Analysis of Large-Scale Groundwater-Driven Cooling Zones in Rivers Using Thermal Infrared Imagery and Radon Measurements

Abstract

The role of groundwater (GW) discharge on surface water (SW) quantity, quality and temperature is known to be important. Moreover, the effect of GW contributions to river thermal budgets is critical in natural rivers considering that water temperature plays a vital role in fish survival during extreme heat events. The identification of zones with GW input in rivers can, thus, help river management plans. However, detecting these zones at the watershed scale can be a challenge. This work combines thermal infrared (TIR) imagery of rivers and water sampling for radon measurements for better documentation of GW in rivers. The Sainte-Marguerite and Berard Rivers, both located in Quebec, Canada, are known for their abundance of salmonids. Their water temperature profiles were plotted using TIR imagery, and five cooling zones in the Berard River and two for the Sainte-Marguerite River were identified in which notable GW–SW exchange was the suspected cause. Radon concentrations measured within the cooling zones showed clear GW contribution to SW. TIR imagery is an effective and fast way to identify GW seepage at the watershed scale. Radon can be used as a complementary natural tracer of GW in rivers at finer scales. The combination of both methods was shown to be reliable for the identification of GW in rivers. This can help for a better anticipation of GW effects in management plans to deal with extreme heat waves that are predicted to occur more frequently under future climate change scenarios.