PRS Watershed
A Living Watershed.
Port Royal Sound is a living system of wetlands, tidal creeks, working forests, and working land bound together by water. By tracing changes in land cover and habitat over time, we can begin to see how this connected system is changing and what those changes may mean for the Sound.
959,945
Watershed acres
Full 2024 NLCD analysis extent
210,163
Forest acres (2024)
−32k ac since 1985
328,153
Wetland acres (NLCD)
Woody + emergent combined
2,310
Oyster reef acres
SCDNR · 71,200 mapped polygons
107,889
Developed acres (2024)
1985–2024 · +72%
62,496
Agricultural acres (2024)
1985–2024 · −34%
The connected system
The watershed works as a connected system.
Rain falling on an upland forest begins a connection that reaches far beyond the nearest stream. Trees, soils, and wetlands influence how quickly water moves, what it carries, and where it is stored. Along the tidal edge, salt marshes stabilize shorelines and support food webs, while oyster reefs filter suspended material and shelter fish, crabs, and other wildlife. Together, these habitats connect water quality, biodiversity, and protection from flooding and erosion. Changes in land cover, drainage, and shoreline habitat can affect how the whole system functions.
Upland
Forest & canopy
Canopy intercepts rainfall. Roots stabilize soil and capture nutrients before runoff reaches streams.
Interior buffer
Bottomland wetland
Slows flood pulses. Transforms nutrients biologically before water reaches tidal waters.
Tidal edge
Salt marsh
Buffers waves. Exports organic carbon. Provides nursery habitat for juvenile fish as tides flood and drain the marsh.
Living filter
Oyster reef
Filters the water column. Three-dimensional reef habitat can help indicate estuarine health.
Receiving water
Port Royal Sound
The receiving water reflects how the whole watershed is functioning, together with the influence of Atlantic tidal exchange.
About these connections: USFS forests and water · EPA wetlands · NOAA salt marshes · NOAA oyster reefs
Land cover today · 2024 NLCD Annual
What the watershed looks like now.
The 2024 Annual NLCD maps every acre of Port Royal Sound across 15 land cover classes. Each class tells a distinct ecological story, from the lowest tidal flat to the most upland pine plantation.
2024 land cover · acres
- Woody Wetland
22.5% of watershed
215,858 - Forest
21.9% of watershed
210,163 - Open Water
20.1% of watershed
192,869 - Emergent Wetland
11.7% of watershed
112,295 - Developed
11.2% of watershed
107,889 - Developed, open space54,541
- Developed, low intensity36,879
- Developed, medium intensity14,354
- Developed, high intensity2,115
- Agriculture
6.5% of watershed
62,496 - Shrub / Herbaceous
5.6% of watershed
53,970 - Barren Land
0.5% of watershed
4,406
Wetlands dominate.
Woody wetland
215,858ac · 22.5%
Emergent wetland
112,295ac · 11.7%
Altogether, 328k acres of NLCD-mapped wetland comprise 34% of the watershed. Woody wetland covers bottomland forests and cypress swamps; emergent wetland captures tidal and freshwater marshes.
Forest is the second anchor.
Forest
210,163ac · 21.9% of watershed
Pine plantations and mixed pine-hardwood forests form much of the upland forest cover. Bottomland hardwoods are largely captured in NLCD's Woody Wetlands class above. Forest cover has shrunk by 31,951 acres since 1985.
Development has grown 72%.
All developed
107,889ac · 11.2%
Open space dev
54,541ac · largest subclass
From 62,784 acres in 1985 to 107,889 in 2024. Open-space development (low-intensity residential, golf, parkland) is the largest single subclass, reflecting the coastal resort and residential character of Beaufort County.
Annual NLCD · MRLC 1985–2024
Forty years of continuous change.
The Annual NLCD provides land cover for every year from 1985 to 2024, 40 consecutive snapshots of the watershed. Each class traces a distinct trajectory: development's steady climb, agriculture's long retreat, forest's compression, and the wetland classes holding remarkably stable.
Land cover trajectory 1985–2024 · annual acres
Use the buttons to show or hide groups. Hover for values.
Open Water includes estuarine and freshwater water bodies within the analysis extent.
Land cover transitions · 1985–2024
What changed into what.
Every colored ribbon is land that switched class between 1985 and 2024. The alluvial shows both the dominant conversion flows, forest to development and agriculture back to forest, and the smaller but ecologically significant reversals, including land that returned from development to forest cover.
Class-to-class flows · 1985→2024
Ribbons colored by 1985 source class. Stable land (same class in both years) shown faint. Hover for acres.
Only flows of 500 acres or more are drawn (21 flows). Width is proportional to acres transferred.
