Rivers are the circulatory system of the continents. They are the conduits for water, solute, and sediment movement from land to sea and shape much of the landscape. Throughout history, rivers have sustained communities by providing drinking water, transportation routes, waterpower, hydroelectric power, fisheries, and wildlife habitat. River bottomlands have been transformed into rich agricultural lands, and water diversions irrigate distant farmlands.
Today, rivers provide about 60 percent of the nation’s drinking and irrigation water and 10 percent of the nation’s electric power needs. Boating, birding, swimming, and fishing are multibillion-dollar industries. Rivers and their floodplains moderate floods and process and recycle nutrients; river sediments replenish floodplain soils and prevent the erosion of coastlines.
Human activities have profoundly changed our rivers. Deforestation, industrialization, urbanization, floodplain cultivation, dam and levee construction, and channelization have altered dramatically natural flow regimes. These changes have contributed to flooding, erosion, channel incision, contamination, non-native species introductions, and loss in ecological diversity.
The multiple and sometimes incompatible services we demand of rivers often lead to social conflicts. The policy and management decisions that surround these conflicts increasingly require the integration of science-based information that crosses traditional disciplines. Unfortunately, gaps in our understanding of river processes often limit our ability to manage rivers optimally.
THE STATEMENT OF TASK AND THE COMMITTEE’S RESPONSE TO IT
The U.S. Geological Survey (USGS) has played important roles in advancing the science of rivers and in order to help assure that its activities continue to serve the nation well, the agency sought advice from the National Research Council (NRC) as to how it might best address river science challenges by effectively using its resources and coordinating its activities with other agencies. In response, the NRC Committee on River Science at the USGS was formed to carry out the tasks shown in Box S-1. This report contains the results of that study.
The committee addresses the first task (i.e., to identify the highest priority river science questions for the USGS) in Chapter 4. This chapter proposes three topical areas, namely, environmental flows and river restoration, sediment transport and geomorphology, and groundwater surface-water interactions, for special emphasis. It also recommends two crosscutting science activities, namely, surveying and mapping the nation’s river systems according to key physical and landscape features and expanding work on predictive models, especially those that simulate interactions between physical-biological processes.
Most of the second task (i.e., to identify key variables to be monitored and data-managed) is addressed in Chapter 5. Table 5-1 summarizes some key recommended variables. The chapter proposes enhancements in streamflow, biological, and sediment monitoring; these include establishing multidisciplinary, integrated reach-scale monitoring sites and developing a comprehensive national sediment monitoring program. It also encourages the USGS to be at the forefront of new technology application, including airborne lidar and embedded, networked wireless sensors.
The answers to most elements of the third task—which asks the committee to balance temporal and spatial scales, local intense studies vs. broad regional or national studies, and work on small, pristine streams vs. large, heavily impacted rivers—are topic specific. Thus, they are different for each individual recommendation. Establishment of the recommended reach-scale monitoring sites, and increased work in groundwater and surface-water interactions, imply local intense study of processes. In contrast, recommended river surveying and sediment monitoring programs would be national in scale and might last for many decades or even centuries. Overall, most of the recommended research areas, such as stream restoration, environmental flows, and models that predict ecological change, imply considerable work in highly altered rivers. However, most of these would benefit from and may require comparative sites in more pristine environments. Thus, the committee defers the details of this task to the USGS pending how it chooses to organize its scientific disciplines to most effectively address river science issues (see Chapter 6).
Statement of Task
The NRC will provide guidance and advice to the USGS on the following issues:
WHAT IS RIVER SCIENCE?
The term “river science” refers to the study of processes affecting river systems. River science integrates multiple disciplines; it includes the study of how hydrological, geological, chemical, and ecological processes interact to in-
fluence the form and dynamics of riverine ecosystems and how riverine ecosystems in turn influence these processes across multiple spatial and temporal scales.
