Backbarrier Infilling GSA Talk
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Transcript of 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