Pumping Groundwater to Create Cold-Water Thermal Refuges in Warming Rivers

Abstract

Thermal refuges in rivers and streams provide critical habitat for cold-water species during periods of thermal stress. In this study, we created a new cold-water thermal refuge by pumping cool groundwater to a warm coastal river in Nova Scotia, Canada. Thermal infrared imagery revealed a notable thermal plume, measuring approximately 55 m² at the water surface during low-flow conditions, with mixing limited by the installation of a flow deflector. Above-water and underwater cameras recorded several fish utilizing the created cold-water plume during periods of high ambient river temperatures (up to 30°C). Thermal numerical modelling was conducted to interpret the field data and assess the impact of alternative designs and conditions. Model results revealed that the extent of the created thermal plume substantially increased (+202%) with the use of a deflector and that the plume size was controlled by several factors including the river flow rate and temperature, the pumping rate and the groundwater temperature. The study findings demonstrate the efficacy of creating cold-water habitat in the face of a warming climate and lay the foundation for future proactive thermal management strategies aimed at maintaining thermal diversity in warming rivers.