Erosion and Overbank Deposition: Effects on Mercury Transport in the Carson River, Nevada

Work in progress is presented as part of an on-going investigation of mercury transport in the Carson River in west-central 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 sediment transport processes. In January 1997 a rare, high-magnitude flood generated significant geomorphic change to the system and transported large quantities of mercury. Calibrated bank erosion functions developed for the US EPA water quality model (WASP5), suggest that bank erosion is significantly greater at flows above bankfull discharge when compared to flows confined to the main channel with a single major flood event transporting nearly 87% of the total mass eroded during the period from 1991–1997 (Carroll et al., submitted). Preliminary mercury transport results for the 1997 flood are encouraging as it over predicts the observed value by less than 20%. However, mercury is under predicted following the flood as flows recede back into the channel and highlights the need to revisit Hg transport at moderately high flows.