Instream Flows for Recreation: A Handbook on Concepts and Research Methods

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Exploring the Flow - Environment Relationship In Grand Canyon The Colorado River in Grand Canyon provides a third example of how an altered flow regime can have significant impacts on the river environment. Glen Canyon Dam, just upstream of the Canyon, was authorized on the basis of its ability to control floods, deliver water for irrigation, and generate hydroelectric power (particularly peaking power). In meeting these goals, however, dam operations apparently affected several natural and recreation resources downstream. In recent years, environmental advocates have become increasingly concerned about those effects and federal agencies are in the process of completing a series of comprehensive studies to quantify what is happening as a result of current dam operation, as well as what is likely to happen in the future under different operating regimes. Costing several million dollars, the size of the effort helps suggest the complex and controversial nature of the issues. There may not be any single or simple flow regime that will provide for all desired outputs. Some of the more interesting natural resource questions being explored in the studies include: ❑ Are daily flow fluctuations (to produce peaking hydropower) contributing to beach erosion? Has the loss of spring floods created a situation where beaches are no longer rejuvenated? Can periodic high flow releases be designed to optimize beach rejuvenation? C ❑ How have the less turbid waters from the dam affected aquatic species? Is the introduced trout fishery (which survives because of the colder temperatures) outcompeting native fish species such as humpback chub? Are the fluctuating flows from the dam stranding fish? ❑ Have the newly established fisheries had effects on other wildlife in the Grand Canyon? For example, bald eagles may benefit from the new trout fishery. ❑ Has the loss of spring floods and associated deposition allowed tributaries to expose and erode significant archeological sites? changes from Glen Canyon Dam have had a number of implications for the river environment. Grand Canyon studies have also explored flow needs for rafting safety and challenge, and a comprehensive Environmental Impact Statement on how to operate the dam will include a variety of alternatives that integrate different flow needs for different resources. However, the effort is particularly noteworthy because of the extensive work on how flow changes have affected the long -term environment which is also critical for high quality recreation. 27