River science seeks to understand the linkages between river-related processes and patterns at multiple scales, from small streams to large rivers, from pristine to heavily urbanized watersheds, and from daily- to century-scale dynamics. Watersheds range in size from under one to thousands of square kilometers, and a river’s physical and biological environment changes as water moves downstream. Small-scale or short-term physical processes may influence reach-scale habitat features that in turn influence ecological processes at broader scales and over longer time periods. River science includes the study of relationships between watersheds, riparian zones, floodplains, groundwater, headwaters, and downstream rivers. Thus, river science is not constrained by any arbitrary spatial scale or physical boundaries defined by the morphology of channels, floodplains, or terraces. Rather, its domain and bounds are defined by the scales necessary to understand and predict river processes.
MAJOR RIVER SCIENCE DRIVERS AND CHALLENGES
The nation faces many complex challenges in its stewardship of natural resources. In particular, human alterations of river systems have become so pervasive that society can no longer ignore their impacts. Today’s policy and management challenges in ecological restoration and dam removal, relicensing of hydropower facilities, invasive species, water allocation, climatic variability, urbanization and other land-use changes, and water quality have also become significant drivers for river science.
Human and natural actions have caused the loss or degradation of riverine habitat. Throughout the country, thousands of ecological restoration efforts are being undertaken to improve water quality, manage riparian zones, improve habitat, and stabilize streambanks. Billions of dollars are being spent on small projects and billions more on major restoration projects in the Everglades, coastal Louisiana, and the upper Mississippi River. Yet the science of river restoration—how to best restore these ecosystems—is still in its infancy. Dam removal is a particularly high-profile form of river restoration, with enormous impacts on hydrologic and ecological processes. In the United States there are about 76,000 dams that exceed 2 meters in height and several million smaller ones. Recently, the removal of dams has accelerated. Their structures are becoming obsolete and therefore their economic viability to owners is declining, while at the same time legal and financial liabilities are growing and governments are increasingly recognizing the environmental benefits of their removal. To target the best candidates for removal the costs and benefits of their removal must be weighed; this requires a better understanding of how river systems respond to dam removal.
Hydropower dams are subject to periodic relicensing by the Federal Energy
Regulatory Commission (FERC). In the relicensing process, dam operators must discuss the impact of their operations on the riverine environment and how they might mitigate any negative impacts. Citizen groups and environmental nongovernmental organizations use this as an opportunity to advocate for dam removal or operations modification. Many of their concerns center on the timing and volume of water releases and their impacts on water quality and instream habitat. Addressing these concerns rests on our ability to predict such impacts.
Human actions have spread thousands of invasive species across the nation, including saltcedar in watercourses throughout the western United States, Asian carp in the Mississippi and Illinois Rivers, and zebra mussel in the Great Lakes and elsewhere. Insufficient knowledge exists about how these species spread, how to limit their spread, and how they influence river biodiversity and ecosystem processes.
Severe drought in the western United States and the potential need to reallocate waters of the Colorado River to cope with its prolonged nature, has heightened awareness of water allocation issues. These large-scale issues, coupled with numerous conflicts over smaller streams, involve battles between interests concerned with municipal and agricultural water supply, environmental flows (i.e., flow levels, timing, and variability), and recreation. River science can provide information for decisionmakers working to resolve such allocation conflicts.
The ecological and sociological impacts of climatic variability have been and will continue to be significant. Reduction in precipitation or change in the timing of snowmelt can severely impact agricultural production and increase conflicts among water users. Variations in temperature and the duration, magnitude, and timing of high and low flows affect the quality of river habitat. These impacts are just beginning to be understood.
The quantity and quality of river flows are tied directly to changes in urban occupancy and rural land-use activities. Even seemingly minor changes in land use can create significant changes in runoff patterns. Our ability to predict future water availability and flood risk, manage erosion and siltation, and manage river ecosystems is thus limited by our understanding of these land-use changes.
Despite recent improvements, our nation’s water quality remains at risk. As of 2000, only 61 percent of assessed stream miles fully supported all of their designated uses, and of these, 8 percent were considered threatened for one or more uses. In the remaining assessed reaches, one or more designated uses are impaired by pollution or habitat degradation. High-priority water-quality problems include bacteria, nutrients, metals, siltation, and emerging contaminants such as pharmaceuticals.
