and Computational Fluid Dynamics with applications into fluid-structure interactions. His research applications are aimed at a better understanding of landslide-tsunamis, coastal and hydraulic structures, air-water flows, granular slides, and scaling similarity.

Sebastien Erpicum

Dr Sebastien Erpicum is Associate Professor at Liege University, Belgium, in charge of the Hydraulic Engineering Laboratory – HECE. He develops research activities related to hydraulics and hydraulic structures engineering, including spillway design, fish passage and hydropower development, with the specific objective of more sustainable solutions.

Mario Oertel

Mario Oertel is a full Professor in the Faculty of Mechanical and Civil Engineering at Helmut-Schmidt-University Hamburg, Germany. He is the head of the new Hydraulics Laboratory and his main focus is on experimental models, in-situ measurements, and numerical simulations; especially with focus on block ramp, fishways, fish passage, hydraulic structures, instrumentation and more.

Fabian Bombardelli

Fabian Bombardelli works as faculty member at the University of California, Davis, United States. He is a leader in the development of multi-phase theoretical and numerical models for flows past hydraulic structures, sediment-laden flows, and scour. In addition, he develops field and laboratory research in collaboration with colleagues worldwide. He also undertakes research in lakes and other applied problems in California.

Brian Crookston

Brian’s research and consulting activities are focused on water sustainability and resiliency including: hydraulic structures, fluvial hydraulics, and modeling and technology. Brian has particular interest in spillways, chutes, energy dissipators, non- linear weirs, physical and numerical modeling, machine learning algorithms, flow acoustics, scour and erosion, ecohydraulics, embankment failure, flooding, surface hydrology, and public safety and security at hydraulic structures.

Sean Mullligan

Dr Sean Mulligan is the Founder and CEO of VorTech Water Solutions Ltd, a water technology spin-out company from the University of Galway, Ireland. He holds a PhD from the Atlantic Technological University, Ireland in the field of hydraulic engineering. His research interests are in critical water infrastructure, innovative wastewater treatment technology and in translating water research into practical application to solve key challenges of the water industry.


Integrated flood risk management as a tool to achieve UN Sustainable Development Goals

By Daniela Molinari, Benjamin Dewals, Stefan Haun, Kamal El Kadi Abderrezzak, Ravindra Vitthal Kale with the contribution of the Flood Risk Management Technical Committee of IAHR

•Floods may increase their magnitude and frequency due to changing hydro-climatic conditions in the future; which accelerates the need for incorporating climate policies (SDG 13).

Nonetheless, strong linkages exist between the different SDGs, hence, floods may also have an indirect influence on the sustain- able development of a certain area. For instance, poverty, migra- tion to cities or uncontrollably growing urbanisation exacerbate flood impacts by an increase in vulnerability (Figure 1 left).

Accordingly, increasing flood resilience is an important part of reaching the goals set by the UN. Reducing vulnerability by, at the same time, increasing the resilience, requires the adop- tion of Integrated Flood Risk Management (IFRM), whose key components (Figure 2) are:

•Working in different temporal frames (i.e., during prevention, preparedness, response, and recovery phases of a disaster),

•Working at different spatial scales (from the very local to the global/catchment level) and also beyond national borders (e.g., transboundary catchments) for implementing climate- related policies,

•Addressing the different components of flood risk (to reduce the hazard, exposure, or vulnerability),

•Adopting the best mix of structural and non-structural miti- gation strategies, in a multi-objective perspective, considering ecological goals and compound events, which means the mitigation of co-existing natural (earthquakes, landslides, hurricanes/typhoons, etc.) or human made (nuclear, biolo- gical, etc.) hazards,

•Ensuring public participation at all levels of decision-making, as risk management needs to be open, transparent, and communicative among all stakeholders.

Floods are the most frequent type of hazard around the globe, affecting more people than any other natural hazards. A total of 222 floods were recorded in 2021 with approximately 30 million affected people (www.emdat.be/database). In 2030, this number could rise to 54 million/year according to the World Resources Institute, despite large infrastructure investments made to miti- gate disaster risk. When considering the direct (e.g., loss of life, physical damage of assets and infrastructure) and indirect (e.g., societal disruption, business interruption, environmental damage) consequences of floods, it becomes evident that high vulnerability and lack of flood resilience can undermine countries’ progress towards reaching the Sustainable Development Goals (SDGs), set by the United Nations (UN). Figure 1 shows two areas with a high vulnerability to floods, and measures to increase resilience.