Key change flows (1985→2024)
- Forest → Shrub / Herbaceous32,642
- Forest → Developed32,032
- Shrub / Herbaceous → Forest18,357
- Agriculture → Forest18,113
- Agriculture → Shrub / Herbaceous13,492
- Woody Wetland → Emergent Wetland8,546
- Agriculture → Developed6,610
- Shrub / Herbaceous → Developed4,396
Reversion flows · land that came back
Development → Forest: 1,424 ac
Development → Shrub/Herb: 413 ac · Agriculture: 207 ac
Agriculture → Forest: 18,113 ac
Harvest & regrowth · annual pulse
Forest and scrub trade substantial two-way volume.
The most counterintuitive signal in the 40-year record: shrub and herbaceous cover has grown by 21k acres while 18k acres that were shrub in 1985 are forest again by 2024. This pattern is consistent with active timber harvest, clear-cutting followed by replanting that cycles through the landscape continuously.
Annual forest loss and regrowth signal · 1985–2024
When forest becomes shrub/herbaceous, the bar rises above zero. When shrub/herbaceous becomes forest, the bar falls below zero. The line tracks total forest acres on the right axis.
Shrub/herbaceous includes NLCD Shrub/Scrub (52) and Herbaceous (71). Barren Land is reported separately in the 2024 snapshot and is absent from this historical series. Annual transitions may count the same land more than once as it moves through repeated cycles.
The harvest cycle.
Clear-cut pine stands can read as shrub/herbaceous for a few years, then read as forest again as the canopy closes. The result is a background cycle that the single 1985→2024 comparison does not show.
Net position 1985–2024.
Forest net change
−31,951ac · 242k→210k
Shrub/herb net change
+21,001ac · 33k→54k
Across the annual maps, 160,167 acres changed from forest to shrub/herbaceous and 149,617 acres changed back. These are repeated year-to-year transitions, not unique acres. The 31,951-acre net forest decline reflects transitions among all land-cover groups, not only this pair.
Land CoverNWI wetlands · National Wetlands Inventory
The NWI maps 294k acres of wetland and aquatic habitat within the watershed.
NWI maps wetland and deepwater habitat at a finer resolution than NLCD land cover classes. Together they provide a more detailed picture of the watershed's hydrological fabric.
Estuarine & marine wetland · 117,374 acres
Freshwater forested & shrub wetland · 155,366 acres
Freshwater emergent & pond · 15,468 acres
Freshwater Forested/Shrub Wetland
155,366ac
Estuarine Wetland
117,374ac
Freshwater Emergent Wetland
10,435ac
Freshwater Pond
5,033ac
Riverine
4,194ac
Lake
1,302ac
Estuarine deepwater
672,536ac · the open Sound
Estuarine deepwater is the open Sound, bays, and tidal rivers: the water body itself. It is shown for completeness and reported separately from the wetland-and-aquatic-habitat total above.
Wetland change · Annual NLCD 1985–2024
From 1985 to 2024, mapped woody wetland declined while mapped emergent wetland increased.
About 67% of the combined decline in woody wetland and increase in emergent wetland occurs after 2016. The endpoint transition matrix also identifies land that changed between these classes or to open water. Because these are 30-meter mapped classifications, determining whether the patterns reflect marsh migration, hydrologic change, vegetation disturbance, or classification effects requires additional spatial and field analysis.
Wetland classes · annual acres
Net change in annual series
Emergent wetland
+7,524ac · +7%
Woody wetland
−13,070ac · −6%
Endpoint transitions · 1985→2024
Woody → emergent wetland
8,546ac
Emergent wetland → open water
1,348ac
Marsh DynamicsSE Conservation Blueprint 2025 · SECAS
Biodiversity: what the land cover supports.
The Southeast Conservation Blueprint 2025 scores each acre of the watershed for ecological indicators based on habitat quality, species occurrence, and connectivity. Across Port Royal Sound, positive indicator values identify habitat associated with imperiled herpetofauna, estuarine fish, and beach birds, showing how biodiversity patterns connect with the watershed's land and water.
Imperiled amphibians & reptiles
69.9%
of watershed has positive indicator value
671,756 acres. Positive habitat for species including the eastern diamondback rattlesnake, gopher tortoise, striped newt, and several state-listed salamanders. The highest-scoring HUC12s are the interior headwater swamps and bottomland forests most distant from development.
| HUC12 | Coverage |
|---|---|
| Gillison Branch | 91.8% |
| Cooper River-Calibogue Sound | 91.5% |
| Beech Branch | 90.9% |
| Camp Branch-Coosawhatchie River | 89.0% |
| Harbor River-Trenchards Inlet | 88.7% |
Atlantic estuarine fish habitat
27.1%
of watershed has positive indicator value
260,240 acres. Habitat supporting species including striped bass, shortnose sturgeon, and American shad. Coverage concentrates in the estuarine zone, the tidal rivers, sounds, and adjacent marsh margins where juvenile fish use salt marsh as nursery habitat.
