2/1/20: SHORELINE HISTORY OF SOUTHERN SHORES IS ONE OF LOW LONG-TERM AVERAGE EROSION RATES, SOME ACCRETION; THE BEACON SUPPORTS ANNUAL BEACH PROFILING, NOT NOURISHMENT, AND WE THANK MAYOR PRO TEM MOREY FOR HER THOUGHTFUL QUESTION

Beachsept
The Southern Shores beach between Dolphin Run and Trout Run at 9:53 a.m. on Sept. 5, 2019, before Dorian arrived in town.

After Ken Willson presented APTIM’s latest report on potential beach nourishment in Southern Shores at the Town’s Council’s Jan. 21 workshop meeting, Mayor Pro Tem Elizabeth Morey asked a question that suggested a deeper level of study of APTIM’s analyses than previous Council members have shown. The newly elected Council member asked about Southern Shores’ shoreline history.

Mr. Willson, vice president of Aptim Coastal Planning and Engineering (APTIM), had shown images of the Southern Shores shoreline in 2008 and 2018. Ms. Morey asked if there was “imagery readily available that would give us an idea where the Southern Shores beach was in the seventies, eighties, and nineties, as opposed to in the 2000s.”

Is there any imagery dating back decades, Ms. Morey wondered, that would be “fairly easily” accessed “at low cost”?

In nearly two years of listening to Mr. Willson report to the Town Council—the first time in March 2018 about a 2017 baseline profile by APTIM of the town’s shoreline, then about APTIM’s December 2018 “vulnerability assessment” of the shoreline, in light of the town’s “beach management plan” goals, an update 17 months later of that study, and on Jan. 21 about the width of the beaches—The Beacon has never heard a Council member ask about Southern Shores’ history. It has been a major oversight.

Mr. Willson went from informing the Town Council after the 2017 profiling that “the shoreline is looking fairly stable” and there is “no big rush” to “jump” on beach nourishment to recommending “options” for sand replenishment along the entire Southern Shores shoreline that would cost in the neighborhood of $16 million.

At the Council’s recent workshop, Mr. Willson said that whether or not there is a “need” for beach nourishment in Southern Shores is a “discretionary decision by the Council.”

He also described APTIM’s analysis in support of nourishment as “subjective” and “discretionary.”

“A lot of it has to do with providing sufficient or acceptable level of storm damage reduction,” he explained. “How much [sand] volume do we need in the system to provide a specific level of storm damage reduction” in the event of a severe storm that may never occur?

The answer to Ms. Morey’s thoughtful question, to which Mr. Willson alluded, after first mentioning two other possible sources (one of them being U.S. Army Corps of Engineers data available just up the road at the Field Research Facility (FRF) in Duck), is yes: The N.C. Division of Coastal Management (DCM) has interactive maps accessible online that depict the location of the shoreline at various times, dating back to 1849.

Even more important, the DCM has online maps that document long-term average erosion rates that have been calculated and updated periodically along our beaches and offer a perspective dating back to 1940. The history exists! It is online!

Knowing the history of the Southern Shores shoreline enables today’s decision-makers to put the “risk” that Mr. Willson has identified into realistic perspective.

HISTORY INFORMS THE FUTURE: LAST SEVERE STORM WAS IN 1962

According to coastal engineer and geologist Spencer Rogers, who works with the exemplary research/education/outreach program, N.C. Sea Grant, in its Wilmington office, historical erosion rates provide a model for the future.

They are the “best indicator,” Mr. Rogers said in a telephone interview with The Beacon yesterday, of what will happen to a shoreline.

And yet, these rates have not been part of the conversation that Southern Shores has had during the past two years with APTIM. APTIM’s emphasis has been on erosion in the event of a severe storm, whose parameters (e.g., winds, wave action) it modeled after Isabel, the 2003 hurricane that, as Mr. Rogers noted, “pretty much petered out by the time it got to Kitty Hawk.”

As the highly regarded coastal specialist aptly pointed out, Southern Shores has not been directly hit by a severe storm since the Ash Wednesday storm of 1962, an Extreme Nor’easter that took out the old Sea Ranch Hotel at the current site of Pelican Watch, next to the Kitty Hawk Pier. Since this March 1962 event, no buildings in Southern Shores have been destroyed or threatened by erosion.

