'Understanding Katrina
Everyone knew it was coming. So why couldn't disaster have been avoided?
STORM BUFFER
For every mile of continuous wetland, the height of storm surges can be reduced by three 3 to eight 8 inches. Losing wetland acreage removes this dampening effect that has protected New Orleans and nearby coastal communities in the past.
DISINTEGRATING COAST
There are several factors that contribute to the loss of barrier islands and wetlands.
LEVEES
1. Without a levee, a flooding river carries silt over its banks and gradually replenishes coastal wetlands and barrier islands.
2. Levees, designed to protect low-lying communities from flooding, also cut off this natural flow of sediment, forcing it away from the wetlands.
3. With no way to replenish, the coastal barriers have difficulty recovering from damage attributable to other factors:
HURRICANES AND OTHER STORMS
NATURAL LAND SETTLING AND SINKING
CRISS-CROSS CANALS CUT FOR NAVIGATION AND OIL AND GAS TRANSPORTATION AND DRILLING.
[labels]
Wetlands; Silt; River
Developed flood plain; Levee; Degraded wetlands; Silt; Storm surges; Disintegrating barrier islands
Barrier-island decay also allows salt water to seep into freshwater systems, killing off wetlands plants, further accelerating erosion.
[labels]
Storm surge; Wetlands
[Photo]
A canal levee is breached in New Orleans between the Mississippi River and Lake Pontchartrain.
[Photo label] Breach
[Photo credit] ORBIMAGE/AP
Sources: Census Bureau, Center for the Study of Public Health Impacts of Hurricanes, Louisiana State University; Louisiana Department of Natural Resources; NOAA, USGS, FEMA, United States Army Corps of Engineers
Stephen Rountree and Rob Cady-- USN&WR
With Angie C. Marek, Silla Brush and Alex Kingsbury
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