About the stability of hyporheic flows in a losing river section

Hyporheic fluxes are typically regarded as highly variable both in space and time at the stream‐groundwater interface. However, Active‐Distributed Temperature Sensing (DTS) experiments conducted in a losing river section demonstrated low spatial variability (one order of magnitude) and remarkable temporal stability. In this abstract, we investigate the potential reasons for the observed low variability and notable stability of hyporheic flows.

Experiments were conducted by burying several hundred meters of heatable Fiber‐Optic cables within streambed sediments in a large meander, where permanent stream‐losing conditions are observed. The absence of correlation between water fluxes in the hyporheic zone and variations in streambed topography suggests that the low spatial variability (one order of magnitude) of fluxes serves as an indicator of the low variability in streambed hydraulic conductivities. Repeated measurements taken during several field campaigns over three years demonstrated a remarkable stability of hyporheic flows throughout this period. To explain our findings, we analyzed the temporal variability of river stage and groundwater levels. Despite the rapid and sudden fluctuations of water levels, caused by upstream dam hydropeaking and groundwater pumping in the alluvial aquifer, the hydraulic gradients between the river and the aquifer remained relatively stable over time. Moreover, the speed at which the levels rebalance suggests that flows at the interface are primarily controlled by the high permeability of the streambed sediments rather than by the boundary conditions. These results can be considered for calibrating models that assess hyporheic processes.