When Duck and Kitty Hawk did beach nourishment in 2017, houses in both towns were teetering at the ocean’s edge. Some in Kitty Hawk had already been lost. This has never been the case in Southern Shores.

While APTIM is advising the Town Council how to achieve “storm damage reduction protection” in the event of a monster hurricane, the reality is, as Mr. Rogers observed, that “storm patterns are pretty scattered” in the northern Outer Banks, in contrast to Hatteras Island and the southern Outer Banks.

Another reality—in addition to the town’s known 60-year history since the Ash Wednesday nor’easter—is that no hurricane of the magnitude of Katrina or Michael has ever hit Southern Shores.

(To read about the 1962 Ash Wednesday storm, see: https://en.wikipedia.org/wiki/Ash_Wednesday_Storm_of_1962.)

(For a “snapshot” of N.C. Sea Grant, see: https://ncseagrant.ncsu.edu/wp-content/uploads/2018/10/2017-18_snapshot_final.pdf)

(To learn about Spencer Rogers, see: https://ncseagrant.ncsu.edu/about-us/our-team/spencer-rogers/)

Mr. Rogers, who also serves on the faculty of UNC-W’s Center for Marine Science, was nice (and patient) enough to go through an interactive mapping exploration in Southern Shores with me. I will take you through the process later in this column and hope you will be inspired to do more of your own research.

LOOKING AT TYPES OF BEACH EROSION

As Mr. Rogers explains in his book, “The Dune Book,” there are four types of erosion: 1) seasonal erosion; 2) erosion caused by a severe storm; 3) long-term erosion; and 4) inlet erosion. Beach nourishment projects are designed to address #2, an “extreme storm event” and/or #3, “chronic day-to-day losses,” he said.

Fortunately, we do not have to contend with inlet erosion. Shorelines adjacent to inlets—such as Topsail Beach—experience hazards that shorelines along oceanfront do not.

One such shoreline is along Ocean Isle Beach, which is between Holden and Sunset beaches near the North Carolina-South Carolina line. Beach nourishment done there 20 years ago by the Corps of Engineers “disappeared in a couple of months,” Mr. Rogers said. The town and Corps had to go back to the drawing board.

To compare the Southern Shores’ shoreline with a shoreline where an inlet is the major driver of erosion, as some local property owners have done, is to make the proverbial apples-to-oranges comparison. There are no inlets off of our coast.

(Mr. Rogers also noted that Dare County’s nourishment of unincorporated Buxton and Rodanthe, which had high LT erosion rates, “disappeared very quickly,” too.)

Seasonal erosion occurs because of a variation in wind and wave energy.

As the Sea Mark coastal specialist explained: “The beach oscillates in width from season-to-season and from year-to-year.” During the summer, he noted, sand moves north, so Southern Shores should benefit from Kitty Hawk’s 2017 nourishment project.

The beach is at its widest in late July and early August, according to retired longtime USACE Field Research Facility coastal engineer and former Southern Shores homeowner Bill Birkemeir, who also spoke with me by telephone last week. (To calculate beach widths recently, APTIM used measurements from May, not from the summer.)

In the “seasonal cycle,” Mr. Birkemeier said, the beach is “narrow and steep in winter” and “comes back in the summer.” Passing hurricanes and other storms push the sand off-shore, but it returns. “It’s really simple,” he noted, and very important to understand.

When Mr. Willson attempted to update in September 2019 what he called erosional and accretional “trends” in Southern Shores on the basis of data obtained between December 2017 and May 2019, oceanographers from the Field Research Facility challenged his conclusions.

As The Beacon reported 9/20/19, Dr. Katherine L. Brodie and Dr. Nicholas Cohn, both of whom live in Southern Shores, told the Town Council at its Sept. 19 planning session that APTIM’s conclusions were “based on limited data” and “on short-term trends that are not particularly helpful.”

“It is very challenging to understand what’s really happening to our coastline,” said Dr. Brodie, who characterized the Southern Shores dune system and shoreline as being “stable” over time. (“It is very difficult to eyeball the shoreline,” said Mr. Rogers, who has a master’s degree in coastal and oceanographic engineering from the University of Florida. There are “radical changes” going on that the eye cannot detect.)

Dr. Brodie also told the Town Council that “there is lots of seasonal variability” in erosion (loss) and accretion (gain) of beaches. The time to measure beach erosion is not in the winter, as APTIM had done.

