Wetlands and Hurricanes

By Wynn W. Cudmore, Ph.D.Northwest Center for Sustainable Resources

DUE # 0757239

This project supported in part by the National Science Foundation. Opinions expressed are those of the authors

and not necessarily those of the Foundation.

Wetlands and Hurricanes

Hurricane Gustav

25 August – 1 September 2008

The Gulf Coast

Louisiana, Mississippi, Alabama and Florida

The Lower Mississippi River Basin is probably the most human-impacted large water basin in the world:• Logging of forested wetlands

• Conversion to agriculture

• Altered hydrology

• Extirpation of megafauna

• Fragmentation of the Mississippi River delta

Only about 3.7% of the original wetlands in the basin remain in a natural condition

Largest intact wetland is the Atchafalaya Swamp

2000 10% Forest remaining

1882

Wetlands of the Gulf Coast

Intact wetlands of coastal Louisiana

1. Barrier islands2. Brackish wetlands3. Swamps4. Freshwater marshes5. Bottomland forests

Louisiana contains over 40% of wetlands in the lower 48 states

New Orleans, Louisiana 29 April 2008

New Orleans's growth has required draining wetlands

and a complex system of levees, pumps and canals

Historical Development of New Orleans, Louisiana

Wetlands as buffers to storm surges

Barataria Bay, Louisiana

Every 2.7 miles of wetland lowers storm surge by one foot

Wetland Loss along the Louisiana Coast

1976

1999

Over the past few centuries 25% of

wetlands associated with the Mississippi

Delta have been lost to the ocean

Causes of Gulf Coast Wetland Loss

Sediment flowing from the Mississippi River into the

Gulf of Mexico

1. Levees and dams direct sediment out into the Gulf of Mexico rather than to wetlands

Oil gas extraction rig among eroding wetlands

in coastal Louisiana

2. Canals cut into coastal wetlands allow saltwater intrusion

3. Sea level rise due to climate change

Barrier islands also protect the Gulf Coast

Chandeleur Islands

Hurricane Katrina

28 August 2005

Category 5 hurricane

One day before landfall

Hurricane Katrina

29 August 2005

Landfall as a Category 3 storm

Katrina’s impact

New Orleans flooded

Failed levee

Damage to Hard Rock Casino

Fishing boats on leveeFlood damage

The impacts on wetlands from Hurricanes Katrina and Rita (2005)

Katrina transformed 217 square miles of

marsh into open water

Rita’s impact was less severe with some

marsh impact west of the Mississippi River

AfterBefore

Mississippi Delta - Before and After Katrina

31 August 2005

Post-Katrina

9 August 2005

Pre-Katrina

Impacts of Katrina on the barrier islands

Land area of Chandeleur Islands decreased from 5.6 mi2 to 2.0 mi2

Impact of hurricanes on the Chandeleur Islands, Louisiana

July 2001

Pre-Hurricane Lili (2002), Ivan (2004), Dennis (2005), Katrina (2005)

31 August 2005

2 days post-Hurricane Katrina

Hurricanes as agents of renewal

Katrina wind damage in Pearl River Basin, Mississippi – late 2005

Baldcypress (Taxodium distichum) and water tupelo (Nyssa aquatica)

were mostly unaffected by the storm

Impact of Hurricane Katrina on Coastal Forests

Before Katrina After Katrina

Green – intact forests Red – storm-damaged forests

Wetland restoration as a strategy

• Wetland restoration will require an increase in the sediment load of the Mississippi River

• Current sediment load is 50% lower than historic levels

• Sustaining current levels of wetlands will require an additional 18-24 billion tons of sediment per year

• Future wetland loss seems inevitable

The “Coast 2050” Wetland Restoration Plan

• Diverts a portion of the Mississippi River to deliver more sediment to wetlands south of New Orleans

• Levees below New Orleans opened to increase sediment and freshwater flow into marshes

• Close the Mississippi Gulf Outlet• Oil and gas channels to be filled• Sediment builds and wetland grasses replanted as

needed• Barrier islands replenished with dredged material

Marsh terraces as a conservation practice

• Earthen terraces are constructed to reduce wind and wave energy in shallow open water

• Facilitate establishment of submerged aquatic vegetation• Each terrace is approximately 1000 feet long, 40 feet

wide at the base and 10 feet wide at the top• Surface of the terrace is 2 feet above water level and

planted with native vegetation• Arranged in “V”-shaped patterns in shallow, open water

Marsh terraces

Marsh terraces captured vegetation and soil displaced by

Hurricane Rita

The resulting increase in elevation may

assist in the marsh-building process

Marsh terraces built in Little Vermillion Bay, Vermillion Parish, Louisiana. 

Marsh terraces in Vermillion Bay, Louisiana after several growing seasons

Marsh terraces

Marsh terraces as a conservation practice

• Earthen terraces are constructed to reduce wind and wave energy in shallow open water

• Facilitate establishment of submerged aquatic vegetation• Each terrace is approximately 1000 feet long, 40 feet

wide at the base and 10 feet wide at the top• Surface of the terrace is 2 feet above water level and

planted with native vegetation• Arranged in “V”-shaped patterns in shallow, open water• Create habitat for fish and wildlife species

Hurricanes and Gulf Coast Wetlands – a summary

• The Gulf Coast is vulnerable to damage from hurricanes due to its location, elevation and loss of wetlands and barrier islands

• Wetlands and barrier islands provide significant protection against major storms

• Wetlands have decreased in area due to natural and human-caused events

• Hurricanes result in the loss of additional wetlands and barrier islands, some of which is likely permanent

• Wetland restoration will require additional sediment input, which the current system cannot provide

• The “Coast 2050” wetland restoration plan proposes to alter the hydrology of the Mississippi River Delta to reverse wetland loss

Photo Credits• IAN Image Library (ian.umces.edu/imagelibrary/): Tim Carruthers• Louisiana State University Hurricane Katrina and Rita Cooperative Clearinghouse.• Marine Photobank: David Helvarg, Blue Frontier Campaign, ESA Envisat• NASA/courtesy of nasaimages.org• Jesse Allen, Earth Observatory, using data provided courtesy of Laura Rocchio,

NASA Landsat Project Science Office• NASA Earth Observatory• NASA/GSFC/LaRC/JPL, MISR Team• Image Science & Analysis Laboratory, Johnson Space Center• GOES Project Science Office• National Oceanic and Atmospheric Administration/Department of Commerce:

Dr. Terry McTigue, NOAA Fisheries• U.S. NAVY• USDA Natural Resources Conservation Service: Lynn Betts, • U.S. Geological Survey: National Wetlands Research Center

Additional Slides

The following slides are provided as additional evidence of the impacts of Katrina on wetlands

The impacts on wetlands from Hurricanes

Katrina and Rita (2005)Katrina transformed 217square miles of marsh into open water

Rita’s impact was less severe with some marsh

impact west of the Mississippi River

Before

After

Mississippi Delta –Before and After Katrina

4 September 2005

6 days post-Katrina

9 August 2005

Pre-Katrina

New Orleans –Before and After Katrina

30 August 2005

27 August 2005

New Orleans – Before and After Katrina

31 August 2005

2 days post-Katrina

27 August 2005