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Linking hydrological change and ecological response in streams and rivers
of the eastern United States Days Hotel and Conference Center at Dulles Herndon, Virginia February 8-10, 2005 |
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Attendees | Organizers (Contacts) | Home
WORKSHOP SYNOPSIS: Priority research
topics and strategies to address issues of water for ecological needs In February 2005, the USGS Eastern Region sponsored a workshop, “Linking hydrological change and ecological response in streams and rivers of the eastern United States” in Herndon VA. Our purpose was to bring managers and researchers together to exchange information concerning issues of managing flow alteration to sustain ecological integrity in streams and rivers of the eastern U.S. Workshop participants (>180) included Federal and State resource managers and regulators, and scientists with the USGS and partner agencies, academic institutions, and non-governmental organizations. Across six sessions, invited speakers and participants discussed issues and priority information and research needs relative to managing flow alteration resulting from water diversion, flow-regulation and urban development. Aquatic resource managers expressed a common theme, that agencies lack the information and tools to balance human needs for water resources with protecting the ecological integrity of aquatic systems, including support of imperiled aquatic species. Speakers discussed a wide range of obstacles to better-informed management of aquatic resources, ranging from lack of data on species-specific flow requirements, to the need for landscape level indicators and decision-support technologies. A repeated theme was the necessity of moving from a general understanding of flow regime influences on aquatic ecosystems, to making science-based, site-specific predictions of how species, communities, and stream channels will respond to alternative flow management strategies. Some key needs were highlighted:
Presentations and discussion at the workshop clearly showed that recent and ongoing research by USGS scientists, our partners and others entails a broad scope of activities directed at improving the science of understanding and prescribing ecosystem flow needs. These research efforts include methods development, e.g., for assessing hydrologic change, remote-sensing applications to habitat mapping, and mulidimensional instream flow and habitat modeling. Site- and region-specific studies of biotic responses to changes in hydrologic conditions resulting from water supply development, flow-regulation by dams, urbanization, drought and channel modification are all adding to our understanding of how flow alteration may affect aquatic communities in differing landscape contexts. There are also efforts to integrate this understanding with management at local- and landscape-scales through predictive modeling (e.g., of riparian vegetation responses to flow regulation, and stream fish responses to alternative irrigation schemes), development of stream classification and hydrologic assessment tools, and flow-experimentation to improve ecosystem function. The scientists who presented this work emphasized several general, interrelated research priorities:
The USGS could expand its role in developing water management solutions that meet human and ecosystem requirements. Specifically, the Survey, in collaboration with DOI agencies and other partners, could develop a research strategy that focuses on providing science to support landscape- or basin-scale water management decisions. This strategy would entail multiple research components focusing on:
Individual research efforts should be designed as interdisciplinary efforts that will expand our capability to apply conceptual understandings of physical and biological linkages in flowing water ecosystems to solving management problems. Projects could be focused in systems where elevated management concerns (e.g., because of the occurrence of imperiled species) or opportunities (e.g., development of State-wide water management plans) provide for direct and valued application of USGS science. A competitive funding process could ensure that near-term resource investments are placed to achieve the greatest science and application benefit. In the long-term, the USGS is well suited to work with our partners in developing the scientific basis for water resource management. Specific opportunities include:
The USGS currently is engaged in numerous research activities that address priority needs identified during the workshop. To give a few examples: instream flow methodology development is ongoing in the western U.S.; multidimensional hydraulic modeling is providing guidance for flow management and endangered species protection in the lower Missouri River; the Survey is engaged in long-term monitoring in the upper Mississippi River; eastern biologists and hydrologists are quantifying effects of flow depletion and land use change on stream fish and macroinvertebrate assemblages; and eastern and western scientists are collaborating to develop stream classification and hydrologic index tools. At this juncture, the Survey is in a position to build on this work and take a lead in developing landscape-level, integrated science to address the large issue of achieving long-term sustainability of the Nation’s flowing-water resources. (Top) Session 1: Issues and Information Needs of Federal Agencies (Moderator: Gary Brewer) Representatives from five Federal agencies (including four Departments –Interior, Commerce, Defense, and the Environmental Protection Agency) offered their views on information needs related to river and stream flow issues. Case studies and examples were drawn from many eastern states and as far west as California. Clearly, ever-growing demands to tap and alter rivers and streams are challenging Federal policy-makers, regulators, and resource managers. A common topic of the five talks was that agencies lack the necessary knowledge and decision-support tools to make informed, balanced decisions that objectively weigh the needs and values of society with environmental safeguards that will sustain aquatic biological diversity and ecological integrity. Jerry Ziewitz (U.S. Fish and Wildlife Service) described efforts to protect the ecosystem integrity of the Apalachicola-Chattahoochee-Flint (ACF) River Basin. A suggested concept for water allocations within the ACF system would:
Bill Hansen (National Park Service) explained the charge of the NPS to protect Federal parklands and leave them unimpaired for future generations. Hansen described the greatest challenge for NPS as the assessment of “impairment.” The Buffalo National River, Obed Wild and Scenic River, Missouri River National Recreation Area, and Delaware Water Gap National Recreation Area where given as examples of where the following NPS needs are foremost:
Prescott Brownell (National Marine Fisheries Service) described the relationships between declining stocks of shad, herring, sturgeon, and American eel and the damming of Atlantic coast river systems. Brownell emphasized the need for scientists to better clarify the connectivity among rivers, diadromous species, and marine ecosystems. He also called for safe and effective measures to ensure fish passage, citing evidence that over 15,000 dams from Maine to Florida have blocked 84% of historic river habitat and resulted in unprecedented, global-scale changes in river processes, including:
“Ecosystem connectivity,” in a different context, was also the theme for the talk given by Tracie-Lynn Nadeau (Environmental Protection Agency). Nadeau discussed lingering controversies over a jurisdictional ruling by the U.S. Supreme Court involving the Clean Water Act (CWA) (Solid Waste Agency of Northern Cook County v. U.S. Army Corp of Engineers), which invalidated the use of the “migratory bird rule” as the basis for CWA jurisdiction. The ruling addressed intrastate, non-navigable waters and has had far-reaching implications on the ability of managers to protect “isolated” wetlands. Key questions expressed by Nadeau involve:
Seven Ashby and Beverley Getzen (U. S. Army Corps of Engineers) suggested that establishment of ecological goals must involve close linkages between scientists and decision-makers, and that scientists must inform decision-makers by characterizing the ecological conditions that are achievable under particular management regimes. Suggested research needs included:
(Top) Session 2: Issues and Information Needs of State Regulatory Agencies (Moderator: Bill Lellis) Representatives from four State agencies (Georgia, Michigan, New Jersey, and Florida) and one interstate commission (Delaware River Basin) offered comments on establishing and implementing stream flow guidelines from a regulatory perspective. Common to all states is a conflict between meeting the water needs of rapidly expanding population centers and protecting the ecological integrity of source streams and groundwater. Managers need scientifically sound and defensible information on the full life cycle flow needs of aquatic species, communities, and their habitats for inclusion in water diversion models used in the permitting process. Nap Caldwell (Georgia Environmental Protection Department) discussed the difficulties of moving beyond 7Q10 minimum flow regulations towards more protective site-specific flow requirements. Even though a Joint House-Senate Water Policy Study Committee adopted a policy of using site-specific studies as a basis for establishing stream flow in 2001, drought and economic downturn have left this essential element of flow maintenance policy languishing. Needs include:
Gary Whelan (Michigan Department of Natural Resources) discussed key science gaps from a state agency perspective. State agencies are responsible for protecting commonly held natural resources, but must have substantial evidence to support recommendations in court. Failures to challenges are most often due to key understanding gaps. Gary felt we have good fundamental understanding of flow dynamics, water chemistry, sediment transport, and aquatic community function, but much is theoretical and not site-specific. Key gaps include:
Michele Mateo Putnam (New Jersey Department of Environmental Protection) discussed the decision tree used by New Jersey to evaluate new water diversion permit applications. Factors considered include public interest, effects on other users, protection of critical areas, potential for salinity intrusion, spread of groundwater contamination, safe yield, impacts on wetlands and listed species, and use of the lowest quality water for the intended purpose. Incorporating ecological flow requirements into water diversion permits introduces complications in managing for seasonal variability, enforcement, and allotments for areas already over-allocated. Specific needs include:
