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.