USACE Survey Team gets Laser Focused on Lock 12
By Kelcy Hanson
USACE, Rock Island District
March 21, 2023
The U.S. Army Corps of Engineers, Rock Island District, was founded in 1866 when Lt. Col. James H. Wilson arrived in Keokuk, Iowa, to survey portions of the Upper Mississippi River. Since that time, surveying has changed, and so has the river, but the need for mapping and measuring remains.
During a recent visit to Lock and Dam 12 in Bellevue, Iowa, Nathan Shanley and Steve Gekas from the Rock Island District’s land survey section, demonstrated how their new, 3D terrestrial LiDAR laser scanner was being used for the first time to conduct inspections of the dewatered lock.
“The new scanner has capabilities to do things that we’ve never been able to do before,” said Gekas.
Land surveyors, Nathan Shanley and Steve Gekas set up new 3D terrestrial LiDAR laser equipment in the bottom of the dewatered chamber at Lock and Dam 12 in Bellevue, Iowa.
(USACE photo by Kelcy Hanson)
According to Shanley, the high-intensity scanner sends out 500,000 laser pulses per second, while spinning, and uses built-in GPS, and a control point to accurately determine its precise location on the Earth. It can be moved from one location to another, capturing 30 million points per scan.
The high-intensity scans create specific and extremely accurate measurements which are impossible to acquire by other means. “For visualization purposes it is great, but beyond that anything you see in the scan can have a precise (+/- 5mm) coordinate extracted after the survey is complete. This is useful for design engineering, planning, quantity analysis, historical record keeping and monitoring, and pre and post as-built conditions.” Said Shanley. Engineering teams across USACE can benefit from the data collected by each scan.
Because the lock chamber at Lock and Dam 12 has a concrete bottom with weep holes for equalizing pressure, roughly four to six inches of water remained in it during the dewatering this winter. To prevent damage to the new equipment, Shanley and Gekas designed an elevated triangular platform on wheels that could be used to safely move the scanner in and out of the water transfer tunnels.
Every square inch of Lock 12 had been scanned by the time the team completed their work at the lock, but scanning is only the first step in the process.
“We tie the new control points into some control points that have been here since it’s been built,” explained Shanley. “With this, we’ll be able to see how each piece of the lock, like these giant monolithic stones, have been moving or not.”
After scanning, the images are uploaded into a computer and chained together using specialized software to create 3D digital models. In this case, the team was looking at the integrity of the structure and to see if it has shifted overtime. Information gathered at Lock 12 could also be used to assist in designing new locks, add to existing locks or help engineers troubleshoot issues they may be having at a lock.
The Rock Island District’s Unmanned Aerial Vehicle team also visited Lock and Dam 12 to get aerial control points while it was dewatered.
“They did the mapping with the drone and we’re going to mesh our data together,” said Shanley. “Although the drone information isn’t as precise, it has a better vantage point aerially so it will be very interesting to combine all this information for the first time.”
Future uses for this data is still unknown but the District is constantly learning new ways to integrate this innovative technology into forthcoming projects. The data collected is the same type of information used in robotics and to create virtual reality (VR) video games, so maybe someday people will be able to walk through a dewatered lock virtually!