4
Priority Areas for USGS River Science

This report has identified a compelling national need for an integrative river science, a 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 cumulative effects of human activities. This need is reflected in the growing number of conflicts that arise over the beneficial use of river resources and the environmental health of river ecosystems, as well as in Congress’s repeated calls for the best available science to support policy and management decision making. As outlined in Chapter 3, the USGS role should reflect its own mandate and capabilities and build upon its core strengths. The design and activities of a USGS river science initiative should be guided by the overarching goal to provide unbiased, policy-relevant, science-based information to advance understanding and support decision making for the nation’s river systems.

Neither the USGS nor any other agency or organization can carry out all the science involved with water, sediment, chemical constituents, and organic material in river systems and their ecosystems. To this end, USGS river science priorities must be directed toward prioritizing research with respect to funding sources that can be brought to bear, answering the key questions of national interest and those the USGS is best positioned to address, and leveraging USGS research strengths with the needs of other federal agencies.

Of the many river science questions, the committee has identified specific science priority areas where the USGS can contribute to the national understanding of rivers. These priority areas are derived essentially from the intersection of society’s needs, as described in Chapters 1 and 2, with the USGS’s capacities, as



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River Science at the U.S. Geological Survey 4 Priority Areas for USGS River Science This report has identified a compelling national need for an integrative river science, a 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 cumulative effects of human activities. This need is reflected in the growing number of conflicts that arise over the beneficial use of river resources and the environmental health of river ecosystems, as well as in Congress’s repeated calls for the best available science to support policy and management decision making. As outlined in Chapter 3, the USGS role should reflect its own mandate and capabilities and build upon its core strengths. The design and activities of a USGS river science initiative should be guided by the overarching goal to provide unbiased, policy-relevant, science-based information to advance understanding and support decision making for the nation’s river systems. Neither the USGS nor any other agency or organization can carry out all the science involved with water, sediment, chemical constituents, and organic material in river systems and their ecosystems. To this end, USGS river science priorities must be directed toward prioritizing research with respect to funding sources that can be brought to bear, answering the key questions of national interest and those the USGS is best positioned to address, and leveraging USGS research strengths with the needs of other federal agencies. Of the many river science questions, the committee has identified specific science priority areas where the USGS can contribute to the national understanding of rivers. These priority areas are derived essentially from the intersection of society’s needs, as described in Chapters 1 and 2, with the USGS’s capacities, as

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River Science at the U.S. Geological Survey described substantively in Chapter 3. Each of these priority areas addresses actions that would improve the scientific foundation and enhance the scope of river science. The first two science priority areas are crosscutting activities that would strengthen the holistic river science approach. These translate into recommendations for the USGS to (1) conduct a national inventory to survey and map the nation’s stream and river systems according to key landscape features that act as determinants of hydrologic, geomorphic, and ecological processes in streams and rivers and (2) develop conceptual and predictive models that could be used to couple surface water, groundwater, geochemistry, and sediment fluxes, and to quantify ecological responses. Although we pose these crosscutting science priority areas individually, there is great potential for these activities to enhance each other. A national river science survey would provide a framework or template through which the multiple disciplines within river science could communicate both monitoring information and model results about rivers across the landscape. Additionally, modeling river processes can help indicate the key variables that are most important to monitor and synthesize nationally. Thus, these activities would underpin the USGS’s science contribution to a broad national effort in river science. In addition to suggesting ways to enhance the interdisciplinary river science vision, the committee has identified three areas of river science for which improved knowledge and understanding is needed, and for which the USGS can play a leading role. These are (1) the characterization of environmental flows in rivers (flow levels and patterns necessary to maintain healthy aquatic ecosystems), (2) basic research, synthesis, and monitoring of fluxes (bed load and suspended load) and their relation to channel dynamics, and (3) full integration of floodplain processes and groundwater hydrology as a basic component of river systems. Investigations into each of these topical science activities are more targeted, both in their geographic extent and specific processes monitored, than the crosscutting activities, although each of these science activities would involve enhanced monitoring and modeling and would be key components of the overall river science framework. In each section below, the committee outlines the science recommendation and then expands on this recommendation by addressing four overarching questions: Why is the recommendation in the national interest? Why should the USGS be involved in this river science issue? What is a compelling problem related to the recommendation? What are some examples on how the USGS might do this?

