Concrete wall
the dam is continously monitored for cracks, and when one is discovered they trace it and mark at what time it was found, one example is in the upper right corner of the photo
📅 2023-10-04 @ 15:14
📷 Camera: NIKON Z 6_2 (NIKON CORPORATION) using a NIKKOR Z 14-24mm f/2.8 S @14mm (1/15 f/2.8 ISO: 900)
