Reconnaissance‐Scale Methods for the Identification of Groundwater Discharge to Streams

Abstract Identifying groundwater discharge locations is critical for understanding and monitoring groundwater contributions to streams in terms of water quantity and quality. Streams and rivers are under increasing strain from factors, including increased urbanization, agricultural land use, groundwater extraction, and climate change, which can alter groundwater–surface water exchange and increase contaminant loadings to surface water. Recommendations are needed to weigh the advantages, disadvantages, and applicable spatial scales of available discharge detection techniques. The current study evaluated the efficacy of employing a combination of manual point measurement techniques (visual analysis, infrared (IR) imaging, and streambed sediment temperature probing) to identify gaining stream reaches within a mid‐sized watershed (~ 80 km 2 ) in southern Ontario. A reconnaissance survey was conducted where access was possible more than ~20 km (20%) of the total watercourse network, including the main channel and several tributaries. Two study sites identified as discharge hotspots based on the reconnaissance survey were selected for verification and detailed site characterization. Darcy's law flux estimates based on piezometer measurements and streambed flux estimates derived from multidepth vertical temperature profiling confirmed net groundwater discharge conditions at both sites. Differential stream gauging revealed net gaining conditions when applied at one site. Results suggest that a reconnaissance approach combining visual, handheld infrared, and streambed sediment temperature observations is a highly effective method for identifying locations of discharge hotspots and is recommended for other similar shallow streams (~ ≤ 1 m depth). The approach is particularly useful along streams where overhanging vegetation impedes aerial IR imagery and/or discharge is largely submerged.