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River Science at the U.S. Geological Survey CROSSCUTTING SCIENCE PRIORITY AREAS Surveying and Synthesizing 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. The form of rivers and their internal dynamics are driven by a diversity of processes that occur throughout the watersheds they drain. The defining characteristics of a river—its hydrologic regime, sediment load, nutrient assimilation, and ecology—reflect the intimate connection of the river network to the surrounding landscape. Thus rivers integrate the climatic, geologic, and land-use processes in their watersheds. River science seeks to understand how streams and rivers are influenced by these complex watershed processes and therefore gain a better understanding of how they might respond to natural and human-influenced environmental changes. Across the nation, there are large, regional gradients in climate, geology, topography, land cover, and human impacts on rivers. This extensive variation makes meaningful generalizations about how streams and rivers function challenging. It also complicates how information collected in one river can be appropriately transferred to another geographically distant river. Yet obtaining this type of knowledge is fundamental to attaining both regional-scale understandings and national synthesis in river science. Determining regionally representative monitoring sites and criteria, so knowledge gained from those sites can be transferable, requires understanding the variety of river settings within regions and across the nation. Therefore, a survey and synthesis of existing information is needed to generate a spatial framework or baseline map that can be used to organize empirical data, extrapolate information to locations lacking data, and stratify variations in river processes to assist in the selection of appropriate monitoring or reference sites for regional studies. This framework should flexibly characterize spatial variation in key landscape processes that control many instream river processes. Such a mapping project would produce a valuable tool that other agencies and the public would benefit from, and it would integrate information across agencies (e.g., riparian [USDA], dams [USBR, USACE], water quality [EPA], and water quantity [USGS]). The USGS should consider stratifying the nation’s rivers at a reach scale based on both the natural setting of a river (comprising climate, topography,

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River Science at the U.S. Geological Survey soils, gradient, and geology) and the type and magnitude of human alteration (comprising upstream diversions and impoundments and land-use characteristics) that dictate key physical and chemical processes that are known to drive the ecological structure and function of river channels and their riparian buffers. Rather than a comprehensive new surveying and mapping exercise, this could be a preliminary stratification based upon national-scale, spatial datasets that are readily available and that can be analyzed quickly using existing Geographic Information System (GIS) technology. Why Is the Recommendation in the National Interest? River science and management questions arise in a diversity of settings, and the USGS is called upon to provide information in all these settings. Additionally, many questions in river science do not require detailed process-based information (fine-grained data expensive to acquire at large spatial extents such as synoptic studies). Therefore, to ensure that monitoring information is transferable to all locations of interest, it is important that USGS river science research cover the full range of river settings and processes. Survey information on river attributes, which is used to stratify river reaches, is a prerequisite to ensure coverage and thus support the transferability of river science knowledge. The survey to support stream reach stratification will also produce a rich set of attributes that will be of value to federal and state agencies involved with river use, water-quality protection, and restoration. Applications of such a baseline map include identifying river reaches having similar (or different) attributes that influence ecological condition, flood risk, landslide potential, invasive species spread, water-quality impairments, and many others. Evaluating changes in our river systems in response to climatic, regulatory, and other anthropogenic impacts is clearly a national issue. This attribute-rich, spatial coverage was already suggested as a basis for a sampling design in the context of the National Streamflow Information Program streamgaging network (NRC, 2004d). Many elements necessary for stratification of the nation’s rivers at a reach scale are present in the National Hydrography Dataset products that are under development in partnership with the EPA (NHDPlus); (http://www.horizon-systems.com/ NHDPlus/index.htm). Why Should the USGS Be Involved in This River Science Issue? The USGS is the nation’s mapping agency and is therefore uniquely capable of integrating the information necessary to stratify stream reaches. Mapping attributes associated with stream reaches would draw heavily on USGS resources, such as the national elevation dataset and its derivatives, national hydrography dataset, geology, land use, and land cover. Further, under the direction of both the legislative and executive branches, the USGS has recently

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River Science at the U.S. Geological Survey been increasing its efforts to examine and characterize water availability in the nation. This mapping effort would therefore provide an opportunity to integrate information on the nation’s water infrastructure (e.g., dams, diversion structures, groundwater pumping) into a comrehensive river science perspective that would allow visualization of the human imprint on rivers and streams at the regional to national scale. What Is a Compelling Problem Related to the Recommendation? Like topographic and geologic maps, the spatial framework envisioned here will provide a foundation upon which a wide variety of science and management applications in river science would be based. In this case, the nation needs a way to describe the multifaceted characteristics of river reaches that does not yet exist. Streams and rivers are complex integrators of multiple watershed processes, and mapping the overlay of the many factors (both natural and anthropogenic) that drive riverine processes is a necessary first step toward erecting a national framework for river science that will support many issues in river science of national importance. Such maps would be useful for identifying or stratifying reaches (or subwatersheds) with similar or dissimilar potential in terms of environmental responses to natural or anthropogenic drivers. For example, many river science questions emerge at the regional scale where spatial distribution of resources must be assessed. This requires sampling designs that accurately and adequately ensure that samples are representative. A GIS-based map of stream and river reaches will provide end users the flexibility to define and develop a map from some combination of drivers to address regional-scale questions. What Are Some Examples on How the USGS Might Do This? Because rivers integrate processes across diverse environments and multiple scales (i.e., the flow regime in rivers depends on the watershed’s climate, topography, geology, land cover, and river size), a scientific understanding of river processes requires a framework that incorporates these differences. Identifying this conceptual framework would allow for site matching, a method for identifying where environmental conditions are similar, implying similar response in riverine function. Such a framework would allow for observations to be appropriately interpreted and differences meaningfully studied. Frameworks similar in principle to the proposed mapping program have been undertaken as classification systems, which are typically based on one or two important physical-chemical drivers (e.g., flow regime, channel geomorphology). These classification systems are incomplete and may not be adequate for the purposes of interdisciplinary river science at the national scale.

