Dam removal continues to garner attention as a potential river restoration tool. The increasing possibility of dam removal through the FERC relicensing process, as well as through federal and state agency actions, makes a critical examination of the ecological benefits and costs essential. This paper reviews the possible ecological impacts of dam removal using various case studies. Restoration of an unregulated flow regime has resulted in increased biotic diversity through the enhancement of preferred spawning grounds or other habitat. By returning riverine conditions and sediment transport to formerly impounded areas, riffle/pool sequences, gravel, and cobble have reappeared, along with increases in biotic diversity. Fish passage has been another benefit of dam removal. However, the disappearance of the reservoir may also affect certain publicly desirable fisheries. Short-term ecological impacts of dam removal include an increased sediment load that may cause suffocation and abrasion to various biota and habitats. However, several recorded dam removals have suggested that the increased sediment load caused by removal should be a short-term effect. Pre-removal studies for contaminated sediment may be effective at controlling toxic release problems. Although monitoring and dam removal studies are limited, a continued examination of the possible ecological impacts is important for quantifying the resistance and resilience of aquatic ecosystems. Dam removal, although controversial, is an important alternative for river restoration.

As part of the Glen Canyon Environmental Studies, we have developed a discharge model that routes daily discharge waves released from Glen Canyon Dam to Diamond Creek, 386 km downstream. Owing to the length of the diurnal discharge wave and the sparseness of the available topographic data, the latter were averaged over the entire length of the system. Terms too small to be significant in the momentum equation were identified by scaling arguments based on data from past dam releases and on channel hydraulic geometry. Channel friction results primarily from form drag on large topographic elements and from variations in cross-sectional area and flow depth, rather than bed roughness, producing a stage-dependent friction that is not well represented by a constant value of standard channel roughness parameters, such as Manning's n. Channel friction as a function of stage was determined from field data available at high discharge and intermediate discharge and by using simple kinematic wave theory together with wave speed measurements to determine channel friction at low discharge. Model predictions of wave speed and shape agree well with data from five streamflow gaging stations and 42 stage gaging stations located along this segment of the Colorado River.

One of the most popular models for simulating the effect of regulated streamflow on fish habitat is the Instream Flow Incremental Methodology (IFIM). This model was developed by the Instream Flow Group (IFG) and is composed of components which simulate water temperature, water quality, and physical habitat. The physical habitat component (PHABSIM), however, is so frequently the only p art of the method used that PHABSIM and IFIM are often confused.
PHABSIM (and therefore IFIM) is based on several assumptions which are not always met. Tests relating fish biomass to amounts of habitat based on these assumptions have given inconsistent results. Because IFIM has become so widely used for water management decisions (it is now a legal requirement in Idaho, California, Colorado, Washington, and Oregon and is receiving increasing use in Canada and New Zealand) there is a danger of extensive damage to natural resources if its predictions are inaccurate. The purpose of our paper is to examine the validity of PHABSIM's assumptions, to review the accuracy of PHABSIM's predictions, and to discuss other methods that have been used for determining instream flow needs in New Zealand.

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.

The most often heard claims in support of large scale hydroelectric development are: (1) hydropower generation is 'clean', (2) water flowing freely to the ocean is 'wasted', and (3) local residents (usually aboriginals) will benefit from the development. These three claims are critically examined using case histories from Canada and elsewhere in the world. The critique is based mainly on journal articles and books, material that is readily available to the public, and reveals that the three claims cannot be supported by fact. Nevertheless, large scale hydroelectric development continues on a worldwide basis. The public needs to be well informed about the environmental and social consequences of large scale hydroelectic development in order to narrow the gap between its wishes for environmental protection and what is really occurring.