Floods influence the sustainable development of countries in several ways:

• Floods impact people’s health and well-being (SDG 3), which in turn worsens existing poverty, especially in developing countries (SDG 1),

• Floods may slow down or even stop the progress towards a sustainable economic growth (SDG 8), sustainable industria- lisation and innovation (SDG 9), and the related development of inclusive, safe, resilient, and sustainable cities and human settlements (SDG 11),

• Floods impact key sectors for eradicating hunger, such as agriculture (SDG 2). Still, floods are a vital source of freshwater (SDG 6) in semi-arid or arid regions, hence there a coexis- tence of flood and drought needs to be considered,

• Floods may cause several forms of water pollution, e.g., when damaging sanitation facilities, impeding safe and affordable access to drinking water (SDG 6), and may at the same time impact water ecosystems and services they provide (SDG 14),

Figure 1 | (Left) Residential area in Bangkok, Thailand, with high vulnerability, and (right) increased resilience of houses by technical flood protection measures implemented in the United Arab Emirates.


Implementing IFRM requires a holistic view on drivers, system state descriptors as well as responses (Figure 3).

Drivers, such as climate and socio-economic changes are processes that act autonomously on changing the state of the system. However, responses are purposeful measures, which can be implemented in a holistic manner.

Given the complex interplay among natural/physical phenomena and the anthropogenic alterations of the system, such a holistic understanding requires the adop- tion of comprehensive, integrated and sophisticated modelling tools, addressing the various steps of IFRM.

These are data acquisition, hydrologic/hydraulic modelling, damage potential analysis, ecological impact assessment, design and sizing of flood protection measures (including alternatives and optimization), and stakeholder involve- ment among several others (Figure 2). Nonetheless, an

“adaptive/flexible” implementation of IFRM is required to properly consider existing uncertainties associated with complex models, (possible) data limitation, and changing boundary conditions due to climate change and urbanisation.

Figure 2 | Components of Integrated Flood Risk Management (IFRM) and associated SDGs.

These challenges are nicely exemplified through studies and projects in which members of the IAHR Technical Committee on Flood Risk Management have been involved. We shed light here on a small sample of them, with the aim of emphasising the instrumental contribution of the IAHR community for impro- ving IFRM across the globe, and hence our contribution to achie- ving the UN SDGs. A focus is thereby set on SDG 11 (Sustainable cities and communities) and SDG 13 (Climate action), which appear as the backbone of most IFRM-related projects.

The challenge of modelling compound flood processes in a coastal environment as well as the complex physics-human interplay is addressed in the ongoing STARS project, funded by the Ministry of Education (Ministry of Human Resources Devel- opment), Government of India. The study area is the low-lying Brahmani-Baitarani river basin (Figure 4 left), located in the eastern part of India, which faces backwaters from sea surges, fast sea-level rise (+ 3.8mm/year), climate-induced extreme preci-pitation combined with increased runoff from urban/peri- urban areas, sub-optimal reservoir operation, riverbed changes due to upstream mining and agriculture, as well as floodplain en-croachment. As many tangible and non-tangible benefits for human well-being can be reaped from coastal areas, their pro-tection from natural hazards and environmental degradation is key to the achievement of sustainable development. A novel short-to medium-range flood-forecasting system is under deve- lopment in the basin, integrating more processes than before

(i.e., rainfall-runoff, hydraulic routing, sediment flux, land use and river morphology changes due to anthropogenic activities, reservoir operation rules, real-time sea level), thus increasing the capability of local communities to deal with flood events.

Integrated flood modelling is also key for enabling a robust appraisal of combined pluvial and river floods. These two pro- cesses interact closely in relatively small catchments, charac- terised by a quick hydrological response, as well as in urban areas. The complexity of urban environments, characterised by multiple pathways and flow-sensitivity to micro-scale topo- graphic features, still requires deeper research, based on labo- ratory experiments, to improve our understanding of processes and accuracy of numerical modelling tools. An ongoing initiative in this direction is the EU-funded Co-UDlabs network of expe- rimental infrastructures (https://co-udlabs.eu/) that enables tackling complex, multidisciplinary open questions related to urban drainage systems (like the transport and turbulent dis- persion of contaminants in urban flooding or other polluting agents such as macro- and micro-plastic) by means of coopera- tive research between 17 facilities across Europe and the wider scientific community.

