Hydropower dams play a critical role in the health of river ecosystems throughout the United States, and hundreds of these dams will be relicensed by the Federal Energy Regulatory Commission (FERC) in the coming years. Such licenses lock in the operating and environmental protection requirements of such dams for periods of up to 50 years. Given the complex, dynamic nature of river ecosystems, as well as the impacts of climate change, there is pervasive scientific uncertainty about how to best manage dams for power production while protecting and enhancing environmental values such as water quality and fisheries. Unless dams are managed adaptively, with licenses that provide pathways for gathering and applying new knowledge and responding to changing conditions, we run the risk of locking in mistaken approaches and stymieing environmental improvements on our rivers for the next half century.

Many river restoration projects are focusing on restoring environmental flow regimes to improve ecosystem health in rivers that have been developed for water supply, hydropower generation, flood control, navigation, and other purposes. In efforts to prevent future ecological damage, water supply planners in some parts of the world are beginning to address the water needs of river ecosystems proactively by reserving some portion of river flows for ecosystem support. These restorative and protective actions require development of scientifically credible estimates of environmental flow needs. This paper describes an adaptive, inter-disciplinary, science-based process for developing environmental flow recommendations. It has been designed for use in a variety of water management activities, including flow restoration projects, and can be tailored according to available time and resources for determining environmental flow needs. The five-step process includes: (1) an orientation meeting; (2) a literature review and summary of existing knowledge about flow-dependent biota and ecological processes of concern; (3) a workshop to develop ecological objectives and initial flow recommendations, and identify key information gaps; (4) implementation of the flow recommendations on a trial basis to test hypotheses and reduce uncertainties; and (5) monitoring system response and conducting further research as warranted. A range of recommended flows are developed for the low flows in each month, high flow pulses throughout the year, and floods with targeted inter-annual frequencies. We describe an application of this process to the Savannah River, in which the resultant flow recommendations were incorporated into a comprehensive river basin planning process conducted by the Corps of Engineers, and used to initiate the adaptive management of Thurmond Dam.

Adaptive management is appraised as a policy implementation approach by examining its conceptual, technical, equity, and practical strengths and limitations. Three conclusions are drawn: (1) Adaptive management has been more influential, so far, as an idea than as a practical means of gaining insight into the behavior of ecosystems utilized and inhabited by humans. (2) Adaptive management should be used only after disputing parties have agreed to an agenda of questions to be answered using the adaptive approach; this is not how the approach has been used. (3) Efficient, effective social learning, of the kind facilitated by adaptive management, is likely to be of strategic importance in governing ecosystems as humanity searches for a sustainable economy.

This paper provides an example of a practical integration of probabilistic policy analysis and multi-stakeholder decision methods at a hydroelectric facility in British Columbia, Canada. A structured decision-making framework utilizing the probabilistic judgments of experts, a decision tree, and a Monte Carlo simulation provided insight to a decision to implement an experimental flow release program. The technical evaluation of the expected costs and benefits of the program were integrated into the multi-stakeholder decision process. The framework assessed the magnitude of the uncertainty, its potential to affect water management decisions, the predictive ability of the experiment, the value of the expected costs and benefits, and the preferences of stakeholders for alternative outcomes. As a result of the analysis, the initial experimental design was revised, and a multi-stakeholder group reached consensus on a program of experimental flow releases to test the response of salmonids to flow. The approach treats adaptive management as a policy alternative within a broader decision problem, and it demonstrates the utility of combining expert judgment processes and stakeholder values with adaptive management to improve the likelihood that proposed experimental approaches will deliver net value to society.

The concept of adaptive management has, for many ecologists, become a foundation of effective environmental management for initiatives characterized by high levels of ecological uncertainty. Yet problems associated with its application are legendary, and many of the initiatives promoted as examples of adaptive management appear to lack essential characteristics of the approach. In this paper we propose explicit criteria for helping managers and decision makers to determine the appropriateness of either passive or active adaptivemanagementstrategies as a response to ecological uncertainty in environmental management. Four categories of criteria-dealing with spatial and temporal scale, dimensions of uncertainty, the evaluation of costs and benefits, and institutional and stakeholder support- are defined and applied using hypothetical yet realistic case-study scenarios that illustrate a range of environmental management problems. We conclude that many of the issues facing adaptive management may have less to do with the approach itself than with the indiscriminate choice of contexts within which it is now applied.

