Groundwater-Driven Intermittency Regimes in a Seventh-Order Intermittent River

Abstract:

Intermittent streams are hydrologic systems which experience periodic no-flow conditions, and the controls on groundwater-surface water interactions in intermittent systems are understudied relative to their perennial counterparts. As irrigation-driven groundwater depletion has led to unsustainable declines in groundwater levels throughout Western Kansas, the streamflow regime has shifted from net hydrologic gains and perennial streamflow to net hydrologic losses and intermittent flow. The focus of this study is to characterize the impact of subsurface heterogeneity, climatic factors, and anthropogenic changes on the drying regime and groundwater-surface water exchange in an intermittent, seventh-order reach of the Arkansas River in Western Kansas. We analyzed intermittency patterns through time, historical discharge, groundwater level data, and climatic data to determine the drivers of flow and drying. Direct push well data are utilized to estimate the subsurface heterogeneity within the river bed and generate a conceptual model of the hydrogeologic conditions. Additionally, electrical resistivity tomography transects of the riverbank and a sandbar indicate that subsurface of the riverbed has a high degree of heterogeneity. We find that the flow regime alternates between multi-year wet and dry regimes. This indicates that the system has a storage-dominated intermittency regime, in which flow conditions are driven by transitions between gaining and losing conditions over annual to interannual timescales. Transitions between these two states are driven by water supply and demand over multiple months, rather than individual events. This indicates that excessive groundwater pumping may increase the frequency and duration of dry regimes in large-order streams.