Here Comes the Sea

There are still a lot of questions to be answered, but the sea level is rising and communities along the coast are working to understand just what that means and how to prepare for it.

WILMINGTON — The sea, and the rivers that flow from it, have defined Wilmington since it’s founding the 1720s. It has become a major port city during the past three centuries.

Now city leaders are planning for how rising sea levels will define the city's future.

“Sea level is rising, it has been rising and it will continue to rise,” says Paul Prete, Senior Environmental Planner with the City of Wilmington. “We’ve got indisputable evidence about all of that, but the real question now is how much will it rise.”

And because nobody really knows the answer to that “how much will it rise” question, Prete is working with other Wilmington city officials to identify how sea level rise could threaten the city’s vulnerable infrastructure, such as roads and water treatment facilities.

“We’re talking about protecting investments that are put in the ground and must keep working for 50 to 100 years,” explains Prete. “And when you’re talking in that kind of time frame, even if you aren’t sure how high sea level might rise, it changes your thinking.”

Prete is quick to emphasize that, at least for now, the planning process does not include any wholesale ripping up of older infrastructure and the building of something new. But as infrastructure is repaired, city officials want to know if it makes sense to relocate the infrastructure, change the elevation, or add other types of protection.

The planning comes as a new report from the Coastal Resources Commission’s Science Panel warns sea level is rising at different rates along the coast. The new report projects sea level rise over the next 30 years. However, because of the uncertainty over how much sea level might change, the panel looked at several scenarios.

The first scenario shows a gradual rise in sea level based on historical data from five tidal gauges along the coast.

Station Location Sea Level Rise (Based on Historical Data)
Duck 5.4"
Oregon Inlet 4.3"
Beaufort 3.2"
Wilmington 2.4"
Southport 2.4"

Variations in geography and ocean currents mean the state’s southeast coast will see the smallest increases. Tidal gauges show that the ocean has risen faster at Duck (about 5.4 inches), which is north of Nags Head, than farther south in Wilmington and Southport (2.4 inches). Essentially, sea levels are projected to rise gradually moving north up the coast.

“There is no debate about those numbers because those numbers stand on their own,” says Margery Overton, Chairperson of the Coastal Resources Commission Science Panel and a professor in the Department of Civil Construction and Environmental Engineering at North Carolina State University. “If one believes the history that what has happened in the past will continue, those numbers stand on their own and the sea is rising.”

The second projections are based on data from the Intergovernmental Panel on Climate Change (IPCC) and contain two different scenarios based on the lowest and highest projections for greenhouse gas emissions. The numbers in the middle column in the table below show the estimated sea level rise based on the lowest projections for greenhouse gas emissions. The numbers in the right column show the estimated sea level with the highest emissions. These projections still show sea levels rising less in Southport (5.9 inches) than in Duck (7.1 inches) in the less severe scenario for climate change. The worst case example projects sea levels rising one inch higher all along the coast, with 6.9 inches in Southport and 8.1 inches in Duck.

Station Location Estimated Sea Level Rise (Based on the Lowest Projections for Greenhouse Gas Emissions)
Estimated Sea Level Rise (Based on the Highest Projections for Greenhouse Gas Emissions)
Duck 7.1" 8.1"
Oregon Inlet 6.3" 7.3"
Beaufort 6.5" 7.5"
Wilmington 5.8" 6.8"
Southport 5.9" 6.9"

"We took the lowest and the highest numbers, corresponding to the lowest and highest amounts of greenhouse gas releases, and then we modified them based on what we knew about local conditions to make it more meaningful,” explains Overton.

State lawmakers rejected a sea level rise report in 2010 using a 100-year time frame. That’s why the Coastal Resources Commission chose to look at sea level rise over a 30-year time frame in this report. The Science Panel warns the shorter time frame may not be long enough for some planning purposes and it recommends the report be revised every five years.

North Carolina becomes the first state with a comprehensive forecast showing the sea rising at different rates along the coast. The report is open for public comment, due to the legislature in March 2016.

“While we don’t know exactly what is going to happen, we have some pretty good records of changes over the past 50 to 100 years so we can project what might happen,” says Braxton Davis, Director of the North Carolina Division of Coastal Management. “Fortunately, we already require beachfront setbacks for construction which take into account historic erosion rates as well as various flood management programs, so the things we are doing to reduce risk from yearly storms will also help us cope long-term with sea level rise.”

“You can think about this in the most simple terms and that is the flooding of our shoreline,” adds Overton. “We love our coastline, but we know what is happening to the land and to the bits and pieces of the barrier islands because it is not a static place — the coastline is dynamic. And because the coastline is in constant transformation, our maps will look totally different in the next 50 to 100 years.”

— Frank Graff

Frank Graff is a producer/reporter with UNC-TV, focusing on North Carolina Science Now, a weekly science series that airs Wednesdays, beginning in August 2013, as part of North Carolina Now on UNC-TV. In addition to producing these special segments, Frank will provide additional information related to his stories through this North Carolina Science Now Reporter's Blog!

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