Inspection of elevated water reservoirs using unmanned aerial vehicle: case studies

Visual inspection techniques and industrial climbers are currently being applied for water infrastructure inspections to ensure regular maintenance. Although effective, these methods are expensive, time-consuming, and expose workers to risks. The literature about elevated water reservoirs (EWRs) inspection to pathological manifestations identification is scarce and lacks standardized methodological protocols that ensure reproducibility and comparability. This knowledge gap is also accompanied by the need to define the most effective visual resource for EWRs pathological manifestations diagnosis. Therefore, this study proposes and validates a standardized protocol that integrates unmanned aerial vehicles (UAVs) and digital photogrammetry to inspect EWRs. Two case studies under real-world operating conditions were conducted, generating three visual resources: digital photographs, three-dimensional models, and orthomosaics, which were compared effectiveness and suitability for detecting pathological manifestations. The results show that UAV inspections reduce execution time from 3 days to 3 h and lower costs to approximately one-third of conventional methods, allowing the identification of pathological manifestations such as corrosion, efflorescence, fissures, and cracks. However, they have limitations in adverse weather conditions, light variations, and surrounding obstacles, in addition to requiring high computing power. The main contribution of this study lies in the UAV and digital photogrammetry integrated application, inside the specific EWRs inspection context, enabling the damage maps construction and geometric reconstructions, establishing a standardized, replicable, and validated protocol useful for managers, companies, and scientific community.