September 2025 Vol. 80 No. 9
Tech Tips
Sonar technology gives sewer inspections a clearer view below the waterline
By NASSCO Member David Hamberlin, HydromaxUSA
TECH TIPS is a bimonthly article on trends, best practices and industry advice from NASSCO’s Trenchless Technology membership professionals.
(UI) — As communities invest in smarter and more cost-effective infrastructure maintenance, the need for comprehensive and accurate sewer system assessments continues to grow. While CCTV remains the foundation of internal pipeline inspection, it has one critical limitation: it cannot see below the waterline. This is where sonar inspection technology becomes an essential complement, offering valuable insights in environments where visibility is limited, debris is heavy, or flow conditions make standard inspection methods ineffective.
What Is Sonar Inspection?
Sonar, or Sound Navigation and Ranging, uses sound waves to map the interior geometry of a pipe, focusing especially on the submerged portion that CCTV cannot capture. In sewer applications, a sonar head emits acoustic pulses outward. A receiver then measures the time it takes for those pulses to return. These signals are translated into a cross-sectional visual profile of the pipe, allowing operators to identify sediment buildup, structural defects, and capacity restrictions hidden below the waterline.
Benefits of Sonar Inspection
- Enhanced Data Collection – Sonar complements CCTV by delivering a complete picture of the sewer environment. Where CCTV shows the condition above the waterline, sonar reveals sediment accumulation, submerged obstructions, or structural deterioration beneath it.
- Improved Maintenance Planning – By quantifying the amount and location of debris or sediment, sonar helps agencies prioritize cleaning schedules, allocate resources effectively, and reduce unnecessary maintenance.
- Rehabilitation Design Support – Accurate cross-sectional profiles enable engineers to design more precise rehabilitation solutions, such as lining or pipe replacement, tailored to the pipe’s actual condition.
- Operational Efficiency – With the ability to capture data in low-visibility or surcharged conditions, sonar minimizes inspection delays, making it a valuable tool in challenging environments.
- Integration With PACP Codes – Many software platforms allow sonar data to be integrated with PACP codes, resulting in unified, standardized reporting that supports clearer communication and more informed decision-making.
Conclusion
Sonar is not a replacement for CCTV, but a powerful enhancement. Together, these technologies deliver a complete and detailed picture of sewer system conditions, leading to smarter maintenance strategies, more effective rehabilitation planning, and stronger long-term asset management. As collection systems become more complex and inspection challenges increase, adopting tools like sonar will be essential to maintaining reliable and sustainable utility services.
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