Environmental Science Rivers
by
Ellen Wohl
  • LAST REVIEWED: 10 May 2017
  • LAST MODIFIED: 29 September 2014
  • DOI: 10.1093/obo/9780199363445-0004

Introduction

River networks, and even individual river segments, are complex ecosystems that can be studied from many perspectives. Arguably the most common differentiation is between studies that focus on various aspects of rivers, such as contemporary physical processes (river engineering, hydrology, or geomorphology); physical processes over longer time spans (geomorphology); chemical processes (geology or aqueous chemistry); individual species or groups of organisms (fish biology); and biological communities (aquatic and riparian ecology). Each of these approaches to understanding rivers has an extensive technical literature. The works cited in this bibliographic entry draw from these sometimes disparate bodies of literature and focus on rivers in an environmental context rather than treating a specific river as an isolated feature or focusing solely on one component of rivers. River segments and river networks provide a wealth of information about past and contemporary environmental conditions, for rivers inherently integrate fluxes of matter and energy within a landscape through the entity of a drainage basin. The entire land surface that drains to a specified point makes up the drainage basin for that point. In addition to water, sediment, solutes, and organic matter enter the river network via atmospheric, surface, and subsurface pathways. Matter and energy move upstream, laterally, and vertically within a river network, as well as downstream. A well-studied example comes from the upstream migration of spawning salmon that then die and transfer ocean-derived nutrients to the river network and adjacent riparian zone. Because a river so effectively integrates diverse inputs and reflects conditions across the entire drainage basin, investigators have used physical, chemical, and biological characteristics of rivers as metrics for the environmental state of the river itself, and of the larger drainage basin. Three of the sections within this bibliographic entry include works that provide examples of these metrics for prehistoric, historic, and contemporary environmental conditions. Rivers also provide numerous ecosystem or environmental services, such as clean water and recreational fisheries, and another section provides examples of studies focusing on this aspect of rivers. Attempts to manage rivers and preserve desired attributes such as clean water, flood control, or fisheries constitute an important subset of environmental management, and are addressed in the final section of this entry.

General Overviews

The works cited in this section include all aspects of riverine environments, either written for scientists, as in Calow and Petts 1992, or written for a more popular audience, as in Waters 2000 or Middleton 2012. Patrick 1994–2003 represents a hybrid that is accessible to nonspecialists, but contains useful syntheses and overviews, particularly for students starting to learn about rivers or specialists in one area of river science starting to learn about other aspects of the science. The common theme among these works is that rivers—rather than being simple conduits for water, sediment, or fish—are complex environments that interact with the adjacent uplands, oceans, atmosphere, and underground waters.

  • Calow, P., and G. E. Petts, eds. 1992. The rivers handbook: Hydrological and ecological principles. 2 vols. Oxford: Blackwell Science.

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    Volume 1 provides a comprehensive review and synthesis of diverse aspects of river physical, chemical, and biological environments and case studies. Volume 2 reviews perturbations and biological impacts, monitoring, modeling, management options, and case studies. Individual chapters are written by recognized experts, and the organization ensures continuity between chapters.

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  • Middleton, N. 2012. Rivers: A very short introduction. Oxford: Oxford Univ. Press.

    DOI: 10.1093/actrade/9780199588671.001.0001Save Citation »Export Citation »E-mail Citation »

    Part of a series of very short introductions to diverse topics. This little volume manages to cover physical, biological, historical, and environmental aspects of rivers very concisely and elegantly. A good starter for anyone interested in learning about rivers as environments.

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  • Patrick, R. 1994–2003. Rivers of the United States. 5 vols. New York: Wiley.

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    Five volumes published between 1994 and 2003 systematically examine chemical, physical, and biological characteristics of US rivers, including regional emphases. Patrick helped to draft the nation’s Clean Water Act. This synthesis of her life’s work on rivers is readily accessible to nonspecialists and provides an excellent overview of river environments.

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  • Waters, T. F. 2000. Wildstream: A natural history of the free flowing river. St. Paul, MI: Riparian.

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    Although written for a popular audience, this highly readable book aptly summarizes a variety of relevant technical knowledge about rivers, including physical process and form, water chemistry, biological energy sources and river metabolism, and biological communities. Basic technical information is interspersed with numerous specific case studies, here called “RiverSketches.”

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Textbooks

The works cited in this section are textbooks that emphasize one particular aspect of riverine systems, but also consider rivers in a broader environmental context. Leopold, et al. 1964 is a foundational text of river form and process that emphasizes the physics governing river environments. Schumm 1977 is another foundational text on the physical characteristics of rivers, but with a greater emphasis on drainage basin and landscape setting. Naiman, et al. 2005 is one of the first systematic, book-length examinations of riparian systems, which are transitional environments between river channels and adjacent uplands. Allan and Castillo 2007 provides a comprehensive examination of the ecology of rivers, including physical and chemical influences on stream biotic communities. Dunne and Leopold 1978 is a widely used text that examines rivers and other aspects of hydrology in the context of resource management and environmental planning. Wohl 2014 focuses on the physical processes and forms of riverine systems, but also considers how biota—including humans—influence and respond to physical process and form.

  • Allan, J. D., and M. M. Castillo. 2007. Stream ecology: Structure and function of running waters. 2d ed. Dordrecht, The Netherlands: Springer.

    DOI: 10.1007/978-1-4020-5583-6Save Citation »Export Citation »E-mail Citation »

    This fundamental stream ecology text includes chapters on streamflow, fluvial geomorphology, streamwater chemistry, and the abiotic environment, all of which examine how river ecosystems reflect environmental inputs and controls. A chapter on human impacts to streams discusses how river ecosystems respond to human-induced environmental changes.

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  • Dunne, T., and L. B. Leopold. 1978. Water in environmental planning. San Francisco: W. H. Freeman.

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    This classic textbook includes diverse aspects of hydrology, with an emphasis on the context of river management and planning. Individual sections address surface water and groundwater, river form and process, riverine biota, water quality, and field examples. The text also includes some engineering hydrology, such as flood hazards.

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  • Leopold, L. B., M. G. Wolman, and J. P. Miller. 1964. Fluvial processes in geomorphology. San Francisco: W. H. Freeman.

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    A classic textbook on river form and process that emphasizes environmental context in the sense of how rivers reflect their landscape setting (climate, geology), as well as human influences. Although written decades ago, this text still provides a useful introduction to rivers as environments.

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  • Naiman, R. J., H. Decamps, and M. E. McClain. 2005. Riparia: Ecology, conservation, and management of streamside communities. Burlington, MA: Elsevier Academic Press.

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    Summarizes diverse ecological processes and patterns in riparian environments, defined as transitional semiterrestrial areas regularly influenced by fresh water. Chapters on catchments and biophysical connectivity examine how riparian ecosystems reflect environmental inputs and controls. Chapters on disturbance and management explore how riparian ecosystems respond to natural and human-induced environmental changes.

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  • Schumm, S. A. 1977. The Fluvial System. New York: Wiley.