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River Science at the U.S. Geological Survey The USGS should review existing river classification systems to identify the driving variables that determine the range of physical, chemical, and biological features of streams and rivers. These features can be attributed to river reaches nationally and thus serve as a comprehensive inventory of the spatial distribution of combinations of key environmental drivers of river structure and function. This richly detailed map will serve as the underpinning reference for USGS-based river science and observations, and it will provide a point of reference for process study and scientific hypothesis testing. Furthermore, this information will be available to a diversity of users (government, academia, and the public), some of whom may wish to use this information to develop question-specific classification systems. An excellent example of a national river mapping program is the New Zealand River Environment Classification (REC) (Snelder and Biggs, 2002; Snelder et al., 2004, 2005). The REC classifies individual river reaches in terms of physical factors: climate, source of streamflow, geology, land cover, position of the reach in the river network, and channel (and valley) shape. These factors are known to control important river processes, such as flow regime, temperature regime, rates of land soil erosion and nutrient release, instream flux and storage of sediment, and local habitat structure. These factors are also hierarchically related (e.g., climate influences whole watersheds whereas channel form is a very local factor). This hierarchical framework allows maps to be created at different scales of resolution, from whole watershed maps of climate and flow regime to reach-scale maps that show how all six factors interact. These maps are provided as a GIS layer (Figure 4-1). This tool has been used in New Zealand to test hypotheses about how variations in biological and chemical water quality are related to reach-scale classes, and it has been shown to perform better than more traditional and less process-based classifications such as ecoregions (Snelder et al., 2004). The power of the approach is the user-defined ability to generate maps that include different driving environmental factors at different degrees of spatial resolution to test specific hypotheses or to identify similar types of habitat for monitoring or resource evaluation. In the context of USGS river science, developing a comprehensive set of map layers based on key environmental factors would provide a tremendous resource to a number of potential end users; the USGS would not necessarily be compelled to develop a classification system per se. USGS data resources and mapping capability are well suited to the task of developing and implementing this mapping program. Given the many and diverse applications that such a map could serve, developing such a map should involve broad participation with as many sectors of the river science community as possible. Indeed, many data components of this national synthesis exist at USGS and elsewhere (e.g., the streamgaging network, regional hydrologic analysis of flows [peaks and flow statistics], the national hydrography layer, the USACE national inventory of dams, land-cover maps, and geologic maps).

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River Science at the U.S. Geological Survey FIGURE 4-1 A classification of the South Island of New Zealand showing classes at the climate level of the River Environment Classification, as well as zooming to three progressively more detailed scales that demonstrate sources of flow, geology, and landforms respectively. SOURCE: Reprinted, with permission, from Snelder and Biggs (2002). © 2002 by the American Water Resources Association.

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River Science at the U.S. Geological Survey

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River Science at the U.S. Geological Survey Modeling River Processes Recommendation: The USGS should add capacity in developing predictive models, especially models that simulate interactions between physical-biological processes, including transport and transformation of chemical constituents, pollutants, and sediment. These tools provide the underpinning for predicting ecological change. Quantitative models that integrate physical, chemical, and biological processes can provide detailed information on pathways and interactions that are difficult to measure directly in the field or are nonstationary in time. Point measurements and synoptic surveys of hydroecological processes are essential components of river science; however, the measurements needed to describe these interactions are often time consuming and costly. Thus there is a growing need for numerical models and instrumentation that can be used in place of labor-intensive field surveys. Additionally, these models can be used as tools to compliment and help focus monitoring efforts, thus allowing researchers to investigate across greater spatial extents. Why Is the Recommendation in the National Interest? In addition to integrating field studies and minimizing costly, labor-intensive surveys, models have predictive ability that if used appropriately, can provide insight on physical-biological responses to changes that are likely to occur in the future. For example, Riverine habitats that are used by fish and other aquatic organisms are formed and maintained by a range of flow conditions. A critical need exists for the development of more advanced ecohydraulic models that focus on the structure of flows, and that can be used to investigate the physical-ecological response of river systems to changes in flow regime. Water flowing within a river channel exchanges with water present in the streambed and the banks and floodplain. This flow can be a source or sink for nutrients used by organisms at all trophic levels, in addition to providing “bank storage” that mitigates flooding and provides baseflow to the channel. Why Should the USGS Be Involved in This River Science Issue? The USGS has a long history of developing quantitative process-based models of both heuristic and real-world hydraulic systems. Suites of publicly available software are used to model a wide range of processes, including runoff in large river basins, flow and sediment transport in rivers and estuaries, and groundwater transport of solutes and pollutants in aquifers. Of these, the ground-

