Stream and fluvial plain ground water interactions: Rescaling hydrogeologic thought

Management of near-channel ground water and surface water to maintain strea m health and floodplain ecological function requires hydrogeologists to ref ocus their conceptual models of water exchange between the aquifer and stre am. The high hydraulic conductivity fluvial plain directs ground water flow down-plain where it exchanges with the stream channel creating gaining, lo sing, flow-through, and parallel-flow reaches. The resulting complex flow s ystem requires consideration when profiles representing ground water flowpa ths are constructed. In addition to interaction at the scale of the fluvial plain, exchange of ground mater and surface water within and immediately a djacent to the stream channel creates hyporheic zones. The physical and bio geochemical extent of these zones depends on the head distribution and grou nd water flow directions, stream hydraulics, and channel bed conditions, an d magnitudes and distributions of hydrogeologic parameters. Simulated conce ptualizations of flow dynamics caused by slight increases in hydraulic pote ntials at the surface water-stream bed interface indicate stream-ground wat er mixing could occur to a depth of 1.7 m below the channel. Rescaling of t raditional hydrogeologic approaches to include the fluvial plain and channe l scale will result in opportunities to expand hydrogeologic research and p articipate in interdisciplinary research teams attempting to decipher and m anage fluvial systems.