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    A classic textbook on river form and process that emphasizes rivers in a landscape setting, with sections on land use and river engineering. This text is particularly effective at explaining adjustments between individual river segments, other portions of the rive network, and adjacent uplands and oceans.

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  • Wohl, E. 2014. Rivers in the landscape: Science and management. Hoboken, NJ: Wiley-Blackwell.

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    This textbook on fluvial geomorphology emphasizes the landscape context when studying river process and form. Landscape context here includes the continuing effect of geologic history; connectivity of individual stream segments with the subsurface, adjacent uplands, and the atmosphere; interactions among water, sediment, and aquatic and riparian biota; and human influences.

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Journals

The works cited here include journals that focus specifically on some aspect of rivers, such as River Research and Applications, and journals that typically include numerous articles on some aspect of rivers. In the latter category, Geomorphology and Earth Surface Processes and Landforms include articles on river process and form. Water Resources Research, Journal of Hydrology and Journal of the American Water Resources Association are examples of journals that deal with all aspects of hydrology and water resources, and also include articles on river process and form, river water quality, and river management. The Canadian Journal of Fisheries and Aquatic Sciences and Freshwater Science that include many articles on biological and ecological aspects of rivers.

Rivers as Indicators of Paleoenvironmental Conditions

The works cited in this section describe diverse geological records created by rivers that can be used to infer prehistoric conditions prior to human alteration of a river or drainage basin. Inferences drawn from geological records are based on the assumption that observed contemporary relations between the environment and a river can be extrapolated backward in time. If a meandering river creates distinctive sediment deposits with a consistent correlation between mean annual discharge and the cross-sectional area of the river channel or the wavelength of the meanders, for example, then channel area or meander wavelength as preserved in prehistoric floodplain sediments can be used to infer past variations in mean annual discharge. The age, grain size, stratigraphy, and geochemistry of river alluvial sequences can also record relatively abrupt events, such as large floods, as explored in Ely, et al. 1993 and O’Connor 1993, or displacement along faults, as illustrated in Whittaker, et al. 2008. Many of the paleoenvironmental inferences drawn from rivers use portions of the landscape once modified by rivers that are now either removed from the active channel or only affected very infrequently by active channel processes. Examples include portions of floodplains, as in Hall 1990; deltas, as in Siegel, et al. 1995; alluvial fans, as in Pierce and Meyer 2008; and river terraces, as in Pederson, et al. 2006. Extrapolation based on the assumption of consistent relations between a river and the greater environment allows us to use changes in water and sediment discharge, channel geometry, and riverine chemistry and biota that are recorded in sediment deposits to infer associated changes in climate, land cover, and topography over time intervals ranging from hundreds to tens of thousands of years. As numerous individual case studies of this type accumulate, metadata analyses can be used to search for regional- or continental-scale patterns, as discussed in Macklin and Lewin 2008.

  • Ely, L. L., Y. Enzel, V. R. Baker, and D. R. Cayan. 1993. A 5000-year record of extreme floods and climate change in the southwestern United States. Science 262:410–412.

    DOI: 10.1126/science.262.5132.410Save Citation »Export Citation »E-mail Citation »

    Flood sediments deposited at tributary junctions and in caves and channel-margin alcoves along bedrock canyons can be used to infer peak flow magnitude and, when combined with 14C and other dating techniques, flood chronology. Floods in the southwestern United States correlate with cool, moist climatic periods and frequent El Nino events.

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  • Hall, S. A. 1990. Channel trenching and climatic change in the southern U.S. Great Plains. Geology 18:342–345.

    DOI: 10.1130/0091-7613(1990)018%3C0342:CTACCI%3E2.3.CO;2Save Citation »Export Citation »E-mail Citation »

    Stratigraphic exposures along streams in Texas and Oklahoma record sediment accumulation and formation of floodplain soils during a period of cooler, wetter climate between 2,000 and 1,000 years ago. Synchronous regional incision of streams occurred as the climate became drier. This study illustrates how sediments record river responses to climatic variation.

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  • Macklin, M. G., and J. Lewin. 2008. Alluvial responses to the changing Earth system. Earth Surface Processes and Landforms 33:1374–1395.

    DOI: 10.1002/esp.1714Save Citation »Export Citation »E-mail Citation »

    An example of the type of metadata analysis now possible as a result of numerous case studies. River sediments across Eurasia record periods of rapid response to even relatively minor but regionally synchronous climatic variations such as the end of the Little Ice Age at around 1850 CE.

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  • O’Connor, J. E. 1993. Hydrology, hydraulics and geomorphology of the Bonneville Flood. Geological Society of America Special Paper 274. Boulder, CO: Geological Society of America.

    DOI: 10.1130/SPE274Save Citation »Export Citation »E-mail Citation »

    This volume exemplifies the study of enormous outburst floods that occurred as the Pleistocene ice sheets began to retreat about fifteen thousand years ago. Geologic records of flood stage and erosional and depositional features are used with hydraulic modeling to infer the velocity and discharge of peak flood flows.

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  • Pederson, J. L., M. D. Anders, T. M. Rittenour, W. D. Sharp, J. C. Gosse, and K. E. Karlstrom. 2006. Using fill terraces to understand incision rates and evolution of the Colorado River in eastern Grand Canyon, Arizona. Journal of Geophysical Research 111:F02003.

    DOI: 10.1029/2004JF000201Save Citation »Export Citation »E-mail Citation »

    Geologic ages of alluvial terraces exposed along the Colorado River in Grand Canyon suggest a long-term bedrock incision rate of 140 meters per million years. The terraces indicate that the Colorado has been an alluvial, rather than a bedrock, river for more than half of the past two million years.

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  • Pierce, J., and G. Meyer. 2008. Long-term fire history from alluvial fan sediments: The role of drought and climate variability, and implications for management of Rocky Mountain forests. International Journal of Wildland Fire 17:84–95.

    DOI: 10.1071/WF07027Save Citation »Export Citation »E-mail Citation »

    Alluvial fans are river depositional features that accumulate sediment over thousands of years. This study uses changes in charcoal abundance within fan sediment to infer fire frequency, which is then correlated with climatic variation. Fan sediments in Idaho and Yellowstone indicate greater fire activity during periods of warm, dry climate.

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  • Siegel, F. R., N. Gupta, B. Shergill, D. J. Stanley, and C. Gerber. 1995. Geochemistry of Holocene sediments from the Nile delta. Journal of Coastal Research 11:415–431.

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    An example of using geochemical characteristics of sediment records to infer past environments. Ratios of specific elements in Nile delta sediments indicate the Ethiopian Highlands as a major sediment source during the past ten thousand years. Clay minerals also reflect changing salinity in the nearshore depositional environment.

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  • Whittaker, A. C., M. Attal, P. A. Cowie, G. E. Tucker, and G. Roberts. 2008. Decoding temporal and spatial patterns of fault uplift using transient river long profiles. Geomorphology 100:506–526.

