Understanding the Spatial and Temporal Variability of Groundwater and Surface Water Interaction Using a Multi-year Multi-sensor Dataset

The mass and energy exchanges between groundwater and river water are governing the biogeochemical processes within the interaction zone of the two water bodies. The spatial and temporal variability of such exchanges are a result of the inherent heterogeneity of hydrogeologic properties along the terrestrial-aquatic transition zone interacting with the flow dynamics in the river induced by natural and anthropogenic perturbations. Long-term spatially distributed observations of water elevation, specific conductance (SpC), and temperature provide unique and valuable resources for understanding the hydrologic flowpaths under different hydrologic regimes, which consequently lead to enhanced mechanistic understanding of biogeochemical hot spots and hot moments. We present a 9-year spatially distributed dataset from a network of monitoring wells located within the hyporheic corridor of the Columbia River. The 9-yr window spans large variation of climate conditions, from low-flow to high-flow hydrograph regimes. The spatial and temporal analyses of water level, SpC, and temperature revealed significant inter-annual variability in hydrologic flowpaths and the spatial pattern of groundwater and river water mixing. The extent of river water intrusion varied more than 50% between a low-flow year and a high-flow year. Further synthesis of this dataset with complementary geophysics and biogeochemical measurements can guide the development of a predictive hydro-biogeochemical model for capturing the hot spots and hot moments of biogeochemical activity within this highly heterogeneous and dynamic interaction zone.