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River Science at the U.S. Geological Survey water and multiphase solute transport models are industry standards (e.g., MODFLOW and SUTRA). USGS researchers also have a collective knowledge and experience in model calibration. The network of over 7000 streamflow-gaging stations, with standardized and quality-controlled streamflow and water-quality data, contributes to the USGS’s development and testing of numerical models of streamflow, sediment transport, nutrient cycling, and ecosystem responses to variations in water-quality constituents, such as dissolved oxygen, temperature, and salinity. A number of USGS researchers are illustrating the strengths and potential applications of integrated multicomponent models. Some examples include mapping of land cover and terrain characteristics for use in modeling sediment supply and contaminant transport to a reservoir in the foothills of the Sierra Nevada; estimation of water supply, aquifer storage, and water reuse within the highly urbanized watershed of the Santa Ana River in southern California; and coupling of hydraulic habitat models to assess the effects of channel modification on fish habitat in the upper Yellowstone River. Recently, USGS scientists coupled their groundwater flow model, MODFLOW, with BRANCH, a surface-water simulation program to simulate streamflow with both regular and irregular channel cross sections. This powerful model calculates temporal changes in water levels, flow discharges, and velocities in a spatially explicit channel network and is especially suited to evaluate streamflow in upland rivers with backwaters and where discharge is highly regulated. BRANCH also is used to explore the interaction of freshwater inflows, tidal action, and changing weather conditions. Much of the support for USGS investigations and data acquisition activities comes from federal and nonfederal agency cooperators. The breadth of USGS activities and their capabilities in modeling are strengthened by the diversity of the cooperator base. In addition to federal agencies (e.g., COE, EPA, USFWS), the cooperators include state agencies or municipalities that often lack the resources and/or expertise to undertake specific projects. The USGS has unique capabilities in combining its expertise in mapping, modeling, and data serving to provide cooperators with near real-time information for a range of needs, including flood forecasting, specification of streamflows for environmental maintenance, and the development and management of groundwater resources. What Is a Compelling Problem Related to the Recommendation? Almost all aspects of river science can be addressed using process-based models developed from strong conceptual models. Consider, for example, the growing need to manage water for an expanding number of uses, including uses that were unforeseen 40 to 50 years ago, such as environmental maintenance flows. The key parts of this problem are (1) knowing how much water currently exists within a surface-water and groundwater system, and (2) understanding the hydrology of the system well enough to predict the response to changes in water

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River Science at the U.S. Geological Survey supply and/or water use. Inferences drawn from field observations and data collected over a period of years are often used to address the first part of the problem, whereas modeling is the most practical and efficient way to address the second part of the problem. The computational efficiency and accessibility of models has changed significantly in the last decade, and probably most river scientists see modeling as a key part of their research. The challenge in the near term is not really in the development or use of hydrologic models for specific purposes but rather in the refinement and linking of existing models to address multi-objective water management strategies. Recently, the USGS and others have been promoting the development of an open-source numerical model for sediment transport in coastal regions, named the Community Coastal Sediment Transport Model (http://woodshole.er.usgs.gov/project-pages/sediment-transport/). In a similar way, the USGS could also play a leadership role in developing a Community River Sediment Transport Model in collaboration with other federal agencies, academic institutions, and private industry, with the goal of adopting and/or developing one or more models for use as scientific tools by the river science community and government agencies responsible for river management. What Are Some Examples of How the USGS Might Do This? An example that illustrates the potential of integrated modeling can be found in the Klamath River Basin, where the USGS is involved in broad-based efforts to better manage water resources within this river system. The USGS and the Oregon Water Resources Department are developing a regional groundwater flow model to simulate aquifer responses to changes in agricultural use and variations in climate. Additional work is being done in the Klamath basin to assess the feasibility of using a “water bank” to store surplus water in wet years to meet biological flow requirements in dry years (http://oregon.usgs.gov). Statistical models coupling measurements of precipitation, air temperature, snow-water equivalence (SWE), and groundwater levels are being developed to reduce uncertainties in streamflow forecasts for upper Klamath Lake (http://or.water.usgs.gov/klamath/). Hydrologists from Utah State University are using the USGS Multidimensional Surface Water Modeling System (MSWMS) to evaluate habitat suitability for Chinook salmon and Steelhead along ~ 300 km of the Klamath River. In related work USGS scientists from the Fort Collins and Portland Science Centers have linked a water-resource planning model to a water-quality model to simulate seasonal changes in water temperatures with and without the dams that are currently in place. Because river science is inherently integrated, promoting the use and development of these integrated models fits naturally into its future direction and vision. Having the tools to better investigate the integrated system through cou-

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River Science at the U.S. Geological Survey FIGURE 4-2 Map of suspended sediment concentrations in selected river basins within the continental United States and estimated sediment discharges for some of the country’s major rivers. SOURCE: Meade and Parker (1985). from Lake Michigan. Accurately measuring such discretionary flow is a challenge due to the presence of density currents laden with suspended sediment, which result in bidirectional flow during certain times of the year (Garcia et al., 2006). This is also a matter of national interest, in particular for the Great Lakes region, because a consent decree by the U.S. Supreme Court dictates how much water can be diverted by Illinois and other states bordering the Great Lakes and Canada. Further, to maintain natural processes in altered river systems, periodic morphologically significant flows are required, but the timing, magnitude, and duration of these flows are not well understood. Many river restoration projects require specification of a dominant water discharge, or a series of flows that perform important ecological or geomorphologic functions. For example, when restoring habitat for a salmon fishery, managers need to be able to accurately estimate the timing, magnitude, and duration of the flow needed to rid spawning grounds of fine-grained sediments downstream of dams. The recent man-made flood in the Colorado River, created to revitalize the river system after years of

