Field-scale artificial channel experiments for fluvial DAS observations

Understanding river sediment transport, and bedrock incision remains a major challenge in fluvial geomorphology Capturing their full temporal dynamics requires long-term monitoring of experimental catchments. This study explores the potential of Distributed Acoustic Sensing (DAS) technology to advance our understanding of fluvial sediment transport and riverbed evolution. DAS not only records strain or strain rates at meter-scale resolutions, similar to riverine dense geophone arrays but also captures a broad frequency range (mHz to kHz), comparable to hydrophones. Two experiments were conducted in meandering and straight artificial channels, with boundaries lined by waterproof membranes and stone protections, allowing for systematic effects of boundary and meandering shape. The experimental channels had a trapezoidal cross section, with widths ranging from approximately 2 to 4 m and bed slopes of 4–5°. During the experiments, the maximum flow depth reached about 0.3–0.4 m, the discharge ranged between 0.5 and 1 m³ s⁻¹, and the median grain size (D50) was approximately 10–20 mm. The experiments were monitored using a synchronized multi-sensor framework that combined UAV- and ground-based photogrammetry, particle tracking velocimetry, water-level gauges, stand-alone hydroacoustic sensor, riverine seismic dense array and DAS monitoring. Two fiber-optic burial configurations were examined for strain-rate sensing: (1) burial within a 30 cm thick sediment layer, and (2) installation beneath the armored riverbed (riprap) layer, allowing assessment of coupling conditions. Two-gauge lengths (2 m and 10 m) were also tested to evaluate their influence on strain-rate measurements. In our artificial channel experiments, the DAS measurements successfully captured high–spatiotemporal-resolution riverbed erosion and deposition dynamics. Fibers buried beneath the armored riverbed layer exhibited less sensitivity to riverbed morphological changes compared to those embedded within the sediment layer. In addition, the integration of DAS strain-rate, hydrophone, and riverbank seismic array data provided a comprehensive characterization of sediment transport processes across the channel. This study demonstrated that fluvial DAS enables continuous, high–spatiotemporal-resolution monitoring of sediment transport and riverbed evolution.