Bathymetric Survey and Underwater Structure Inspection for Hydraulic Engineering in Shallow Waters Using Unmanned Surface Vehicles

Bathymetric surveys and underwater structure inspections are critical for ensuring the safe operation of hydraulic engineering projects. Accurate data on topographical changes and structural conditions help mitigate operational risks caused by erosion, scouring, or structural deficiencies. However, traditional manned vessels face significant limitations in shallow and complex areas, such as downstream spillways, due to accessibility and maneuverability challenges.

The development of unmanned surface vehicles (USVs) offers an efficient and precise alternative for surveying and inspection in shallow water environments. This study utilized the Huawei-3 USV to conduct a bathymetric survey and underwater structure inspection in the shallow downstream area of the spillway at the Wangfuzhou Hydropower Station, Hubei Province, China.

The survey employed the Huawei-3 USV, equipped with high-precision echo sounders and RTK systems, to collect bathymetric and structural data. Water surface elevation data were acquired using RTK measurements, with water levels observed five times before and after the survey to establish a reference elevation. In areas less than 2 meters deep, RTK was also used to directly measure the bottom elevation. The USV combined its draft depth and transducer depth with RTK-derived water surface elevations to calculate the bottom elevation. Satellite imagery was used for pre-planning survey lines, which were aligned parallel to the downstream protective apron, spaced 5 meters apart, ensuring a point spacing of approximately 2 meters. In complex or nearshore areas, manual control was applied to densify survey lines. Data processing involved converting depth to elevation, noise filtering, and generating CAD and 3D models.

The results revealed significant scouring near the downstream protective apron, forming a scour pit with an area of 2,897.2 m², a minimum elevation of 70.26 m, and a proximity of 6.87 m to the reinforced apron edge. The overall underwater topography of the reinforced apron section closely matched the design, with a minimum measured elevation of 70.937 m, differing by only 6.3 cm from the designed elevation of 71 m, indicating stability. However, a portion of the 73 m design elevation zone showed scouring depths up to 25 cm, with an average depth of 12.5 cm. No significant deepening of scour was observed between 2022 and 2024.

The findings demonstrate that USV-based bathymetric systems are highly applicable in shallow water environments, achieving data accuracy that meets regulatory standards. These systems effectively identify scour pits and structural changes, providing reliable data support for ensuring the safe operation of hydraulic engineering projects. Moreover, the method shows significant potential for application in other shallow, complex water environments in the future.