The scientific understanding necessary to respond to these challenges will not come easily. The approach must be multidisciplinary and integrative, and it must be process-based and predictive. River science can provide such an approach.
Recommendation: USGS river science activities should be driven by the compelling national need for an integrative multidisciplinary science, structured and conducted to develop a process-based predictive understanding of the functions of the nation’s river systems and their responses to natural variability and the growing, pervasive, and cumulative effects of human activities.
THE ROLE OF THE USGS
The demands for river science information cannot be met by any one organization. Given the number of entities studying rivers—including federal, state, and local agencies, public and private institutions, universities, and the public— what is the role of the USGS in river science?
The USGS has collected river-related data since the 1800s, emphasizing consistent methodology and quality control. It is the primary science agency of the Department of the Interior, with strengths in hydrology and hydraulics, sediment transport, biology and ecology, aquatic chemistry, hydroclimatology, geology, and resource mapping. The USGS also has a reputation for impartiality because of its lack of regulatory authority; and it has abundant interconnections with academia, federal natural resource agencies, and local and state agencies. For these reasons, the USGS is ideally suited to provide “policy relevant and policy neutral” information and understanding to develop the integrative multidisciplinary river science initiative envisioned in this report, including bottom-up (driven by individuals or small teams), top-down (organized through an institute initiative), and community-driven (originated to support a particular management concern) science. In addition, the USGS is uniquely positioned among federal agencies to provide integration and synthesis to many ongoing river science activities.
Recommendation: The USGS should establish a river science initiative to bring together disparate elements of the USGS to focus its efforts to deal with growing river science challenges. The initiative should build upon USGS’s history, mandate, and capabilities. It should take advantage of key attributes of the institution, such as its
mission as provider of unbiased science information,
data collection and monitoring expertise,
experience in science synthesis at many scales, and
organizational structure that combines national research programs with state-, watershed-, and university-based cooperative programs.
In carrying out the initiative, USGS should closely coordinate with other federal agencies involved in river science and related activities.
SCIENCE PRIORITY AREAS FOR USGS RIVER SCIENCE
Society has a clear need for river science, and the USGS has a variety of strengths and capacities that can be brought to bear on these needs. The intersection of society’s needs and the USGS’s strengths suggest a number of science priorities for USGS river science. These priorities are grouped into crosscutting science activities and topical science focus areas where recommendations for USGS research are offered.
Crosscutting Science Activities
The following two science priority areas are disciplinarily crosscutting activities that would strengthen the holistic river science approach. These activities would underpin the USGS’s science contribution to a broad national effort in river science.
Surveying and Synthesizing
River networks are intimately connected to the landscape and are integrators of climatic, geologic, and land-use processes within their watersheds. Throughout the nation, there are large regional gradients in climate, geology, topography, land cover, and human impacts. This extensive variation makes meaningful generalizations about how streams and rivers function challenging and complicates how information collected in one river can be transferred to another, geographically distant river. Therefore, generating a national baseline survey that characterizes the spatial variation in key landscape features and processes would provide insights into the controls of in-stream river processes and allow for more cross-site comparisons.
A multidisciplinary survey and mapping of rivers and streams should provide a preliminary structure of multiple information layers at a reach scale. This stratification of information would be based upon readily available data, including climate, topography, soils, and geology. It should also include land use and human alteration information, such as upstream diversions and impoundments that alter the flow regime. Many other elements necessary for this collection of data layers are now available in the National Hydrography dataset products that are under development in partnership with the U.S. Environmental Protection Agency. Ultimately, this mapping effort would provide an important resource nationally useful to risk-based analyses of floods, invasive species spread, and many other issues.
Recommendation: The USGS should survey and map the nation’s stream and river systems according to the key physical and landscape features that act as determinants of hydrologic, geomorphic, and ecological processes in streams and rivers. This synthesis will provide a scientific baseline that can be used to support many regional-scale river science questions and afford geographic information of use to state and federal agencies, academia, and the public.
