Evaluating the Impacts of Uncertainty in Geomorphic Channel Changes on Predicting Mercury Transport and Fate in the Carson River System, Nevada

The Carson River is one of the most mercury-contaminated fluvial systems in North America. Most of its mercury is affiliated with channel bank material and floodplain deposits, with the movement of mercury through this system being highly dependent on bank erosion and sediment transport processes. Mercury transport is simulated using three computer models: RIVMOD, WASP5, and MERC4. Model improvements include the addition of a bank package that accounts for flow history. The rates at which river stages are rising or falling will, in turn, impart time-dependant and vertically variable MeHg concentrations within the channel banks along the Carson River. Also, Lahontan Reservoir’s geomorphic characteristics have been refined along with the explicit tracking of a temporally and spatially varying colloidal fraction. The augmented and refined modeling approach results in more accurate and realistic simulation of mercury transport and fate. An extensive uncertainty analysis, involving characterizing the co-variance of two calibration parameters used to define bank erosion and overbank deposition, will define the degree of expected variation in model predictions relative to limitations posed by available field data.