Responses Structural responses, preparedness, warning,

insurance System State

descriptors Sources, pathways

and receptors Drivers

e.g., climate change, population growth

Figure 3 | Interplay between intrinsic and extrinsic variables in IFRM.


Figure 4 left | Spatial distribution of simulated wind vectors and pressure fields over the study region during cyclone ‘Yaas’ and flood inundated area in Brahmani-Baitrani Delta region.

Figure 4 right | 2D hydraulic and fine sediment transport modelling along Piura river until the mouth of the river.

Inter- and transdisciplinary approaches are also necessary when assessing the impact of hydro-climatic change on reservoirs.

Reservoirs provide a unique opportunity for controlling floods and delivering a wide range of services. Within the ongoing project DIRT-X, as part of AXIS, an ERA-NET initiated by JPI Climate, a consortium of partners from five European countries investigates how changing climate- and socioeconomic condi- tions alter future water availability and soil erosion processes in the catchment. Based on these findings changes in the storage volume of reservoirs due to sedimentation and the influence on services they provide to different economic sectors will be determined. This newly gained knowledge serves as the basis for the implementation of future reservoir management to ensure sufficient retention volume for more frequent and more severe flood events occurring in the future (https://dirtx- reservoirs4future.eu/). Since reservoirs are often used as multi- purpose structures, this initiative also serves SDG 6 (Clean water and sanitation) and SDG 7 (Affordable and clean energy).

A meaningful example of stakeholder engagement is re- presented by flood risk management activities carried out in the Piura River basin in Peru. One-hundred and fifty years of anthropogenic interventions, such as channelization and river diversion towards an artificial river mouth, have resulted in complex issues regarding the river morphology in this system (https://www.youtube.com/watch?v=HiS-azK8WgY).

After a destructive El Niño flood event in 2017, large-scale actions have been performed for addressing the existing flood risk. Besides advanced hydro-morphological modelling, which is strongly required for a comprehensive understanding of the river morphodynamic (Figure 4 right), more than 100 workshops and meetings with social, environmental, and political stake- holders had taken place, with the aim of promoting sustainable engineering measures.

Engagement of stakeholders is not only a key element in the de- cision-making phase; their involvement from the design phase is vital to turn resistance to the implementation of risk reduction measures into endorsement and support. A remarkable example of a collaboration of scientists and practitioners is the award- winning MOVIDA initiative in the Po River District, Italy (https://

sites.google.com/view/movida-project). Tailored models and related IT tools were developed in accordance with the European Union (EU) Floods Directive (2007/60/EC) requirements for the appraisal of flood damage in the district. The models were then applied in a participatory process to inform on the prioritisation of flood risk mitigation strategies (www.gwptoolbox.org/case-study /italy-movida-models-and-tools-integrated-damage-assessment).

Further acknowledging the central role of the human com- ponent is a necessary milestone to leap forward towards effective, sustainable, and fair flood risk reduction strategies (Compare figure 5). This is a prerequisite to achieve SDGs 1 (No poverty) and 10 (Reduced inequalities). Worldwide, the population at risk of flooding is mostly a part of underprivileged socio-economic groups. Following similar assessments in the United Kingdom (for coastal flooding) and in the United States of America (including pluvial flooding), a recent study conducted in Belgium highlighted that underprivileged population is significantly more exposed to river flood hazard for moderate floods, and this trend is further exacerbated in the case of extreme events (www.frontiersin.org/articles/10.3389/frwa.2021.633046/full).

Similarly, energy-efficiency, land conservation and improved mobility require spatial planning policies, such as urban densifi- cation, which may contradict the needs of flood risk reduction (https://doi.org/-10.1016/j. jenvman. 2018.07.090). Disentangling such a dilemma is only possible through the lens of a compre- hensive system-approach, in which the main societal needs and their couplings are evaluated in an integrated way.


