Storm Protection & Coastal Restoration: Moving in to the 21st Century

Denise J. ReedUniversity of New Orleans Restore or Retreat

March 2009

Master Plan Objectives• Objective #1: Reduce economic losses from storm

based flooding• Objective #2: Promote a sustainable coastal

ecosystem by harnessing the processes of the natural system

• Objective #3: Provide habitats suitable to support an array of commercial and recreational activities coastwide

• Objective #4: Sustain the unique heritage of coastal Louisiana

Main Points• It’s an ever changing system• What does it take to achieve

sustainability?– Maximize the use of our resources– Capitalize on natural processes

• What do we need to do now?– Establish leadership and engage national

stakeholders and technical experts

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Lafourche Parish

Lafourche Parish

Terrebonne Parish

Terrebonne Parish

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AshlandAshland 56

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Morganza to the Gulf of Mexico

Project

Morganza to the Gulf of Mexico

Project

REACH AREACH AREACH AREACH A

REACH BREACH BREACH BREACH B

Houma Navigation Canal LockHouma Navigation Canal Lock

Sector GatesSector Gates

Work in Kind (WIK) LeveesWork in Kind (WIK) Levees

Federal Levee AlignmentFederal Levee Alignment

MontegutMontegut

REACH EREACH EREACH EREACH E

REACH FREACH FREACH FREACH F

REACH HREACH HREACH HREACH H

REACH GREACH GREACH GREACH G

REACH IREACH IREACH IREACH I

REACH JREACH JREACH JREACH J

REACH KREACH KREACH KREACH K

REACH LREACH LREACH LREACH L

REACH J-1REACH J-1REACH J-1REACH J-1

HoumaHouma

MINORS CANAL

REACH A

REACH B

REACH E

REACH F

REACH H-1

REACH H

REACH I

REACH J REACH K

REACH L

REACH G

Wetlands Behind Levees = Opportunities?

More tidal exchange = more opportunity for sediment input

Existing levees

Existinglevees

Roads

MORGANZA-TO-THE-GULF TECHNICAL PANEL REVIEW

• Robert Twilley (Chair), Ph.D.• Mead Allison, Ph.D.• Louis Capozzoli, Sc.D., P.E. Retired• Shirley Laska, Ph.D.• Larry McKee, P.E.• Ehab Meselhe, Ph.D., P.E.• Denise Reed, Ph.D.• Tim Ryan, Ph.D.

http://www.lacpra.org/assets/docs/MtG%20Final%20Report_5%20Dec%2008.pdf

Basic Assessment

•Continue work on levees, floodgates and environmental structures on the current authorized levee alignment with the goal of providing a minimum system-level of protection (e.g., equivalent to that currently provided by the J1 reach) to the planning area (Phase 1 construction).

•Continue work on the HNC lock-floodgate structure given its vital role in the protection system and its potential to be used to benefit the ecosystem.

Basic Assessment

•Integrate proactive wetland restoration approaches (funded under other authorities) into the ongoing design and operation of the Morganza project.

•Routinely (e.g., every 5 years), revisit the project to reassess risk to communities and the economy, evaluate ecological impacts and benefits, and revise future construction and operation plans and schedules as appropriate.

Planning for Flood Risk Reduction

•Initiate a comprehensive, community-based planning process to identify the elements that need to be protected for the Terrebonne communities to thrive.

•Increase efforts to inform the business community and the general public of the level of protection and risk reduction provided.

•Implement a comprehensive flood management approach for the area that leverages existing programs for non-structural flood risk reduction, provides incentives to businesses and the general public, and provides for the safe location of future development.

USACE Slide courtesy of Pete Rabbon

Planning for Flood Risk Reduction

• Develop conservation easements, land-use plans and zoning ordinances to protect existing wetlands in the planning area from loss to development.

• Initiate a public education program to communicate scientifically based assessments economic benefits of improved construction standards on residual risk in the context of future storm frequency, sea level rise and subsidence, oil and gas activities.

Improved Tools and Analyses for Assessment of Integrated Risk Reduction Outcomes

•Continue to develop a system-wide model and use it, as well as conceptual models and monitoring, to design and operate environmental structures within the levee system; and convene an independent expert panel to guide this adaptive management process.

•Hold a workshop and/or convene a panel to consider the effects of flooding and salinity changes on wetland plant communities and soil development processes to inform evaluation of project effects on wetlands.