Colin Apse (The Nature Conservancy) described the challenges and opportunities of interstate flow management using the Delaware River Basin Commission as an example. The commission has established an advisory subcommittee to define ecological flow requirements for the maintenance of self-sustaining aquatic ecosystems in the basin. The subcommittee has no dedicated budget, but relies on federal funding and volunteers. It plays a critical role in opening dialog between scientists, user groups, and policy makers. Key to water management decisions is recognition that the Delaware is a highly altered system with no appropriate reference conditions, leading mostly to development of mitigation scenarios. Key needs include:
Eric Nagid (Florida Fish and Wildlife Conservation Commission) described Florida’s ongoing efforts to meet the consumptive needs of a growing human population while ensuring the hydrological needs of source streams. The Florida Water Resources Act of 1973 mandates regulation of streams through establishment of site-specific minimum flows, which are defined as the point where further withdrawal would significantly harm water resources or ecology. Conflict has arisen because minimum flow guidelines consider recreation, storage, supply, aesthetics, and navigational needs equal to the habitat needs of fish and wildlife. Further conflict has arisen in that the Florida Fish and Wildlife Conservation Commission has only an advisory role in the process, with no regulatory authority to set flow limits for protection of aquatic communities. Needs include:
(Top) Session 3: Traditional and innovative approaches to characterizing hydrologic alteration and assessing changes in stream biota (Moderator: Marty Gurtz) The third session of the workshop emphasized traditional and innovative approaches to characterizing hydrologic alteration and assessing changes in stream biota. Instream flow methods have become more sophisticated since first introduced nearly 30 years ago, and techniques have been developed for a more holistic assessment of ecological responses to flow management, including large rivers, and for incorporating hydrologic changes as part of a human disturbance gradient in streams. Brian Richter (The Nature Conservancy) introduced the methods of the Indicators of Hydrologic Alteration (IHA), which have been used since 1996 to compare ecologically relevant hydrograph statistics before and after flow modifications such as reservoir construction, or to assess gradual trends in hydrology over time. Five important characteristics of flow regimes are the magnitude, duration, frequency, timing, and rate of change of extreme flows. A recently released revision of the IHA software includes 34 new parameters called “environmental flow components”, or EFCs, that are based on statistical characteristics of flow patterns, including: extreme low flows, low flows, high flow pulses, small floods, and large floods. The Limits of Hydrologic Alteration (LOHA) method compares streams for these 5 categories, yielding a “River Health Category” designation based on degree of departure from the natural or native flow condition. This software lends itself to an approach consistent with the Clean Water Act, i.e., designated hydrologic uses can be defined; it will be important to be able to characterize societal benefits that are compromised if a stream moves from a river health category indicating a natural condition to one that indicates that the hydrology has been altered. According to LeRoy Poff (Colorado State University), the key scientific challenges in assessing ecological responses to flow alteration include: (1) characterizing appropriate scale(s) of flow, (2) identifying key flow determinants, (3) separating flow from other environmental drivers, and (4) selecting sensitive ecological response variables (indicators) to flow. Poff distinguished between hydroecology (examining hydrographs at the watershed scale, with an emphasis on statistical analysis and extremes) and ecohydraulics (emphasizing hydraulic habitats at the site scale, using time-series models and “wadeable” flows). Poff suggested important characteristics of flow regimes need to be considered in the context of how multiple hierarchical scales (sensu Frissell and others, 1986) interact with flow. Identifying sensitive ecological response variables (indicators) requires matching “mechanistic” species traits to environmental selective forces (“drivers” or “filters”) (the habitat template; Townsend and Hildrew, 1994). Site-specific questions (e.g., point disturbances such as a dam in unique settings) require process-based understanding of flow alteration, whereas regional questions (such as monitoring status and trends) require statistical characterization of hydro-ecological linkages. Poff discussed a study (Brian Bledsoe, principal investigator) to develop a multi-scaled physical habitat classification of western U.S. streams in order to derive models for predicting biological condition. The Hierarchical Filtering Model (HFM; Poff, 1997) is a biologically based approach to understanding local community composition by explicitly considering environmental constraints imposed at different scales. Habitats with similar sets of multi-scale filters should have species with similar attributes. Using invertebrate data from a pre-2000 study by USEPA’s (6) (R)EMAP data from 197 sites in 3 Western states, Poff identified 19 insect traits that could be ranked based on their disturbance or thermal tolerance. Developing a framework for assessing flow variation requires capturing natural spatial variation in processes that influence habitat structure and dynamics. Poff proposed using a hydrogeomorphic (HGM) classification