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River Science at the U.S. Geological Survey suffering from sediment starvation, is another good example of why a better understanding of the coupling between fluid mechanics and sediment transport is needed if large dams are to be operated to promote channel and habitat restoration. Re-meandering of streams that were once channelized also requires knowledge about channel plan form stability that can only come through sound hydraulic and morphologic analyses (Abad and Garcia, 2005). Overall, these examples illustrate the clear need for the USGS to develop a program on riverine sediment transport and morphodynamics that uses state-of-the-art sediment technology, which will improve our ability to address these problems and better manage ecosystems. The movement of sediments is also of interest to the nation because of the pollutant potential of washload and chemicals (either fertilizer or industrial waste) that attach to fine particles. Silt is often considered the number one stream and river pollutant, particularly in the Midwest. Preventing the pollution of streams, bays, and estuaries by fine-grained sediment is one of the biggest challenges facing sedimentation engineers. For example, the issue of hypoxia in the Gulf of Mexico is controlled largely by the washload made up of fine sediments from agricultural land in the heartland of America. Additionally, after years of industrial growth, there are numerous water bodies with contaminated bed and floodplain sediments, making it necessary to determine the risk of contaminated sediment resuspension so appropriate measures can be taken to manage these contaminated areas. Why Should the USGS Be Involved in This River Science Issue? This research could involve all of the major USGS disciplines: hydrologists (Water Resources Discipline), geomorphologists (Geologic and Water Resources Disciplines), ecologists (Biological and Water Resources Discipline), and satellite imagery and GIS (Geographic Discipline). The USGS is also positioned to partner with existing groups (e.g., support National Sediment Monitoring Program and Hydroacoustics Program) to synthesize and integrate the sediment transport work of federal and state agencies with sediment-related programs and provide comprehensive analysis to support national applications. While other agencies (U.S. Army Corps of Engineers and U.S. Bureau of Reclamation, Fish and Wildlife Service, Natural Resources Conservation Service, Agriculture Research Service, and EPA) are involved in sediment research, the USGS is uniquely positioned to serve as the synthesizer of this activity. Additionally, the USGS has historical roots in such work (i.e., Gilbert, 1914, 1917) and is currently involved in sediment research in various rivers in Kansas, the lower Virgin River of Arizona and Nevada, and the Little Colorado River, as well as combined laboratory and field research.

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River Science at the U.S. Geological Survey What Is a Compelling Problem Related to the Recommendation? As indicated, in the United States, sediment management is a multibillion-dollar issue, and the environmental impacts and financial losses associated with accelerated surface erosion are a growing problem (Osterkamp et al., 2004), as are concerns about the effects of sedimentation in rivers and reservoirs (Stallard, 1998; Syvitski, 2002). Additionally, limitation in sediment supply also degrades river deltas, making coastal areas more vulnerable to flooding and ocean inundation. In most regions of the United States, the landscape has been extensively modified by changes in land cover and land use associated with population growth. The specific effects of land-cover change are, however, highly variable and existing methods for predicting soil erosion and sediment yield under different land uses are not much more advanced than they were 50 years ago. Material fluxes generated from surface erosion are uneven in both space and time. Therefore, it is important to evaluate the processes of mobilization and storage across a range of terrain types, under existing conditions and for projected changes in land cover and climate. To do this, better tools and methods need to be developed to evaluate spatial and temporal discontinuities in streamflow and sediment transport at a range of scales. This information is essential for evaluating land-based water fluxes, as well as sediment and carbon fluxes to the ocean. A more specific and compelling problem relates to the Illinois River as mentioned earlier. The Illinois Waterway with its system of locks and dams links Chicago and the Great Lakes to the Mississippi River and thereby to the Gulf of Mexico. This linkage has significant transportation and commercial values for the state and the nation. In addition, with its numerous backwater lakes, wetlands, and floodplain forests, the Illinois River valley provides a significant habitat for fisheries, waterfowl, and other birds, and animals, making it an important ecological resource. Adaptive management of the Illinois River and many other important waterways in the nation hinges upon the development of a strong sediment monitoring program with the USGS playing a leading role and in collaboration with other federal agencies (U.S. Army Corps of Engineers, EPA, Fish and Wildlife Service). What Are Some Examples on How the USGS Might Do This? The potential exists within the USGS to play a lead role in developing an integrated database to monitor (and potentially model) regional patterns of erosion and sediment yield, both as natural processes and responses to disturbance. As an example of what this might look like, Figure 4-2 shows a map of suspended sediment concentrations in selected river basins within the continental United States and estimates of sediment discharges of some of the nation’s major rivers. The patterns of higher and lower sediment concentration are broadly con-

