Report availability: Portable Document Format (PDF).
Few scientific data have been collected on pre-dam conditions of the Colorado River corridor through Grand Canyon National Park. Using historical diaries, interviews with pre-dam river runners (referred to as the “Old Timers”), and historical scientific data and observations, we compiled anecdotal information on environmental change in Grand Canyon. The most significant changes are the: lowering of water temperature in the river, near-elimination of heavily sediment-laden flows, erosion of sand bars, invasion of non-native tamarisk trees, reduction in driftwood, development of marshes, increase in non-native fish at the expense of native fishes, and increase in water bird populations. In addition, few debris flows were observed before closure of Glen Canyon Dam, which might suggests that the frequency of debris flows in Grand Canyon has increased. Other possible changes include decreases in bat populations and increases in swallow and bighorn sheep populations, although the evidence is anecdotal and inconclusive. These results provide a perspective on managing the Colorado River that may allow differentiation of the effects of Glen Canyon Dam from other processes of change.
ABSTRACT
INTRODUCTION
PURPOSE AND SCOPE
Units and Nomenclature
Acknowledgments
SOURCES OF INFORMATION
The Old Timers
Other Pre-Dam or 1960s River Runners
Diaries and Other Accounts
Repeat Photography
Interviews and Interpretation of Observations
SPECIFIC CHANGES OBSERVED IN GRAND CANYON
Aesthetics in Grand Canyon
Water Temperature
Geomorphology
Debris Flows and Floods
Rockfalls
Rapids
Sand Bars
Channel Bars
Driftwood
Riparian and Desert Vegetation
Riparian Vegetation
Marshes
Desert Vegetation
Terrestrial Animals
Birds and Bats
Insects
Beavers
Otters
Large Mammals
Fishes
CONCLUSIONS
REFERENCES CITED
For additional information write:
Regional Research Hydrologist
U.S. Geological Survey
345 Middlefield Road
Menlo Park, CA 94025
Copies of this report can be purchased from:
U.S. Geological Survey
Information Services
Building 810
Box 25286, Federal Center
Denver, CO 80225-0286
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