Coupled Barrier-Backbarrier Dynamics and the Formation and Stability of Barrier-Island Systems
Christopher Hein, Duncan FitzGerald, Ioannis Georgiou, & Emily Hein Geological Society of America 22 Oct. 2014
Barrier-Backbarrier Coupling & The Runaway Transgression Hypothesis
FitzGerald et al., 2008, Annual Reviews of Earth Science
Barrier-Backbarrier Coupling & The Runaway Transgression Hypothesis
Barrier-Backbarrier Coupling & The Runaway Transgression Hypothesis
Study Site: Plum Island, MA
Gulf of Maine
Study Site: Plum Island, MA
An Ancient Inlet
Paleo-Parker Inlet Open: 3.6 – 2.0 ka Inlet Fill Sequence Area: 2800 m2 Equivalent Tidal Prism: 36 x 106 m3 Jarrett, 1976, USACE Report
An Ancient Inlet Larger Tidal Prism
TP ~ 32 x 106 m3*
TP >> 32 x 106 m3
* - Vallino and Hopkinson, 1998, Estuarine, Coastal and Shelf Science
Approach: Backbarrier Infilling Merrimack River
N
0
Barrier Sands 2 km
Marsh / Peat Tidal Flat Parker River Rowley River
Backbarrier Sands
Parker River Inlet Castle Neck
Data: 6 grad theses & 4 govt data sets
Glaciomarine Clay Till / Bedrock
Stratigraphic Surfaces: Modern Surface N 2 km
3m+ Elevation with respect to MLW (m)
0
Merged LiDAR & Bathy (soundings)
-15 m
Plum Island Sound drainage basin
Points tied to MSL
Stratigraphic Surfaces: Backbarrier Sediment N 2 km
3m+ Elevation with respect to MLW (m)
0
156 cores penetrate to backbarrier sediment
-15 m
Backbarrier: strip off marsh, barrier sands, modern organics, etc
Stratigraphic Surfaces: Backbarrier Base N 2 km
3m+ Elevation with respect to MLW (m)
0
63 cores penetrate to backbarrier base
-15 m
Backbarrier Base: basal freshwater peat, glaciomarine clay, till, bedrock Volume of Backbarrier Sediment: 420 x 106 m3
Paleo-Topo / Bathy Surfaces: Backstripping
N 2 km
3m+ Elevation with respect to MLW (m)
0
-15 m
A
= A • dt
Tbs: thickness of backbarrier backstripped A: accretion rate Pa: mean marsh accretion rate (0.1 cm/yr) Sa: backbarrier sediment accretion rate (0.25 cm/yr)
Backstripping Results
Backstripping Results
Backstripping Results
Backstripping Results Inlet Open
Backbarrier During Open Inlet N 2 km
3m+ Elevation with respect to MLW (m)
0
Volume Sediment Removed: 309 x 106 m3
-15 m
Backbarrier Tidal Prism: 77 x 106 m3 (2.8x modern) Additional Tidal Prism: 50 x 106 m3 Max Paleo-Parker Inlet: X-C Area: 2800 m2 TP: 36 x 106 m3
Refining Paleo-TP: Hydrodynamic Modeling • Model: Delft3D (Deltares, 2013) – hydrodynamics & morphology • Structured curvililnear grid (below); depth-integrated hydrodyn. • Boundary conditions; major tidal constituents offshore (Mukai et al., 2002) • Grid Extent: 17 x 8 km (PI Sound & Essex Bay) • Grid resolution: 20 m (in sound) –100 m (offshore)
Modeling Results – Tides, Q, Tidal Prism
Modeling Results – Tides, Q, Tidal Prism
3
108 3
4000
6 m3 TP: 31-35 x 10 P is 30-35 x 10
Tidal Prism (m )
3
Inlet Discharge - Q (m /s)
3
Inlet Discharge - Q (m /s) Tidal Prism (m3)
107
2000 0
106
-2000 10 -4000 650
700 Simulation Hour
750
5
Conclusions: Coupled Barrier-Backbarrier Processes • Run “runaway transgression” conceptual model backwards • Backbarrier infilling drives barrier formation • Backbarrier degradation drives barrier erosion & instability?
Funding: NSF Coastal SEES Grant OCE-1325430