USING WATER TEMPERATURE TO INFER RECHARGE TYPE AND FLOW PATH GEOMETRY IN KARST AQUIFERS (Invited Presentation)

Karst aquifers are important water resources for up to a quarter of the world’s population. The mode of recharge in these systems may be highly variable, with significant implications for groundwater quality. In addition, flow and transport predominantly occur through conduits, but the location and geometry of the conduits are generally poorly characterized. These factors highlight some of the challenges in effective management of karst water resources. We show how water temperature may be used as an indicator and tracer to address these challenges. Water temperature in karst systems informs understanding of recharge conditions, as recharge type provides a fundamental control on thermal response. Water temperature may also be used to provide constraints on flow path geometry, due to water temperature’s non-conservative nature in the environment. All water temperature signals will undergo some modification while flowing through karst aquifers because of heat exchange between water and rock. Analytical solutions for damping and retardation of thermal signals in karst conduits demonstrate that modification is primarily dependent on the flow path’s hydraulic diameter, the flow-through time, and the timescale of the recharge temperature variation. With the analytical solutions, we estimate flow path geometry with data collected in the field. Ongoing research is identifying the extent of thermal modification in field settings and assessing the usefulness of the analytical solutions along additional flow paths in nature.