Morphology-Adaptive YOLO for Underwater Crack Detection in Hydraulic Structures

Accurate underwater crack detection is essential for the condition monitoring of hydraulic structures. However, reliable detection in underwater inspection imagery remains challenging because of low visibility, complex backgrounds, large-scale variation, and irregular crack morphology. To improve detection under these conditions, we develop MA-YOLO, a YOLOv11-based detector that adapts feature representation to underwater crack morphology. The proposed method integrates a broader receptive field spatial pyramid pooling module to enhance multi-scale feature extraction, a morphological attention module to improve the representation of irregular crack patterns, and an extra-large detection head to better detect magnified cracks in close-range underwater images. Experiments on the underwater crack dataset (UCD) show that MA-YOLO outperforms both conventional detectors and recent underwater object-specific detectors. Relative to YOLOv11, MA-YOLO increases mAP@0.5 from 91.2% to 92.9% and mAP@0.5:0.95 from 60.0% to 63.0%, while maintaining a lightweight architecture and real-time inference capability. The results demonstrate the effectiveness of morphology-adaptive feature modeling for image-based underwater crack detection and its potential for practical monitoring of submerged hydraulic structures.