    DOI: 10.1016/j.geomorph.2008.01.018Save Citation »Export Citation »E-mail Citation »

    Using longitudinal profiles of rivers in the Italian Apennines, compares river response to constant uplift versus increased uplift. Rivers crossing faults with constant uplift rates have the concave-upward profiles expected of stable rivers, whereas those crossing faults with increased displacement during the past million years have convexities in their profiles.

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Rivers as Indicators of Past Human Environmental Alteration

The works cited in this section describe how human activities alter river environments, as in James and Lecce 2013 and Marcus and James 2006, and how diverse geological and biological aspects of rivers can be used to infer more recent, historic environmental conditions within a river drainage basin. The time interval covered by the word “historic” typically refers to the period during which human activities significantly altered land cover, sediment and water yield, or channel geometry within a drainage basin, and varies enormously in this context. The historic period covers two or three thousand years in some portions of Eurasia, for example, but may cover only slightly more than a century in parts of the Americas, Australia, or New Zealand. Diverse types of historical human environmental alteration are commonly referred to as “legacy effects.” Accumulations of sediment associated with human activities are referred to as “legacy sediments.” Examples include sediment deposited upstream from abandoned milldams, as discussed in Walter and Merritts 2008; discussions of sediment accumulating along valley bottoms as a result of replacement of native upland vegetation by crops or grazing lands in Trimble 2009 and Brown, et al. 2013; or sediments contaminated with heavy metals from historical mining, as described in Miller, et al. 1999. Attention to legacy effects is important for at least two reasons. First, these effects may provide a record or reminder of past environmental alteration that is otherwise forgotten. Second, legacy effects continue to influence contemporary environments and create a context for contemporary environmental management and predictions of future environmental change. These continuing legacy influences are illustrated by stream insect communities (Harding, et al. 1998) and riparian vegetation that reflect past human activities (Schulze and Walker 1997).

  • Brown, A., P. Toms, C. Carey, and E. Rhodes. 2013. Geomorphology of the Anthropocene: Time-transgressive discontinuities of human-induced alluviation. Anthropocene 1:3–13.

    DOI: 10.1016/j.ancene.2013.06.002Save Citation »Export Citation »E-mail Citation »

    This review paper summarizes the evidence for a stratigraphic discontinuity in river sediments that appears on all continents except Antarctica. The age of the discontinuity varies widely between individual sites, but it reflects the start of agriculture and associated changes in land cover and sediment yield to rivers.

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  • Harding, J. S., E. F. Benfield, P. V. Bolstad, G. S. Helfman, and E. B. D. Jones. 1998. Stream biodiversity: The ghost of land use past. Proceedings of the National Academy of Sciences of the United States of America 95.25: 14843–14847.

    DOI: 10.1073/pnas.95.25.14843Save Citation »Export Citation »E-mail Citation »

    This study compares contemporary diversity of stream invertebrates and fish to past and present land use in twenty-four small watersheds in Tennessee and North Carolina. Land use during the 1950s correlated more strongly with biodiversity than did contemporary land use, indicating the persistent effect of human activities on stream biota.

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  • James, L. A., and S. A. Lecce. 2013. Impacts of land-use and land-cover change on river systems. In Treatise on geomorphology. Vol. 9, Treatise on fluvial geomorphology. Edited by E. Wohl, 768–793. Amsterdam: Elsevier.

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    Systematic summary of how humans have altered and continue to alter river environments via deforestation, agriculture, urbanization, warming climate, flow regulation, mining, and other industrial activities. Examines changes in water and sediment inputs to rivers and movement of water and sediment along river networks.

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  • Marcus, W. A., and L. A. James, eds. 2006. Special issue: 37th Binghamton Geomorphology Symposium—The human role in changing fluvial systems. Geomorphology 79.3–4: 143–506.

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    Special issue that includes sixteen papers exploring diverse aspects of how human activities have altered rivers in the context of specific geographic regions, specific human alterations (e.g., flow regulation, changed land cover), or global syntheses. Individual papers include historical examples and potential future changes under a warming climate.

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  • Miller, J., R. Barr, D. Clow, et al. 1999. Effects of the 1997 flood on the transport and storage of sediment and mercury within the Carson River Valley, west-central Nevada. The Journal of Geology 107:313–327.

    DOI: 10.1086/314353Save Citation »Export Citation »E-mail Citation »

    Exemplifies papers describing the history of mining contaminant dispersal along riverine corridors from sites around the world. Here, late-19th-century metal mining resulted in mercury dispersal as mill tailings moved downstream along the Carson River. Mercury concentrations in channel and floodplain sediments record the history of dispersal.

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  • Schulze, D. J., and K. F. Walker. 1997. Riparian eucalypts and willows and their significance for aquatic invertebrates in the River Murray, South Australia. Regulated Rivers: Research and Management 13:557–577.

    DOI: 10.1002/(SICI)1099-1646(199711/12)13:6%3C557::AID-RRR485%3E3.3.CO;2-HSave Citation »Export Citation »E-mail Citation »

    Paper exemplifies studies of the sometimes subtle environmental effects of accidentally or deliberately introduced exotic species. The leaves of exotic riparian willow (Salix) trees that fall into streams host different invertebrate assemblages than the leaves of native redgum (Eucalyptus) trees, and native freshwater shrimp prefer the invertebrates colonizing redgum leaves.

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  • Trimble, S. W. 2009. Fluvial processes, morphology and sediment budgets in the Coon Creek Basin, WI, USA, 1975–1995. Geomorphology 108:8–23.

    DOI: 10.1016/j.geomorph.2006.11.015Save Citation »Export Citation »E-mail Citation »

    Updates a 1975 study that exemplifies the response to upland clearing of native vegetation. Hillslope sediment yield increased substantially during clearing. Subsequent regrowth of native vegetation and conservation practices decreased upland sediment yield, but sediment yield from the basin remained constant as stored sediment continued to be eroded from valley bottoms.

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  • Walter, R. C., and D. J. Merritts. 2008. Natural streams and the legacy of water-powered mills. Science 319:299–304.

    DOI: 10.1126/science.1151716Save Citation »Export Citation »E-mail Citation »

    A seminal paper that documents the continuing effects of sediments deposited upstream from abandoned 17th- to 19th-century milldams in the US Mid-Atlantic region. Erosion of these sediments creates problems in downstream river and coastal environments. Stream incision into the sediments has created misperceptions of how affected rivers should be restored.

