Innovative use of passive and active distributed temperature sensing for estimating infiltration rates in a managed aquifer recharge framework

Managed Aquifer Recharge (MAR) has become an essential strategy for sustainable water management. Effective design of surface recharge systems relies on the accurate estimation of the soil infiltration capacity. In this context, the use of heat as a tracer has recently gained attention to quantify infiltration dynamics. Particularly, methods relying on Distributed Temperature Sensing (DTS) along fiber optic (FO) cables have been developed to account for the spatial variability of the recharge. This study explores an innovative approach that combines two types of temperature sensing techniques, passive and active-DTS measurements, to evaluate infiltration rates in a MAR pilot site. An FO cable, buried in the loess sediments of an infiltration basin, recorded temperature changes during an infiltration test. First, the passive method monitored natural temperature changes as cooler water filled the basin, enabling the estimation of initial infiltration rates. Twenty-four hours later, the active method involved heating part of the cable to further assess infiltration rates during ongoing infiltration. The analysis of DTS data facilitated the mapping of the recharge within the MAR system. Furthermore, results show that the infiltration rate is significantly higher at the start of the infiltration test, demonstrating that combining passive and active-DTS measurements provides a better understanding of the infiltration dynamics. The findings demonstrate the viability of MAR in loess-based systems at the studied site and highlight the potential of DTS methods for long-term monitoring of MAR operations.