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River Science at the U.S. Geological Survey FIGURE 4-3 An estimate of suspended-sediment discharge in the Mississippi River basin. The amount of sediment entering the Gulf of Mexico has decreased significantly, leading to coastal erosion. SOURCE: Meade (1995). sistent with regional variations in climate, rock types, and vegetative cover. Rivers draining the Great Plains and the Colorado Plateau tend to have high suspended sediment concentrations, as do some rivers in California, Oregon, and Washington. The particular combinations of precipitation, land cover, rock type, and topography in these regions combine to produce relatively high rates of erosion. Rivers draining the more humid regions of the country, including the upper Midwest and the East Coast, tend to have much lower sediment suspended concentrations. Further investigations and validations into the factors controlling erosion and sediment transport would give a clearer understanding of regional sensitivities and how regions will likely respond to future change. In addition to spatial variations in sedimentation across the nation, sedimentation rates also change with time. Figure 4-3 shows a temporal perspective of sediment transport in the Mississippi River basin. Most notable is that the overall sedimentation into the Gulf of Mexico has decreased, leading to coastal erosion. However, where sediment yields increased or decreased depends on the location. In the 1980s, dams captured most of the sediment from the erodible Missouri River subbasin, whereas sedimentation in the Ohio River subbasin increased. Therefore, understanding sedimentation requires a better understanding of the impacts both of erosion and dams. With the help of remote sensing techniques, flow and sediment transport during floods can be studied in a quantitative way. Acoustic Current Doppler Profilers (ACDP), coupled with global positioning systems and depth sounders,

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River Science at the U.S. Geological Survey can provide detailed pictures of the flow structure in rivers. The phenomenon of density currents (stratified flows) in the Chicago River was discovered thanks to the ACDP measurements taken by the USGS to assess diversion flows from Lake Michigan (Garcia et al., 2006). Similar technologies are emerging to measure concentrations and sizes of suspended sediments (Szupiany et al., 2006). Swath mapping with acoustic sensors provides exceptionally detailed three-dimensional pictures of riverbed morphology, making it possible to distinguish even the smallest of bed forms (Parker and Garcia, 2006). Sediment transport technology needs to be advanced by the USGS in partnership with other federal agencies and universities to assess sediment fluxes in rivers, deltas, and estuaries (http://water.usgs.gov/osw/techniques/sedtech21/). These advances could be focused around: determining the risk of contaminated sediment resuspension; the designing and maintaining of flood-control channels, including wetlands; predicting the behavior of channels that convey sediment mixtures; understanding sedimentation and hydraulic roughness in mountain channels; preventing the pollution of gravel spawning grounds by fine sediment; quantifying bidirectional flows in density-stratified rivers; restoring and re-meandering previously channelized streams; assessing the impact of dam removal on river sedimentation and habitat; developing a technique for prescribing flushing flows for removing sand and silt from gravel-bed streams; understanding erosion in streambanks (particularly for cohesive materials) and throughout the watershed by surface runoff; and improving sedimentation management in lakes and reservoirs. Groundwater Surface-Water Interactions 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. The USGS has about 7400 active stream gages, and operates hundreds of

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River Science at the U.S. Geological Survey monitoring wells around the country. However, a comparatively small number of integrated studies provide only a modest database and limited understanding of the factors controlling the exchange process. Most investigations have focused on large-scale effects of water supply developments adjacent to rivers or on physical and geochemical processes occurring during exchanges in streams with small discharges (first-order mountain watersheds). Why Is the Recommendation in the National Interest? There are two pressing reasons why groundwater-river exchange locations, rates, and timing should be evaluated. First, these processes are being interrupted when groundwater that normally discharges to streams (see Figure 4-4) is being captured prior to reaching the river. This commonly occurs in locations where rivers are the unconfined aquifer discharge area and where groundwater use consumes or exports water from the groundwater system. Also stage modifications in regulated river systems have altered stream groundwater exchange processes, an issue that is difficult to evaluate because preregulation data are often missing. Additionally, urbanization of river systems that requires channel modi- FIGURE 4-4 Average base flow fraction of streamflow attributed to groundwater. Map modified, with permission, from Becker (2006). © 2006 by Blackwell Publishing. Original map created from USGS data (Wolock, 2003) and physiographic sections of the continental United States (Fenneman and Johnson, 1946).

