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Watershed-scale Assessment of Salinity Loads in the Upper Colorado River Basin
Project Chief: Terry Kenney, USGS Salt Lake City, Utah
The economic effects of increased salinity in the Colorado River have prompted a number of water-quality related legislative actions. In particular, the Colorado Salinity Control Act and its amendments provide the means and authority for Federal agencies to implement or assist local entities with projects that mitigate the discharge of dissolved-solids in the Colorado River. Salinity in streams of the Upper Colorado River Basin (UCRB), as measured by total dissolved-solids (TDS) concentration and load, is variable. Geologic and vegetation characteristics, land use practices, and precipitation are some of the sources and controlling mechanisms in the production and delivery of waters high in TDS to rivers and streams. Optimal management and (or) mitigation of salinity requires an improved understanding of the spatial distribution of salinity sources, load accumulation, and transport mechanisms.
The principle goal of the proposed project is to calibrate a SPARROW model to better understand and estimate the sources, transport, and accumulation of dissolved-solids load throughout the UCRB. Once calibrated, the TDS SPARROW model will provide estimates of median annual TDS concentration and load for all subwatersheds, catchments between 10,000 and 40,000 acres, within the basin.
RELEVANCE AND BENEFITS
The proposed project will provide statistically based estimates of dissolved-solids loading sources and transport for reaches at the subwatershed level throughout the UCRB. The estimates and associated uncertainties obtained from the calibrated dissolved solids SPARROW model will provide guidance for future salinity related data collection and assessment. Up to date load statistics for more than 180 monitored locations in the UCRB will be computed. A web-accessible GIS data base will be developed and populated with input and output data from the proposed study.
High-resolution GIS data coverages specific to salinity sources, and transport mechanisms for the UCRB will be acquired. Some unique coverages will be created to help examine the influences of anthropogenic land-use practices. A network of monitored and unmonitored stream reaches complimentary to the subwatershed level of drainage basin delineation will be defined. Watershed attributes for each of these reaches will be computed from the various GIS coverages. Historic streamflow and salinity data will be used to compute median annual TDS loads for monitored reaches in the UCRB. Streamflow data also will be used to estimate median annual discharges for the unmonitored reaches. Monitored reach TDS load data together with various combinations of the computed watershed attributes will be examined statistically through a non-linear least squares model calibration. Along with estimates of median annual TDS loads for the UCRB, the model calibration will provide insight into TDS sources, transport mechanisms, and losses throughout the UCRB. A web-accessible GIS database will be developed for all model input and output data.
A technically reviewed USGS Scientific Investigations Report will be published documenting the methods and procedures used in developing the TDS SPARROW model of the UCRB. All model input data along with model output will be contained in a web accessible GIS database.