A load modeling approach for evaluating selenium stream standards compliance

This research involves the demonstration of water quality modeling methods for assessing management alternatives for in-river standards compliance in a basin with impaired water quality. The modeling case study involves using available flow and water quality data to explain the water distribution and processes that change concentrations of salinity and dissolved selenium in the extensively irrigated Uncompahgre and Gunnison River Basins in western Colorado. A relatively simple top-down modeling method is proposed, in which observed data and physical principles of mass balance are used as the basis to describe large-scale processes driving constituent loading. The model development process reveals the historic agricultural water use, adherence to current and proposed water quality standards and major contributing factors influencing water quality throughout the basin. The model is then used to simulate a range of Best Management Practices for irrigated agriculture and basin development scenarios to predict changes in water quality throughout the Uncompahgre River and its region of influence. The goals of this research are twofold: to illustrate the value of using top-down methods to describe drivers of water quality and to specifically quantify these processes and offer potential solutions for the problem of elevated selenium levels influenced by water use in the Uncompahgre Basin in western Colorado.