Coastal Engineering
Poplar Island: Grading for the Marsh That Develops After Placement
Photo credit: Poplar Island dredged-material placement equipment; historical photograph.
Photograph: Thomas I. Deaton, U.S. Army Corps of Engineers, Baltimore District, 17 March 2022, via DVIDS. Public domain; historical placement-equipment context. Cropped by IMWO. Thomas I. Deaton, U.S. Army Corps of Engineers, Baltimore District / Original source. News use with credit and non-endorsement conditions: Public domain; DVIDS public-use conditions.
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At Poplar Island, the grading level helps determine how a constructed marsh develops after planting. A 2024 field study compared two areas of Cell 5AB with initial platform elevations of 0.22 m and 0.32 m NAVD88. Three surface elevation tables monitored each area. Mean elevation gains were 13.2 and 7.8 mm/year respectively over the study record through 2021. The lower area gained height faster; the higher area began with 0.10 m more elevation above the same datum. [1]
Ten centimetres of starting elevation
The study follows seven restored marsh cells and a natural reference marsh in Chesapeake Bay. Six cells use fine-grained dredged material; Cell 4D uses locally dredged sand. The fine material was dewatered for two to six years before tidal creeks were excavated. Tidal exchange began approximately six months before planting, helping neutralise acidity produced during drying. [1] USACE's project description places this habitat work within the beneficial use of material from Baltimore Harbor and its approach channels. [3]
Root growth and sediment redistribution change the surface
The Cell 5AB comparison combines elevation with local geometry. Its two areas occupy separate creek systems, and the lower area includes a marsh pond. The authors identify redistribution from creek and pond banks as a possible contributor to its higher surface deposition. They also explain a belowground mechanism: roots and rhizomes colonise the new substrate, adding volume as the marsh establishes [1]. Morris and Staver's companion modelling study treats this developmental growth as an additional, temporary contribution to elevation gain [2]. A placement design therefore needs to consider starting position in the tidal frame, sediment characteristics and creek geometry together. The field-study authors favour initial low-marsh elevations on the higher side of the productive range, preserving elevation capital as water levels rise. Their measurements describe developing marshes at this microtidal site.
The common 2013-21 comparison in the field study. Lines show cumulative elevation change from that observation baseline, with standard-error bars; they follow established marsh cells of different ages.
Evidence conclusion
Specify the consolidated level and retain its baseline
A future placement specification can connect the earthworks quantity to a defined consolidated surface, then follow that surface through establishment. The finishing envelope needs a vertical datum, local tidal references and a stated survey stage after consolidation. The as-built record can include the sediment grading, dewatering history, planted zones and creek layout alongside the levels. Those records explain what a later elevation change is being measured against. For estimating, a 0.10 m consolidated lift over one hectare represents 1,000 m3 in place. Converting this in-place volume to a pumped quantity requires the material's solids content and consolidation allowance. That conversion affects dredging, pumping time and the capacity reserved for future placement. Monitoring can then pair repeat surface elevation tables with marker horizons, which record deposition above a marked surface, and vegetation observations. The measures separate overall level change, surface accumulation and establishment. The owner can review them by marsh zone and age when deciding whether to add sediment, adjust a creek or replant. The Cell 5AB results give the owner a reason to retain the original grading and hydraulic layout throughout that decision, including the period after the early growth pulse slows.
Outstanding evidence
- Consolidated as-built elevations and local tidal references for each planted zone
- Material grading, dewatering history, porewater condition and establishment age
- Repeat level, marker-horizon and vegetation records beside evolving creeks and ponds
Subject index
Related subjects
These subject pages bring together related projects, technical articles, reports, and evidence methods.
Sources used 3
- Elevation Changes in Restored Marshes at Poplar Island, Chesapeake Bay, MD: I. Trends and Drivers of Spatial Variability, pp. 1784-1798 Staver, Morris, Cornwell, Stevenson, Nardin, Hensel, Owens and Schwark; Estuaries and Coasts, 31 January 2024; monitoring record through 2021
- Elevation Changes in Restored Marshes at Poplar Island, Chesapeake Bay, MD: II. Modeling the Importance of Marsh Development Time Morris and Staver; Estuaries and Coasts, 15 April 2024
- Paul S. Sarbanes Ecosystem Restoration Project at Poplar Island U.S. Army Corps of Engineers, Baltimore District, Live project overview; accessed 5 November 2026
Card photo credit: Poplar Island dredged-material placement equipment; historical photograph.
Photograph: Thomas I. Deaton, U.S. Army Corps of Engineers, Baltimore District, 17 March 2022, via DVIDS. Public domain; historical context. Detail crop by IMWO. Thomas I. Deaton, U.S. Army Corps of Engineers, Baltimore District / Original source. News use with credit and non-endorsement conditions: Public domain; DVIDS public-use conditions.
Changes: Crop x=120, y=920, 1400 x 678 pixels; JPEG compression.
The appearance of U.S. Department of War (DoW) visual information does not imply or constitute DoW endorsement.
This notice covers this photograph and the stated image changes only; article text and other site content are excluded.
View credited photo · Credit as text · Download photo with credit
