Reconciling Environmental and Flood Control Goals on an Arid- Zone River: Case Study of the Limitrophe Region of the Lower Colorado River in the United States and Mexico Edward P. Glenn Æ Kate Hucklebridge Æ Osvel Hinojosa-Huerta Æ Pamela L. Nagler Æ Jennifer Pitt Ó Springer Science+Business Media, LLC 2007 Abstract Arid zone rivers have highly variable flow rates, and flood control projects are needed to protect adjacent property from flood damage. On the other hand, riparian corridors provide important wildlife habitat, especially for birds, and riparian vegetation is adapted to the natural variability in flows on these rivers. While environmental and flood control goals might appear to be at odds, we show that both goals can be accommodated in the Limitrophe Region (the shared border between the United States and Mexico) on the Lower Colorado River. In 1999, the International Boundary and Water Com- mission proposed a routine maintenance project to clear vegetation and create a pilot channel within the Limi- trophe Region to improve flow capacity and delineate the border. In 2000, however, Minute 306 to the international water treaty was adopted, which calls for consideration of environmental effects of IBWC actions. We conducted vegetation and bird surveys within the Limitrophe and found that this river segment is unusu- ally rich in native cottonwood and willow trees, marsh habitat, and resident and migratory birds compared to flow-regulated segments of river. A flood-frequency analysis showed that the existing levee system can easily contain a 100 year flood even if vegetation is not removed, and the existing braided channel system has greater carrying capacity than the proposed pilot channel. Keywords Colorado River Á Limitrophe Á Arid river Á Flood control Introduction The world’s major rivers have been dammed and regu- lated to control floods and to provide water for human needs (Graf 1999; Baron and others 2002). These alter- ations degrade the habitat value of the riparian corridor for native and migratory wildlife (Nilsson and Svedmark 2002). Arid-zone rivers typically have low base flows but extremely variable hydrographs and native vegetation and associated wildlife have adapted to the natural flow regime of these rivers (Poff and others 1997). Flood control projects and water diversions have reduced many of these rivers to channelized conduits, with little over- bank flooding to support riparian habitats (Shafroth and others 2002). As an example, the Lower Colorado River in the Son- oran and Mohave Deserts of North America has been highly regulated by dams and flood control structures (Pataki and others 2005). Little over-bank flooding now E. P. Glenn (&) Environmental Research Laboratory, 2601 East Airport Drive, Tucson, AZ 85706, USA e-mail: eglenn@ag.arizona.edu K. Hucklebridge Department of Civil and Environmental Engineering, University of California, Berkeley, CA 94720, USA O. Hinojosa-Huerta Pronatura Noroeste, Avenue Jalisco 903, entre 9 y 10, San Luis Rio Colorado, Sonora 83440, Mexico P. L. Nagler U. S. Geological Survey, Southwest Biological Science Center, Sonoran Desert Research Station, 125 Biological Sciences East, University of Arizona, Tucson, AZ 85721, USA J. Pitt Environmental Defense, 2334 North Broadway, Boulder, CO 80304, USA 123 Environmental Management DOI 10.1007/s00267-007-9056-4