THE COMPLEXITIES OF CHANNEL BAR FLUXES

Large-scale fluvial obstructions such as channel bars, unlike simple bedform features, result in complex spatially and temporally variant gradients in hydraulic head and biogeochemistry. Heterogeneities within the geomorphic structure influence flowpath delineation, porewater fluxes, solute mixing, and biogeochemical effects. Hydrodynamic processes within channel bars, specifically groundwater/surface water exchange, are not well understood due to the difficulty in interpreting dynamic gradients and subsurface heterogeneities.

Several methodologies are being simultaneously utilized to quantify water and mass fluxes and to interpret the hydrodynamic processes through a channel bar. The channel bar is located within the Truckee River, a 4th order river in northwest Nevada. A high-resolution network of nested piezometers has been installed within the channel bar. Detailed instrumentation of the study area includes temperature dataloggers, multi-directional flowmeters, seepage meters, solute tracer injections, and biogeochemical analyses.

Preliminary results suggest complex flow patterns near the channel bar and surface water interface. The preferential flow patterns are consistent with increased hydraulic and chemical gradients.