An effective measure for evaluating sewer condition: UAV screening in comparison with CCTVS and manhole cameras

Most of the water/sewer pipes in Japan were constructed after the high economic growth that occurred in the 1970s. Those pipes are now aging, and the water business is shifting from construction to rehabilitation. NJS, as a consulting company in Japan, has had to shift focus to reflect the increasing need for rehabilitation in the water sector and the limited budget available. Doing business efficiently and better managing water assets has become a critical part of the business. NJS has been searching for a way to inspect sewer pipes efficiently, not just a few times in a service life but in increased frequency – in the range of every year or two. During this process, a focus on UAVs (Unmanned Aerial Vehicles) was considered beneficial. However, one that could stably fly through a confined space, such as a sewer, did not yet exist. Hence, NJS decided to develop a UAV for this purpose in cooperation with a partner company. To evaluate the performance of the UAV, the NJS team has inspected an actual sewer section, in cooperation with Yokosuka city, Kanagawa prefecture, Japan. The result shows that the UAV is capable of inspecting more than 1,000 m a day without personnel needing to enter a manhole. The team has also inspected the same section by CCTV and manhole camera to compare the inspection speed, operator's safety and the reliability of data. From the obtained result, it can be said that UAV is an effective screening method to efficiently conduct CCTV inspection; in other words, to prioritize the sections that need a detailed inspection.