INVESTIGATING MORPHOLOGICAL CONTROLS ON HYPORHEIC EXCHANGE IN A MEANDERING RIVER

The hyporheic zone (HZ) is critical to the biogeochemical and ecological processes of river corridors. The HZ is an active ecotone between surface water and groundwater (Boulton et al. 1998). In rivers that meander within an alluvial floodplain, exchange between groundwater and surface water is common, leading to the development of a HZ. Many factors control HZ hydraulics and chemistry. This study is an investigation on how channel morphology, meandering, and deposition influence hyporheic exchange along a reach of the east fork of the Jemez River in the Valles Caldera, New Mexico.

Using electrical resistivity data and auger/borehole cores, we intensively mapped the subsurface lithological composition of the site and identified flowpaths controlled by the deposition and burial of high hydraulic conductivity layers. The water table and groundwater flowpaths were mapped across the floodplain using a dense network of piezometers. Geochemical sampling and mapping for major cations, anions, and field parameters were used to supplement and support groundwater flow observations. Using water table monitoring, we found that an abandoned channel next to the streambed is hydraulically connected to the groundwater. The suite of observations collectively shows that deposition in a meandering fluvial environment influences the spatial patterns and properties of hyporheic exchange. This insight can be applied to issues pertaining to the transport of biogeochemically-important solutes through the river corridor. Further studies involving a more sophisticated and detailed modeling technique, a more extensive chemical analysis of the site, and comparison of this site to other similar settings are necessary in completing the understanding of the morphological controls of the hyporheic zone.