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Rivers as Indicators of Contemporary Environmental Conditions

As noted in the introduction, rivers integrate diverse aspects of the greater environment over temporal and spatial scales much larger than the present moment along a short length of river. The works cited in this section provide examples of the many specific river metrics that have been used to characterize the contemporary environment. Water quality was the first aspect of rivers to be used as an indicator of conditions throughout a drainage basin. This likely reflects the fact that water quality is of vital importance to people who use rivers for drinking water, and to a wide variety of other organisms, such as fish, insects, and waterfowl. Houghton 2006 provides an example of how water quality influences riverine insect communities. Some aspects of water quality are also easily measured and change over very short time spans in response to inputs at a point or throughout a drainage basin. Consequently, water quality can be like the proverbial canary in the coal mine, providing an important early indicator that something is wrong. Water quality can also reflect more sustained environmental changes, as when rising radionuclide concentrations in rivers fed by groundwater passing near nuclear processing facilities indicate that radioactive waste is not effectively contained. Other widely used metrics of river environmental condition focus on biological characteristics. Karr 1981 proposes what is now a commonly used Index of Biotic Integrity based on fish communities, and Harris and Silveira 1999 illustrates an example of using this index to evaluate river health. Rather than tallying species composition and diversity, as is done for indices of biotic integrity, Bunn, et al. 1999 focuses on the processes of primary production and respiration as measures of river environmental condition. Some assessments of rivers use indicators of physical habitat, as illustrated in Maddock 1999, and many assessments focus on streamflow characteristics. Nilsson, et al. 2005 evaluates the degree to which streamflow has been altered in major global rivers, and Poff, et al. 2007 assesses similarity among streamflow regime across diverse regions of the United States. Norris and Thoms 1999 integrates these diverse measures into the concept of river health, which remains controversial among scientists because it is difficult to define and measure.

  • Bunn, S. E., P. M. Davies, and T. D. Mosisch. 1999. Ecosystem measures of river health and their response to riparian and catchment degradation. Freshwater Biology 41:333–345.

    DOI: 10.1046/j.1365-2427.1999.00434.xSave Citation »Export Citation »E-mail Citation »

    Noting that metrics of river species composition do not directly measure river ecosystem processes, this paper proposes measures of benthic gross primary production and respiration as direct indicators of the amounts of organic carbon produced and consumed. These measures provide an indicator of river health relative to undisturbed reference catchments.

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  • Harris, J. H., and R. Silveira. 1999. Large-scale assessments of river health using an Index of Biotic Integrity with low-diversity fish communities. Freshwater Biology 41:235–252.

    DOI: 10.1046/j.1365-2427.1999.00428.xSave Citation »Export Citation »E-mail Citation »

    An example of applying a biological index to assessing contemporary environmental conditions as reflected in river ecosystems. The Index of Biotic Integrity uses fish-community attributes such as species richness, percent of native species, and proportions of specific species categories to quantify condition of a river ecosystem.

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  • Houghton, D. C. 2006. The ability of common water quality metrics to predict habitat disturbance when biomonitoring with adult caddisflies (Insecta: Trichoptera). Journal of Freshwater Ecology 21:705–716.

    DOI: 10.1080/02705060.2006.9664134Save Citation »Export Citation »E-mail Citation »

    Numerous measures parameters are used to assess water quality, including dissolved oxygen, temperature, pH, total dissolved solids, heavy metals, synthetic chemicals, and microorganisms. This paper provides an example of relating these parameters to habitat disturbance and river biota to assess river and greater environmental condition.

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  • Karr, J. R. 1981. Assessments of biotic integrity using fish communities. Fisheries 6:21–27.

    DOI: 10.1577/1548-8446(1981)006%3C0021:AOBIUF%3E2.0.CO;2Save Citation »Export Citation »E-mail Citation »

    The first paper to propose an Index of Biotic Integrity (IBI), a concept now widely applied to assess river ecosystem condition. The IBI uses several metrics of fish species composition and richness, including the proportion of species in certain categories such as omnivore or insectivore.

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  • Maddock, I. 1999. The importance of physical habitat assessment for evaluating river health. Freshwater Biology 41:373–391.

    DOI: 10.1046/j.1365-2427.1999.00437.xSave Citation »Export Citation »E-mail Citation »

    Discusses the importance of physical habitat to river ecosystems, and reviews physical river habitat assessment methods in the context of evaluating improvements made by fishery enhancement and river restoration. Methods reviewed include reconnaissance level surveys and more complex appraisals such as IFIM and PHABSIM modeling.

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  • Nilsson, C., C. A. Reidy, M. Dynesius, and C. Revenga. 2005. Fragmentation and flow regulation of the world’s large river systems. Science 308:405–408.

    DOI: 10.1126/science.1107887Save Citation »Export Citation »E-mail Citation »

    A global overview of the effects of dams on the flow of large river systems. Over half (172 of 292) of the world’s large rivers have altered flow regimes because of dams, with only a few large rivers at very high latitudes or in sparsely populated regions remaining unimpacted.

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  • Norris, R. H., and M. C. Thoms. 1999. What is river health? Freshwater Biology 41:197–209.

    DOI: 10.1046/j.1365-2427.1999.00425.xSave Citation »Export Citation »E-mail Citation »

    Introduces the concept of river health, an integrative measure of river ecosystem functionality and a reflection of the broader context of environmental health. Stresses the need to examine environmental variables that affect aquatic biota, as well as measuring aquatic biota, in order to accurately characterize river health.

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  • Poff, N. L., J. D. Olden, D. M. Merritt, and D. M. Pepin. 2007. Homogenization of regional river dynamics by dams and global biodiversity implications. Proceedings of the National Academy of Sciences of the United States of America 104.14: 5732–5737.

    DOI: 10.1073/pnas.0609812104Save Citation »Export Citation »E-mail Citation »

    This study compares long-term streamflow records from 186 dammed rivers and 317 undammed rivers in the United States to illustrate how dams reduce seasonal and interannual streamflow variability. Alteration of ecologically important flow variability homogenizes rivers, potentially favoring the spread of generalist, exotic species rather than locally adapted native species.

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Rivers as Sources of Environmental Services

A disproportionate number of the world’s great cities are located along rivers. Concentrations of human population historically grew up along rivers because of the vital services provided by rivers, including water supply, navigation, fisheries, and waste disposal, as well as irrigation water and fertile soil for crops. Although people have likely recognized the inherent importance of rivers for as long as we have been human, attempts to quantify the economic value of the ecosystem or environmental services provided by rivers date mostly to the late 1990s and first years of the 21st century. As explained in Thorp, et al. 2010, ecosystem services can be defined as the quantifiable or qualitative benefits of ecosystem functioning. These benefits can be subdivided into a number of services: supporting services such as biogeochemical cycling or habitat; regulating services such as regulation of water quality or floods; provisioning services such as food or fresh water for humans; and cultural services such as esthetic or recreational sites. Monetary values can be assigned to some of these services, as discussed in Loomis, et al. 2000, or relative importance can be assigned using an expert scoring system, as in Gilvear, et al. 2013, but these types of quantification remain very challenging and controversial. Tuvendal and Elmqvist 2011 explores how loss of the ecosystem service of providing clean water results in greater costs for water treatment, and Elsin, et al. 2010 examine the flip side of this issue by considering how to value the clean water inputs provided by a river to water treatment plants. Zhou, et al. 2011 discusses the loss of river ecosystem services as a result of urbanization. Nelson, et al. 2009 discusses the intriguing idea that numerical models of ecosystem services and commodity production can be used to assess different scenarios of river environmental condition, and Brauman, et al. 2014 presents a framework for evaluating such tradeoffs.