•Apply planning tools that allow integrated, spatially explicit assessments of structural and non-structural measures in risk reduction and that consider a range of possible future economic, social and environment scenarios.  

Sustainability?Master Plan Planning Objective 2• Promote a sustainable coastal ecosystem by

harnessing the processes of the natural system.– providing for daily, seasonal, and episodic fluctuations in

water levels and salinities, and/or reestablishing natural pathways of sediment movement and nutrient uptake.

– Appreciation of the dynamic nature of the coastal system must be integral to the planning and selection of preferred alternatives

– route riverine waters through estuarine basins

The Past

Open bay Open bay

Min

imum

Ma

xim

um Growth Decay

DEL

TA

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LO

BE

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Z

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(A

RE

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Time

Subaqueous leveesMudflats

Freshwater marshBrackish marsh

Saline marshSwamp

LakesOyster reefs Oyster reefs

Marginal beachesBarrier islands

UBMERGED GROWTHS APID AERIAL GROWTHR ETERIORATIOND

BIOLOGICAL

DIV

ER

SIT

Y

Plaquemine

Lafourche

St. Bernard

Teche

Maringouin

Current stage of specific delta lobes

Na

tura

l env

iron

me

nts

Continuing Current Management

Achieving Sustainability

Coast 2050 Coast 2050 Coast 2050 Coast 2050

Is it achievable?

• There’s not as much sediment in the river as there used to be……

• It’s futile to try and build new land in the face of sea-level rise and subsidence……

ECOGEOMORPHOLOGY of Deltaic Coast

Wax Lake Delta – An analogue to study the

processes of a growing delta;

In contrast to Terrebonne & Lafourche that represent degrading stages of delta

.

SUMMARY: The Delta Mass Balance

The Dynamic Delta Top = competition between sea-level rise + subsidence and deposition of sediment and organic matter:

Atop the area of the delta

top

where H is eustatic sea level,

σ 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,

Wonsuck Kim, Gary Parker, David Mohrig, Robert Twilley, submitted 1990

.

SUMMARY: The Delta Mass Balance

The Dynamic Delta Top = competition between sea-level rise + subsidence and deposition of sediment and organic matter:

Atop the area of the delta

top

where H is eustatic sea level,

σ 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,

Wonsuck Kim, Gary Parker, David Mohrig, Robert Twilley, submitted 2000

.

SUMMARY: The Delta Mass Balance

The Dynamic Delta Top = competition between sea-level rise + subsidence and deposition of sediment and organic matter:

Atop the area of the delta

top

where H is eustatic sea level,

σ 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,

Wonsuck Kim, Gary Parker, David Mohrig, Robert Twilley, submitted 2002

.

SUMMARY: The Delta Mass Balance

The Dynamic Delta Top = competition between sea-level rise + subsidence and deposition of sediment and organic matter:

Atop the area of the delta

top

where H is eustatic sea level,

σ 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,

Wonsuck Kim, Gary Parker, David Mohrig, Robert Twilley, submitted 2005

MIGRATION OF THE MODEL FROM WAX LAKE TO THE MISSISSIPPI RIVER BELOW NEW ORLEANS:

Two diversions: Barataria Bay and Breton Sound (Envisioning the Coast)

BASE CASE: SEA-LEVEL RISE = 2 mm/yr, SUBSIDENCE = 5 mm/yr = 918 km2

Solid line: variant caseDotted line: base case

“Worst case”:

still 701 km2 of new land

And extra land-building due to organics is not yet included

Developing a Self-Maintaining Coast is Possible

VARIANT CASE: SEA-LEVEL RISE = 4 mm/yr, SUBSIDENCE = 10 mm/yr = 701 km2

A New Approach to River Management for the 21st Century

Captain A. A. Humphreys

Lieutenant H. L. Abbot

Delta Report

19th Century River Management19th Century River Management

Tributary Basin Improvements

Levees

Floodways

Channel Stabilization

20th Century River ManagementMississippi River & Tributaries Project

20th Century River ManagementMississippi River & Tributaries Project

21st CenturyProtection, Restoration

AND Navigation

Main Points• Morganza can balance protection and

restoration – we have to make sure it does• Levees are not the only thing we need to do

to protect ourselves• Sustainable restoration takes bold action and

will mean change• 20th century - change for the worst• 21st century – change for the better?