Coastal Resilience
Duke Marine Lab: Quantifying a Living Shoreline's Elevation Deficit
Photo credit: Duke Marine Lab western Pivers Island shoreline, historical 2019 aerial photograph in the NOAA site report.
Source: NOAA NCCOS, Site Report: Duke Marine Lab, Figure 1 (p. 1). Aerial photograph, 2019; historical context. NOAA NCCOS (institutional source) / Original source. NOAA material reuse and credit conditions: NOAA source-use policy.
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Duke Marine Lab's living shoreline has retained its granite sill while the water around it has risen. NOAA's site report records consistent sill elevations between the post-construction survey and a 2025 resurvey. Its 2004-24 monitoring summary puts lower-marsh elevation gain at 2.0 mm/year and mid-marsh gain at 0.3 mm/year, against a local mean sea-level rise of 4.5 mm/year [1]. Those measurements describe different maintenance demands within one functioning coastal asset.
Stable stonework in a changing tidal frame
Completed in 2002 on Pivers Island, North Carolina, the project replaced a seawall and cement fish pens with clean sand fill, marsh planting and an 80 m granite sill. The fill was graded to an 8% slope. Two lowered sill sections provide fish access [1]. The 2015 field study identifies this same stone-sill site as Pivers Island West, distinguishing it from the oyster-reef shoreline on the island's east side [3].
The elevation account differs by marsh zone
Subtracting the marsh rates from the sea-level rate gives relative-elevation deficits of 2.5 mm/year in the lower marsh and 4.2 mm/year in the mid-marsh. These deficits are calculated from the reported 2004-24 averages. The lower marsh gained elevation faster than the mid-marsh, yet both occupied progressively lower positions relative to the local mean water level. A settlement-only inspection would follow the stable stonework; the water-relative account also follows the marsh surface and inundation. NOAA reports average wave attenuation of 45%, with a maximum of 88%, from gauges on either side of the sill [1]. The site's short fetch and reported 10-15 cm average waves define the setting for that result.
The relative-elevation deficit is sea-level rise minus marsh elevation gain over the reported 2004-24 period. The two marsh zones require separate elevation accounts.
IMWO calculations and chart; source: NOAA NCCOS, Duke Marine Lab site report, page 4.
Evidence conclusion
Define the maintenance trigger in water-relative levels
A maintenance plan for this shoreline can carry three repeat surveys on a common vertical datum: sill crest and access depressions, marsh-surface elevations by zone, and local water levels. Each answers a different intervention question. Stone displacement calls for structural repair; a persistent loss of marsh elevation relative to water calls for a review of inundation, sediment supply and planting conditions. Raising the sill would also change the water and fish-exchange openings, so its crest and lowered sections belong in the same design review. The owner can agree review thresholds against the intended habitat and wave-protection functions, then retain the original levels and subsequent surveys in the asset record. NOAA's archive lists long-term observations from October 2004 to April 2025 [2]. That monitoring history supports a maintenance decision based on the asset's measured condition and intended functions.
Outstanding evidence
- Current common-datum crest, marsh-zone and local water-level surveys
- Site-specific inundation and wave-protection review thresholds, including the two lowered fish-access sections
- The chosen intervention's sediment, vegetation and water-exchange effects
Subject index
Related subjects
These subject pages bring together related projects, technical articles, reports, and evidence methods.
Sources used 3
- Site Report: Duke Marine Lab Living Shoreline, pages 1-5 Davis, Walker, Puckett, LeClaire, Bost and Giannelli; NOAA NCCOS, Undated posted version, including 2025 surveys; accessed 4 November 2026
- Duke Marine Lab Sill monitoring archive, NCEI Accession 0306220 NOAA NCCOS, 30 April 2026; observations 12 October 2004-10 April 2025
- Living Shorelines: Coastal Resilience with a Blue Carbon Benefit Davis et al.; PLOS ONE 10(11), e0142595, 16 November 2015; site identity and methods, pages 3-5
Card photo credit: Duke Marine Lab western Pivers Island shoreline, historical 2019 aerial photograph in the NOAA site report.
Source: NOAA NCCOS, Site Report: Duke Marine Lab, Figure 1 (p. 1). Aerial photograph, 2019; historical context. Cropped and resized. NOAA NCCOS (institutional source) / Original source. NOAA material reuse and credit conditions: NOAA source-use policy.
Changes: Cropped at x=0, y=255 to 1,049 x 590 pixels; resized to 1,200 x 675 pixels and JPEG re-encoded by IMWO.
Retain NOAA and source-report credit with the stated image changes. Reuse must preserve the source context and avoid implying government endorsement or affiliation.
This notice covers this photograph and the stated image changes only; article text and other site content are excluded.
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