Four members of our Cadillac Desert group - Will Graf, Ellen Wohl, Tushar Sinha, and John L. Sabo - just published this paper in Water Resources Research.
Download Sedimentation_Sustainability_Western_Reservoirs
Looks like things are better than we thought.
Abstract
Reservoirs are sustainable only as long as they offer sufficient water storage space to achieve
their design objectives. Life expectancy related to sedimentation is a measure of reservoir sustainability. We used data from the Army Corps of Engineers, U.S. Bureau of Reclamation, and U.S. Geological Survey (Reservoir Sedimentation Survey Information System II (RESIS II) to explore the sustainability of American reservoirs. Sustainability varied by region, with the longest life expectancies in New England and the Tennessee Valley and the shortest in the interior west. In the Missouri and Colorado River basins, sedimentation and rates of loss of reservoir storage capacity were highly variable in time and space. In the Missouri River basin, the larger reservoirs had the longest life expectancies, with some exceeding 1000 years, while smaller reservoirs in the basin had the shortest life expectancies. In the Colorado River basin at the site of Glen Canyon Da, sediment inflow varied with time, declining by half beginning in 1942 becuase of hydroclimate and upstream geomorphic changes. Because of these changes, the estimated life expectancy of Lake Powell increased from 300 to 700 years. Future surprise changes in sedimentation delivery and reservoir filling area are expected. Even though large western reservoirs were built within a limted period. their demise will not be synchronous becuase of varying sedimentation rates. Popular literature has incorrectlyemphasized the possibility of rapid, synchronous loss of reservoir storage capacity and underestimated the sustainability of water control infrastructure.
Click on the figure (Annul Reservoir Storage Loss) to enlarge it.
"Rivers are roads which move, and which carry us whither we desire to go." ~Blaise Pascal
This is going to infuriate James Powell, author of "Dead Pool". He claims that Lake Powell will fill within the lifetimes of many of us living in the SW US.
http://www.orionmagazine.org/index.php/articles/article/5617/
"All things being equal, to fill a Lake Powell of 2 million acre-feet with sediment will take not 700 years but about 55 years."
A very bold claim by Mr. Powell (no relation to the Lake's namesake). Even bolder, Powell uses no supporting mathematical calculations, despite his background and experience as Executive Director of the National Physical Science Consortium. Instead his goal is to sell books, and so, he throws out a number that is sure to catch the book shopper's eye. In researching this further, I found the publicly available, analysis and math:
http://library.nau.edu/speccoll/images/text/pdf/15332.pdf
and now this PDF link your blog offers, again shows people using math and science, to estimate Lake Powell's useful lifetime, to be....700 years.
As the PDF details, most of the Missouri River Basins dams are likewise in this for the long haul. For those who are somewhat disappointed in the findings of this study, I wonder if you also secretly root against levees, bridges, buildings, and all manners of infrastructure upon which our survival is dependent.
Posted by: BxCapricorn | Friday, 24 December 2010 at 04:05 PM