Evaluating groundwater–surface water interactions at selected streams in the Mississippi River Valley alluvial aquifer, USA, and comparison to regional potentiometric surfaces

Abstract Field measurements of groundwater–surface water interactions (GWSW) are critical for quantifying stream leakage, but are often limited in availability. In the Mississippi River Valley alluvial aquifer (MRVAA), USA, GWSW interactions are often inferred through interpolated potentiometric surfaces, which can provide information on GWSW changes through time, but are often limited in spatial resolution. Field measurements of GWSW interactions were conducted at several locations and compared with potentiometric surfaces using objectively calculated cell sizes. The potentiometric surfaces showed similar regional-scale groundwater-flow patterns irrespective of grid cell size. Field measurements of GWSW interactions exhibited a broader range of gaining and losing conditions not previously documented across the MRVAA that were not identifiable from potentiometric surfaces. Spearman rank correlation coefficients ( r s = 0.078 to 0.98) between hydraulic head ( h ) and river stage covaried with depth to the water table and the h relative to estimated streambed elevations. This correlation was inferred to result from increased lateral groundwater flows and attenuating groundwater pressure waves with distance from streams. A revised conceptual model of GWSW in the MRVAA is proposed, where connected and gaining streams are more likely to be prevalent outside regional cones of depression. Furthermore, streams that are transitioning from gaining to losing are hypothesized to potentially become disconnected from the MRVAA in areas subject to regional cones of depression. Increased monitoring of GWSW interactions is needed both within and beyond regional cones of depression to test these conceptualizations and better quantify actual GWSW volumetric exchange in the MRVAA to quantify water resource availability.