as a framework based on a watershed-scale natural flow regime; implementing such a framework requires mapping stream networks to identify similar HGM types and testing with biological data. Don Orth (Virginia Tech University) was emphatic in his encouragement for the science to go beyond the emphasis on physical habitat that has been the historical basis for the Instream Flow Incremental Methodology (IFIM). There is a real need for hypothesis testing, and the ability to gather data from flow alterations has never been easier – e.g., because of experimental floods (such as the Glen Canyon Dam) or operations of reservoir releases. The Philpott Reservoir, for example, was constructed on Smith River by the U.S. Army Corps of Engineers in 1953 for flood control and peak power generation; the daily peaks in river flows below the reservoir contrast sharply in both frequency and magnitude of high flows with nearby rivers. Abundance of the native fish, brown trout, is reduced in abundance in proportion to increasing peak flow occurrence and magnitude. Modifying the reservoir release method (e.g., ramping up in two steps instead of instantaneously) reduces shear stress and increases adaptation time for fish. Flow pulsing also affects egg scatterers (e.g., the endangered Roanoke logperch, which deposits eggs in coarse or medium sand) more than egg attachers (e.g., the more common fantail darter, which uses large cobbles for spawning). Plant communities respond to flow changes, but little research has been down in the eastern U.S. Geomorphological changes also occur as a result of dam operations; for example, the Trinity River (California) lacks shallow slow microhabitats due to decades of flood scalping. Orth noted that instream flow studies are indirect and highly complex, experiments are rare, and there is no unifying theory. Other notable issues include the relations between low flow and water quality; the benefits of 3-dimensional over 2-dimensional models for capturing wakes or vortices at peak flow; Orth feels that only incremental improvements can be expected until there is a more systemic revolution in the science of instream flow. Adaptive management will not be adopted, and multiple competing hypothesis will continue until the science improves and scientific issues are considered together with the emotional, legal, historical, and political issues. A historical perspective of instream flow issues was introduced by Ken Bovee (USGS, Fort Collins, CO). During the period 1975-1985, complete dewatering of rivers in the western U.S. was a serious problem. Methods were developed to identify a minimum reservoir release or a state-issued instream flow water right. Reservoir operations and relicensing of hydroelectric dams by the Federal Energy Regulatory Commission (FERC) were important issues during 1980-1995, and stimulated development of incremental methods for assessing alternative water management options, including the Instream Flow Incremental Methodology (IFIM, Bovee 1982; Bovee and others, 1998); the most common decision variable for this approach is habitat area, but temperature and water quality can also be used. Alternatives are evaluated on the basis of feasibility (but note the distinction between “it can’t be done” versus “I don’t want to do it”), effectiveness (change in habitat area), and risk. From 1990 to the present, there have been several paradigm shifts, such that instream flow issues have evolved from species-oriented habitat management to community habitat and ecosystem restoration or rehabilitation. Advancements in GIS capabilities and use of 2-dimensional models have enabled new IFIM applications. As an example, Bovee presented an application of landscape ecology concepts in a study of patch dynamics in the Yellowstone River, Montana. Patch dynamics and landscape ecology fit with the concepts of IFIM, but will require redefinition of baseline or reference conditions, at least for hydrology and geomorphology. Basic concepts of feasibility, effectiveness, and risk analysis are still valid, regardless of the application. Large, highly engineered rivers, can have morphological dynamics that are practically independent of the flow regime. Robb Jacobson (USGS, Columbia, MO) used the Lower Missouri River (LMOR) as an example of a river whose morphology is controlled not by equilibrium between flow and sediment regimes, but rather by its management by the U.S. Army Corps of Engineers. Classes of physical habitat in the LMOR are designed for individual species – e.g., terns and plovers (emergent sandbar habitat) or pallid sturgeon (shallow water habitat); 2-dimensional models are used to estimate area of each habitat class under different discharge conditions, with large differences in areas between the channel as it existed in 1894 versus 2000. Detailed mapping shows promise for characterizing habitat used by threatened and endangered, and invasive, species. Flow and channel form are practically independent, but management of timing of habitat availability requires the hydrograph. From the mid-1800s to the 1930s, the large rivers of the eastern U.S. were extensively altered by the U.S. Army Corps of Engineers to support commercial shipping; ongoing restoration efforts seek to enhance or recover ecological services in these highly altered large rivers. Steve Gutreuter (USGS, La Crosse, WI) noted 2 types of management in the Mississippi River, making it an appropriate system for comparative studies: in the north, navigation depths are maintained using both low-head dams and