Fibre optic sensing technology for field assessment of thermal conductivity of aquatic sediments

Abstract

Abstract Purpose This study explores the in situ variability of sediment thermal conductivity (K) in a pond, integrating field-deployed fibre optic sensing with laboratory analyses of sediment properties to enhance our understanding and management of aquatic systems. Materials and methods A 20-m cable setup, consisting of a fibre optic cable (FOC) and a heating tape, was buried at two depths within a channel-shaped section of a pond. Induced temperatures along the FOC were recorded during several heating and cooling periods using distributed temperature sensing (DTS). Thermal conductivity (K) was estimated at five locations along the FOC during the heating periods using the heat conduction theory for an infinite line source. Sediment core samples collected from these locations were analyzed to determine dry bulk density (DBD), organic matter content (OM), and particle size distribution (PSD), exploring their effects on K variability. Results Analysis of core samples identified three distinct layers, each with varying PSD, OM, and DBD. The study revealed substantial spatial differences in the thermal conductivity of sediments, even over very short distances along the FOC, attributed to variations in sediment properties. Through a combination of field and laboratory results, we developed quadratic regression models (R2 > 0.9) to characterize the influence of DBD and OM on K. These models enabled detailed vertical and horizontal characterization of K within specific sediment contexts. Conclusion The study demonstrates the effectiveness of active DTS in detecting in-situ variations in K, emphasizing the impact of OM and DBD on temperature propagation. This study highlights the necessity of considering sediment property variability in modelling heat transfer for accurate water resource management and environmental assessments.