| HUC12 | Coverage |
|---|---|
| Harbor River-Trenchards Inlet | 86.2% |
| Broad River-Port Royal Sound | 84.0% |
| Cooper River-Calibogue Sound | 78.4% |
| Lower Beaufort River-Atlantic Intracoastal Waterway | 76.4% |
| Whale Branch | 75.7% |
South Atlantic beach birds
0.6%
of watershed has positive indicator value
5,618 acres. A small, concentrated footprint. Species including American oystercatcher, Wilson's plover, least tern, and piping plover depend on undisturbed beach and shell-hash habitat concentrated in Trenchards Inlet, the ACE Basin edge, and the outer barrier islands. Its limited mapped extent should not be read as a measure of conservation priority.
| HUC12 | Coverage |
|---|---|
| Harbor River-Trenchards Inlet | 6.9% |
| Broad Creek | 3.7% |
| Lower Beaufort River-Atlantic Intracoastal Waterway | 2.9% |
| Gaskins Banks-Atlantic Ocean | 2.0% |
| Calibogue Sound | 1.5% |
What the Blueprint indicators measure
Imperiled amphibians & reptiles Scores each acre based on species occurrence models, habitat suitability, and landscape connectivity. Forest cover, wetland condition, and connectivity to unfragmented natural land are its primary drivers.
Atlantic estuarine fish habitat Reflects the condition of the estuarine zone and its upstream connectivity. Intact salt marsh, low turbidity, and tidal exchange drive the indicator; those conditions depend on the land cover and wetland fabric upstream.
South Atlantic beach birds Scores undisturbed beach and wrack habitat along the Atlantic coast. Sensitive to human access, predator pressure, and storm overwash dynamics; in Port Royal Sound it is concentrated on outer barrier beaches with limited development exposure.
SCDNR oyster reef survey · 71,200 polygons
2,310 acres of living infrastructure.
SCDNR has mapped the identifiable intertidal oyster reefs of the Port Royal Sound estuary. Their density pattern reflects tidal circulation and the history of water quality in each embayment; reefs are most dense where tidal exchange is strong and turbidity is low.
Oyster reef location and density · Port Royal Sound
Each point is a mapped reef, sized and colored by area. Zoom in to see individual reef polygons.
Reef sizes range from under 0.001 to 8.73 acres; 8,080 reefs exceed 0.05 acres. SCDNR data retrieved September 9, 2026.
Scale of the reef system.
Total reef polygons
71,200
Total reef acres
2,310
Median reef size
<0.01acres
Largest single reef
8.7ac
What oysters do for the watershed.
Filtration
Structural habitat
Water-quality connection
BiodiversityDevelopment pressure · annual rate of change
Mapped land conversion slowed after 2008, then increased again.
Annual NLCD identifies acres newly classified as developed from one year to the next. The mortgage-rate line provides national housing-market context, but the two series do not move closely enough to establish a direct relationship. Local conversion also reflects demand, land availability, infrastructure, and policy.
Annual newly developed acres and U.S. 30-year mortgage rate · 1986–2024
Bars: acres newly classified as developed each year (left axis). Line: U.S. 30-year fixed mortgage rate, annual average (right axis).
Peak 2006: 2,730 acres in a single year. 1.0k acres per year on average from 2015 through 2024.
Three periods in the mapped record
Highest-conversion period · 1998–2007
Sharp slowdown · 2008–2014
Renewed conversion · 2015–2024
Share of subwatershed classified as developed · 2024
- Broad Creek62.3%
- Battery Creek40.3%
- Colleton River34.5%
- Upper Beaufort River-Atlantic Intracoastal Waterway30.7%
- Calibogue Sound27.4%
- May River25.3%
- House Fork23.0%
- Upper New River-Atlantic Intracoastal Waterway22.3%
Top eight of the 40 official subwatersheds. Percentages use each subwatershed’s total mapped area, including open water. This is a 2024 snapshot, not change since 1985.
Development map · % developed by HUC12 subwatershed (2024)
Color intensity shows the share of each subwatershed classified as developed in 2024, using its total mapped area including open water. The dark overlay shows land classified as developed in 2024 but not in 1985.
From pressure to action · GIFT strategies
From watershed data to parcel-level action.
The Green Infrastructure Framework Tool (GIFT) pairs four decades of land-cover change with parcel-level indicators of flood risk, water quality, habitat, heat, and development. The whole-watershed strategy mix below is a starting point; open the Strategy Explorer to compare subwatersheds and select parcels for recommended Preserve, Enhance, Mitigate, or Retrofit strategies.
Resilience