Ultimately, the IFRM framework is an essential part of a broader coordinated effort to make societies more resilient, carbon-neu- tral, and sustainable. The implementation of this framework is therefore indispensable for the achievement of several targets of the SDGs. However, large differences exist in its implementation, so that different priorities and related actions can be identified to ensure the adoption of IFRM in the near future. In low-income countries, the improvement of knowledge of both the natural phenomena and the vulnerability pattern of affected areas is the future challenge to increase the resilience of cities and human settlements and, hence, people’s health and well-being. An increased adoption of concepts like best-mix strategies (including risk awareness campaigns and community empowerment), multi- risks solutions (including nature-based ones) and participatory decision-making (based on a wider implementation of Multi Cri- teria Analysis) is already conducted in many high-income countries.

However, IFRM is a dynamic framework and continuous develop- ment is necessary to cope with challenges related to hydro-

environment engineering and research to achieve the SDGs. Figure 5 | Recent adapted construction in floodplains in Belgium as a part of IFRM.

Daniela Molinari

Prof. Daniela Molinari (Politecnico di Milano) is an expert in flood risk assessment and management, with particular expertise in flood damage evaluation. Prof. Daniela Molinari got a PhD in Hydraulic Engineering at Politecnico di Milano in 2011.

Soon after she started the collaboration with the Department of Civil and Environmental Engineering of Politecnico, first as researcher and now as associate professor. In 2020, she has also been nominated Delegate of the Director for the communi- cation policies of the department.

Benjamin Dewals

Benjamin Dewals is a Professor in Hydraulic Engineering and Water Resources Management at the University of Liege where he received his PhD in 2006. His main research interests cover flood risk management, fluvial hydraulics and reservoir sedi- mentation. He conducted research in several leading European institutions, including at EPFL (Switzerland) and in Germany.

Stefan Haun

Dr. Stefan Haun is a civil engineer and since 2019, he is the Head of the Hydraulic Laboratory at the Institute for Modelling Hydraulic and Environmental Systems at the University of Stuttgart. He obtained his doctoral degree in hydraulic and envi- ronmental engineering from the Norwegian University of Science and Technology, Trondheim, Norway, in 2012. His research focuses on the development and assessment of integrated flood protection measures in combination with river engineering features and sediment management.

Kamal El Kadi Abderrezzak

Kamal El Kadi Abderrezzak is a researcher Expert at The National Laboratory for Hydraulics and Environment (LNHE), Division of Research and Development(R&D) of Électricité de France (EDF). Mr El Kadi is chair of the IAHR working group on Reservoir Sedimentation. He is also an associate editor of the IAHR Journal of Applied Water Engineering and Research (JAWER). His main research interests cover fluvial hydraulics, sediment transport and flood risk management.

Ravindra Vitthal Kale

Dr. Ravindra Vitthal Kale is an Scientist D at National Institute of Hydrology, Roorkee, India. He has more than 12 years of research experience in the fields of hydrology and hydraulics dealing with Surface water assess-ment using deterministic, conceptual & Remote Sensing approaches; Irrigation and hydropower; Integrated Water Resources Management involving Eco-hydrology & Climate Change; Spring Hydrology, Disaster Risk Assessment & Management; Soft-computing technqiues in hydrology etc.


Climate Change Prediction and Adaptation in Ecohydraulics

By Gregory B. Pasternack, Daniele Tonina, Roser Casas-Mulet, Ana Adeva-Bustos, Davide Vanzo, Andrew John and Rafael Tinoco

thermal regimes with feedback to riparian and aquatic environs, including effects from altered riparian and floodplain vegetation.

This climate-change mechanistic chain will also interact with and likely be amplified by the broad scope of continuing local and regional anthropogenic pressures on inland waters and coasts, such as land-use, land-cover change, water abstraction, flow regulation, fish, and vegetation over harvesting, and exces- sive dispersal of nutrients, toxic chemicals, microplastics, and sediment. Together, local, regional and global pressures pose severe alterations to inland and coastal waters and may cause habitat degradation, shrinkage, and fragmentation8, organism physiological distress, higher risk of stranding, food-web dis- ruptions, increase in excessive riparian vegetation density, and alteration of many ecological functions. While ecohydraulics is spreading to address more species at the population scale and develop methods for community-level dynamics, it is unclear where climate change adaptation will require comprehensive assessment of all organisms or achieve success using a limited number of abiotic and biotic indicators. Nevertheless, ecohy- draulics is posed to provide the tools to quantify the impact of both climate change and anthropogenic needs on inland and coastal ecosystems and to weight different scenarios and alternative solutions including the use of nature based solutions.

