Hurricanes, and now earthquakes. Both could contribute to scouring away sand and mud from around bridge pilings.
The Virginia Department of Transportation now has the equipment and training to conduct sophisticated underwater surveys of riverbeds to check for erosion that could threaten the safety of a structure. The technology is also used to identify obstructions that could interfere with navigation or with bridge construction and demolition.
VDOT staff members are using side-scan sonar and multiple-beam sounding equipment mounted on a boat to produce 3-D color contour maps and sonar images, and to view elevations of river bottoms and other bodies of water.
The equipment, which cost $133,000, provides more accurate...
data than what VDOT's hydrographic team previouslycould produce - and in a shorter amount of time, which saves money, officials said.
"It allows us to do everything more frequently," said VDOT spokeswoman Nora Chivers.
VDOT is responsible for inspections of 19 bridges and tunnels in Hampton Roads.
"We can take readings at intervals and create profiles so we can easily compare to see if material has eroded away or...
piled up," said Danny Williams, VDOT's survey manager. "We actually get a visual of pilings or footings to provide engineers, who determine if there's a problem."
Chivers said that soon the hydrographic team will do work in the Elizabeth River in preparation for the construction of a parallel Midtown Tunnel. State highway officials are close to finalizing a deal with a private consortium to build the structure starting next year.
"This will be extremely beneficial when they start to dredge the area to lay down the tube sections," she said.
The team also takes the equipment to other parts of the state to survey underwater areas. Recently, they've done work for the demolition of the old Chincoteague bridge and surveyed under a New River bridge in southwest Virginia.
VDOT bought the equipment two years ago and has spent time training and practicing with the new procedures. Jeff Bevins, VDOT engineer technician, said the staff has become proficient in the last several months.
The old equipment, he said, could scan only 10-foot swaths of riverbed at a time, whereas the new technology handles 300 feet.
Mounted to the side of a motorboat, the equipment sends out sound waves or acoustic impulses, which are displayed on a computer screen onboard the boat as three-dimensional images and as contour maps. It shows changes in elevations and also obstructions, including old pilings, boats and boat parts, trash and other debris.
"We're saving money because we're saving time," Chivers said. "We were spending hours and hours on survey measurements and then taking them to the office and drawing and charting by hand."
Source: Debbie Messina, The Virgina Pilot