Modeling River Processes
Quantitative models that integrate physical, chemical, and biological processes provide detailed information on pathways and interactions that are difficult to measure directly in the field or whose characteristics change over time. Models complement point measurements and surveys by interpolating across the data and providing a mechanism to predict future changes. The USGS has a 40-year history of developing mathematical models of natural systems, including estuarine ocean circulation, surface-water runoff and river hydraulics, groundwater flow and solute transport, sediment transport, biological processes in streams, and groundwater and surface-water interaction. The USGS is unique among federal agencies for its breadth of modeling applications.
Potential applications of predictive integrated models are many. The construction of ecohydrologic models that focus on the structure of stream flows coupled to models linking flow to watershed and meteorological variables could be used to test the physical and ecological response of river systems to changes in flow regime with changing climate or anthropogenic drivers. These models, if properly multidisciplinary and robust, could be invaluable in river restoration, planning, and multiple water resource issues. Models can also be used to address how flow can be decreased by groundwater pumping or enriched in excess nutrients from agricultural fields.
Recommendation: The USGS should add capacity in developing predictive models, especially models that simulate interactions between physical and biological processes, including transport and transformation of chemical constituents, pollutants, and sediment. These tools provide the underpinning for predicting ecological change.
Topical Science Focus Areas
The following three priority areas are designed to address gaps in specific research areas for which improved scientific knowledge is needed. Each of these science activities will occur through enhanced monitoring and modeling, and will be key components of the overall river science framework.
Environmental Flows and River Restoration
The nation is spending billions on riverine restoration and rehabilitation projects, yet the science underlying these projects is not currently well understood and thus the approaches and their effectiveness vary widely. Therefore, a fundamental challenge is to quantitatively understand how rivers respond physically and biologically to human alterations from dredging to damming, and to specifically address: What are the required “environmental flows” (i.e., flow levels, timing, and variability) necessary to maintain a healthy river ecosystem? And which biota and ecological processes are most important and/or sensitive to changes in river systems?
For future restoration projects to be most successful, they should be adaptively managed. This requires long-term monitoring of quantitative measures of flow regime, groundwater activity, and ecosystem responses, such as primary productivity and habitat diversity along targeted reaches. Quantitative models relating ecological function to flow regimes are also needed to allow natural resource managers and citizens to forecast the impacts of proposed water management decisions. These efforts need to go beyond just stating the potential impacts of policy and management decisions to actually assessing the outcomes these activities have on rivers. Improving and synthesizing the scientific information on environmental flows before, during, and after river restoration could lead to an improved ability to predict outcomes and thus more effective, cost-efficient habitat restoration.
Recommendation: The USGS should develop the means to characterize environmental flows in rivers by developing quantitative models that link changes in the ecological structure and function of river ecosystems (aquatic and riparian) to management-scale changes in river flow regimes.
Recommendation: The USGS should, in cooperation with and support of other federal agencies involved in restoration, serve as a leader to evaluate the scientific effectiveness of river restoration approaches to achieve its goals, synthesizing results from past restoration efforts, and designing standard protocols for the monitoring and assessment of river restoration projects.
Sediment Transport and Geomorphology
Erosion, transport, and deposition of sediments in fluvial systems control the very life cycle of rivers and are vulnerable to changes in climate and human landscape alternations. Yet, compared with water quality and quantity information, there is relatively little available information on sediment behavior in river systems, particularly large-order reaches. By advancing basic research on sedi-
ment transport detection, quantification of bedload, suspended load, and wash load, and monitoring flow velocity and water temperature associated with such sediment transport conditions, the USGS could better detect morphologically significant flows, develop methods to mitigate future problems arising from sediment movement, and play a guiding role in multiagency efforts to deal with the increasingly important national sediment challenges.