Both Dr. Brodie and Dr. Cohn offered their professional expertise to the Town Council in helping it to make an informed and educated decision about beach nourishment. But the majority did not accept their offer.

Because Southern Shores has not been annually profiling its shoreline, we do not have what Mr. Birkemeier called “built-up knowledge” to evaluate short-term data. Some of us thought that APTIM’s 2017 profile would be the first in a series of annual surveys to keep track of the shoreline. But it did not take long for Mr. Willson to shift into recommendations for beach nourishment, with encouragement from the Town.

SOUTHERN SHORES HAS HISTORY OF LOW LONG-TERM AVERAGE EROSION RATES

According to its website, the N.C. Division of Coastal Management evaluates long-term average erosion rates for North Carolina’s 300-mile ocean coastline every five years. It updates these rates by obtaining new aerial photographs of the shoreline to add to its database and running the data through computer programs that yield “thousands of numbers.” It started this effort in 1979, using photographs that date back to 1940.

In a January 2019 report about the methods it used to update LT average erosion rates in 2016, the DCM reported that 88 percent of the Southern Shores shoreline had measured erosion, while the remaining 11 percent had measured accretion. The DCM calculated the average LT erosion rate for our beaches to be 0.5 feet per year.

This does not mean that every year part of the Southern Shores shoreline is losing six inches of width while another part is gaining sand.

The DCM explains the calculation by comparing a 1992 shoreline with a 1942 shoreline. To derive the long-term average erosion (or accretion) rate, you would divide the distance that the shoreline has moved by 50, which represents the 50-year time period. If it has eroded 100 feet, you have a long-term average erosion rate of 2 feet per year, 100 divided by 50.

According to Mr. Rogers, the median long-term average erosion rate for North Carolina shorelines is currently one foot per year, a figure that he said is driven by sea-level rise.

**

Let’s do some long-term erosion-rate research of the Southern Shores shoreline. We will start on a DCM page called “Oceanfront Shorelines and Setback: Interactive Mapping,” which you can access at https://deq.nc.gov/about/divisions/coastal-management/coastal-management-data/shorelines-setback-interactive-mapping.

*Once you are there, click on “skip intro” at the top. A map of North Carolina should appear on your screen. When it does, type “Southern Shores” into the location box and click the search key.

*You now should be looking at a map of the Southern Shores area that shows the Currituck County mainland, the Wright Memorial Bridge, and U.S. Hwy. 158 into Southern Shores, as well as some of the main streets in the southern part of town, including South Dogwood Trail and Ocean Boulevard.

*In a column to the left of the map, you should see some icons, including what looks like a stack of papers, second from the top. This is the “layers list.” Click on it.

*Eliminate the checkmark in the box next to “DCM Office Locations” by clicking on it, then scroll down. What you seek are “Erosion Rates—2019 (oceanfront)—pending adoption,” and, for comparison purposes, “Erosion Rates—2013 (oceanfront)” and “Erosion Rates—2004 (oceanfront). You and Mayor Pro Tem Morey also will want to look at “Shorelines: Oceanfront and Inlet,” which is the fourth choice beneath the 2004 Erosion Rates.

*Check “Erosion Rates—2019 (oceanfront) and type in your location box, next to Southern Shores, a street name, such as Mullet Circle, which is the example that Mr. Rogers used with me.

*You now should see a street map, depicting Mullet Circle, east of Ocean Boulevard; Pompano Court will be to the north, and Dolphin Run to the south.

*Move your cursor out to the shoreline and click on one of the red lines you see. Red denotes erosion; green denotes accretion. The LT average erosion rate for the Southern Shores beach at Mullet Circle is 0.7 feet/year. This rate was determined over a 76-year period, from 1940 to 2016.

*Let’s look at another section of the Southern Shores shoreline. Type in “Seventh Avenue” next to Southern Shores in the location box and click.

*When you get to the map of the shoreline at Seventh Avenue, you should see small green lines at the oceanfront. Click on one of these. You will learn that the DCM has calculated a long-term average accretion rate of 0.2 feet/year over the same 76-year period at the Seventh Avenue oceanfront.

If you move to the beach at Chicahauk Trail, you will learn that a number of spots along the Southern Shores shoreline between Chicahauk Trail and Skyline Road have LT average accretion rates of 0.1 to 0.2 feet/year. There is long-term accretion on the oceanfront at Third Avenue and Hickory Trail, too.