Efforts by a citizen's group, Putah Creek Council, to improve the flow regime of a California stream for ecosystem, aesthetic, recreational, educational, and research purposes led to a successful court trial in which fish conservation played a key role. A major issue around which the trial revolved was the proper interoperation of section (5937) of the California Fish and game Code, which states that fish must be maintained in "good condition" below a dam. We defined good condition to mean there had to be healthy individual fish in healthy populations that were part of healthy biotic communities. This definition resulted in a conceptual model for instream flows for the creek that favored native resident and anadromous fishes. The stream flow recommendations from this model had four components: living space flows for the entire creek, resident native fish spawning and rearing flows, anadromous fish flows, and habitat maintenance flows. The trial judge, in attempting to balance competing demands for the water, ordered the implementation of only the first two recommendations. The order has been appealed by the water interests, but regardless of the final outcome, the court's decision reflects the growing public interest in protecting streams, the need for innovative use of existing legal tools to try and protect aquatic resources, and the importance of biological information in developing flow recommendations for complex fish assemblages.

This paper examines the effects of dam construction and operation in the Columbia River Basin on salmon populations. While the hydrograph of the Columbia River has been significantly impacted by dams, the seasonality of regulated flow on the Snake River has been less affected. The Snake River storage has been used for agricultural diversion while the Columbia has been for electrical generation. The reservoir system has effects on flow velocities, water chemistry (nitrogen supersaturation), habitat availability and reliability, and stream temperatures. Dams block about one third of the Columbia River watershed to access by anadromous fish.
Effects of Dams on Salmon;
Fish kills occur as a result of several characteristics of dams. Bruising, descailing, and stress caused by by-pass facilities; susceptibility to prey following delivery from by-pass to outfall; estuary damage; effects on the homing ability of fish; limited success in fish use of by-pass facilities. The effect of migration speed on smolt survival is uncertain but assumed to have an impact. More research is necessary.
Mitigation of Dam's Effects on Salmon:
Seven measures for mitigation of dams' effects on salmon are discussed
1. Fish passage facilities 2. Predator control 3. Transportation 4. Spill 5. Flow augmentation 6. Reservoir drawdown 7. Dam removal.

We studied the role of technical clarity in successful multi-party negotiations. Our investigations involved in-depth interviews with individuals who were the principal participants in six consultations conducted under the Federal Energy Regulatory Commission's (FERC) hydroelectric power project licensing process. Technical clarity was especially important in the cases we studied because they concerned questions that were science-based. The principal issues in the six cases were fish passage, instream flow for fish habitat, and entrainment of fish in hydropower turbines. We concluded that technical clarity was one of the most critical elements in these conflicts. The most successful negotiations were marked by a shared understanding of technical issues among the parties.

Utility companies release water to mitigate the effects of hydroelectric projects on fish habitats. Utility companies, government agencies, and research communities in Canada, the United States, Europe, New Zealand, and Australia were surveyed as part of a Canadian Electrical Association study to evaluate the effectiveness of water release as a mitigation. Respondents identified only 28 projects in which water was released specifically to protect fish habitats. Fewer than half of these projects (12) were judged as being effective. Six case histories with preimpact assessment and postimpact monitoring were reviewed. In four cases fish habitat or fish populations or both were maintained; in two cases they were not. The effectiveness of water release differed among rivers and fish species, and was greatest when designed to meet the habitat requirements of each life-history stage. A review of the literature did not support the theory that a particular fraction of the mean annual flow provides the best fish habitat. Although smaller changes in the flow regime had smaller effects, increasing minimum flows above those historically observed did not necessarily increase fish production.

The economic value of water that flows over a scenic waterfall was measured using the contingent valuation method. Allowing both the value per day and trips to vary with flow resulted in values per cubic feet per second (cfs) of flow ranging from $1000 for the first 100 cfs to $300 for additional flow at 550cfs. Accounting for the value of foregone hydropower, the economically optimum flow just considering aesthetics of the falls was about 235-240 cfs during the main recreation season. Monthly analysis during the recreation season suggested that optimum flows varied from 165-175 cfs during the early and later recreation season to 500-600 cfs during the four prime recreation months. These flows were three to ten times greater than current minimum flows. Recommendations are made that the Federal Energy Regulatory Commission should use non-market valuation techniques such as contingent valuation surveys to ensure that environmental values are given equal consideration with power values in dam licensing and relicensing decisions.