Repairs to the Interstate 526 span over the Wando River are needed because of “scour” affecting the foundation of three main supports, the state Department of Transportation said Thursday.
“Due to an increase in scouring of the foundation at three pier locations of the east and westbound-lane bridges, the department has moved to perform scour repairs in order to protect the foundations,” the DOT said.
Scour happens when material around the base of a bridge support is lost because of currents, according to the Federal Highway Administration.
The repairs to the James B. Edwards Bridge connecting Mount Pleasant and Daniel Island are estimated to cost $1.5 million and will be funded as part of the previously approved 2012-13 Federal Aid Bridge Replacement and Rehabilitation Program.
“It’s basically routine stuff. It’s a standard-type repair. It’s not a structural problem. The bridge is fine right now,” said Lee Floyd, state bridge maintenance engineer.
Changes in the Wando River flow have caused the scour. The DOT has been monitoring the situation for about five years. The affected foundation is toward the Mount Pleasant side of the bridge, he said.
Plans for the repairs are about 95 percent complete. They will include measures to protect the three piers and prevent future erosion. One of the piers supports both spans of the Edwards Bridge. The other two piers support one span each, he said.
The DOT has an underwater pier foundation-inspection program in which divers take a close look at the condition of bridge supports. The I-526 Wando River bridge was built in 1989.
In a recent report on the state’s bridges, AAA Carolinas said that six of Charleston’s bridges are among the state’s worst.
The report, which lists substandard bridges for 2012, shows Charleston has more substandard bridges than any other county in the state. Among those are the U.S. Highway 17 bridge over the Ashley River; a section of Interstate 26 that crosses over S.C. Highway 7 and the bridge that crosses the Wappoo Creek on S.C. Highway 171.
Although substandard, the bridges are structurally sound and are inspected regularly. The Edwards bridge is not on the substandard list.
South Carolina has 1,880 substandard bridges. Addressing them all would cost an estimated $2 billion, according to AAA Carolinas.
Some of the substandard bridges are classified as “structurally deficient,” meaning the bridge is in relatively poor physical condition or inadequate to handle truck weight. Others are categorized as “functionally obsolete,” meaning the design is inadequate to handle current traffic volume. Bridges are inspected twice a year. All open bridges are safe for use by the motoring public within whatever weight restrictions are posted, officials said.
The percentage of state bridges rated substandard decreased to 20 percent this year, from 23 percent in 2011. That’s better than in neighboring North Carolina, at 32 percent. Still, other Southeastern states, including Tennessee and Georgia, have done a better job addressing their bridge and road needs, according to AAA Carolinas.
The DOT estimates that bridge maintenance, repair and replacement needs for state-owned bridges cost roughly $200 million a year.
South Carolina’s gas tax is the main funding supply for the DOT and has been unchanged since 1987.
The DOT is accepting comments on the Edwards bridge work through Oct. 11. An amendment to the Statewide Transportation Improvement Program is required for the repairs to happen. Comments may be submitted online at the DOT website, scdot.org.