John G. Williams is a retired consultant with a PhD in physical geography who has published on botany, climatology, hydrology and salmon biology as well as on environmental flow assessment. He has served as an elected director of a water management district in California, and as special master for important litigation regarding environmental flows. He can be reached at jgwill@frontiernet.net.

Peter B. Moyle is Distinguished Professor Emeritus at the University of California, Davis. He has been working on flows and fish issues since the 1970s. He is particularly proud of his role in designing a flow regime to benefit fish, plants and birds for Putah Creek, near the UCD campus. (See https://watershed.ucdavis.edu/cws‐wfcb‐fish‐conservation‐group.)

J. Angus Webb is an Associate Professor at the University of Melbourne, Australia. He leads the Ecohydraulics laboratory group in the Water, Environment and Agriculture Program within the Melbourne School of Engineering, and is heavily involved in the monitoring, evaluation and adaptive management of environmental flows being delivered under Australia’s Murray–Darling Basin Plan. He was awarded the 2012 Early Career Achievement Award from the Australian Society for Limnology, and the 2013 Award for Building Knowledge in Waterway Management from the Australian River Basin Management Society. (See www.ie.unimelb.edu.au/research/water/)

G. Mathias Kondolf is a fluvial geomorphologist and environmental planner at the University of California Berkeley and a fellow at the Collegium, Institute for Advanced Study at the University of Lyon, France. He works on sustainable river management and restoration, including managing sediment in regulated rivers. (See https://riverlab.berkeley.edu.)

Advancing river restoration and management

The field of river restoration and management has evolved enormously in recent decades, driven largely by increased recognition of ecological values, river functions and ecosystem services. Many conventional river‐management techniques, emphasizing strong structural controls, have proven difficult to maintain over time, resulting in sometimes spectacular failures, and often a degraded river environment. More sustainable results are likely from a holistic framework, which requires viewing the “problem” at a larger catchment scale and involves the application of tools from diverse fields. Success often hinges on understanding the sometimes complex interactions among physical, ecological and social processes.

Thus, effective river restoration and management require nurturing the interdisciplinary conversation, testing and refining of our scientific theories, reducing uncertainties, designing future scenarios for evaluating the best options, and better understanding the divide between nature and culture that conditions human actions. It also implies that scientists should communicate better with managers and practitioners, so that new insights from research can guide management, and so that results from implemented projects can, in turn, inform research directions.

This series provides a forum for “integrative sciences” to improve rivers. It highlights innovative approaches, from the underlying science, concepts, methodologies, new technologies and new practices, to help managers and scientists alike improve our understanding of river processes, and to inform our efforts to steward and restore our fluvial resources better for a more harmonious coexistence of humans with their fluvial environment.

In a 2010 review, Arthington et al. remarked that: “There is now wide recognition that a dynamic, variable water regime is required to maintain the native biodiversity and ecological processes characteristic of every river and wetland ecosystem. Yet it remains a challenge to translate this ‘natural flow regime’ paradigm into quantitative environmental flow prescriptions for individual reaches from source to sea” (citations omitted). This book is about methods and approaches for meeting this challenge.

Environmental flow assessment is largely about flow, as the name suggests, but not just about flow. Other biotic and abiotic factors influence flowing water ecosystems, and environmental flow assessment (EFA) needs to take them into account. And, EFA is a social process, probably more than a scientific process. We treat EFA mostly as a kind of applied ecology, but we do not ignore the complications arising from human nature.

People working on EFA have diverse backgrounds, so we expect the same of readers of this book. Some will see themselves primarily as managers, rather than as scientists or engineers, and many will be familiar mainly with one region or even one stream system. Therefore, we have included material that will seem elementary to some readers, mostly to emphasize the variety of stream ecosystems that are the subject of assessments. Similarly, although we expect that many readers will already know a lot about EFA, we have tried to avoid assuming that they do. And, we do not try to be comprehensive. For example, we say little about riparian systems, and almost nothing about estuaries, although dealing with them is an important part of the overall problem. Rather, we try to elaborate an approach or point of view that can be applied generally.

