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Science and Values in River Restoration in the Grand Canyon f There is no restoration or rehabilitation strategy that will improve the status of every riverine resource John C. Schmidt, Robert H. Webb, Richard A. Valdez, G. Richard Marzolf, Lawrence E. Stevens Restoration of riverine ecosys- tems is often stared as a man- agement objective for regu- lated rivers, and floods are one of the most effective tools for accomplish- ing restoration. The National Re- search Council (NRC 1992) argued that ecological restoration means re- turning 'I an ecosystem to a close approximation of its condition prior to disturbance" and that "restoring altered, damaged, or destroyed lakes, rivers, and wetlands is a high-prior- ity task." Effective restoration must be based on a clear definition of the value of riverine resources to soci- ety; on scientific studies that docu- ment ecosystem status and provide an understanding of ecosystem pro- cesses and resource interactions; on scientific studies that predict, mea- sure, and monitor the effectiveness of restoration techniques; and on engineering and economic studies John C. Schmidr (e-mail: jschmidr@cc.usu. edu) is an associate professor in the Depart- menr of Geography and Eanh Resources, Urah Srate University, Logan, UT 84322. Robert H. Webb (e-mail: rhwebb@ sunlpaztcn.wr.usgs.gov) is a research hy. drologist at the Desen Laboratoty, US Geological Survey, Tucson, AZ 85745. Richard A. Valdez (e-mail: valdezra@aol. com) is a senior aquatic ecologist at SWCA Inc., Salt Lake City, UT 841 01. G. Richard Marzolf (e-mail: rmarzolf@usgs.gov) is chief of the Branch of Regional Research, Eastern Region, Water Resources Division. US Geological Survey, Reston, VA 21092. Lawrence E. Stevens (e-mail: lstevens@gcrs. uc.usbr.gov) is an ecologist at the Grand Canyon Monitoring and Research Center, Flagstaff, AZ 86001. @ 1998 American Institute of Biological Sciences. September 1998 If flooding is crucial to the recovery of flood-adapted species but the absence of floods is crucial to the conservation of terrestrial endangered species in new habitats, then managers face an intractable dilemma that evaluate societal costs and ben- efits of restoration. In the case of some large rivers, restoration is not a self-evident goal. Indeed, restoration may be impos- sible; a more feasible goal may be rehabiliration of some ecosystem components and processes in parts of the river (Gore and Shields 1995, Kondolf and Wilcock 1996, Stanford et al. 1996). In other cases, the ap- propriate decision may be to do noth- ing. The decision to manipulate eco- system processes and components involves not only a scientific judg- ment thar a restored or rehabilitated condition is achievable, but also a value judgment that this condition is more desirable than the status quo. These judgments involve prioritiz- ing different river resources, and they should be based on extensive and continuing public debate. In this article, we examine the appropriate role of science in deter- mining whether or not to restore or rehabilirate the Colorado River in the Grand Canyon by summarizing studies carried out by numerous agen- cies, universities, and consulting firms since 1983. This reach of the Colorado extends 425 km between Glen Canyon Dam and Lake Mead reservoir (Figure 1). Efforts to ma- nipulate ecosystem processes and components in the Grand Canyon have received widespread public at- tention, such as the 1996 controlled flood released from Glen Canyon Dam and the proposal to drain Lake Powell reservoir. The importance of the river and the dam The Grand Canyon is the most fa- mous and extensive canyon in the world; approximately 5 million people visit Gtand Canyon National Park each year. Whitewater recre- ation on the Colorado River is inter- nationally renowned, and 25,000 people travel the river through the Grand Canyon annually. This seg- ment of the Colorado River is a fed- erally designated critical habitat for two endemic endangered fish: the razorback sucker (Xyrauchen texa- nus) and the humpback chub (Gila cypha). Riparian vegetation along the Co Iota do River in the Grand Canyon is a fedetally proposed criri- cal habitat for the endangered Kanab ambersnail (Oxyloma haydeni kana- bensis) and the southwestern willow flycatcher (Empidonax traillii). The 735