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River Science at the U.S. Geological Survey fications and alters the floodplain and riparian character impacts water exchange. The effects are, however, poorly characterized. As the demand for water grows, groundwater extraction from river floodplain aquifers is commonly used as a source of additional potable water. Yet, the impacts of such operations on all aspects of river functions are poorly known. One observed effect is the alteration of stream hydrographs (e.g., the Ogallala Aquifer; Sophocleous, 1998). Therefore, a national effort is needed to characterize both the spatial, temporal, and magnitude of this exchange process in varied river and hydrogeologic settings, and the impact water use and management have on the exchange process in a river system. Hyporheic exchange processes also underpin other stream and riparian functions including sediment transport and deposition, water and quality, and water temperature, which all relate to the quality of the ecological habitat. Such hyporheic issues are not just limited to the dry western states like they once were. With population growth in the eastern United States, the demand on shallow, river-connected groundwater systems to supply water has increased. Second, to regain natural hydrologic, geomorphic, and ecologic functions, the nation has begun to restore thousands of kilometers of modified river systems. Yet little is known about how the groundwater-river exchange processes influence riverine natural, altered, and restored conditions. For example, there is a national need to determine how rivers function as water treatment systems as they process and cycle nutrients, carbon, and other elements in the channel and floodplain systems, and how water exchange supports ecological systems. They do this partly by exchanging river water with the river bed and bar water, and the adjacent floodplain groundwater system. Though it is recognized that hydrologically generated disturbance to river riparian systems (e.g., Resh et al., 1988; Junk et al., 1989; Poff et al., 1997; Schlosser, 1987; Townsend, 1989; Poff and Ward, 1990; and Townsend and Hildrew, 1994) and extreme events like floods and droughts reset fluvial ecosystems, the influence of groundwater and river exchange locations and rates on these disturbances is poorly understood (Poff et al., 1997; Gasith and Resh, 1999; Bunn and Arthington, 2002). Why Should the USGS Be Involved in This River Science Issue? The USGS is the national leader and has a long history of conducting unbiased studies of the nation’s aquifers and rivers (e.g., Regional Aquifer Systems Analysis, Groundwater Atlas, the National Stream Quality Accounting Network [NASQAN], and NAWQA). It is also a leader in developing many, now standard, hydrologic methods and tools used to characterize groundwater and surface-water interactions (Rorabough, 1963; Stallman, 1963; Lapham, 1989; Constantz and Thomas, 1996; Constantz, 1998; Constantz et al., 2003; Stonestrom and Constantz, 2003). The extensive USGS streamgaging network combined with the large num-

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River Science at the U.S. Geological Survey ber of regional and special project synoptic survey datasets housed at the state and regional centers provides a wealth of data. With these datasets and existing networks, the USGS seems the logical place to focus resources to investigate the stream-groundwater exchange process at a national scale. The lake program of the USGS, with some modification, provides a template for the development of aggressive data mining efforts and the approaches for determining the location and timing of new field instrumentation to understand exchange rates. Therefore, the expertise needed to design and initiate hyporheic and riparian zone hydrology and ecosystems research is already present in the research conducted at regional USGS offices. Existing research efforts in groundwater-stream interaction include investigations to quantify denitrification and related processes in an agricultural watershed of the Mississippi River basin (Böhlke et al., 2004). What Is a Compelling Problem Related to the Recommendation? The capacity of river systems to affect water quality by processing pollutants such as nutrients has enormous application to a nationwide problem of the unsuitability of large numbers of waterbodies for their designated uses. The Clean Water Act is a major driver for research in this area, through requiring estimates of total maximum daily loads (TMDLs) of dissolved and suspended material in rivers. Thousands of water bodies throughout the country, and a vast area of the Gulf of Mexico, receive excess N and P, and much of the supply comes from nonpoint sources, notably agriculture. Although construction of forested riparian buffer zones and other initiatives are important to solving this problem, an in-depth understanding of how nutrients cycle between rivers, groundwater, and sediment is critical to developing long-term solutions and the most effective mitigation strategies. What Are Some Examples on How the USGS Might Do This? Future synthesizing and expanding upon current and past studies involving groundwater and surface water are natural extensions of what the USGS already does. Such future work, if coupled to the strengths of the Biological and Geographic Disciplines and partnered with other agencies, offers an unprecedented opportunity to learn how groundwater and surface-water interaction affects riverine and riparian environments and biota across the spectrum of different hydrologic and climatic regions of the United States. Groundwater and surface-water interaction can be studied within current National Research Program initiatives (water.usgs.gov/nrp/) and incorporated as part of ongoing national initiatives, such as NAWQA. The most long-standing of these projects is outlined in Box 4-2. Long-term hydrologic data from USGS streamgages would be the starting

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River Science at the U.S. Geological Survey BOX 4-2 Shingobee Headwaters Aquatic Ecosystems Project The USGS program studying the role of lakes in the hydrologic system incorporates close cooperation between the National Research Program (NRP) and Water Science Center offices and is an example of how interdisciplinary science in rivers could be done. The Lakes Research Program of the USGS has been active for more than 25 years, beginning in the late 1970s with the study of Williams Lake in northern Minnesota (see figure below). At that time the Minnesota Division of Waters provided funds to the Minnesota District Office to collaborate with Tom Winter, director of the Lake Research Program, in his field studies and interpretation. This collaborative approach ultimately embraced scientists from other divisions of the USGS, numerous universities, state agencies, other federal agencies such as NASA and NSF, and the International Atomic Energy Agency. The overall effort is now well known as the Shingobee Headwaters Aquatic Ecosystems Project (SHAEP). The purpose of SHAEP is to develop interdisciplinary tools and information on how atmospheric water, surface water, and groundwater function as an integrated system. Participating scientists provide their own funding, and there are no constraints on the number of scientists participating, their discipline, or on duplication of effort. Involved scientists from both within and outside the USGS cover the gamut of multidisciplinary fields from the physical, geochemical, and biological sciences. The research results of SHAEP have led to major interdisciplinary understanding of lake systems, including their biology, geochemistry, and hydrology (http://wwwbrr.cr.usgs.gov/projects/SHAEP/index.html). This program is an outstanding example of how multiple parties and organizational branches of the USGS have worked in concert to achieve a scientific organization model where the sum of the parts is actually greater than the whole. The larger NRP lake program includes studies of lakes throughout the United States, with long-term sites equivalent in length and scope located in New Hampshire, North Dakota, and Nebraska. These studies are all being done in an interdisciplinary way incorporating district, university, and state and federal agency scientists collaborating with the NRP. Location of the USGS Shingobee Headwaters Aquatic Ecosystems Project (SHAEP). SOURCE: http://wwwbrr.cr.usgs.gov/projects/IRI/WSPintro1.html.

