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Western Dam Engineering 18 be used. While ROVs or CCTVs can compensate for the inherent limitations of underwater dive inspections (depth, temperature, altitude, time, etc.) extreme caution is advised when using an ROV for inspection. The ROV operator should be qualified, experienced, and knowledgeable of the potential hazards involved. The primary concern when using an ROV for inspection is that the ROV can become entangled or get stuck in a small-diameter conduit, causing an obstruction. Retrieving ROV units can be difficult and expensive work, so care should be taken prior to the inspection to develop a retrieval plan for the ROV unit. Often, a steel umbilical cable is connected to the unit prior to deployment to assist in retrieval. In contrast to ROVs, CCTV can be utilized. CCTV units are typically manually operated, mounted onto an external carrier, and pushed into the conduit using a rod to direct the mounted CCTV. Historically, it has been difficult to obtain real time video or images captured by the CCTV but with the advent of mobile technology, cameras that allow for some mobile viewing and control have become commercially available. In terms of costs, ROV units are typically rented at rates ranging from $1,000/day to $3,000/day, depending on the sophistication of the unit. ROV units can usually be rented directly and the unit shipped or picked up for use. For the reasons previously listed, it is recommended that experienced and certified personnel be used to operate ROV units whenever possible. The cost for a small crew to mobilize, operate the ROV unit, and demobilize depends on the travel required for the crew but usually ranges between $1,500 and $3,000. Most inspections can be conducted in one working day with two days spent traveling to and from the site. In contrast to ROV units, CCTV units are typically purchased by the dam owner and assembled on site. With minimal maintenance, CCTV units can be re-used for future inspections and are a cost-effective solution for many dam owners of small to intermediate sized dams. One CCTV device that has been used successfully for years by members of the Colorado Dam Safety Branch is a sled-mounted camera attached to a metal push pipe with couplers to extend the sled in 6-foot lengths as necessary. Originally designed by Jim Norfleet in the 1990s and recently modernized by Jason Ward, the sled unit can be constructed for about the cost of a single ROV rental. Details of the sled are provided as an attachment to the PDF of this Tech Note issue and a photo is shown below. Photo 3: Manually operated CCTV sled.3 Common issues with CCTV units include difficulty in obtaining real-time images, lack of spatial reference, and the potential for getting the unit stuck and causing an obstruction. In addition, when inspecting longer conduits or those with bends, CCTV can be problematic and ROV units are typically used instead. Even if man- entry is not an option, the conduits would preferably be unwatered prior to inspection, because particles floating within the water often reflect back during the lighted camera inspection and prevent full view of joints and damage around the conduit. In addition, both ROV and CCTV inspections should be monitored by a qualified engineer. When viewed continuously during the inspection, qualified inspectors can spot locations where additional time and video angles are warranted. Modern ROV equipment includes pan and zoom capabilities that can be used to get the most from the inspection. Without adequate oversight, untrained technicians can unknowingly move past areas of interest too quickly and diminish the value of the inspection. If the conduit is accessible for man-entry, the inspection should be documented using photographs or video equipment and whenever possible, the interior of the conduit should be pressure washed prior to the inspection. Locations of all damaged or questionable areas should be documented using 3 Photo courtesy of www.water.state.co.us