Large catchment basisns may be viewed as ecosystems in which natural and cultural attributes interact. Contemporary river ecology emphasizes the four-dimensional nature of the river continuum and the propensity for riverine biodiversity and bioproduction to be largely controlled by habitat maintenance processes, such as cut and fill alluviation mediated by catchment water yield. Stream regulation reduces annual flow amplitude, increases baseflow variation and changes temperature, mass transport and other important biophysical patterns and attributes. As a result, ecological connectivity between upstream and downstream reaches and between channels, ground waters and floodplains may be severed. Native biodiversity and bioproduction usually are reduced or changed and non-native biota proliferate.
Regulated rivers regain normative attributes as distance from the dam increases and in relation to the mode of dam operation. Therefore, dam operations can be used to restructure altered temperature and flow regimes which, coupled with pollution abatement and management of non-native biota, enables natural processes to restore damaged habitats along the river's course. The expectation is recovery of depressed populations of native species. The protocol requires: restoring peak flows needed to reconnect and periodically reconfigure channel and floodplain habitats; stabilizing base-flows to revitalize food-webs in shallow water habitats; reconstituting seasonal temperature patterns (e.g. by construction of depth selective withdrawal systems on storage dams); maximizing dam passage to allow recovery of fish metapopulation structure; instituting a management belief system that relies upon natural habitat restoration and maintenance, as opposed to artificial propagation, installation of artificial instream structures (river engineering) and predator control; and, practising adaptive ecosystem management.
Our restoration protocol should be viewed as an hypothesis derived from the principles of river ecology. Although restoration to aboriginal state is not expected, nor necessarily desired, recovering some large portion of the lost capacity to sustain native biodiversity and bioproduction is possible by management for processes that maintain normative habitat conditions. The cost may be less than expected because the river can do most of the work.

1. Seventy-two per cent of the Flathead River catchment (22,241 km^2) is federally designated and protected as wilderness or national park. Thus, the catchment remains one of the more pristine areas of its size in the temperate latitudes of the world.
2. Discharge in the downstream reaches of the river system outside the protected areas is regulated by three dams for flood control and hydropower production. These dams have blocked natural migration of native fish from Flathead Lake (496 km^2) and isolated populations in sub-catchments. Temperature and erratic flow fluctuations have altered phenologies of river zoobenthos and fish, and in dam tailwaters aquatic biodiversity is drastically reduced in comparison to unregulated segments.
3. Ecological problems caused by changing water quality conditions, altered land-use patterns and introductions of no-native biota are interactive with the impacts of stream and lake level regulation , thereby emphasizing the complexity of this river-lake ecosystem.
4. Mitigation of the effects of regulation is compromised by differing management priorities and regulatory mandates of County, State, Tribal, and Federal agencies responsible for natural resource management within the catchment. Moreover, economic and ecological interests outside the Flathead influence the way flows are regulated within the catchment.
5. The most pervasive influences of stream and lake regulation can be ameliorated by retrofitting the hypolimnial release dam with a selective depth outlet structure to allow temperature control, and by controlling changes in flow rates to create a more natural hydrograph in the tailwaters of the large dams. Allowing fish passage by construction of fish ladders is problematic because upstream passage will commingle native species that were isolated upstream by construction of the dams with non-native species that were introduced subsequently below the dams. Cascading food web interactions elicited by invasions of non-native biota may offset any advantage to native stocks gained by passage and/or augmentation with hatchery stocks.
6. Mitigation must be adaptive in the sense that unanticipated effects and interactions with other management objectives can be documented and alternative action can be implemented.
7. This case history of the effects of stream and lake level regulation, and the approaches to management reviewed in this paper, should serve as a lesson in river conservation.

1. This paper introduces a new approach for setting streamflow-based river ecosystem management targets and this method is called the 'Range of Variability Approach' (RVA). The proposed approach derives from aquatic ecology theory concerning the critical role of hydrological variabliity, and associated characteristics of timing, frequency, duration, and rates of change, in sustaining aquatic ecosystems. The method is intended for application on rivers wherein the conservation of native aquatic biodiversity and protection of natural ecosystem functions are primary river management objectives.
2. The RVA uses as its starting point either measured or synthesized daily streamflow values from a period during which human pertubations to the hydrological regime were negligible. This streamflow record is then characterized using thirty-two different hydrological parameters, using methods defined in Richter et al. (1996). Using the RVA range of variation in each of the thirty-two parameters, e.g. the values at +/- 1 standard deviation from the mean or the twenty-fifth to seventy-fifth percentile range, are selected as initial flow management targets.
3. The RVA targets are intended to guide the design of river management strategies (e.g. reservoir operations rules, catchment restoration) that will lead to attainment of these targets on an annual basis. The RVA will enable reiver manageres to define and adopt readily interim management targets before conclusive, long-term ecosystem reesearch results are available. The RVA targets and mangement strategies should be adaptively refined as suggested by research results and as needed to sustain native aquatic ecosystem biodiversity and integrity.

Conserving river biota will require innovative approaches that foster and utilize scientific understanding of ecosystem responses to alternative river-management scenarios. We describe ecological and societal issues involved in flow management of a section of the Tallapoosa River (Alabama, U.S.A.) in which a species-rich native fauna is adversely affected by flow alteration by an upstream hydropower dam.

This essay highlights the necessity for the establishment of new instream flow standards, as well as the revision of existing standards. This presents a problem since the standards themselves cannot be defined scientifically. The authors recommend the implementation of an adaptive management program involving three elements; setting conservative interim standards; establishment of an adequate monitoring program involving active manipulation flows; and establishment of effective procedure to revise the interim standards. The program details should vary from case to case, especially for species like salmon, where adult populations depend on a myriad of factors, not simply instream flows. Examples of current and previous uses of these standards are given.