In my interactive mapping explorations, I discovered that the only areas of the Southern Shores shoreline that have LT average erosion rates above the state median rate of 1.0 ft./yr. are a section around Trout Run, south to Yellowfin, and the southern part of the beach, from Ocean View Loop to the Kitty Hawk line. These erosion rates are generally 1.0 ft./yr. to 1.1 ft./yr. The 2017 nourishment at Pelican Watch should have made a difference at the southern end.

The time period covered by the 2013 rates is 1940-2009; and for the 2003 rates, it is 1949-1998. Please check them out.

If you and Ms. Morey click on “Shorelines: Oceanfront & Inlet” box in the layers list, you will see how the shoreline has shifted. In 1849, it is out in the ocean. As Mr. Rogers explained, the 1849 shoreline is based on a “coastal geodetic survey” and is not entirely reliable. It was President Thomas Jefferson who initiated the idea of surveying the coast in order to ensure safe navigation and stimulate international trade.

In addition to the 1949 shoreline representation, the DCM map shows shoreline positions from 1940, 1998, 2002, 2004, 2009, 2012, and 2016. Of interest is the 2002 shoreline, which is considerably west of all of the others—a testament to the changing dynamics of the coastal environment. The shoreline subsequently “corrected” itself.

DECIDING WHETHER TO DO NOURISHMENT; ANNUAL PROFILING

When asked how he would evaluate the Southern Shores beach-nourishment decision if he were a member of the Town Council, Mr. Rogers said he would look at:

  • the long-term erosion rates;
  • the benefits and costs; and
  • how the town can pay for it

It would be a “personal” decision, he said.

The Town Council has not considered erosion rates, because APTIM did not, nor has it done a cost-benefit analysis. No one has talked about how the town, which has few commercial properties, financially benefits from beach nourishment, except in terms of the relatively small amount that it receives as its share of the Dare County occupancy taxes. We suppose Southern Shores theoretically could become a ghost town, but neither its shoreline nor its tourist economy is in crisis.

Despite a report by a Seventh Avenue homeowner that he talked with tourists who said they will go elsewhere because the beach there has substantially deteriorated, that anecdote illustrates a very rare exception. Rental companies can tell the Town Council that they are not hearing that complaint. I can tell the Council that after 50 years of seasonal rentals in my family’s quaint 1970s-era oceanfront beach box, business remains robust. We rent out—and we are just north of Trout Run!

During the two years that I have been attending presentations by Mr. Willson—and also at the January 2017 beach nourishment conference, in which Mr. Rogers participated as a guest expert—I have never heard a rental-property owner outside of Pelican Watch complain about losing income because of poor beach conditions.

There is no reason, however, to treat the north end of the Southern Shores shoreline, where Seventh Avenue is, the same as the center of the shoreline or anywhere else along what the DCM says is a 4.5-mile shoreline.

“You don’t have to put sand everywhere,” Mr. Rogers said, in addressing the perceived “need” for beach nourishment, “or put the same amount everywhere.”

(Indeed, property owners may petition to be excluded from a municipal service district because they do not benefit. That is a subject for tomorrow’s post.)

You can distinguish among different sections of the beach, but first, The Beacon believes, you should know your beach. Both Mr. Rogers and Mr. Birkemeier recommend annual surveys. We do not know where the sand on our beaches is and where it goes. We need to start keeping track.

“It helps a lot to understand what your beach is doing,” Mr. Rogers said, “and to design a project [to suit your beach] when you do” decide nourishment is warranted.

Everyone on the Town Council should be familiar with the easy-to-access, no-cost data provided by the DCM. Everyone should know the erosion-rate history of Southern Shores’ beaches. Everyone should view the shoreline as more than just a series of modern-day snapshots.

The Town Council needs to get behind annual profiling now . . . and to keep asking thoughtful questions . . . of thoughtful and experienced professionals who will answer them thoroughly and without bias.

Spencer Rogers would be happy to come to Southern Shores for a public meeting, and the invitation from the FRF oceanographers is probably still open. Time is on our side.

TOMORROW: MORE ON BEACH NOURISHMENT AND THE TOWN COUNCIL’S JAN. 21 WORKSHOP

Ann G. Sjoerdsma, 2/1/20

 

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