Using ROVs to image underwater infrastructure for structural integrity

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ROV-Lakebed-Assessment
An ROV equiped with a sediment sampler was used for one Lake Ontario zebra mussel assessment.

By Blake Spittle

Underwater remotely operated vehicles (ROVs) have come a long way with the acceleration of technology. Historically, they had huge operating costs and logistics, including the need for vessels to carry them to sites, power sources to run them, and teams of technical personnel to navigate and maintain them below the water’s surface.

Advancements in computers, batteries, cameras, drones and robotic engineering have resulted in the manufacture of small and compact ROVs. This has opened up new opportunities for engineering and scientific professionals to use them, no matter the geographic location or water type. There is no longer a need for a vessel to launch from, a power source for operation, or a team of technical personnel. This saves time, reduces costs and increases safety.

As developments accelerate, often left behind is the knowledge and understanding of how these small underwater robots can be applied and utilized.

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Imaging civil infrastructure underwater for structural assessments and reporting is becoming very popular and is achieved by an ROV in a very efficient and safe way. Engineers do not have to worry about hiring a dive crew and the health and safety implications and liability that can pose. Using an ROV means no one enters the water. It is navigated from the surface by a “ROV Pilot”, with all imagery, including video and photos, relayed live back to the controller and recorded simultaneously.

The result is hours of imagery of submerged assets in a single day, giving non-biased, high definition video and photo data.

Remote bridge inspection

In one example, a small river runs under a remotely located trail bridge, located 50 km away from the nearest town. The bridge is accessed by a trail in the forest, and its last inspection date is unknown. Engineers want to do a below surface visual structural check first.

It would be too costly to use a professional diver and too remote for a power source. The mini ROV is fully battery powered, offers 4K HD filming, and has a 2.5 knots maximum speed so the small current is no issue. Within an hour the bridge is imaged, all pillars, beams and supports are inspected, and the imagery is sent to the project engineer.

Public boat launch

Floods have put pressure on a public boat launch dock, so municipal staff want an imagery analysis to determine if there was any damage to it. Working from the dock, or from the shoreline, the mini ROV can be placed into the water and all pillars, beams, cribs, concrete and supports can be imaged.

Water treatment plant clear wells

Periodically, water treatment plant clear wells need to be inspected to determine the condition of the concrete and the piping. Also, there is the need for overall structure visuals, if installation of new pumps is planned.

With equipment designed to be disinfected and operated safely in potable water, mini ROVs allow for inspections in clear wells. This eliminates the need to send scuba divers into these tight spaces, and the concerns about confined space entry, or having to drain the clear well just for an inspection. Operators of the plant only need to shut down and isolate the clear well for a limited time.

Other uses

Imaging is not the only capability of mini ROV equipment. While cameras have changed substantially, other technologies have also become more powerful and compact. This includes imaging sonar, designed for low visibility waters.

ROVs can also be equipped with steel thickness gauges, multi parameter water quality sensors and water sediment sampling. Laser scalers can measure cracks and separation in concrete, bolt head sizes and even aquatic wildlife size. Multi-function manipulator arms give ROVs the ability to retrieve items from the water.

Aquatic habitat research and reporting is also done now with ROVs. With six to eight hours of battery life, they are a systematic and efficient way to get the maximum amount of underwater time. This means much more can be achieved in a day than using divers, where time under water is limited and stand down time is mandatory.

A world of regulation around monitoring and researching aquatic habitats has meant efficient workflows to capture as much underwater data as possible, often on limited budgets.

An ROV helped retrieve this water testing frame by attaching a carabiner and rope.

On one marine construction project, the lakebed and fish habitat condition needed to be evaluated. Before construction began, a mini ROV systematically imaged all areas that would be affected by the construction. It was used again after construction and rehabilitation to document before and after conditions.

In a fresh water mussel assessment, a mini ROV was equipped with a sediment sampler. Sediment samples were collected and returned to the surface for on-site or laboratory analysis.

Tight closing mechanisms allow for a good seal, so the sample is not compromised. This was all imaged at the same time, so the researcher could see on video the aquatic environment around the sampling location.

A water sampler can also be integrated in this scenario if water analysis at varying depths and locations across the area is required, or if it helps the researcher understand the underwater environment in further detail. Multi parameter ROV water quality sensors mean the collection of water samples can be eliminated and replaced with live time water quality data collection while imaging.

Recovery

Another use of mini ROVs is the retrieval of lost or hard to get to research equipment. Take an acoustic receiver, unable to resurface as damage to its floats or releasing mechanisms occurred during its deployment underwater. With multi-function grabber arms attached, the mini ROV can easily be taken to remote locations anywhere.

If the location is known by GPS, the ROV dives in that area and through a variety of claw like attachments, can lock onto the body of the acoustic receiver. The ROV can then be tethered or driven back to the surface. Imaging sonar can be viewed on screen also, if the ROV is equipped for the identification of such items in low visibility waters. This is a low risk operation, as no one is entering the water. It is cost-effective as not only is the expensive unit returned safely, but the valuable data that it contains is also retrieved.

Retrieving larger items can also be done by using a mini ROV with retrieval lines. In one instance, a water sensor frame had to be recovered. A float/buoy and line was attached to it, but over the season it disappeared. A retrieval line with a carabiner held in the open position by the ROVs grabber claws was taken down, all while being viewed in live time by the surface controller. It was piloted carefully onto the correct part of the sensor frame. Once in place, the grabber arms released the carabiner, closing it on the item. Then, the retrieval line was used to lift the frame back to the surface.

Blake Spittle is with Completewaters. Email: info@completewaters.com

Read the full article in ES&E Magazine’s June/July issue below.

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