  • Brauman, K. A., S. van der Meulen, and J. Brils. 2014. Ecosystem services and river basin management. In Risk-informed management of European river basins. Edited by J. Brils, W. Brack, D. Müller-Grabherr, P. Négrel, and J. E. Vermaat, 265–294. Berlin: Springer-Verlag.

    DOI: 10.1007/978-3-642-38598-8Save Citation »Export Citation »E-mail Citation »

    Presents a framework for identifying stakeholders whose actions affect the provision of ecosystem services in a river basin and stakeholders whose well-being is impacted by changes in ecosystem services. The framework can be used to assess trade-offs among services provided under future land-use scenarios. Includes several European case studies.

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  • Elsin, Y. K., R. A. Kramer, and W. A. Jenkins. 2010. Valuing drinking water provision as an ecosystem service in the Neuse River basin. Journal of Water Resource Planning and Management 136:474–482.

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    Paper provides an example of valuing a specific riverine ecosystem service, drinking water provision, by quantifying the economic benefits of improving the quality of water used as input to water treatment plants in the Neuse River basin of North Carolina, USA. The water quality parameter used here was turbidity.

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  • Gilvear, D. J., C. J. Spray, and R. Casas-Mulet. 2013. River rehabilitation for the delivery of multiple ecosystem services at the river network scale. Journal of Environmental Management 126:30–43.

    DOI: 10.1016/j.jenvman.2013.03.026Save Citation »Export Citation »E-mail Citation »

    Paper summarizes a conceptual framework and methodology for river rehabilitation designed to enhance multiple ecosystem services, using a case study from a catchment in Scotland. Ecosystem services are evaluated based on an expert scoring system that reflects how rehabilitation measures affect physical and ecological processes.

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  • Loomis, J., P. Kent, L. Strange, K. Fausch, and A. Covich. 2000. Measuring the total economic value of restoring ecosystem services in an impaired river basin: Results from a contingent valuation survey. Ecological Economics 33:103–117.

    DOI: 10.1016/S0921-8009(99)00131-7Save Citation »Export Citation »E-mail Citation »

    An example of studies that evaluate willingness to pay for river ecosystem services. Surveys of residents along the South Platte River indicate that residents are willing to pay higher water bills to provide funds for leasing water and creating farmland conservation reserve easements to provide services such as wastewater dilution.

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  • Nelson, E., G. Mendoza, J. Regetz, et al. 2009. Modeling multiple ecosystem services, biodiversity conservation, commodity production, and tradeoffs at landscape scales. Frontiers in Ecology and the Environment 7:4–11.

    DOI: 10.1890/080023Save Citation »Export Citation »E-mail Citation »

    Paper provides an example of applying a spatially explicit model that predicts changes in ecosystem services, biodiversity, and commodity production. This case study from the Willamette basin in Oregon, USA, analyzes tradeoffs between ecosystem services and commodity production, as well as methods such as carbon sequestration that alleviate such tradeoffs.

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  • Thorp, J. H., J. E. Flotemersch, M. D. Delong, et al. 2010. Linking ecosystem services, rehabilitation, and river hydrogeomorphology. BioScience 60:67–74.

    DOI: 10.1525/bio.2010.60.1.11Save Citation »Export Citation »E-mail Citation »

    Useful overview of the challenges of assigning values for natural ecological benefits and anthropocentric ecosystem services in riverine systems. This paper presents a framework for relating hydrogeomorphic attributes of rivers (e.g., shoreline complexity, floodplain connectivity to channel) to specific ecosystem benefits and services.

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  • Tuvendal, M., and T. Elmqvist. 2011. Ecosystem services linking social and ecological systems: River brownification and the response of downstream stakeholders. Ecology and Society 16:21.

    DOI: 10.5751/ES-04456-160421Save Citation »Export Citation »E-mail Citation »

    A slow increase in dissolved organic carbon results in brownification of the water, which can decrease the growth of aquatic plants, mobilize some heavy metals and pollutants, decrease the aesthetic appeal of the river, and result in greater costs for water treatment. This case study from Sweden explores consequences of brownification.

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  • Zhou, H., P. Shi, J. Wang, D. Yu, and L. Gao. 2011. Rapid urbanization and implications for river ecological services restoration: Case study in Shenzhen, China. Journal of Urban Planning and Development 137:121–132.

    DOI: 10.1061/(ASCE)UP.1943-5444.0000051Save Citation »Export Citation »E-mail Citation »

    This case study documents the loss of wetlands and small streams as a result of urbanization in southern China. These changes result in the loss of ecosystem services, including nutrient cycling and storage, water retention, soil conservation, and gas regulation, such as absorbing carbon dioxide and producing oxygen.

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Major River Basins

Major river basins are those that drain substantial areas of individual continents, commonly including territory of more than one country. Any portion of a river integrates and is influenced by everything within the upstream drainage basin. Consequently, major rivers integrate the environmental conditions across large portions of Earth. Major rivers are challenging to study and to understand as a whole, both because they commonly include very diverse sub-basins and because conducting field-based research on hydrology, hydraulics, riverine chemistry, biota, and so forth is logistically difficult when the river under study can be kilometers across, tens of meters deep, and moving at rapid velocities. Advances in space-based remote sensing technology during the latter half of the 20th century dramatically improved our ability to image and study very large rivers, and this has given rise to a growing body of technical literature on individual large rivers and on the properties of very large rivers that are distinctive relative to smaller rivers. The works cited in this section provide examples of the syntheses now being published for individual large rivers and for large rivers as a group. The edited collections Miller and Gupta 1999 and Gupta 2007, as well as Wohl 2011, exemplify volumes focusing on large rivers as a group. Crane and Galasso 1999 provides a comprehensive environmental overview of a region that is fed by several of the world’s largest rivers, and the maps and summary figures in this volume provide a wealth of information on each river. Goulding, et al. 2003 and Collins 2002 are examples of books treating all aspects of a particular large river basin. Fitzmaurice 1996 and Alley 2002 exemplify treatments of a particular issue, although in the course of discussing flow regulation on the Danube and water quality in the Ganges, respectively, each work also provides a great deal of broader information on the river basin being examined.

  • Alley, K. D. 2002. On the banks of the Ganga: When wastewater meets a sacred river. Ann Arbor: Univ. of Michigan Press.

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    An example of an examination of a major river basin that focuses on a specific issue—in this case, water pollution and treatment.

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  • Collins, R. O. 2002. The Nile. New Haven, CT: Yale Univ. Press.

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    A highly readable account of the natural and human history of the Nile River basin. This book provides a good example of general interest books written about specific rivers.

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  • Crane, K., and J. L. Galasso. 1999. Arctic environmental atlas. Washington, DC: Office of Naval Research.

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    Focuses on the Arctic, but includes summaries of many aspects of major rivers draining to the Arctic Ocean, including the Mackenzie and Yukon in North America and the Ob, Lena, and Yenisey in Eurasia. Abundantly illustrated, with maps and graphs covering physical, chemical, biological, and human aspects of the region.

