Multiple Lines of Defense STRATEGY
The coast has always been our first line of defense against hurricanes for southeast Louisiana. Recognizing this, the Lake Pontchartrain Basin Foundation (LPBF) developed the Multiple Lines of Defense Strategy (Adobe pdf) designed to help save our coast. In the simplest terms, this strategy highlighted below shows how natural features of our coast (like barrier islands, marshes, and ridges) compliment manmade features (like levees) to protect the Greater New Orleans area from hurricanes. (View The Rise and Disappearance of Southeast Louisiana by Dan Swensen on nola.com.)
By building up the 11 lines of defense and restoring the historic wetland habitats to their past natural health, we can protect our region.
The Multiple Lines Of Defense Strategy
Lopez, John A., 2006, The Multiple Lines of Defense Strategy to Sustain Coastal Louisiana, Lake Pontchartrain Basin Foundation, Metairie, LA January 2006
There are 11 Lines of Defense (LOD), 5 natural and 6 manmade. They are
1st LOD Offshore Shelf: During Hurricane Katrina there was 60 foot waves in the Gulf Of Mexico. These huge waves did not hit land because the offshore shelf greatly reduces wave height by reducing the depth of the water. However, the offshore shelf does cause the storm surge to increase. The shape of the shelf needs to be studied to determine the effect its shape has on wave and surge height.
2nd LOD Barrier Islands: Barrier islands cause the waves associated with tropical storms to break, protecting the interior sound and coastal marsh. They also help to reduce storm surge.
3rd LOD Sounds: Sounds provide a buffer to the strong currents that occur in deeper water. Sounds do however allow waves to re-generate.
4th LOD Marsh Land Bridges: These are areas of continual marsh, commonly adjacent to natural ridges or levees. Land bridges reduce waves and impede storm surge, protecting areas further inland that perform the same function.
5th LOD Natural Ridges: Natural ridges are the remains of natural levees from abandoned river channels. They can extend for miles and typically have an elevation of a few feet above sea-level. Many have state highways along them. They commonly determine the natural flow of water throughout the region. They reduce waves and storm surge.
6th LOD Highways: Many highways in the coast are elevated several feet to reduce their probability of flooding, which can reduce the height of waves and storm surges similar to natural ridges.
7th LOD Flood Gates: Floodgates are designed to hold high waves and storm surge out of an area but allow natural flow during calm weather. Because our coast is only a few feet above sea level floodgates must be placed along levees or spoil banks
8th LOD Levees: Levees are designed to be an absolute barrier to flooding, storm surge, and high waves. Levees are commonly used to protect highly developed areas such as Orleans, Jefferson, and St. Bernard parishes.
9th LOD Pump Stations: Pump stations are designed to remove runoff from heavy rainfall. They are not designed to deal with the type of flooding that can occur if a levee is breached.
10th LOD Hurricane : All homes and businesses in southeast Louisiana are subject to flooding if they are not raised above the recommended height. Elevating our assets that cannot be easily moved is their last line of defense.
11th LOD Evacuation: Evacuation is the last Line of Defense for anyone living in hurricane prone areas. While highways are the most common form railroads and airline travel can also be used.
Applying the Multiple Lines of Defense Strategy, LPBF reviewed the 100 plus project proposals designed in the Comprehensive Habitat Management Plan to improve the sustainability of forests, swamps, marshes, and barrier islands. The result was the identification of 10 coastal restoration project areas that provide the dual benefits of restoring coastal habitats while simultaneously enhancing hurricane protection for our region. These 10 projects grouped together are called the Pontchartrain Coastal Lines of Defense Program.
For detailed technical reports on these programs click here.
Adobe pdf version:
Multiple Lines of Defense Strategy Report
John Lopez, Ph. D
Coastal Sustainability Program Director