Backbarrier Infilling GSA Talk

Christopher Hein, Duncan FitzGerald,

Ioannis Georgiou, & Emily Hein

Geological Society of America

22 Oct. 2014

Coupled Barrier-Backbarrier

Dynamics and the Formation and

Stability of Barrier-Island Systems

Coupled Barrier-Backbarrier

Dynamics and the Formation and

Stability of Barrier-Island Systems

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

Gulf of

Maine

Study Site: Plum Island, MA

Study Site: Plum Island, MA

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

TP ~ 32 x 106 m3* TP >> 32 x 106 m3

* - Vallino and Hopkinson, 1998, Estuarine, Coastal and Shelf Science

An Ancient Inlet � Larger Tidal Prism

Approach: Backbarrier Infilling

Merrimack

River

Parker

River Inlet

Parker River

Castle

Neck

Rowley River

0 2 km

N

Data: 6 grad theses &

4 govt data sets

Barrier Sands

Marsh / Peat

Tidal Flat

Backbarrier

Sands

Glaciomarine

Clay

Till / Bedrock

Stratigraphic Surfaces: Modern Surface

3 m +

-15 m

Ele

vat

ion w

ith

res

pec

t to

ML

W (

m)

0 2 km

NMerged LiDAR & Bathy

(soundings)

Plum Island Sound drainage basin

Points tied to MSL

Stratigraphic Surfaces: Backbarrier Sediment

3 m +

-15 m

Ele

vat

ion w

ith

res

pec

t to

ML

W (

m)

0 2 km

N156 cores penetrate to backbarrier

sediment

Backbarrier: strip off marsh, barrier

sands, modern organics, etc

Stratigraphic Surfaces: Backbarrier Base

3 m +

-15 m

Ele

vat

ion w

ith

res

pec

t to

ML

W (

m)

0 2 km

N 63 cores penetrate to backbarrier

base

Backbarrier Base:

basal freshwater peat,

glaciomarine clay, till, bedrock

Volume of Backbarrier Sediment:

420 x 106 m3

3 m +

-15 m

Ele

vat

ion w

ith

res

pec

t to

ML

W (

m)

������ = A • dt

A � �� � � ������ � � ���

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)

Paleo-Topo / Bathy Surfaces: Backstripping

0 2 km

N

Backstripping Results

Backstripping Results

Backstripping Results

Inlet Open

Backstripping Results

3 m +

-15 m

Ele

vat

ion w

ith

res

pec

t to

ML

W (

m)

Backbarrier During Open Inlet

0 2 km

N Volume Sediment Removed:

309 x 106 m3

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

Simulation Hour

Inle

tD

ischarg

e-

Q(m

3/s

)

Tid

alP

rism

(m3)

650 700 750

-4000

-2000

0

2000

4000

105

106

107

108Inlet Discharge - Q (m

3/s)

Tidal Prism (m3)

P is 30-35 x 103

Simulation Hour

Inle

tD

ischarg

e-

Q(m

3/s

)

Tid

alP

rism

(m3)

650 700 750

-4000

-2000

0

2000

4000

105

106

107

108Inlet Discharge - Q (m

3/s)

Tidal Prism (m3)

P is 30-35 x 103TP: 31-35 x 106 m3

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