lighter, more agile, and easier and less expensive to own and operate. While early inland-oriented units were primar- ily “flying photo/video cameras” with limited mobility, today’s inspection ROVs are capable of operating against river flow velocities commonly experienced during underwater bridge inspections and employ multiple thrusters oriented to yaw the vehicle into proper position to inspect the element. Today’s ROVs are smaller (some less than 12 in. [30.5. cm] in diameter to fit into confined spaces) and offer integral mounting of a sonar imaging head or UTT transducer (see Figure 10). As such, ROVs can be used in lieu of crewed commercial diving for select inspection operations, such as working in polluted waters, or in conjunc- tion with convention diving operations. Modern Inspection Procedures A few scenarios illustrate the benefits of integrating imaging sonar and/or ROVs with conventional diving-based inspection: Ñ A sector-scanning, multibeam, or volumetric 3D sonar system or sonar-enabled ROV can be used by a dive team to preview piers to evaluate potential hazards, such as drift/debris accumulations, prior to deploying a diver (see Figure 11). This significantly increases inspection efficiency and enhances safety by allowing the dive team to preplan the inspection of each individual bridge pier. Using the appropriate technology, this “pre-inspection sonar scan” can be quickly accomplished as a first step in the inspection process. Ñ This same sonar system or ROV could then be used to monitor divers’ progress and help ensure diver safety during the inspection. With adequate water clarity, the ROV could also provide video of the inspection. This “over-the-shoulder supervision” approach is common practice offshore and allows topside personnel to collaborate with and direct the diver. Ñ Sonar and ROVs can be used to help evaluate confined spaces, such as areas of foundation undermining, Figure 9. Volumetric 3D sonar image of bridge pier. Figure 10. ROV with mounted UTT transducer. Figure 11. Drift at pier foundation easily detected using sector scanner sonar. J A N U A R Y 2 0 2 3 • M AT E R I A L S E V A L U AT I O N 41 2301 ME Jan New.indd 41 12/20/22 8:15 AM COURTESY: CODA OCTOPUS PRODUCTS LTD. COURTESY: RICH ARRIETA, NAVAL INFORMATION WARFARE CENTER

which by regulation require a minimum five-person dive team to inspect. Considering that underwater inspections are often conducted by an OSHA-compliant, three-person minimum dive team, this approach could help determine the need to revisit only a specific area with a larger crew, rather than staffing the entire inspection with a larger crew. For longer bridges, this may prove espe- cially beneficial. Ñ Both sonar and ROV technologies may be used during emergencies such as flood events to provide first-response or even mid-event scour assessment (see Figures 12 and 13). The aforemen- tioned autonomous vessel assessment using sidescan sonar provides valuable assistance to the bridge engineer and owner. Similarly, boat-mounted sonar equipment can be deployed imme- diately after high-flow events or after impact events, to identify damage before a dive team can arrive onsite. AUTHOR Dave Severns: Principal - Underwater Inspec- tion Services Lead, Stantec Consulting Services Inc. 6920 Professional Parkway East, Sarasota, FL 34240 dave.severns@stantec.com CITATION Materials Evaluation 81 (1): 36-42 https://doi.org/10.32548/2023.me-04299 ©2023 American Society for Nondestructive Testing REFERENCES FHWA. n.d. “Long-Term Bridge Performance.” Turner-Fairbank Highway Research Center, Federal Highway Administration (FHWA), fhwa. dot.gov/research/tfhrc/programs/infrastructure/ structures/ltbp/. FHWA. 1995. Recording and Coding Guide for the Structure Inventory and Appraisal of the Nation’s Bridges. Report No. FHWA-PD-96-001. fhwa.dot. gov/bridge/mtguide.pdf. FHWA. 2018. Underwater Inspection of Bridge Substructures Using Imaging Technology. FHWA Technical Report FHWA-HIF-18-049. fhwa.dot. gov/bridge/nbis/hif18049.pdf. FHWA. 2022a. National Bridge Inspec- tion Standards. 23 CFR Part 650. Federal Register 87, (88), Friday, May 6, 2022, Rules and Regulations federalregister. gov/documents/2022/05/06/2022-09512 /national-bridge-inspection-standards. FHWA. 2022b. Specifications for the National Bridge Inventory. Publication No. FHWA-HIF-22- 017. fhwa.dot.gov/bridge/snbi/snbi_march_2022_ publication.pdf. FEATURE | UNDERWATERINSPECTION Figure 12. Sonar attached to bucket truck, to evaluate scour during flood conditions. Figure 13. Sidescan sonar output from an autonomous vessel during flood conditions. 42 M AT E R I A L S E V A L U AT I O N • J A N U A R Y 2 0 2 3 2301 ME Jan New.indd 42 12/20/22 8:15 AM COURTESY: BRIAN ABBOTT COURTESY: HYDRONALIX