Unraveling Spatial Water Infiltration Patterns in a Retention Pond Using Fiber Optic Distributed Temperature Sensor

Traditional temperature sensors often lack the capability for continuous, high-resolution soil temperature monitoring. This study employs Fiber Optic Distributed Temperature Sensing (FO-DTS) to establish a large-scale, horizontal experimental site for observing shallow soil temperature variations with high spatial resolution. The research investigates the spatial distribution of water infiltration in a retention pond by analyzing temperature variations in soil layers. The study site near Douliu Irrigation in Gukeng Township, central Taiwan, encompasses a 2-hectare retention pond comprising a precipitate pool and an infiltration pool. Fiber optic cables were deployed around both pools and buried in three layers to a total depth of 60 cm, with 20 cm intervals between each layer, enabling stratified soil temperature monitoring. By leveraging the phase delay in cyclical temperature variations between surface and subsurface layers, the FO-DTS system assesses water infiltration rates and their contribution to groundwater recharge. The results indicate that water infiltration significantly impacts soil temperature beneath the retention pond, exhibiting daily cyclical variability. The average soil temperature shows a negative correlation with depth, demonstrating that the FO-DTS effectively captures the thermal front caused by water infiltration. This approach highlights the potential of FO-DTS for accurately evaluating infiltration dynamics and its implications for regional groundwater management.