channel-training structures, resulting in extensive floodplain aquatic areas that coexist with commercial navigation; from about St. Louis south, however, navigation depths are maintained entirely by constriction of flow into the navigation channel using wing dikes and revetments, resulting in floodplains that have largely been dried and converted to agriculture. Gutreuter noted that in attempting to link hydrology with biological production, “we are drowning in concepts”: the River Continuum Concept (watershed transport and processing of terrestrially derived nutrients), Flood-Pulse Concept (floodplain processing of terrestrially derived nutrients), and Riverine Productivity Concept (aquatic photosynthetic C fixation) all attempt to explain the high productivity of large rivers. Examples from both the Orinoco River and the Mississippi River emphasized the importance of algal photosynthesis in supporting fish production, even in highly heterotrophic rivers; further, the linkages between algal primary production and hydrology are well known. Gutreuter also found linkages between hydrology and annual growth rates of fishes during years of widely different hydrographs; for example, annual production of floodplain fish species were significantly greater during a high-water summer than low-water summers, whereas riverine species were similar between high- and low-water years. Other studies raised questions about whether navigation channels create “attractive” habitat for some fish species, such as low-flow velocities in troughs of bedforms. Research needs include development of predictive ecosystem models to compare relative benefits of alternative restoration strategies; such models, however, do not yet exist, and are much more challenging for large rivers than for smaller systems. Other needs are measurement of responses of ecological processes to hydrologic change, as well as food-web dynamics, carbon and nutrient processing, and local-scale hydraulic attractors. JoAnna Lessard (TetraTech, Owings Mills, MD) described how assessment of aquatic life uses by States requires an understanding of biological, chemical, habitat, and landscape influences on aquatic biota. Landscape disturbances (e.g., urbanization, agriculture, mining) cause stress on the aquatic ecosystem in six general categories (habitat structure, flow regime, water quality, toxics and bioengineered chemicals, energy sources, and biotic interactions). The Human Disturbance Gradient (HDG) is an approach to quantifying the cumulative effects of multiple stressors, and often accounts for half of the variability in biological response scores. Alterations in flow regime represent one of the six major stressor classes in the HDG, and can be classified among the tiers of aquatic life uses, ranging from natural flows to hydrographs that reflect only extreme flows or inter-basin transfers. (Top) Session 4: Case studies linking hydrology and ecology in lotic systems (Moderator: Jonathan Kennen) The intent of session four was to assemble a series of timely case studies representing the state of the science for investigating the inter-relationships between water development, hydrologic and hydraulic alteration, landscape and geomorphologic disturbance, and aquatic community response. Papers presented during this session provided strong evidence linking changes in aquatic communities (e.g., fish, invertebrates and mussels) to changes in hydrologic conditions resulting from water development, urbanization, hydro-geomorphological modification, and drought. Case studies revealed strong effects of reduced streamflows on biota. David Armstong (USGS, Northborough, MA.) described a cooperative study in Massachusetts which established that surface flow dewatering and lowered groundwater tables resulted in significant losses of important instream habitat (e.g., riffles and woody debris) with concomitant effects on fish and native mussel species. All three case studies in this session that directly quantified fish assemblages, identified fluvial dependant fish species as being highly sensitive to hydrologic stress (i.e., Mary Freeman, USGS, Athens, GA, Allison Roy, EPA, Cincinnati, Ohio, and David Armstrong, USGS, Northborough, MA). Conversely, abundances of habitat generalists increased in response to reduced streamflows in two studies (i.e., Allison Roy, EPA, Cincinnati, Ohio, and David Armstrong, USGS, Northborough, MA). Mary Freeman and Dave Armstong found that endemic and sensitive species also responded negatively to reduced summer streamflow, and increased permitting and use of instream reservoirs significantly altered downstream fish communities. Mary Freeman’s work also indicated that fish species loss appeared to increase as withdrawal permitting increased and Steve Golladay (J.W. Jones Ecological Research Center, Newton, GA.) indicated that mussel species diversity was reduced during low flow events and further losses were associated with increased demand for irrigation water supply. This session further established strong linkages between stormflow alteration due to landscape alteration and ecosystem response, primarily as a result of hydro-geomorphic changes. Christopher Konrad (USGS, Tacoma, WA) and Allison Roy (EPA, Cincinnati, Ohio) presented results indicating that anthropogenic effects such as increases in stormflow and fine sediment loads associated with increases in impervious surface cover resulted in direct and indirect effects on fish and invertebrate communities. According to Allison Roy, increased stormflow and percent of fine