Temporal river channel changes in the Gila Box Riparian National Conservation Area, Arizona, USA

Abstract

Human activities have led to the serious decline and degradation of riparian areas in the Southwestern United States. Areas in Arizona, such as the Gila Box Riparian National Conservation Area, are protected to conserve and restore these unique ecosystems. This study investigated temporal change in the channel form and sinuosity of the Gila River in the Gila Box Riparian National Conservation Area. Specifically, cross sections were measured in 1994, 2001, and 2008 to evaluate changes in channel form. Aerial photographs between 1935 and 2007 were also compared to assess changes in channel sinuosity. Based on cross-sectional measurements, the thalweg was significantly deeper in 1994 than in 2001 and 2008, while width-depth ratios were significantly lower in 2008 than in 1994 and 2001. These measurements indicate that the channel is stabilizing. Sinuosity changed only slightly. Overall, climate patterns that cause large flood events appear to have been the major influence on the channel form. Still, exclusion of livestock and all-terrain vehicles, which increased vegetation in the riparian areas, also appeared to mitigate flood impacts. The stream channel appears to have been more resilient to the impacts of the flood in 2005, when vegetation was better established, than to the flood of 1993, when past management influences were still lingering.

Keywords:

• stream channel
• conservation
• riparian area
• cross sections
• floods
• semi-arid regions
• Gila Box

Acknowledgements

The authors extend their thanks and appreciation to Rich Law, Christopher E. Morris, Andrew Brischke and Shane Clark for their assistance and hard work in the field. In addition, the authors are indebted to Dr Suzanne Fouty and Marlin Whetten for their meticulous data collection. The authors also gratefully acknowledge the support and advice of McKinley-Ben Miller, Bridget Olberg, Gwen Dominguez, Heidi Blasius, Diane Drobka, Marlo Draper, Scott Cooke, Tom Schnell, Larry Thrasher, Kim McReynolds, Tasha Layton, George Ruyle, Dan Quintana and Bill Brandau. Finally, we would like to thank the Renewable Resources Extension Act for providing the financial support for the field measurements of 2008.