Water is typically viewed as the definitive feature of rivers and coasts, but these systems also involve essential sediment dynamics. Traditionally, many ecohydraulics approaches assume a static terrain to evaluate how changes in flow or other controls affect biota. Over time, this will have to change so that sediment dynamics are incorporated. Sediment continuity from river headwater to coast is sensitive to climate, with significant impacts on morphodynamics, ecological processes, and river management and safety11. The quantification and modelling of sediment dynamics and its ecological impacts are critical in ecohydraulic research. Climate adaptation requires under- standing how river habitat responds to morphological changes induced by either natural or artificial floods12, 9 as well as river engineering activities (e.g., Figure 12).


Ecohydraulics is the process-based study of intertwined abiotic- biotic phenomena in aquatic and riparian inland and coastal zones across a wide range of scales. As a community, ecohy- draulicists have been developing a diversity of new environmental observational methods, solving the fundamental science about how many abiotic-biotic interlinks function5 and developing practical tools for both diagnosis and treatment of environmental problems6 typically caused by human impacts to inland and coastal waters. Examples of the latter include procedures and software for predicting spatial patterns of habitat quality for target species in each lifestage, likelihood of occurrence of specific ecological functions, organism migration and behavioral dynamics, and riparian vegetation dynamics. Such tools are available in a rapidly growing plethora of custom algorithms (e.g., FishXing, Dottertools, and Riverconn), and built into ecohy- draulic synthesis suites (e.g., CASiMiR, River Architect, HABBY, and MesoHABSIM) and decision-support systems (e.g., DRIFT and IFIM) for use in river restoration, environmental flows, fish passage, and other such engineering efforts. Despite the caution that emerging practices remain largely unproven, ecohydraulics is a hopeful, forward-looking endeavor tightly coupling scientific exploration, technological development, and engineering practice.

Now and into the future, ecohydraulics will need to quantify the effects of climate-change-induced physical and biological alterations on aquatic habitats and improve the applicability of its tools for climate change adaptation.

The role of ecohydraulics for climate change research For a global problem like climate change, ecohydraulics is the final set of links in the mechanistic chain by which oceanic- atmospheric-terrestrial systemic drivers force intertwined local physico-chemical environmental conditions and biotic function- ing. For example, climate change is expected to alter aquatic physical quantities globally via increases in global air temperature and altered precipitation and wind patterns. These climate con- ditions will in-turn modify water flow, sediment transport, water

Figure 1 | Map of river depths at 10 m3/s without dredging (left) and after dredging (right). Dredging of the riverbed may reduce flood damages and impact habitat diversity2.


Ecohydraulic remote sensing of climate change

Remote sensing (RS) is likely to play a decisive role in climate change progression and adaptation by society and nature itself.

This holds true for ecohydraulic responses to climate change.

A key RS advantage is its use for repeated surveys through time. Ecohydraulicists have been developing workflows for change detection and analysis that can be deployed to track and quantify ecohydraulic effects of climate-changed flow regimes, sediment regimes, and civil infrastructure.

RS customized for ecohydraulics is expected to provide the tools and methodologies to map spatial and temporal distributions of aquatic and riparian physical aspects as well as potentially the distribution of habitat directly. RS measurements will quantify the input parameters for modeling the spatial and temporal quality of habitats. Further, overwater and underwater RS measurements are already used to map the morphology and behavior of plants and animals, and RS systems will be essential to characterizing and tracking climate change impacts on eco- hydraulic patterns and dynamics.

Advances in overwater RS include passive imagery and ac- tive topo-bathymetric LiDAR enable direct mapping of vegeta- tion, terrain, water, snow and ice surfaces topping rivers, and infrastructure as well as changes in all of these. Satellite RS can measure discharge and bathymetry in large rivers. Video or repeat-image analysis is being used to map patterns of water surface velocity and monitor streamwood fluxes. Normalized Difference Vegetation Index methods and multispectral cameras provide vegetation distribution and their status.

Ecohydraulicists were early adopters of unoccupied aerial vehicles (aka drones) as low-cost tools for mapping and moni- toring rivers and coasts, and continue to explore novel applica- tions. For example, drone-mounted thermal infrared imagery technologies are effective for cold-water-refugia (CWR) assess- ment and prediction, and further progress in this domain will be critical to inform long-term adaptation measures that main- tain resilient cold-water habitats to support key organisms’

persistence. Drones have also been used to map riparian and aquatic vegetation, especially where invasive species are a problem and may expand with climate change.

