A new USGS report address the "continuing debate exists on whether and how controlled releases from Glen Canyon Dam, ...are impacting rates of site erosion, artifact transport, and the preservation of archeological resources" in the Grand Canyon National Park.
The authors warn that "Continued erosion of archeological sites threatens both the archeological resources and our future ability to study evidence of past cultural habitation."
In conclusion they found that "distribution and magnitudes of surface change are specific to each site and that a thorough understanding of the geomorphology, weather, and sand supply is requisite for a complete understanding of the data."
And as many studies discover, more work is needed.
Ref: Collins, B.D., Minasian, D., and Kayen, R., 2009, Topographic change detection at select archeological sites in Grand Canyon National Park, Arizona, 2006-2007: U.S. Geological Survey Scientific Investigations Report 2009-5116, 58 p. [http://pubs.usgs.gov/sir/2009/5116/].