To assess sediment fluxes, sediment transport technology needs to be advanced by the USGS in partnership with other research entities. These advances could be applied to problems such as determining the risk of contaminated sediment resuspension, designing and maintaining flood control channels, predicting channel behavior, understanding sedimentation and hydraulic roughness in mountain channels, restoring and remeandering previously channelized streams, assessing the impact of dam removal on river sedimentation and habitat, estimating flows needed for removing sand and silt from gravel-bed streams, and improving sedimentation management in lakes and reservoirs. Knowing the science of these sediment-related processes is critical to the multibillion-dollar efforts to restore wetlands, reestablish flow regimes, and maintain river reaches for transport.
Recommendation: The USGS should increase its efforts to improve the understanding of sediment transport and river geomorphology in the nation’s rivers. Activities should include advancing basic research on sediment transport processes, developing new technologies for measuring fluxes of bedload, suspended load, and wash load, and monitoring flow velocity and water temperature associated with such sediment transport conditions.
Groundwater and Surface-Water Interactions
River flows throughout the nation are affected when groundwater that normally discharges to rivers is captured for agriculture or other uses. Yet few of the USGS’s approximately 7400 active stream gages or hundreds of monitoring wells incorporate data on groundwater and surface-water exchange. Limited investigations have been done on the end members of potential hyporheic interactions— large-scale effects of water supply developments adjacent to large rivers and detailed hyporheic interactions on first-order streams—but the full continuum of how groundwater and river water interact is relatively unknown.
The USGS has the tools, datasets, and existing networks that make it a logical place to focus resources to investigate stream-groundwater exchange processes at a national scale. The USGS has been a leader in developing many hydrologic methods and tools used to characterize groundwater and surface-water interactions. This, combined with the USGS’s extensive streamgaging network and synoptic survey datasets, provides an important foundation. Lake and
reservoir studies of the USGS, with some modification, provide a template for the development of an aggressive data mining effort and provide approaches to new field instrumentation of exchange rates.
Recommendation: The USGS should expand its current river monitoring and river study programs so they fully integrate the floodplain, channel, and groundwater, and the exchange of water between these systems (hyporheic exchange). The exchange of water between groundwater and rivers needs examination and quantification at multiple scales in a range of different hydrologic and geologic settings, as this process is a key component influencing river discharge and water quality, geomorphic evolution, riparian zone character and composition, and ecosystem foundation, maintenance, and restoration.
MONITORING AND DATA MANAGEMENT FOR USGS RIVER SCIENCE
A river monitoring strategy and a data management infrastructure are needed to support the proposed activities in river science. The following sections on integrated monitoring and management recommend an approach to handling the diversity of information and data that would be generated by these science activities.
Integrated Data Collection and River Monitoring
Monitoring our nation’s rivers is the foundation of USGS’s contribution to river science. Historically, the USGS has been a leader in river monitoring, distinguished for its scientific rigor, quality control, and innovative river monitoring techniques and instrumentation. Therefore, the USGS is well positioned to fulfill the growing need to concurrently monitor hydrologic, geomorphic, chemical, and ecologic river conditions.
Currently, streamflow data are available for many higher-order river systems, but data on water quality, sediment transport, biology, and ecology are often lacking. To make gage data more useful for river science initiatives, the USGS should investigate cost-effective ways to collect more integrative biophysical data. The USGS should consider the incorporation of index biological reaches, where coupled measurements of river flows, groundwater levels and fluxes, and water quality are combined with riparian cover mapping. The USGS should prioritize based on those variables with broad science and management applications, and seek opportunities to collaborate with other programs that monitor rivers so efforts build on and do not duplicate one another.
By building on its existing capabilities and leading an effort to enhance river
monitoring to fill the science data gaps in critical or neglected areas, the USGS will be able to better support all its priority research areas in river science.
Recommendation: The USGS should expand its monitoring activities on rivers to better incorporate river physical, chemical, and biological conditions within its existing river and streamflow monitoring programs. Its goals should include development of a 21st-century river monitoring system for data collection, transmission, and dissemination.
