2/1/21: 2019-20 DUCK DRONE SURVEYING SHOWS BOTH EROSION AND ACCRETION OF ITS SHORELINE. SOUTHERN SHORES LACKS INTEREST IN SUCH MONITORING AND DATA.

The Southern Shores shoreline near Trout Run just days after Hurricane Dorian passed by.

In August 2019, the Town of Duck laid the groundwork for what would be a yearlong monitoring program of its dunes and beaches using an Unmanned Aerial System (UAS), which relies upon what are commonly known as drones.

Duck partnered with APTIM Coastal Planning & Engineering of North Carolina—the Wilmington-based firm with which Southern Shores has contracted since 2017 for all of its coastal engineering surveys and plans—to monitor the dunes and beach berm on its coastline before and after storms, starting with Hurricane Dorian in September 2019.

APTIM, now known as Coastal Protection Engineering of North Carolina (CPE), used UAS technology and special software to measure the volumetric change of sand along Duck’s shoreline above the mean high-water mark (MHW). Other sand within the beach profile, such as the off-shore sand that is under water, was not measured. (See The Beacon, 1/26/21, for “How the Beach Works 101.”)

The bottom line: Although Duck’s dunes and berm generally (but not all) experienced an erosion of sand when Dorian passed by and when two other storm events occurred in October and November 2019, they also experienced an accretion (an addition) of sand by September 2020, when data were collected after Hurricane Teddy, which became a nor’easter.

With the exeption of Duck’s beach-nourishment project area, which is approximately from the northern end of Skimmer Way south to Spindrift Court, the overall accretion in cubic yards after the Teddy nor’easter was substantial.

But even in the project area, 8,600 cubic yards of sand were added between Skimmer Way south to just north of Canvasback Drive.

Unlike the Southern Shores Town Council, which has committed to a townwide nourishment project despite the lack of need along most of the beaches north of Skyline Road, the Duck Town Council has carefully evaluated the variability in its shoreline.

Also, unlike Southern Shores, the Town of Duck had substantial shoreline erosion and houses teetering on the ocean in its project area before it did beach nourishment. It did not proceed with a proactive project based on speculation, as Southern Shores is doing.

For purposes of the drone surveying and analysis, Duck divided its shoreline into three sections, designated as:

1) “Area North of Project,” between North Baum Bay, near the Sanderling development, and Skimmer Way;

2) “Project Area,” between Skimmer Way and Spindrift Court; and

3) “Area South of Project,” between Spindrift Way and the Southern Shores town line.

Southern Shores had an opportunity to join Duck in this UAS monitoring program and to obtain aerial photographs of its 3.7-mile-long shoreline before and after storm events, but the Town Council declined to make the small investment. It declined, even though the same coastal engineering firm that Duck hired to perform the monitoring was already doing Southern Shores’ annual beach surveys. 

Indeed, Ken Willson, who is now managing all of the myriad details of Southern Shores’ $14-$16 million 2022 beach nourishment project, filed the first report in the Duck drone monitoring program.

Thereafter, his colleague, Adam Priest, who submitted the draft report of Southern Shores’ June 2020 beach survey, which The Beacon reviewed 1/26/21, submitted Duck’s other reports.       

HURRICANE DORIAN, THREE OTHER STORM EVENTS MONITORED

Between Aug. 26 and Aug. 29, 2019, APTIM installed 70 painted and pole-mounted Ground Control Points (GCPs) on the backside of the dune and on roadways and walkways along the Duck shoreline.

GCPs are used to “georeference data collected during UAS flights,” Mr. Willson wrote in a letter Nov. 5, 2019 to former Duck Town Manager Christopher Layton.

APTIM also “created and provided UAS flight plans to the Town, which were used to conduct rapid assessment UAS aerial surveys of the Town’s beach and dune,” he continued, “. . . Flights were planned to maximize coverage of the beaches while maintaining the resolution needed to derive an accurate topography of the ground.”

Drones are unmanned or uncrewed aerial vehicles: You may think of them as small aircraft without pilots whose mission is to take aerial photographs.

While Mr. Willson goes into detail in his letter about how APTIM collected data within the GCP network and then analyzed them, we will stop here in the methodology and refer henceforth to the data collection and processing as “drone surveying.”

The Beacon has this letter from Mr. Willson to Mr. Layton because the leadership of the Southern Shores Civil Assn. shared with us the files it received from the Town of Duck about its 2019-20 drone surveying. We have imagery as well as written reports.