sediment significantly predicted sensitive fish species and reduced baseflow predicted lentic tolerant and cosmopolitan fish species. Christopher Konrad’s work established significant patterns between many ecologically relevant streamflow attributes and the structure of benthic assemblages. For example, the fraction of time that streamflow exceeds a ½ year flood and the frequency of peak flows greater then the 10th percentile was directly related to a benthic index of biotic integrity. J. Bruce Wallace (University of Georgia, Athens, GA) emphasized that catastrophic landscape changes as a result of steep slope mining appeared to result in significant modification of the flow regime and stream communities. Bruce Wallace further noted that the loss of biotic diversity in headwater streams was most evident due to increases in sedimentation, changes in temperature and chemical composition, and alterations in flow. Numerous challenges in linking hydrologic alteration to biotic response were recognized by the presenters. Andy Warner (TNC, University Park, PA) discussed the many difficulties that need to be addressed in directly connecting hydrologic change to aquatic assemblage response in altered landscapes due to the complex ways landscape alteration modifies streamflow and how these processes are intricately linked and are directly affected by differing timescales and co-varying stressors. For example, many of hydrologic changes were further complicated by complex issues associated with local geology, land use practices, rainfall, and antecedent conditions. In addition, challenging issues associated with quantifying hydraulic responses of benthic biota were identified. Under most conditions, benthic biota inhabit environments that are difficult to characterize using available techniques. David Hart (Academy of Natural Sciences, Philadelphia, PA) presented some experimental modeling approaches that show great promise in providing direct, quantitative evidence demonstrating how particular ecosystems characteristics respond to specific changes in flow. David Hart suggested that more accurate streamflow models and tools need to be developed to assist with evaluating specific biotic response relationships. It was also recognized that ecologically sustainable water supply strategies and targeted and adaptive management actions need to be developed to preserve river flow for ecosystem support. An inter-disciplinary, science-based framework for assembling data to make environmental flow recommendations and conducting adaptive experimentation was provided by Andy Warner (TNC, University Park, PA). Such recommendations were particularly relevant to dam operations and are highly useful for the regulation of monthly low flows, high flow pulses throughout the year, and floods with targeted inter-annual frequencies that inundate floodplains and promote ecosystem function. The case studies presented during this session provide insight into needed scientific information on streamflow and biological requirements that ultimately improve our understanding of biological responses to altered streamflow conditions. Water-resource managers will benefit from an improved understanding of the mechanisms that drive ecosystem change and the conditions necessary to maintain and protect ecosystem function for future generations. As was stated several times during this session, it’s not necessarily a question of how much water a river needs, but how much can flow regimes be altered before having an appreciable affect on ecosystem integrity. Studies suggested that management practices that promote natural hydrographic patterns are likely to reduce the affects of both stormflow and baseflow alteration on stream biota. Ultimately, a balance needs to be established between water supply processes intended to meet human needs and conservation of biological integrity. (Top) Session 5: Modeling to support water supply planning and decision-making (Moderator: Mary Freeman) Formally or informally, water managers must make predictions as to the ecological and social outcomes of alternative water management strategies, and make decisions based on those predictions in light of possibly competing management objectives. Formalizing the decision process through modeling allows one to specify management objectives and hypothesized linkages between management actions and ecological variables. Models also provide a framework for quantifying the uncertainty inherent in predicting the responses of complex aquatic ecosystems to management alternatives. In this session, five presenters gave overviews of new and developing modeling tools intended to support water supply and dam operation decision making:
Development of model-based tools clearly has the potential to improve the integration of ecological objectives, such as conserving species, assemblages and habitats, with water and river management. Federal agency representatives emphasized the need for better decision tools in Session 1, and the need for developing adaptive approaches to management of rivers used for water supply and hydropower was discussed repeatedly during the workshop. Effective models will be central to supporting decision-making and adaptive management processes. The presentations in this session highlighted a number of issues where research is needed to advance model development, including: identifying the most appropriate biological responses to model; methods for incorporating uncertainty into models; and identifying ranges of acceptability for predicted outcomes. (Top) |