Spatiotemporal Assessment of Groundwater Interactions With a Regulated River: A Case Study of the Nechako River, Canada

ABSTRACT Regulated rivers represent complex hydrological systems where groundwater–surface water interactions are governed by natural conditions and human interventions. This study investigates the spatiotemporal dynamics of groundwater–surface water exchanges in the Nechako River, British Columbia (Canada), using numerical simulations. Steady‐state and transient models were developed to evaluate interactions under various hydroclimatic conditions, including the influence of regulated water releases and projected climate change. Results show that spatial patterns of groundwater seepage are driven by underlying geology, river morphology, and aquifer connectivity, particularly around Vanderhoof where seepage hives align with areas of thin overburden and steeper gradients. Temporally, river water level exerts greater control over short‐term interaction rates than precipitation, which has a delayed effect due to storage buffering. Long‐term simulations under medium (SSP2‐4.5) and high (SSP5‐8.5) emission scenarios reveal contrasting trends. Although groundwater discharge is projected to rise over time due to heavier rainfall during the wet season, climate scenario simulations indicate reduced groundwater seepage during the annual high river water temperature interval, spanning mid‐July to mid‐August. These findings underline the importance of incorporating groundwater processes in river management plans, particularly where thermal refuges for cold‐water adapted species, such as salmon and sturgeon, are critical.