Culvert inspection in Ardnacrusha

A head race canal built over two rivers

At Ardnacrusha there is a large man-made canal, built around a hundred years ago to transport water from up-river in the Shannon down to the dam itself. When it was built, this canal was one of the major engineering wonders of the world, one of the most impressive projects on the planet at the time.

Because the canal crossed the path of two pre-existing rivers, the builders had to carry those rivers beneath the canal so their water would not mix with the canal water. To do this they built culverts over the rivers but under the canal, water on top and water underneath. The rivers themselves were relatively small: maybe two metres across at that point, and perhaps a foot high to two feet deep at the most.

Two culverts, two very different sets of conditions

The client wanted to capture the interior state of these culverts, and the two structures could hardly have been more different to work in.

The first culvert was straightforward. It held water, but only about two inches deep, quite shallow in the middle of summer, and no problem at all. The culvert itself was roughly 75 to 100 metres long, and there was plenty of room to walk inside it, with ample space for a drone to fly all the way down and all the way back to capture the entire culvert in detail.

The second culvert was more challenging. It was built into Parteen Weir itself, so on top of the weir the River Shannon flowed over, while beneath the weir a built-in culvert carried a pre-existing river, what is called the Old Shannon River in that area, into the Shannon. To inspect it, the culvert had to be continually drained, with pumps running full time, and the work involved working at height and confined space access requirements. Like the first, it was also a dark, enclosed interior space.

Flying the ELIOS 3 the full length of each culvert

The team used the ELIOS 3, which Bob Foley, founder of Engineers With Drones, describes as "probably the premier confined space inspection and surveying drone on the planet". The drone was flown down through each culvert and back again, capturing all the detail of the side walls, the roofs, and the interior, while a high-resolution survey-grade point cloud was captured alongside it.

Because these culverts are quite dark, the confined space inspection drone’s high-powered LED onboard lighting system was able to light up the walls and roofs as it flew along, bringing out high-resolution detail of any defects. Working to the site engineer’s requirements, the team captured any and all details that were asked for during the projects.

A point cloud and video record of both culverts

The deliverables were a high-resolution point cloud of both culverts and a high-resolution video data set of both, a record the client found extremely useful for all future work.