Integrated Data Archiving, Dissemination, and Management
Integrative river science is supported by diverse measurements and observations. In contrast to streamflow data and point measurements of nutrient concentrations, observations to support river science include two-dimensional data and observations describing stream channel geometry, time-varying data on bed forms, channel sediments, and the land uses and vegetative cover of riparian corridors and upstream drainage areas. Three-dimensional data describing flow velocity fields are now available from innovative acoustic Doppler technologies that have been enhanced by USGS, and even four-dimensional measurements (i.e., time-varying, three-dimensional fields) are both technologically and economically practical data forms with great potential value for river science. The USGS maintains and stores considerable information in databases including the National Water Information System (NWIS), National Water-Quality Assessment (NAWQA) program Data Warehouse, National Biological Information Infrastructure (NBII), and The National Map.
It is in the national interest for river science data holdings to be standardized and archived in a consistent way with sufficient ancillary information (metadata) to provide traceable heritage from raw measurements to useable information and allow the data to be unambiguously interpreted and used. Coordination and co-operation among the federal resource management agencies and their nonfederal partners will be critically important as the scope, scale, and intensity of data needs to support river science evolves. No single federal agency can collect, quality assure, manage, and disseminate all data and observations relevant for river science. Yet all federal agencies, nonfederal partners, and stakeholders with an interest in river science data will benefit from access and availability of accurate, reliable, and well-documented data. A common data model would provide an intellectual framework under which river science data holdings are catalogued and accessible. To develop such a model, a strategic plan put together by informatics experts from the USGS and other agencies and academics needs to be developed.
Recommendation: The USGS should include in its river science initiative an informatics component that includes developing a common data model for river science information that can be used to archive the diverse river science metadata and data. This data model should be developed in coordination with and capable of supporting other federal agency river science data needs. The data model should accommodate data from multiple sources, including nonfederal sources. Such a program would facilitate the integration and synthesis of river science data to address the diverse range of river science questions discussed in this report.
ORGANIZING AND MANAGING RIVER SCIENCE AT THE USGS
River science at the USGS and elsewhere covers a wide variety of basic and applied research and usually incorporates a broad range of partners. Because the USGS has strengths in many of the subdisciplines of multidisciplinary river science, there may be no single best institutional “place” for a river science within the current structure of the USGS.
Future river science coordination mechanisms within the USGS should incorporate certain key strengths within existing USGS programs. These include the place-based experience and long-term datasets of some of the Biological Resources Discipline (BRD) Science Centers and Priority Ecosystems Science sites, two-way flow of information between the Water Resources Discipline (WRD) personnel doing research and those doing applied science, the close links with universities of the BRD Cooperative Research Units and many of the WRD Science Centers, and the close ties between the BRD Science Centers and other federal agencies and between the WRD Science Centers and state and local agencies. These coordination efforts should work closely with programs within the USGS’s Geography Discipline and National Geospatial program office to build on the wealth of existing mapping capabilities. They should also further promote the consistent data collection standards and national synthesis strengths of the USGS.
Overall, the current fragmented nature of the USGS’s approach to river science needs organization and focus. Any managerial approach that addresses river science must be born of an institutional culture that fosters integrative cooperative research. An initiative that contributes fully to regional and national needs will require interdisciplinary research teams that, if not housed together, are regularly brought together to plan, direct, and execute USGS river science activities.
Recommendation: The USGS should employ innovative managerial approaches to combine the best elements of existing Water and Biological Resources river programs and other USGS programs, and refocus a portion of existing research and field team efforts on examining and answering nationally important river science questions.
Overall, society’s linkages to rivers run deep and these linkages—from agriculture to transportation and from water supply to recreation—drive a broad need for advances in river science. The USGS, by virtue of its unique strengths among the many actors in river science, has an important part to play in meeting this need. By showing leadership in monitoring, modeling, surveying, synthesizing, and data management—concerning topics such as environmental flows, behavior of sediment, and groundwater and surface-water interactions—the USGS can contribute a great deal toward answering some of the most difficult and interdisciplinary questions involving rivers. Wise application of the knowledge gained will lead to better, more informed policy and management decisions throughout the nation.