Meanwhile, underwater ecohydraulics technologies include side scan and multibeam sonar, dual frequency identification sonar (DIDSON), videography, stationary cameras, and infrared scanners. For one of the important topics in ecohydraulics, fish passage, DIDSON has been used to monitor passage rates and behavioral responses to passage infrastructure besides to quantify behavior and path selection by migrating fish when they arrive at a river confluence. Stationary cameras and scan- ners have become instrumental to management of fish passage structures, because users cannot only quantify passage rates, but also determine organism species, identify wild versus hatchery origin, and measure size and shape attributes. Acoustic telemetry may also be considered a form of RS; it is used to map organism movements in two or three dimensions (i.e., 2D or 3D). Once organism tracks are georeferenced within water bodies, results inform on organism individual and group behaviors

as well as responses to external drivers. Current telemetry ad- vances continue to miniaturize transmitters that are surgically implanted in organisms and improve the processing of the mas- sive amount of data these systems yield (e.g., ACTEL, fishtrack3d, and YAPS on GitHub).

Spatial variations of stream temperature and the processes governing thermal heterogeneity within the riverscape are of key concern for managers. Thermal heterogeneity is increasingly considered a key aspect of river habitat structure (e.g., Figure 23), given its potential to provide CWR in some areas of the world and warm water refugia in others. Thus, it will be an important water management target in climate adaptation strategies. Rivers are complex dynamic ecosystems with a physical structure that can be represented as a hierarchical organization of interconnected spatial scales. Whilst river tem- perature is driven by climatic, topographic, land cover and hy- drological controls at the air-water interface, such an array of multi-scalar physical features will play a key role in determining how heat is distributed, including groundwater inputs, hyporheic flows, in-channel physical complexity, and shading.

Figure 2 | Changes in stream thermal habitats between present and future (with a predicted 4 °C warming) water temperatures, in different river morpho- logies of the River Ovens, Australia. Modified from Kuhn et al. (2021).


Ecohydraulic modeling as a bridge across scales

Because many aspects of ecohydraulics cannot be directly observed, ecohydraulicists use spatially explicit (2D or 3D) mechanistic numerical models to produce meter-resolution, spatially explicit maps of aquatic and riparian “micro-habitat”

over increasingly long kilometers of river as well as for coasts and estuaries. Micro-habitats are coherent areas with charac- teristic physical attributes where organisms perform ecological functions. Beyond hydraulics, landforms, and physical habitats, ecohydraulicists have increasingly been using algorithms to extend simulations to address bioenergetic, individual-organism behaviors, and a growing list of diverse ecological functions.

Mechanistic ecohydraulic models enable understanding of, prediction of, and adaptation to the effect of physical drivers such as water, streamwood, and sediment management and climate change on aquatic habitat quantity and quality distri- bution.

Studies and forecasts of the effects of climate change on regional to local environments often link together a series of models and analysis tools to enable simulation of alternative future scenarios. As ~1-m resolution topo-bathymetric river

and coast datasets are collected and made available, spatially explicit hydrodynamic and possibly morphodynamic modeling could be driven by climatic-hydrological forecasting models, taking the existing practice to a whole new level of direct rele- vance to environmental stewardship and provision of ecosystem services to society. The hope is to obtain reduced risk and dam- ages for society by using early warning systems, river rehabili- tation (including connectivity), and environmental flow regimes, thereby reducing the need for traditional engineered flood measures that have been widely shown to negatively impact riverine and coastal ecosystems.

Organism physiology, behavior response, and survival can be predicted with a cascade of models. A recent study by Reeder et al.7 used a cascade of models, from climate change to hydrological model, to ecohydraulic model and to a statistical fish growth model, to understand the impact of climate change on Chinook salmon (Oncorhynchus tshawytscha) size before migrating to the ocean. The study showed that climate change may increase fish size, and potentially their fitness, negligibly limit rearing habitat but significantly reduce spawning habitat (Figure 3).

Figure 3 | Rearing habitat distribution at 2 m3/s discharge along a section of Bear Valley Creek (Idaho, USA) bankfull width of 15 m (a), effect of climate change on mean summer temperature, mean annual weighted usable area for rearing and spawning habitat (b) and their effect on fish mode length (c).




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