A GEOPHYSICAL INVESTIGATION OF THE SEDIMENT FACIES OF THE EAST RIVER FLOODPLAIN NEAR CRESTED BUTTE, COLORADO

Fluvial sediment packages and bedforms can exert strong controls on local groundwater flow and subsurface hydrologic exchange in river corridors. The grain size distribution and layering of buried sediment bedforms creates hydraulic resistance and forms preferential flow paths for water moving both vertically and laterally beneath the surface in and around river channels. The primary hydrologic exchange process of interest is hyporheic exchange, which is defined as vertical subsurface flow beneath the river channel, and lateral flow beneath the banks. Hyporheic exchange plays a key role in the transport and storage of both nutrients and contaminants. Studying the composition and geometry of bedforms at the meander scale provides insight into physical controls on hyporheic exchange that have a major impact on catchment-scale hydrology. However, sediment packages and bedforms can be difficult to map with traditional methods due to their heterogeneity. Ground penetrating radar (GPR) surveys have proven to be useful for identifying sediment facies changes in fluvial settings. This study uses GPR and other complimentary methods to constrain meander-scale bedform composition and geometry at the East River near Crested Butte, Colorado. GPR data is interpreted alongside sediment samples and hydraulic conductivity data from existing wells at the field site. These data illuminate the history, evolution, and subsurface hydrology of the East River floodplain.