Tag Archives: Cape Hatteras lighthouse

North Carolina’s mobile Outer Banks and its new, immovable Bonner Bridge

Cape Hatteras Lighthouse being moved

The Cape Hatteras Lighthouse being moved in 1999. Image from International Chimney Corporation website

The iconic Cape Hatteras lighthouse no longer sits on the ground on which it was built in 1870. Under threat from the encroaching sea, the 210 ft., 5,000 ton masonry structure was moved in 1999 about 2800 feet southwest from its original location. Masonry buildings, when shaken (during earthquakes, for example) tend to come apart along mortar lines, or even fall completely to pieces. So it isn’t easy to move them safely.

International Chimney Corp. of Buffalo NY and Expert House Movers of MD Inc., were awarded the moving contract. The job was carried out successfully; not a single brick was dislodged during the operation. The lighthouse is now about a third of a mile from tide water, distant enough, it’s hoped, to keep it safe from the sea until at least the end of this century. In recognition of the difficulties involved in moving the structure, the two company’s jointly won the American Society of Civil Engineers 40th Annual Outstanding Civil Engineering Achievement Award.

The following map shows the location of the lighthouse before it had to be moved:

Map showing shoreline recession at Cape Hatteras NC

History of shoreline recession at Cape Hatteras, Outer Banks, North Carolina (map also shows pre-1999 location of the lighthouse). Image: pubs.usgs.gov (paper 1177-B)

To visit the lighthouse up close, drive south from Bodie Island on Highway 12. The H. Bonner Bridge carries the road across Oregon Inlet, linking Hatteras Island to the northern Outer Banks. The economic life of Hatteras Island depends on it. By early next year, the new Bonner Bridge will be ready to take over from the old one.

Aerial photo ofOregon Inlet and old H.Bonner Bridge, Outer Banks NC

Oregon Inlet and the old H. Bonner Bridge. Photo taken from above Pamlico Sound looking east towards the Atlantic. Image: usgs.gov

Built in 1963 with a life expectancy of 30 years, the old Bonner bridge is in danger of falling down. The new bridge (due to open for traffic early next year) is built to last 100 years according to the designers, HDR Inc., an engineering company based in Omaha, Nebraska. The bridge is built on shifting sand, so that longevity claim is based on the company’s confidence in their engineering abilities. Domenic Coletti, HDR design manager, quoted in the company’s website, said this:

To our knowledge, no one has previously designed and built a [bridge] foundation where piles had to be jetted and driven through nearly 140 feet of soil [sand] in a way that still provided adequate capacity [stability] after 84 feet of scour occurs.”

SCOUR is the anticipated tearing away of the sand around the support piles due to ocean currents in the inlet.

Photo of the old and the new H. Bonner Bridges, Outer Banks, North Carolina

The old and the new H. Bonner Bridges crossing the Oregon Inlet, Outer Banks, North Carolina. Image from The Outer Banks Voice, 13/11/2018. Photo by Bob Moris

But consider this: although the new bridge may very well last 100 yeas, how many years will the inlet over which the bridge crosses remain in its present location?After all, storms have opened and closed numerous inlets along the Outer Banks since records began in the 16th century. A hurricane formed the Oregon Inlet in 1846. Another one could close it. The steady migration of the Outer Banks over time, may also cause problems. Here’s part of an October 16 email I sent to Pablo Hernandez, Resident Engineer, NCDOT, asking about that matter:

According to the US Geological Survey, the Outer Banks have historically migrated south at the rate of 60 to 70 feet per year, a process that sea level rise may speed up. This suggests that in 20 or 30 years, the Oregon Inlet may no longer be where it is now, thus leaving the new bridge without a function. I’m wondering what actions DOT plan to take to avoid such an outcome?”

No answer yet. My guess is that the Army Corps of Engineers will be kept busy dredging the channel for the indefinite future. What other solution is there? Unlike a lighthouse, a bridge can’t be moved. When Mr. Hernandez gets back to me I’ll update this post.

Map of North Carolina’s Outer Banks

Map of North Carolina’s Outer Banks showing location of Cape Hatteras lighthouse and Oregon Inlet. Image from U.S. National Parks Maps