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Mike Blum1 Department of Geology and Geophysics Louisiana State University Baton Rouge, Louisiana Ha

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Title: Mike Blum1 Department of Geology and Geophysics Louisiana State University Baton Rouge, Louisiana Ha


1
Mike Blum1 Department of Geology and
GeophysicsLouisiana State UniversityBaton
Rouge, LouisianaHarry RobertsCoastal Studies
Institute,Louisiana State UniversityBaton
Rouge, Louisiana
INEVITABLE DROWNING OF THE MISSISSIPPI DELTA
DUE TO INSUFFICIENT SEDIMENT SUPPLY AND GLOBAL
SEA-LEVEL RISE
1Now at ExxonMobil URC
2
Sea Level History and Geologic ResponsesPre-Anth
ropocene Sediment Storage- recent geologic
history- time-averaged rates of storage for the
post-glacial period- comparison with modern
sediment loadsProjections of Sea-Level Rise and
Subsidence- IPCC Sea-Level Rise Estimates to
Year 2100- Relative Sea-Level Rise (IPCC
sea-level rise and subsidence)- Static
Submergence Model- Projections of Land
LossSediment Mass Balance to the Year 2100-
Accommodation and Sediment Supply- Role of
sediment trapping (supply-limited condition)-
Inevitable drowning due to accelerated sea-level
rise
TOPICS OF DISCUSSION
3
SEA LEVEL HISTORY
4
SEA LEVEL HISTORY
5
Post-Glacial Alluvium and Deltaic
Sediments 60.500 km2
Post-Glacial Alluvium and Deltaic
Sediments 60.500 km2
6
Quaternary Deposits
Mississippi River Alluvial Valley
7
SEA LEVEL HISTORY
8
Block Diagram of Mississippi Alluvial Valley at
the Latitude of Natchez, MS
9
MISSISSIPPI RIVER DELTA Holocene History of Delta
Growth
  • 6 major coupled channel belts and delta complexes
  • like most major deltas, growth occurred after ca.
    7000 yrs BP

10
MISSISSIPPI DELTA LAND LOSS AND GAIN
Barras et al. (2003)
11
PRE-ANTHROPOCENE SEDIMENT STORAGE
12
Post-Glacial Alluvium and Deltaic
Sediments 60.500 km2
Post-Glacial Alluvium and Deltaic
Sediments 60.500 km2
13
LONGITUDINAL PROFILE OF THE LOWER MISSISSIPPI
VALLEY AND DELTA Tracing Late Pleistocene Braided
Streams into the Subsurface Using Base of
Backswamp Deposits
braided stream deposits
Based on 325 USACE boreholes
from Blum et al. (2008)
14
LOWER MISSISSIPPI VALLEY AND DELTA Magnitude of
Post-Glacial Deposition
Balize Delta gt 100 m Thick
Total storage 1860-2300 km3 or 2790-3450 BT of
sediment Storage rate 230-290 MT/yr over
12,000 yr post-glacial period
sediment isopachs adapted from Kulp (2000)
15
MISSISSIPPI RIVER DISCHARGES AND SEDIMENT STORAGE
Pre-Dam Sediment Load 400 500 MT/yr Mean
Sediment Storage
230 290 MT/yr 1976-2006 Mississippi
Atchafalaya Sediment Load 205 MT/yr Suspended
Sediment Load Meade et al. (1990) Kesel
et al. (1992) Avg. over 12 kyrs
16
LOWER MISSISSIPPI RIVER SEDIMENT LOAD Pre- and
Post-Dam Loads
230-290 MT/yr
Data courtesy of USGS Baton Rouge
Data courtesy of USGS Baton Rouge
Modern post-dam sediment loads are 65 of the
long-term mean storage component alone
17
Human Intervention
The Mississippi River Delta System
  • Dams in the Drainage Basin
  • Levees and Revetments
  • Fluid-Gas Withdrawal
  • Pipeline-Canal Infrastructures
  • Saltwater Intrusion

18
Mississippi River Alluvial Valley
19
LOWER MISSISSIPPI RIVER SEDIMENT LOAD Pre- and
Post-Dam Loads
adapted from Meade (1990)
20
PROJECTIONS OF SEA-LEVEL RISE AND SUBSIDENCE
21
GLOBAL SEA-LEVEL RISE Sea-Level Change Data and
Projections
Satellite observations
Tide-gauge observations
3.0 mm/yr
1.7 2.0 mm/yr
1mm/yr
from IPCC 2007
22
Grand Isle Annual Mean Sea Level 1947-2006
Slow subsidence Fast subsidence Slow subsidence
Relatively constant RSLR stable geologic setting
23
RELATIVE SEA-LEVEL RISE PROJECTIONS IPCC
Sea-Level Rise and Delta Subsidence
24
STATIC LAND LOSS MODEL Relative Sea-Level Rise No
Sediment Input
Model A 1 6 mm/yr Model B 3 8 mm/yr
subsidence model A
subsidence model B
subsidence model A
subsidence model B
25
THE LOUISIANA COAST IN 2000
26
THE LOUISIANA COAST IN 2100?
Projected future land loss of 10,500-13,500 km2
27
SEDIMENT MASS BALANCE TO THE YEAR 2100
28
MISSISSIPPI RIVER SEDIMENT SUPPLY Is There Enough
Sediment to Rebuild the Delta?
29
SEDIMENT MASS BALANCE MODEL Accommodation vs.
Current Sediment Supply
With present sediment loads, accommodation change
significantly outpaces sediment supply
possible start to diversions (optimistic)
subsidence model A
subsidence model B
with trapping efficiency 40
30
SEDIMENT MASS BALANCE MODEL Accommodation vs.
Natural Sediment Supply
With restored sediment loads, accommodation
change outpaces sediment supply if sea-level rise
is gt 1 mm/yrsignificant drowning is
inevitable!!
31
THE LOUISIANA COAST IN 2000
Diversions of Water and Sediment are Proposed as
Possible Solutions to Land Loss How Effective
Can They Be?
LSU CLEAR model creates 700-900 km2 with 25
of sediment load
32
THE LOUISIANA COAST IN 2100?
Diversions of Water and Sediment are Proposed as
Possible Solutions to Land Loss How Effective
Can They Be?
LSU CLEAR model creates 700-900 km2 with 25
of sediment load
Projected future land loss of 10,500-13,500 km2
33
THE LOUISIANA COAST IN 2100?
LSU CLEAR model creates 700-900 km2 with 25
of sediment load
Projected future land loss of 10,500-13,500 km2
34
SUMMARY AND CONCLUSIONS
  • Mississippi-Atchafalaya Suspended Sediment
    Discharge lt50 Pre-Dam Levels
  • Sea-Level Rise Rate is 3 X the Rate When Delta
    Plain was Developed
  • Rate of Sea-Level Rise Predicted To Continue To
    Rise This Century
  • Using Conservative Values For Subsidence, Our
    Submergence Model Predicts A Loss Of 10,000
    -13,500 km2 Of Coastal Plain by 2100
  • Sustaining Existing Delta Surface Would Require
    18-24 BT of Sediment Mass Balance Predicts
    Drowning is Inevitable
  • Restoration Sediment Must Be Used In The Most
    Efficient Way to Build New Land and Restore
    Existing Wetlands
  • An Updated Inventory Of Sediment Resources Is
    Necessary For Restoration To Move Methodically
    Ahead
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