Ecosystem Restoration: Environmental and Social Constraints Robert R' Twilley Department of Oceanogr

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Coastal Planning For Louisiana Adjusting To The
Higher Ground (how high is higher? and how do
we adapt?) Robert R. Twilley, LSU
4th Annual Smart Growth Summit Creating Complete
Communities Center for Planning Excellence
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In a hundred years, Louisiana as a whole had
decreased by a million acres. 1.2 million since
1900, USGS Plaquemines Parish is coming to
pieces like old rotted cloth. A hundred years
hence, there will in all likelihood be no
Plaquemines Parish, no Terrebonne Parish.
Taken from The Control of Nature by John
McPhee, 1989
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The cycle of river-dominated delta, such as
Mississippi River, defines the mosaic of wetland
vegetation and barrier islands as sand and silt
are distributed across the coastal zone landscape
building over 4.6 million acres of wetlands.
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• Natural Systems Vulnerability Susceptibility to
  biogeophysical impacts of sea-level rise and
  river/sediment discharge on wetlands (climate and
  land use changes) relative to their adaptation
  (thresholds)

Increase Sea Level
SUBSIDENCE
61 190 cm change RSL by 2100
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History of Wetland Development
Layers of Sediment Deposition from both River
Floods and Hurricane Storm Surges have built the
elevation upon which Growth of Marsh Plants
contribute to building elevation needed to
stabilize wetlands in the DELTA
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Managing River and Coastal Processes linked with
Engineering Design to Develop a Self-Maintaining
Delta Landscape (footprint)
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There are critical thresholds of accretion
relative to rise in water levels that determine
the stability of coastal wetlands.
Subsidence, 4 mm/yr
Delta HGM
Threshold Accretion Rate, mm/yr
Relative Rise in Water Level, mm/yr
Adaptation Envelope
Subsidence, 0 mm/yr
Sea Level Rise, mm/yr
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ENVISIONING REPORT, JUNE 2006
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Civil engineers Paul Octave Hebert and Absalom D.
Woodridge supported a diversified approach to
flood control that depended on the combination of
outlets and levees. They criticized current
measures that relied solely on levees to prevent
overflow. By urging the state to adopt new
policies aimed at keeping open the last few
remaining outlets and building artificial ones to
replace those already lost, state engineers tried
to temper the drive of many planters to remake
the river.
Annual report of Paul Octave Hebert, State
Engineer to the Louisiana Legislature, Jan. 1847
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THE WAX LAKE DELTA AS ANALOGUE OF HOW TO REBUILD
A DELTA
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SUMMARY The Delta Mass Balance The Dynamic
Delta Top competition between sea-level rise
subsidence and deposition of sediment and organic
matter
Wonsuck Kim, Gary Parker, David Mohrig, Robert
Twilley, submitted
2005
Atop the area of the delta top where H is
eustatic sea level, s spatially averaged
subsidence rate, Qs total volumetric sediment
supply, fr the fraction retained in the delta
top, and rorg the rate of storage of organic
matter in the sediment column,
.
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MIGRATION OF THE MODEL FROM WAX LAKE TO THE
MISSISSIPPI RIVER BELOW NEW ORLEANS Two
diversions Barataria Bay and Breton Sound (for
demonstration purposes)
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Developing a Self-Maintaining Coast is Possible
Base Case SEA-LEVEL RISE 2 mm/yr, SUBSIDENCE
5 mm/yr (980 km2)
Worse Case SEA-LEVEL RISE 4 mm/yr, SUBSIDENCE
10 mm/yr (701 km2)
Solid line variant case Dotted line base case
And extra land-building due to organics is not
yet included
Worst case still 701 km2 of new land
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• Socioeconomic Systems Vulnerability
  Susceptibility of biogeophysical impacts of
  sea-level rise on human systems relative to
  capability of technical, institutional, economic
  and cultural ability to adapt to these impacts

• Risk to Present Protection Levels 16 inch
  increase in sea level may cause a five-fold
  estimate in people at risk.
• Enhanced Protection sea level rise still
  reduces the capacity of enhanced protection

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http//www.louisianaspeaks.org/
http//www.lacpra.org/
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Linking Dynamic Landscape Changes to Land Use
Planning
Options for the Future Depend on Projections of
Self-Maintaining Delta Footprint - Regional
Land Use Planning and Economic Development are
Linked to Sustainable Coastal Footprint.
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HOW?
From First Principles to Innovative Practices
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Larson
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A System of complex risks
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Business Systems
Natural Science
Social Policy Analysis
Engineering
Information Sciences
Design
Requires a System of solutions
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Coastal Risks Management
Development and support of a safer and more
secure coastal landscape will require new ideas
in policy, design, and analysis for social and
built environments
Planning and Design
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Facilities
Coastal Sustainability Studio
Coastal Sustainability Studio a studio at LSU
that will house landscape architecture, coastal
engineering, and oceanography to build the
practice necessary to convert concepts to
construction by designing blueprints of resilient
coastal communities.
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• Ecosystem Restoration and Protection
• Carbon Sequestration