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  • Fitzmaurice, J. 1996. Damming the Danube: Gabčikovo and post-communist politics in Europe. Boulder, CO: Westview.

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    Another example of a book focusing on a specific issue within a large river basin. In the course of examining a particularly controversial flow regulation project, the author addresses numerous social and environmental aspects of the Danube River.

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  • Goulding, M., R. Barthem, and E. Ferreira. 2003. The Smithsonian atlas of the Amazon. Washington, DC: Smithsonian.

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    This beautifully illustrated book contains a wealth of information on the Amazon basin, presented in graphs, charts, and maps, with well-written accompanying text. Abundant color photographs represent the diversity of environments, fauna, and flora in the drainage basin.

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  • Gupta, A., ed. 2007. Large rivers: Geomorphology and management. Chichester, UK: Wiley.

    DOI: 10.1002/9780470723722Save Citation »Export Citation »E-mail Citation »

    Individual chapters in this collection provide overviews of the geology, hydrology, human effects, management, remote sensing, and influence of climate change on large rivers. Other chapters cover specific large rivers, including the Amazon, Mississippi, Colorado, Lena, Danube, Nile, Congo, Zambezi, Indus, Ganga, Brahmaputra, Mekong, Yangtze, Willamette, and Murray-Darling.

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  • Miller, A. J., and A. Gupta, eds. 1999. Varieties of fluvial form. Chichester, UK: Wiley.

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    Volume includes sections with chapters on mixed bedrock and alluvial rivers, arid-region rivers, and patterns of alluvial deposition. Overviews of individual rivers include examples from India, Antarctica, Australia, Africa, New Guinea, Asia, and North America.

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  • Wohl, E. 2011. A world of rivers: Environmental change on ten of the world’s great rivers. Chicago: Univ. of Chicago Press.

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    Written for a general audience, this book follows a hypothetical water droplet through atmospheric, surface, and subsurface pathways as it moves between the world’s major drainages. River geomorphology and ecology are examined within each drainage, particularly in the context of human activities.

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River Management

River management in this context refers to the deliberate manipulation of a drainage basin or river characteristics in order to restore or maintain desired environmental attributes. Management might focus on restoring native upland vegetation, for example, in order to reduce sediment yield to a river and thus restore water quality and aquatic and riparian habitat. Or management might focus on altering river form by breaching artificial levees to restore channel-floodplain connectivity, floodplain wetland habitat, and fisheries, as discussed in Florsheim, et al. 2006. The works cited in this section address the context in which river management occurs and describe concepts broadly applicable to assessing the need for, and success of, river management. Among the most important concepts are ecological integrity, river health, sensitivity, and resilience. “Ecological integrity” typically refers to the degree to which a river approximates characteristics of its natural state, as judged by parameters such as composition and abundance of native species and communities, rates of change, and supporting processes. Downs, et al. 2011 explores how baseline data can be used to set management targets designed to restore ecological integrity. Moog and Chovanec 2000 examine how biological data can be used to assess river ecological integrity. Galat and Lipkin 2000 discuss restoring ecological integrity by restoring more natural streamflow characteristics. Graf 2001 proposes the concept of physical integrity for rivers. Karr 1999 proposes biological indices for integratively assessing river health. “Ecosystem sensitivity” refers to the system’s ability to resist disturbance and its capability to recover following disturbance. Nijssen, et al. 2001 evaluates river hydrologic sensitivity to climatic change. “Resilience” is typically applied to social-ecological systems, and refers to the amount of change that a river ecosystem can undergo and still maintain the same controls on function and structure. This is sometimes described as the ability of the river to maintain its characteristics in the context of internal change and external perturbations. Cumming 2011 examines the resilience of large rivers basins to changes in water quantity. In all of the works cited in this section, some type of physical and/or biological data are used to rate the degree to which a river ecosystem approximates a desired condition, and to design management strategies that will move the river closer to the desired environmental condition.

  • Cumming, G. S. 2011. The resilience of big river basins. Water International 36:63–95.

    DOI: 10.1080/02508060.2011.541016Save Citation »Export Citation »E-mail Citation »

    Uses nine case studies of large river basins to explore resilience to changes in water quantity caused by climate change and human consumptive uses. Highlights the difficulty of evaluating resilience because of scientific uncertainty and system complexity that limit estimation and prediction of many important variables.

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  • Downs, P. W., M. S. Singer, B. K. Orr, Z. E. Diggory, and T. C. Church. 2011. Restoring ecological integrity in highly regulated rivers: The role of baseline data and analytical references. Environmental Management 48:847–864.

    DOI: 10.1007/s00267-011-9736-ySave Citation »Export Citation »E-mail Citation »

    An example of a river management paper explicitly focused on ecological integrity. With the Merced River in California as an example, the authors use baseline data to transform a conceptual model of river system function into specific management goals for aquatic and riparian habitat.

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  • Florsheim, J. L., J. F. Mount, and C. R. Constantine. 2006. A geomorphic monitoring and adaptive assessment framework to assess the effect of lowland floodplain river restoration on channel-floodplain sediment continuity. River Research and Applications 22:353–375.

    DOI: 10.1002/rra.911Save Citation »Export Citation »E-mail Citation »

    Paper exemplifies one technique to restore channel-floodplain connectivity: breaching artificial levees at selected locations in order to facilitate floodplain inundation. Using a case study from the Cosumnes River in California, the authors present a framework for physical monitoring and adaptive assessment focused on processes that create floodplain habitat.

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  • Galat, D. L., and R. Lipkin. 2000. Restoring ecological integrity of great rivers: Historical hydrographs aid in defining reference conditions for the Missouri River. Hydrobiologia 422.423: 29–48.

    DOI: 10.1023/A:1017052319056Save Citation »Export Citation »E-mail Citation »

    This paper uses indicators of hydrologic alteration to assess changes in the natural flow regime of the Missouri River, the resulting impairment of ecological integrity, and potential modifications of reservoir operation that could be used to restore a more natural riverine ecosystem.

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  • Graf, W. L. 2001. Damage control: Restoring the physical integrity of America’s rivers. Annals of the Association of American Geographers 91.1: 1–27.

    DOI: 10.1111/0004-5608.00231Save Citation »Export Citation »E-mail Citation »

    This paper introduces the concept of physical integrity, particularly in reference to dams. Physical integrity refers to a set of active river processes and landforms wherein the overall river configuration remains able to adjust to changes in water and sediment inputs within limits of change defined by societal values.

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  • Karr, J. A. 1999. Defining and measuring river health. Freshwater Biology 41:221–234.

    DOI: 10.1046/j.1365-2427.1999.00427.xSave Citation »Export Citation »E-mail Citation »

    Paper advocates the use of multimetric biological indices to create an integrative assessment of river health and to identify biological responses to human actions. The results of this biological monitoring must be communicated to citizens and political leaders if the information is to influence river management.

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  • Moog, O., and A. Chovanec. 2000. Assessing the ecological integrity of rivers: Walking the line among ecological, political and administrative interests. Hydrobiologia 422.423: 99–109.

