Development of an Image-Based Borehole Flowmeter for Real-Time Monitoring of Groundwater Flow Velocity and Direction in Landslide Boreholes

The velocity and direction of groundwater flow characterize the magnitude and direction of hydrodynamic pressure in landslides, which is critical for landslide stability analysis. However, there is no high-stability, high-precision, and easy-to-operate borehole flowmeter for in situ real-time monitoring of groundwater flow. As such, an image-based borehole flowmeter was developed for this purpose in this study. By integrating hardware such as a high-resolution camera, a cable winch, and a tracer ball, and combining them with feature detection algorithms like the circle Hough transform (CHT), it can realize real-time, high-precision monitoring of groundwater flow velocity and direction. Calibration experiments were conducted to assess the accuracy of flow velocity and direction under various object distances and tracer ball sizes, enabling the determination of their optimal combination. Experimental results indicate that the developed borehole flowmeter demonstrates high accuracy in both flow velocity and direction measurements, with the measured flow velocity and direction exhibiting a high linear correlation with the actual flow velocity and direction. The measurement accuracy of the developed borehole flowmeter is optimal when the object distance is set to 12 cm and the tracer ball diameter is 8 mm. Beyond monitoring groundwater in landslide boreholes, this sensor can precisely measure flow velocity and direction in microflow surface waters, such as rivers and lakes, thus demonstrating the broad potential for diverse applications.