APTIM’s drone surveying covered four events:

  1. HURRICANE DORIAN, which “impacted the Dare County shoreline,” Mr. Willson wrote, between Sept. 6-7, 2019. Duck town staff conducted pre-storm drone flights of the shoreline between Sept. 3-5 and post-storm flights between Sept. 8-12.
  • STORM EVENT TWO, which, Mr. Priest wrote in a Dec. 13, 2019 letter to Mr. Layton “impacted Dare County between Oct. 9-12, 2019,” was “non-tropical,” and was “produced by the combination of two coastal low-pressure systems that stalled off the East Coast creating days of high wind and sea conditions.” APTIM used data taken from the Dorian monitoring Sept. 8-12 to represent the pre-storm conditions for Event Two, and Duck town staff conducted drone flights between Oct. 15-22 to obtain post-storm conditions.
  • STORM EVENT THREE, which, Mr. Priest wrote in a Dec. 30, 2019 letter to Mr. Layton, “impacted the Dare County shoreline” between Nov. 16-18, 2019. This storm also was reportedly non-tropical and produced a nor’easter that “transited offshore of the East Coast creating days of high winds and sea conditions,” he wrote. The post-storm data of Oct. 9-12 from Event Two served as the pre-storm data for Event Three. Duck town staff conducted post-storm flights for Event Three between Nov. 25-26.
  • STORM EVENT FOUR, whose “impacts to the Dare County shoreline,” Mr. Priest wrote Nov. 17, 2020, to then-Interim Town Manager Joe Heard, “occurred between Sept. 19 and 24, 2020.” This storm, the CPE engineer wrote, was “associated with Hurricane Teddy as it moved north in the Atlantic, offshore of the East Coast and reached Category 4 strength.” It created “days of high wave conditions and elevated water levels,” he said. Mr. Priest went all the way back to Nov. 25-26, 2019, and the aftermath of Event Three, for his pre-storm data, while Duck town staff conducted post-storm flights between Oct. 1-6, 2020.

We have, but we will not belabor, the volumetric change data from each of these storm events, over all three sections of the Duck shoreline.  

We will say, however, that, until data were collected after the Hurricane Teddy-associated storm, the drone surveying generally showed erosion of the berm—which is the backshore of the beach, next to the dune—along the upper portion, and scarping at the toe of the dunes.

But not across the board.

Interestingly, a positive volumetric change was measured in the Area North of the Project after both Hurricane Dorian and Event Two, which APTIM attributed to “a result of the visual differences between the pre- and post-storm imagery and not a true representation of measured elevation differences between the datasets.” But it may have been simply a natural occurrence.  

After Event Three, the northern section experienced a volumetric loss of 33,200 cubic yards above the MHW, much of which it had gained back after Event Four.

In his Hurricane Dorian letter, Mr. Willson described the linear coverage area used to calculate volumetric change as being from the backside of the dune seaward about 120 to 150 feet to the waterline.

As we noted earlier, every section of the Duck shoreline experienced accretion, much of it substantial, between Event Three, which occurred in October 2019 and was assessed Nov. 25-26, 2019, and Event Four in November 2020.   

Although we said we would not belabor data, we do think that Duck’s “Area South of Project,” which abuts Southern Shores at its southern end, is worth a closer look.

THE SOUTHERN SHORES LINE

According to SSCA President Rod McCaughey, who has conferred with Duck officials, data were collected in this section as far south as Eleventh Avenue in Southern Shores.

The data analyses by APTIM/CPE show that this southern section experienced the following:

  1. After Dorian: Some erosion in the beach berm, but no escarpments along the toe of the dunes because of the steeper beach slope in this area. The net volumetric change above the mean high-water mark was a loss of about 18,000 cubic yards.
  • After Event Two: Some berm erosion, but no escarpments along the toe of the dunes. Net negative volumetric change was about 16,000 CY of sand above MHW.
  • After Event Three: Erosion along the beach berm resulting in a negative volumetric change of 15,350 CY of sand above MHW.
  • After Event Four: Accretion occurred throughout the section, with a positive volumetric change of 36,000 CY above the MHW.

If drone data were to be continuously collected, would we see that the amount of sand lost eventually returns? Would we see, and would our decision-makers better appreciate and respect, the seasonal and post-storm fluctuations that occur on the shoreline?

When Mr. Willson presented the results of APTIM’s first Southern Shores beach assessment to the Town Council at its March, 6 2018 meeting, he told Council members that “the shoreline is looking fairly stable” and there is “no big rush” to “jump” on beach nourishment.

“I think time is in on your side,” he concluded.

The results of his company’s data collection in the shoreline’s 22 beach stations showed, according to Mr. Willson: 1) the shoreline is “stable,” having lost only 0.4 feet (that’s five inches) between 2006 and 2017; and 2) the volume of sand in the system had actually increased during the same time period.

“The shoreline is looking pretty stable,” he said. “We’re not seeing any hot spots right now. The long-term averages and the short-term averages [for shoreline changes] look to be pretty stable, pretty manageable.”

And yet, here we are just three years later, with the Town Council on the verge of committing to a monster beach-nourishment project that is not only unnecessary, but pits property owners against each other, as it sorts them into different tax districts to pay for this unnecessary project.

Us-versus-Them. My back yard-versus-not my back yard. A town and community divided.

Selling out and moving to Duck is starting to seem like a darn good idea.

Ann G. Sjoerdsma, 2/1/21

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