    DOI: 10.1023/A:1017053829050Save Citation »Export Citation »E-mail Citation »

    Paper uses examples from rivers in Austria to explore how results from biological assessments can be used to assess river ecological integrity. Focusing on benthic macroinvertebrates, the authors discuss balancing scientific accuracy and the practicality of obtaining information necessary to evaluate whether a river meets the legal definition for ecological integrity.

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  • Nijssen, B., G. M. O’Donnell, A. F. Hamlet, and D. P. Lettenmaier. 2001. Hydrologic sensitivity of global rivers to climate change. Climatic Change 50:143–175.

    DOI: 10.1023/A:1010616428763Save Citation »Export Citation »E-mail Citation »

    An example of evaluating river system sensitivity—in this case, hydrologic sensitivity to climate change of nine large, continental-scale river basins. The most sensitive rivers are likely to be snow-dominated basins of mid- to higher latitudes as a result of greater warming, demonstrating the importance of snow in the water balance.

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River Restoration

River restoration is sometimes viewed as an entirely new approach to rivers that is inherently more valuable or well-designed than past versions of river management. It is probably more appropriate, however, to think of river restoration as the most recent iteration of a centuries-long tradition of manipulating rivers to enhance desired characteristics. Characteristics desired by contemporary societies are more likely to include environmental services such as habitat and biodiversity, whereas past forms of river engineering and manipulation focused on immediate economic gains associated with minimizing floods, storing water for consumptive use, or enhancing navigation. River restoration is typically defined as the return of an ecosystem to a close approximation of its condition prior to disturbance, whereas river rehabilitation commonly includes various types of river manipulation, including enhancement, mitigation, and habitat creation. Most river restoration projects are thus actually examples of river rehabilitation and typically focus on very limited segments of a river. As summarized in Bernhardt, et al. 2005, an overview of river restoration projects in the United States, most restoration projects are small scale efforts implemented on less than one kilometer of stream length. A few high-profile, large restoration projects are underway, however, as illustrated in Galat, et al. 1998, which discusses restoration along the lower Missouri River. Regardless of the scale of attempted restoration, both physical and biological scientists emphasize three points. First is the importance of understanding the place-specific geographic and historical context that governs river dynamics, as exemplified by the case studies presented in Brierley and Fryirs 2009 and McDonald, et al. 2004. Second, there is a an emphasis on dynamic processes rather than created, static river form, as argued in Wohl, et al. 2005. This is particularly important because engineered aspects of river form commonly do not function as desired, as discussed in detail in Palmer, et al. 2010 and Thompson and Stull 2002. Third is the importance of modeling coupled physical and biological systems, and of monitoring system response to management actions such as experimental flow releases, as detailed in the case study summarized in Shafroth, et al. 2010.

  • Bernhardt, E. S., M. A. Palmer, J. D. Allan, et al. 2005. Synthesizing U.S. river restoration efforts. Science 308:636–637.

    DOI: 10.1126/science.1109769Save Citation »Export Citation »E-mail Citation »

    Paper summarizes the National River Restoration Science Synthesis database of 37,099 projects across the United States, as of July 2004. The most commonly stated restoration goals are to improve water quality, riparian zones, stream habitat, fish passage, and bank stabilization. Only 10 percent of project records indicated any form of monitoring.

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  • Brierley, G., and K. Fryirs. 2009. Don’t fight the site: Three geomorphic considerations in catchment-scale river rehabilitation planning. Environmental Management 43:1201–1218.

    DOI: 10.1007/s00267-008-9266-4Save Citation »Export Citation »E-mail Citation »

    Paper emphasizes the importance of spatial and temporal context in understanding river behavior. Specifically, it emphasizes the inherent diversity of river forms and processes, river dynamics over time as a framework for understanding contemporary process and form, and reach-scale dynamics in relation to downstream patterns of river type.

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  • Galat, D. L., L. H. Frederickson, D. D. Humburg, et al. 1998. Flooding to restore connectivity of regulated, large-river wetlands. BioScience 48.9: 721–733.

    DOI: 10.2307/1313335Save Citation »Export Citation »E-mail Citation »

    This paper uses the lower Missouri River to illustrate the importance of channel-floodplain connectivity and the role of large floods in promoting connectivity. Relatively natural portions of the river that retain overbank flooding, floodplain wetlands, and higher biological productivity are the focus of a “string of beads” restoration approach.

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  • McDonald, A., S. N. Lane, N. E. Haycock, and E. A. Chalk. 2004. Rivers of dreams: On the gulf between theoretical and practical aspects of an upland river restoration. Transactions of the Institute of British Geographers 29:257–281.

    DOI: 10.1111/j.0020-2754.2004.00314.xSave Citation »Export Citation »E-mail Citation »

    Paper conceptualizes river restoration as a field of dreams approach that emphasizes creating desired form, with processes necessary to maintain form expected to follow, a system function approach that identifies and ameliorates conditions required to achieve restoration goals, or a keystone approach that includes crucial components of form and function.

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  • Palmer, M. A., H. L. Menninger, and E. Bernhardt. 2010. River restoration, habitat heterogeneity and biodiversity: A failure of theory or practice? Freshwater Biology 55 (Suppl. 1): 205–222.

    DOI: 10.1111/j.1365-2427.2009.02372.xSave Citation »Export Citation »E-mail Citation »

    Much of contemporary river restoration focuses on restoring physical river characteristics, with the expectation that biota will respond. This paper raises a very important point, however, by illustrating that there is no evidence that habitat heterogeneity is the primary factor controlling stream invertebrate diversity.

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  • Shafroth, P. B., A. C. Wilcox, D. A. Lytle, et al. 2010. Ecosystem effects of environmental flows: Modelling and experimental floods in a dryland river. Freshwater Biology 55:68–85.

    DOI: 10.1111/j.1365-2427.2009.02271.xSave Citation »Export Citation »E-mail Citation »

    A nice example of a case study that couples physical system models to ecological responses, and verifies empirical relationships between flow and ecological responses by implementing and monitoring experimental flow releases. The paper illustrates response thresholds for riparian trees, beaver, and benthic macroinvertebrates along the Bill Williams River in Arizona.

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  • Thompson, D. M., and G. N. Stull. 2002. The development and historic use of habitat structures in channel restoration in the United States: The grand experiment in fisheries management. Géographie physique et Quaternaire 56.1: 45–60.

    DOI: 10.7202/008604arSave Citation »Export Citation »E-mail Citation »

    This paper traces the history of manipulating river form using instream structures to improve fish habitat. Habitat structures were first used in the United States during the 1880s in upstate New York. Similar structures continue to be used today, despite evidence that they commonly do not work as intended.

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  • Wohl, E., P. L. Angermeier, B. Bledsoe, et al. 2005. River restoration. Water Resources Research 41:W10301.

    DOI: 10.1029/2005WR003985Save Citation »Export Citation »E-mail Citation »

    Paper discusses two themes likely to enhance success of river restoration projects: restoration of process rather than restoration aimed at a fixed end point, and restoration undertaken in a watershed context rather than based solely on consideration of a specific site.

