FROM BEDFORMS TO BASINS: MULTI-SCALE INTERACTIONS BETWEEN GROUNDWATER AND SURFACE WATER AND IMPLICATIONS FOR MANAGING WATER RESOURCES

Tom Winter’s legacy is evident in broad recognition that interactions between groundwater and surface water occur wherever surface waters are in contact with permeable sediments. Through that inspiration we now understand how remarkably similar hydrological processes occur in vastly different settings from steep mountain streams, to lowland rivers, floodplains, lakes and wetlands, all the way to subtidal marine shelves. By extension we also have gained a growing appreciation of how those interactions structure benthic ecological communities by delivering reactants and products of key biogeochemical reactions across the sediment interface. In this manner, groundwater-surface water interactions modulate and structure ecological food webs that sustain highly valued recreational fisheries and wildlife habitat. Of course many research challenges remain. For example, a multi-scale synthesis is needed that recognizes how typical measurements and modeling only describe a small proportion of the full continuum of exchange flows, and their associated fluxes and residence times. New advancements in modeling now encompass multi-scale processes ranging from bedforms to basins. These approaches demonstrate the dominance of the smallest-scale features (e.g. hyporheic flow beneath bedforms) in driving fluxes across the interface, while also illustrating the non-linear dynamics of interactions across different scales. In particular the simulations demonstrate how small scale hyporheic fluxes are substantially modified by the larger-scale bar, meander, and basin-scale groundwater flow. Interpreting multi-scale interactions in streams requires models that are faithful to the physics while retaining enough simplicity to produce meaningful predictions for a wide range of flow, geomorphic, and ecological scenarios. In the coming years it is hoped that these advancements will substantially improve scientifically based strategies to co-manage the hydraulics and ecological health of aquatic ecosystems, with a goal to protect stream, river, and wetland corridors from further degradation brought about by accelerating land use change and an increasingly variable climate.