113: Hyporheic Exchange Flows

Water having entered a stream channel from the surrounding catchment may continue to have connections with the catchment. In the stream’s hyporheic zone, water “in the channel” exchanges with “groundwater” in the bed of the stream. Hyporheic exchange flows typically occur at scales small relative to the length and volumetric transport characteristics of the stream. Nevertheless, it is well documented that hyporheic exchange flows significantly influence nutrient dynamics. Additionally, there is evidence of hyporheic exchange flows similarly influencing the processes establishing the concentrations of major-ions and metals in stream-catchment systems. It is within the contexts of (i) solute transport and (ii) the continuing connections of streams to their catchments that the hydrologic aspects of hyporheic exchange flows are studied. The Transient Storage Model (TSM), a pseudo-two-dimensional representation of stream and hyporheic zone solute transport, is used to identify characteristics of hyporheic zone, physical size, and solute residence times. The TSM is further extended to simulations of reactive solute transport to understand and interpret the biogeochemical processes of streams influencing the solute dynamics of catchments. Active hydrologic research continues to advance the process basis from which quantitative assessments of the role of hyporheic exchange flows will be made.