Figure Eight Coastal Observatory
A complete coastal system, measured as one.
From Rich Inlet to Mason Inlet, about five miles of coast hold every piece of a barrier system: an ocean beach, two tidal inlets, the island itself and the marsh behind it. The observatory is the Center’s study site and the place its methods are built.
On this page: The connected system · Instrument array and status · Baseline vs. monitored change
The connected system
From offshore to sound.
No element of this system can be studied in isolation. The inlets govern how sand and water move between ocean and sound; the beach and dune take the waves; the marsh takes the flood and must build upward as fast as the water rises. The inlet shoals and neighboring Hutaff Island are among the most important shorebird nesting and wintering sites in North Carolina, and Figure Eight’s beach hosts sea turtle nests every summer. The observatory measures sand and water, but the reason to measure is that the birds, turtles, marsh and people all depend on where that sand ends up.
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- 01
Ocean beach & dune
Where wave energy arrives and most visible change happens: the beach face, berm and dune line.
- 02
Tidal inlets
Rich and Mason Inlets: the gates through which sand and water exchange between ocean and sound on every tide, and the shoals that shorebirds depend on.
- 03
Barrier island
Figure Eight Island itself, the sand body that moves, narrows and migrates as inlets and sea level change.
- 04
Back-barrier marsh
The salt marsh and tidal creeks behind the island, which absorb flooding and depend on sediment to keep pace with rising water.
Baseline first
Before-and-after evaluation requires a well-measured before. Establishing baseline conditions is the observatory’s first priority, and it is under way.
Storms and seasons
Coasts change most during storms, especially those that coincide with high tides, and shift with the seasons, so sampling rates are set highest around storms and the beach is re-surveyed after them.
Permitting and coordination
Fixed instruments in the water require permits through the N.C. Division of Coastal Management and, where required, the U.S. Army Corps of Engineers. Installation of the Center’s current and wave instruments is under way.
Lessons beyond the site
Methods developed at Figure Eight are built to transfer to other barrier island and inlet systems, including publicly accessible ones.
The instrument array
What we deploy, and the question each answers.
Where things stand. A weather station is recording continuously, the Center has access to a tide gauge on the Figure Eight Island bridge, and repeat drone lidar flights over the beach are under way. The weather station is a Campbell Scientific logger recording wind speed, direction and gusts, air temperature, humidity, barometric pressure, rainfall and solar radiation at six-minute intervals. The tide gauge, a Hohonu sensor on the Figure Eight Island swing bridge, records water level at six-minute intervals with NAVD88, MLLW and MHHW datums established. Installation of the current profilers, velocimeters and wave buoys is under way. Fixed sensors record around the clock; the beach is re-surveyed by lidar on a schedule and after storms, and the seafloor will be once sonar surveys begin. Status and timing for each step are on the roadmap.
Every instrument answers a specific question that will feed the Center’s coastal models and, ultimately, the evidence base that communities, agencies and the state’s coastal management process can draw on. The standard every measurement is being brought to: tied to common horizontal and vertical reference datums (NAVD88 via RTK GNSS) and checked by documented quality-control procedures before use. Those procedures are being written now, alongside the first records.
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| The question | Instruments | What they produce | Why it matters |
|---|---|---|---|
| What is the weather doing, and how high is the water?Weather and water level | Weather station (recording) · tide gauge at the Figure Eight bridge | Wind speed and direction, pressure, rain, temperature; water level (NAVD88) | Wind and water level set the stage for everything else: they decide how far up the beach waves reach and whether a storm floods the marsh. |
| How fast is the water moving, and where?Currents and near-bed flow | Current profilers (ADCP) · point velocimeters (ADV) · installation under way | Flow speed and direction through the water column; high-rate near-bed turbulence | Currents move sand. Profilers map the flow through the inlets and surf zone; velocimeters sample the near-bed turbulence and stress that pick sand up. |
| What wave energy reaches the shore?Waves | Offshore wave buoy and ADCP wave array · installation under way | Wave height (Hs), period (Tp) and direction | Wave energy is the engine of beach change. Combined with water level, it drives the models of how the shoreline responds to storms and daily tides. |
| How much sand is in the water?Sediment | Turbidity sensors · sediment samples and grain size · planned | Suspended sediment (NTU, mg/L); grain-size distributions | The question at the center of the program is where the sand goes. Measuring how much is in motion, and how coarse it is, links the currents to the changes seen on the bottom and the beach. |
| What does the seafloor look like, and how is it changing?Bathymetry | Sonar (single- and multibeam echosounders) · planned | Bed-elevation grids (NAVD88) | Sand doesn’t disappear; it moves. Repeat sonar surveys of the channels, shoals and nearshore bottom show where sediment accumulates and where it erodes, within the survey’s uncertainty of roughly 10–15 cm. |
| How is the visible landscape shifting over time?Beach face and topography | Drone lidar and imagery (under way) | Elevation models, about 5 cm vertical uncertainty; orthomosaics | Lidar flown from uncrewed aircraft gives precise, repeatable elevation maps of the dry beach and dune. Overlapping surveys make erosion and recovery visible once change exceeds roughly 10 cm. |
Observations are combined with open datasets from NOAA, USGS, the U.S. Army Corps of Engineers and the state (tide gauges, wave hindcasts, decades of aerial photography) and with the peer-reviewed literature. Every finding the Center releases is reviewed by qualified coastal scientists before release. How the observatory’s records will be shared, and how findings will be published, is addressed under Working with the Center.
Baseline vs. monitored change
Before and after, measured against the same zero.
Every later survey is compared with the baseline, so a shift in the dune, the beach face or the nearshore bar shows up as a measured difference rather than an impression. Drag the divider to compare a schematic baseline profile with a later one.