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River Science at the U.S. Geological Survey point for such characterization, particularly in the context of comparative studies among streams reaches within different climatic and geomorphic settings. As indicated in the NRC report on the National Streamflow Information Program (NRC, 2004d), the USGS gage network has been critical to providing the fundamental data supporting the emerging field of hydroecology in the last decade. For example, regional flow regime classifications have been constructed using streamflow data from the USGS National Streamflow Information Program. These kinds of studies could ultimately lead to a groundwater-stream exchange classification that could be used to evaluate stream functions and possibly provide a focus for stream restoration efforts. One example of how large-scale evaluations of riparian and hyporheic zones might be done is by calculating the extent to which groundwater delivers nutrients to streams by conducting focused monitoring in the hyporheic zone at type-reaches across either hydrogeomorphic regions or gradients of human landscape alterations. These monitoring efforts could then be coupled to modeling approaches. This would allow for the evaluation of how the hyporheic zone transforms nutrients at multiple scales of stream order by using a series of field experiments as part of an interagency partnership (i.e., with EPA). As might be expected, there are many approaches that can be used to tackle groundwater and surface-water interaction within streams and the riparian zone in a manner that leads to transfer across the spectrum of riverine environments. Because of uncertainties associated with estimates of hyporheic exchange based on any single technique, different techniques should be developed to conceptually understand hyporheic processes at different spatial and temporal scales. For example, remote sensing may be useful in identifying spatial and temporal variations in groundwater discharge in streams over time based on temperature or soil moisture content proximate to streams (using multiple images). Different remote sensing techniques to characterize riparian zone hydrology likely would have to be investigated for different regions (i.e., arid versus humid regions). CONCLUSIONS Clearly, the USGS is positioned to provide national leadership in a river science initiative for the nation. From the organizational strengths of the USGS, which incorporate the broad spectrum of science and technology needed to study rivers, coupled to its unique nonregulatory or commercial science and information mission, the USGS can play a vital role in addressing problems related to the pervasive changes occurring to our nation’s rivers. Through collaborations with state and local governments, as well as other federal agencies, the USGS is also well suited, perhaps ideally suited, to broker interdisciplinary teams and efforts to do the broad-scale and novel new river science initiatives needed to advance river science for the public good.

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River Science at the U.S. Geological Survey Of the many river science questions, the committee has identified five science priority areas where the USGS should take a leadership role. Through its cartographic capabilities, the USGS has provided the leadership for mapping the nation’s watersheds. Combining this strength with its expertise in the areas of river hydrology, geomorphology, and ecology the USGS should embark on efforts to survey and map multidisciplinary characteristics of our nation’s rivers, providing a geographical baseline that supports an integrative river science. Through its scientific research capabilities, the USGS has developed an essential suite of mathematical and other tools that can be applied to a broad range of river science questions. Building on these accomplishments, the USGS should develop process-based models that simulate the interactions between physical-biological processes, providing the nation with an ability to predict ecological change in river systems to support science and river management. With its multidisciplinary expertise in areas of river science, the USGS should conduct research that provides a scientific-basis for characterizing environmental flows needed to support the ecological structure and function of river ecosystems, and in partnership with other agencies’ activities, evaluate the effectiveness of restoration efforts designed to improve river ecosystem health. Historically, the USGS has been a leader in monitoring river sediment transport and studying the interactions between hydrology and fluvial geomorphology. The USGS should strengthen its research efforts in sediment transport and geomorphology on our nation’s rivers to address the increasing problems due to alterations in river flows and channel morphology. Major gaps remain in our scientific understanding of the exchange of water between a river and connected groundwater systems. The USGS should focus investigations on groundwater and surface-water interactions in rivers at a range of scales, providing information on how the character and composition of these waters affects river water quality and ecosystem characteristics. Although the USGS is poised to provide national leadership in these river science priority areas, these activities must be supported by effective data collection and management and an institutional structure that allows for an agencywide multidisciplinary research initiative. In Chapters 5 and 6, we address the river monitoring, data management, and institutional components that should underpin the USGS’s contribution to river science.