The continual cost of coastal confusion: Ferries the solution

by Orrin Pilkey, Retired Duke Professor for Environment, published in News and Observer, January 14, 2014.

The history of Oregon Inlet offers a superb example of human failure to understand or appreciate the forces of nature at the shoreline. This lack of appreciation continues today.

Mistake 1:Oregon Inlet formed during a hurricane in 1842. The north to south flow of beach sand immediately forced the inlet to migrate south at a rate of 75 to 100 feet per year. In 1872 the Bodie Island Lighthouse was constructed, but as the inlet migrated, the lighthouse was left behind in the dust, 4 miles away.

Mistake 2: In 1962 construction was started on the Bonner Bridge to replace the ferry system. Along came the 1962 Ash Wednesday storm that widened the inlet overnight from a half-mile to 2 miles, deepened it to 60 feet and destroyed the just-completed bridge abutment. It was a case of misjudgement of the reality, frequency and power of storms.

Mistake 3: Construction of the bridge was restarted with no design change, and a fishing platform was put in at the north end of the bridge because engineers did not understand inlet migration and did not realize inlets recover after storms. When the Bonner Bridge was completed, the fishing ramp – it’s still there – was over dry land on Day One.

Mistake 4: The biggest mistake of all was to build the bridge with a single high span for ships to navigate under, requiring the channel of an inlet with a 150-year history of rapid migration to stand perfectly still. The result was 50 years of costly dredging, and numerous bridge problems, like the recent one, caused by scour.

Mistake 5: The Army Corps of Engineers for years resisted the natural attempt of the inlet to migrate to the south by dumping navigation channel sand at the north tip of Hatteras Island (the south side of the inlet). In 1982 the Corps inexplicably started dumping the dredged sand in deep water offshore (hopper dredging). The loss of sand caused immediate severe erosion of the island tip (up to 300 feet per year), destroying a campground and threatening the foot of the bridge as it connected to the island. A state of emergency was declared.

Mistake 6: A 3,000-feet terminal groin (jetty) was built in 1989 at the tip of Hatteras Island, designed by the Corps to repair the erosion caused by its own dredging activities The jetty caused a variety of well-known and predicted problems, including increased dredging costs and scour around bridge pilings. It also added significantly to the erosion problem and beach replenishment costs of the ocean beaches to the south.

Now the DOT plans to replace the aging Bonner Bridge with a twin sister bridge (the short bridge) parallel to the current bridge; a plan that continues the tradition of ignoring and dismissing the reality of natural barrier island processes. The idea is to keep the terminal groin in place and maintain N.C. 12 in its current location next to the beach, even using bridges along particularly frequently overwashed sections. With time, storms and sea level rise, the cost of beach replenishment and road repairs will skyrocket. Sea level rise seems not to be any real part of the new bridge plan, a profound omission for any current coastal design project.

Given projected sea level rise, accelerating coastal erosion and expected increase in storm intensity, the best long-term solution and best public investment for transportation to Hatteras Island is a modern, high-speed, high-capacity ferry system.

If a bridge must be constructed, it should be a causeway off the backside of the island through shallow water in Pamlico Sound, which was originally the DOT’s preferred alternative. Such a bridge (the long bridge) would allow removal of the terminal groin, with all its adverse effects and allow the inlet to migrate. It would avoid expensive beach replenishment, completely avoid the tumultuous beachfront where N.C. 12 is regularly closed preventing access to the existing bridge, and it would be in harmony with the natural processes of barrier islands as they respond to sea level.

Although 50-year projections have been given by the NCDOT, sea level rise will allow a lifespan of around 30 years for the short bridge alternative, at which point maintenance of N.C. 12 will become cost prohibitive and the road will become another distant chapter in the colorful history of the Outer Banks.

Orrin Pilkey is a retired professor in the Nicholas School of the Environment at Duke University.