Understanding sinusoidal flcutuations in the salinity in the Colorado River below Glen Canyon Dam, 1970-2016
The salinity of the Colorado River below Glen Canyon Dam has demonstrated three long-term sinusoidal fluctuations between 1975 and 2016. At Lees Ferry, salinity concentrations have peaked in 1979, 1991, and 2005; with troughs in 1986, 1999, and 2012 (figure 1). Similar, though temporally displaced, patterns are apparent in river salinity concentrations at locations downstream to Morelos Dam. The cause of these 10- to 15-year salinity cycles have been hypothesized by other researchers to be related to geochemical reactions within Lake Powell, precipitation patterns, and drought. A rigorous investigation into the variables controlling the sinusoidal salinity trend, however, has yet to be completed. This proposed work would utilizes statistical methods in conjunction with newly-available data to better understand if the observed salinity fluctuations are a function of climate variables.
Need and Benefit
Minute 242 states that the water delivered to Mexico upstream of Morelos Dam must have an average annual salinity of no more than 115 ppm (± 30 ppm) over the annual average salinity of Colorado River waters which arrive at Imperial Dam (International Boundary and Water Commission, 1973). To meet the binational agreements on the volume and salinity of Colorado River water delivered to Mexico, the correct volume of groundwater must be added or withheld from the river just upstream of Morelos Dam (located 26.1 river miles downstream of Imperial Dam). In order for Reclamation operators to optimize this volume of groundwater, the salinity of the river at Imperial Dam from the current month into the future must be estimated. The salinity of the river at Imperial Dam, however, fluctuates monthly, annually, and on longer-term time scales, resulting in uncertainty in the volume calculations. A better understanding of the factors controlling the observed long-term sinusoidal fluctuations would provide Reclamation with a better understanding of likely future salinity concentrations for the river below Glen Canyon Dam.
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Bureau of Reclamation Review
The following documents were reviewed by experts in fields relating to this project's study and findings. The results were determined to be achieved using valid means.
Investigation of recent decadal-scale cyclical fluctuations in salinity in the lower Colorado (final, PDF, 16.7MB)
By Fred D. Tillman,Alissa L. Coes,David W. Anning,Jon P. Mason, and Tyler B. Coplen
Report completed on March 07, 2019