Challenges and opportunities in restoring the geophysical template of native fish habitat in the U.S. Southwest and Northern Mexico

Authors: John C. Schmidt

Year: 2013 (xlv)

Abstract

The Rio Grande and the Colorado River carry snowmelt from the middle and southern Rocky Mountains across the Colorado Plateau and Basin and Range. Headwater tributaries are typically gravel bed streams with a simple and predictable annual spring flood, but southern tributaries transport very large loads of sand and mud and have highly variable flow regimes and a summer/fall flood season in response to the North American monsoon. The native fish of the region evolved life history strategies that took advantage of the distinctive flow regimes, sediment transport characteristics, temperature regimes, and geomorphology of these rivers. Today, the geophysical characteristics that made these rivers unique have been transformed: flow and temperature regimes have been greatly altered, much of the fine sediment is now trapped in reservoirs, and the sediment mass balance that drives channel change has been perturbed into deficit or surplus. In response, channels have incised their beds in some deficit reaches and narrowed and simplified elsewhere. Significant investment is now underway in some places to reverse these transformations of flow regime and habitat characteristics, but the economic and political costs are substantial. At the same time, climate change and continued growth in human use of water is challenging the existing engineering infrastructure and political agreements that allocate water among states and countries. Today’s nexus of impending water shortage, reconsideration of water distribution agreements, and limited financial resources with which to apply to habitat restoration will provide challenges and opportunities in developing strategies to restore the geophysical template of threatened and endangered fish habitat.