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Natural Flow Regime

Since the 1990s, our understanding of the degree to which rivers have been altered by human activities, and the manner in which rivers can be restored, has increasingly focused on flow regime. As noted in the description of River Management, human activities can indirectly affect rivers by altering the yields of water, sediment, and other materials entering a river segment from the adjacent uplands, the subsurface, and upstream portions of the river network. Human activities can also directly affect rivers by altering channel geometry and the movement of water, sediment, and other materials through the river segment. River management, including restoration, can be targeted at modifying any of these indirect and direct alterations. The movement of water along a river network, however, is arguably the single most important parameter that shapes river form and function. Flow is also a parameter that is relatively easy to quantify, thanks to stream gages, and it is a parameter that has been extensively and severely altered by changes in land cover and flow regulation. For all of these reasons, a great many contemporary river management projects are designed to restore specified parameters of a “natural flow regime,” with “natural” defined as the flow regime that would exist in the absence of extensive human alteration of the drainage basin and river network. This approach to river management was first systematically described in Poff, et al. 1997, a landmark and widely cited paper. Recognition of the importance of diverse magnitudes and recurrence intervals of flow partly developed as a result of the limitations of earlier approaches, such as instream flow, that sought to quantify only a minimum flow necessary to preserve a desired environmental characteristic. Stalnaker, et al. 1995 remains the premier instream flow reference. Minimum flows are not capable of maintaining channel geometry in most rivers, which led to the concept of channel maintenance flows, as discussed in Andrews and Nankervis 1995. Instream flows were designed to preserve primarily biological characteristics, such as fish overwintering habitat, and channel maintenance flows were designed to preserve primarily physical characteristics, such as sediment mobilization associated with pool volume or spawning gravel permeability. Environmental flows are designed to mimic the natural flow regime within existing constraints of resource use in order to preserve biological and physical river characteristics. Tharme 2003 reviews different approaches to estimating environmental flows. Richter, et al. 1996 summarizes the Indicators of Hydrologic Alteration (IHA), a suite of thirty-two hydrologic parameters widely used to characterize ecologically relevant flow parameters and to quantify an environmental flow regime. Gao, et al. 2009 represents one of many subsequent modifications of the original thirty-two IHA parameters. Arthington, et al. 2006 illustrates how flow regime on relatively unaltered reference rivers can be used to develop a regional indicator of environmentally relevant flow parameters. Arthington and Pusey 2003 discusses how the concept of environmental flows can be applied to minimizing river ecosystem degradation.

  • Andrews, E. D., and J. M. Nankervis. 1995. Effective discharge and the design of channel maintenance flows for gravel-bed rivers. In Natural and anthropogenic influences in fluvial geomorphology. Edited by J. E. Costa, A. J. Miller, K. W. Potter, and P. R. Wilcock, 151–164. Washington, DC: American Geophysical Union Press.

    DOI: 10.1029/GM089Save Citation »Export Citation »E-mail Citation »

    Illustrates an approach of computing the minimum flow necessary to mobilize bed particles, based on a bedload transport function and specific reach information that can be used to quantify the amount of bed sediment transported by increments of discharge. Several gravel-bed rivers in the western United States provide case studies.

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  • Arthington, A. H., S. E. Bunn, N. L. Poff, and R. J. Naiman. 2006. The challenge of providing environmental flow rules to sustain river ecosystems. Ecological Applications 16.4: 1311–1318.

    DOI: 10.1890/1051-0761(2006)016[1311:TCOPEF]2.0.CO;2Save Citation »Export Citation »E-mail Citation »

    Paper outlines a generic approach to quantifying environmental flow regimes in the absence of detailed empirical information on flow requirements. The proposed approach identifies vital aspects of natural flow variability shared among rivers within a geographic region by quantifying the frequency distributions of selected flow variables on unaltered reference rivers.

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  • Arthington, A. H., and B. J. Pusey. 2003. Flow restoration and protection in Australian rivers. River Research and Applications 19:377–395.

    DOI: 10.1002/rra.745Save Citation »Export Citation »E-mail Citation »

    This paper addresses two vital questions in an Australian context: (1) How much water does a river need? (2) How can this water be clawed back from other users? The paper discusses how to quantify the percent of natural mean annual flow required to maintain a low risk of environmental degradation.

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  • Gao, Y., R. M. Vogel, C. N. Kroll, N. L. Poff, and J. D. Olden. 2009. Development of representative indicators of hydrologic alteration. Journal of Hydrology 374:136–147.

    DOI: 10.1016/j.jhydrol.2009.06.009Save Citation »Export Citation »E-mail Citation »

    Over 170 hydrologic indicators have been proposed for quantifying river flow regime, including alteration of flow regime. This paper condenses numerous intercorrelated indicators into three indices of ecodeficit and ecosurplus that explain most of the variability associated with a larger ensemble of flow statistics.

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  • Poff, N. L., J. D. Allan, M. B. Bain, et al. 1997. The natural flow regime. BioScience 47.11: 769–784.

    DOI: 10.2307/1313099Save Citation »Export Citation »E-mail Citation »

    This is the seminal paper that first articulated the physical and biological importance of a range of flow characteristics, rather than relying solely on minimum or maximum flow to restore and maintain river ecosystems. The authors emphasize the importance of magnitude, frequency, duration, timing, and rate of change of flow.

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  • Richter, B. D., J. V. Baumgartner, J. Powell, and D. P. Braun. 1996. A method for assessing hydrologic alteration within ecosystems. Conservation Biology 10.4: 1163–1174.

    DOI: 10.1046/j.1523-1739.1996.10041163.xSave Citation »Export Citation »E-mail Citation »

    This is the paper that introduced the Indicators of Hydrologic Alteration (IHA), an ensemble of thirty-two parameters clustered into five groups that are used to statistically characterize hydrologic variation within each year. Numerous modifications and applications of IHA have subsequently been published.

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  • Stalnaker, C. B., B. L. Lamb, J. Henriksen, K. Bovee, and J. Bartholow. 1995. The Instream Flow Incremental Methodology: A primer for IFIM. Biological Report 29. Washington, DC: National Biological Service.

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    This paper reviews the history and application of IFIM, the first systematic, quantitative approach to quantifying aquatic habitat as a function of flow. Designed primarily for fish, IFIM is based on tools such as PHABSIM, a model that quantifies habitat available for different life stages at different flow levels.

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  • Tharme, R. E. 2003. A global perspective on environmental flow assessment: Emerging trends in the development and application of environmental flow methodologies for rivers. River Research and Applications 19:397–441.

    DOI: 10.1002/rra.736Save Citation »Export Citation »E-mail Citation »

    Synthesis of environmental flow assessments that distinguishes (i) reconnaissance-level initiatives focusing on low flow indices, and (ii) more comprehensive scales of assessment that use either the IFIM approach and hydrodynamic habitat modeling, or approaches that consider the flow requirements of the entire river ecosystem.

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