After months of surveying by underwater divers, work crews have begun placing granite boulders to shield the Robert Moses Causeway and other Long Island highway bridges from erosion, state officials said.
“This project has been going on for quite a while, but most of it was underwater, so nobody saw what was going on,” said Department of Transportation spokeswoman Eileen Peters.
As many as 3 million rocks, from 6-inch stones to boulders weighing 600 pounds, will be lowered from barges, Peters said.
Divers will guide the boulders to the correct places, either against the abutments, which support the bridge where it connects to land, or underwater, around piers to fill in holes caused by scour.
They will rest on the smaller stones, which are dropped first, to create a stable base.
The state inspects all its bridges at least every two years, Peters said, but superstorm Sandy necessitated many of these repairs.
“This came out of the heels of Hurricane Sandy,” she said. Its high tides washed away too much of the sand that supports a few of the bridges, forcing the transportation department to carry out emergency repairs where the Meadowbrook Parkway crosses channels.
In 2013, Gov. Andrew M. Cuomo announced a longer-term $261 million plan, largely funded by the Federal Emergency Management Agency, to repair 54 “scour critical” bridges around the state.
Work began last year on about $50 million in repairs for Long Island bridges: Robert Moses Causeway at the Fire Island Inlet bridge and State Boat Channel; Meadowbrook Parkway at the three crossings; Loop Parkway at Long Creek and the Southern State Parkway, Peters said.
About half of the projects will finish by the end of this year; the rest by mid-2017, the DOT said.
Though bridge builders have relied on boulders for centuries, the Long Island spans also are getting the benefit of some of the same modern technology — transducers — that fishermen use.
These small, solar-powered machines use sound waves to detect and report fluctuations in the level of sand or soil next to the piers to off-site computers, according to the department.