A new method for scour monitoring based on distributed fiber optic vibration sensing

• Developed a riverbed scouring monitoring method using distributed optical fiber vibration sensing. • Proposed a dynamic strain transmissibility gradient method for real-time riverbed erosion monitoring. • Model tests validate reliability in anhydrous/dynamic water, enabling simultaneous water level and erosion depth monitoring. • The dynamic strain gradient method shows less than 6% relative error , unaffected by water level. Riverbed scouring by water flow is a key factor in dike damage. Current optical fiber technologies for monitoring riverbed scouring rely on point-type methods, which are costly and lack durability, limiting their use in long, wide rivers. This study develops a riverbed scouring sensing rod using distributed optical fiber vibration sensing technology. Based on Adaptive Threshold Brillouin Optical Time Domain Analysis (AT-BOTDA), a new monitoring method is proposed, leveraging dynamic strain transmissibility and its gradient to achieve scour depth estimation. AT-BOTDA enables high-speed distributed strain measurement by utilizing Brillouin frequency shifts without the need for full-spectrum scanning, thereby improving the monitoring efficiency and accuracy. The proposed method is validated through model experiments under both anhydrous and dynamic water conditions. The results show that the variation in embedded depth correlates with erosion depth, which can be monitored using natural frequency, dynamic strain transmissibility, and its gradient. While the natural frequency method is significantly affected by water depth, the transmissibility gradient method can monitor both water level and erosion depth simultaneously. The gradient-based method outperforms those based on transmissibility and frequency, being less affected by water level and quality. The relative error in scour depth estimation using the transmissibility gradient is less than 6 %. The proposed method not only enhances dynamic strain sensing capabilities, making it more effective in scour monitoring applications but also is cost-effective and adaptable to environmental conditions, This enables timely monitoring of riverbed scouring, thereby ensuring the safe operation of dikes.