Backbarrier Infilling GSA Talk

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