SYNOPTIC SAMPLING AND SALINITY CHARACTERIZATION OF THE COLORADO RIVER AND PERENNIAL TRIBUTARIES BETWEEN CISCO, UTAH AND LAKE POWELL

Salinity loads in the Colorado River Basin are a concern due to adverse impacts on population, soil in irrigated areas, natural resources, and regional economics. The primary goal of the Colorado River Basin Salinity Control Program and other agencies is the cost-effective reduction of salinity in the Colorado River. The Colorado River between Cisco, Utah and Lake Powell traverses an area of saline sedimentary formations and evaporite deposits. The purpose of this study was to assess the magnitude of TDS loading in the Colorado River and identify potential sources of the salinity. Four synoptic sampling events were used to quantify salinity loading and to evaluate the occurrence and impacts of natural and anthropogenic sources. The average TDS load from the Green River into the Colorado River at the confluence was 22.2%, while the TDS loading from the remaining tributaries was less than 0.33%. Measured specific-conductance values of tributaries entering the upper 12 km reach were up to 16 times greater than measurements in the Colorado River below each of the tributaries. Salt Wash was the only tributary other than the Green River that may have contributed observable TDS loading to the main stem of the Colorado River; however, the results are within estimated uncertainty. Chloride and bromide concentrations and stable-isotope values support these conclusions, which show that TDS loading is negligible and within the measurement and analytical uncertainty, with the exception of the Green River. Our results indicate that the Paradox Formation, local salt anticlines, the J. L. Eddy Intrepid potash evaporation ponds, and the perennial tributaries are not major sources of salinity to the Colorado River within the studied reach and the Green River is the only source of salinity loading at this time. However, significant changes to the hydrologic system in the future due to anthropogenic activities or perhaps climate change may alter groundwater flow paths and TDS loading.