We take a more critical attitude about methods for EFA than other books on the same subject, such as Locke et al. (2008) or Arthington (2012). We make recommendations, but we explain the shortcomings of the methods we recommend, as well as of those we don't. Part of our motivation in writing this book is concern about careless use of models in EFA, and we deal with that at length. Reluctance to criticize others' work is generally an admirable trait, but not in science, where it is part of the job, provided it is not mean‐spirited.

It is an unhappy truth that many scientific papers have been published that should not have been, and many published research findings are false (Ioannidis 2005). There are various reasons for this, and a major one is flawed statistical analyses, especially overreliance on and misuse of statistical significance tests. Ioannidis wrote about the biomedical literature, but the same applies in environmental sciences. For example, Bolker et al. (2009) found problems with 311 of 537 applications of generalized linear mixed models in articles on ecology and evolution, and our impression is that papers on EFAs tend to exhibit a lower level of statistical understanding, and to receive poorer reviewing on statistical matters, than papers in related fields. We discuss and illustrate statistical problems with methods for EFA and related studies, but at a conceptual level, without getting into the technical details.

Geographically, the western USA, and especially California, is overrepresented in the book, as are salmonids. This seems parochial, and it is, but the western USA is highly diverse geographically, salmonids have diverse life‐histories, and most of the literature on EFA deals with salmonids. Since three of us have lived and worked in California for decades, we are more familiar with EFA as it is actually done in California than elsewhere, so our California bias results largely from following the advice to “write what you know.” However, we are broadly familiar with EFA elsewhere, and recommend an approach developed in Australia.

On language, we follow more recent (and more appropriate) usage and refer to “environmental flows” instead of “instream flows,” but we do not intend any change in meaning with this terminology. We have tried to write in plain language, and to avoid overly technical or overblown academic writing such as the following, which we did not make up: “Temporary streams naturally experience flow intermittence and hydrologic discontinuity that act to shape fish community structure,” or worse: “Thus, theoretically, although habitat suitability curves underpinning area‐weighted suitability indices apparently invite the intervention of modeling approaches, the more complex and less‐definite relations between physical habitat and ecological response may reduce this potential, with correspondence at best, treated probabilistically.” Why would anyone who has something to say use such language? We expect that some readers will disagree with some of what we write, but we have tried to write it clearly.

With one exception, separate authorship is not listed for the various chapters, although readers with any sense of language will notice immediately that the writing styles varies. Each chapter has a main author, but each of us has read, commented on, and approved the others. The exception, Chapter 8, Dams and Channel Morphology, was written by fluvial geomorphologist Mathias Kondolf and collaborators from his research group in Lyon, France: Remi Loire, Hervé Piégay, and Jean‐Réné Malavoi, who are thus listed as co‐authors for the chapter.

Overall, our somewhat lofty goal is to give users (and students) of environmental flow methods a better understanding of the tools they are using, and especially where they may fall short. Methods for EFA are constantly evolving, especially analytical tools. Practitioners would be well served to be more critical of existing well‐used methods, and to investigate alternatives coming on line. The more EFAs reflect reality, the more likely they will provide useful information, to the benefit of both flowing‐water ecosystems and human populations that derive so much benefit from them.

The ideas presented in Chapter 9 stem largely from development work undertaken in two Australian Research Council Linkage Projects (LP100200170, LP130100174) and eWater Cooperative Research Centre projects. We acknowledge the contributions of the many staff and students involved. We thank Genevieve Smith, in particular, for allowing the use of her Master of Environment research project as the case study presented therein. The material in Chapters 1, 2, 4, and 6 expands on worked funded by the California Energy Commission, Public interest Energy Research Program, through the Center for Watershed Sciences, University of California, Davis. Preparation of Chapter 8 was partly supported by the Collegium, Lyon Institute for Advanced Studies, University of Lyon, and the EURIAS Fellowship Programme and the European Commission (Marie‐Sklodowska‐Curie Actions – COFUND Programme – FP7).