TRANSIT SOURCES OF SALINITY LOADING IN THE SAN RAFAEL RIVER, UPPER COLORADO RIVER BASIN, UTAH

The Colorado River Basin in the western United States covers approximately 155 million acres, of which about 60 million acres are public land administered by the United States Bureau of Land Management. Water quality is an important issue. The Colorado River serves about 7.5 million people in the basin, and through export, the river provides full or supplemental water supply to another 25.4 million people outside the basin. Salt loading from public lands in tributary watersheds feeding the Colorado River originates primarily from Paleozoic and Mesozoic Era sedimentary rocks, which are comprised of different mineral assemblages of sodium-calcium-magnesium sulfates and chlorides with gypsum being one of the dominant minerals. A methodology was created to determine how the salts travel (i.e., major transit source) to the perennial surface water .The study investigated whether salt loading occurred primarily by a surface-runoff process or by a ground-water inflow to-the-stream process. Field data collection included both spatial and temporal measures that focused on the parameters for salt-contributing geologic formations; location, extent, permeability and salinity concentration of soils; geomorphic structures and topographical gradient; ground-water quality and gradient; surface-water quality and discharge, and meteorologic data. Data analysis included exploratory statistical techniques, water quality assessment, and geographic information system (GIS) analysis of salinity source and transport through the display, integration, and geostatistical interpretation of the different parameter map layers. Land managers with knowledge of the salt loading mode in a watershed can more effectively plan and expend to minimize water-quality degradation from public lands. For the study watershed, the San Rafael River, there is evidence of a ground-water inflow to-the-stream process that is occurring during snow melt season and a surface-runoff process during late summer.