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Rebuilding New Orleans



Subsidence, Sea Level Rise, Global Warming, Faults, Hurricanes

The impact of Hurricane Katrina on the city of New Orleans has been called the most anticipated natural disaster in modern American history. Future hurricanes will track over the city and the processes of subsidence and sea-level rise will present additional challenges to this endangered real estate. Are these problems being properly considered as a great social and economic momentum pushes to rebuild the city? Families and businesses who deliberate on the prospect of a future in New Orleans need to know how safe and sustainable their homeplace will be. This information is also essential to the legislators who serve as stewards of reconstruction dollars and more importantly stewards of public safety.

Safety should be the top priority of any plan to rebuild New Orleans. Legislators must insist upon a proper safety analysis and a sustained educational program before large appropriations for redevelopment are made. New Orleans had days of advance warning while Katrina approached the Gulf Coast, yet over 1000 lives were lost. Knowledge of proper hurricane response might reduce a future death toll significantly -- especially if the next evacuation must be done without warning. If the plans for redevelopment do not assure safety and education then they should be cancelled or improved.

The same standard should be applied to sustainability. Can a sinking and below-sea-level city beside a rising ocean be sustained long term? Will the people who buy property there be "owners" or will they simply be "tenants" until government budgets fail to maintain a vast system of levees and pumps? Any family or business considering a home in New Orleans needs this information in advance.


Seventeen Category 3 or Higher Storms Since 1852:

Consider the map below which was produced using the NOAA Historical Hurricane Track Tool. It shows all hurricanes which were Category 3 or higher when they tracked within 100 nautical miles of New Orleans between the mid 1800's and 2004. Including Katrina, seventeen hurricanes of Category 3 or higher have passed within 100 nautical miles of New Orleans since 1852. That is an average of about one storm per decade. Anyone who considers this information with an open mind should realize that within the next century, New Orleans will feel the effect of several significant storms.


New Orleans Hurricane History Map (generated using the NOAA Historical Hurricane Track Tool).
A track for Hurricane Katrina is not shown as the tool runs from a pre-Katrina database.


New Orleans Hurricane History - 17 Category 3+ Storms

Date Storm Wind (Knots) Category
8/25/1852 Not Named 100 3
9/15/1855 Not Named 110 3
8/10/1856 Not Named 130 4
8/11/1860 Not Named 110 3
9/1/1879 Not Named 110 3
10/2/1893 Not Named 115 4
9/20/1909 Not Named 105 3
9/29/1915 Not Named 115 4
7/5/1916 Not Named 105 3
9/15/1960 Ethel 140 5
9/10/1965 Betsy 135 4
8/17/1969 Camille 165 5
9/7/1974 Carmen 130 4
9/13/1979 Frederic 115 4
9/2/1985 Elena 105 3
8/26/1992 Andrew 125 4
8/29/2005 Katrina 125 4


Global Warming - More Powerful Hurricanes (added April 2, 2006)

NASA has published data for global warming as annual trend charts and as surface temperature anomaly maps. As shown in the chart below, the global warming trend for the past 125 years has been an almost steady rise. During 2005 the highest global surface termperature in that 125 years of record keeping was recorded. NASA comments "Record warmth in 2005 is notable, because global temperature has not received any boost from a tropical El Niño this year. The prior record year, 1998, on the contrary, was lifted 0.2 degrees C above the trend line by the strongest El Niño of the past century. Increasing global surface temperature - particularly temperature in the Gulf and areas of Atlantic Storm formation are significant as they could lead to more powerful hurricanes in the future. Full details of the NASA data can be seen at their Surface Temperature Analysis website.


Graph by NASA


Subsidence & Sea Level Rise - The Bigger Problem?

The US Geological Survey has published a report titled: "Sea-Level Rise and Subsidence: Implications for Flooding in New Orleans". A USGS preface for this report:

"The rates of subsidence and sea-level rise are important considerations in the restoration of the city of New Orleans and the wetlands that protect it. New Orleans is sinking two inches per decade, and it is anticipated that it will sink roughly one meter in the next 100 years relative to mean sea level. The ocean is also rising. During the last century, the ocean rose one to two millimeters per year. Within the next century if nothing is done to modify the existing infrastructure, some areas of the city that did not flood as a result of Hurricane Katrina will likely flood in a future storm due to subsidence and sea-level rise."

This places New Orleans an additional meter or more below sea level by the end of this century. Continued subsidence and sea-level rise will demand a corresponding upgrading of levees and pumping systems to sustain the city. The long-term risk from subsidence and sea level rise could be a greater threat to New Orleans real estate than the hurricane threat. As subsidence and sea-level rise continue, the costs of protecting the city from seepage and storms will become more expensive than practical. Who should pay the costs of this losing battle? How long will government foot the bill? Anyone who owns or plans to purchase New Orleans real estate should understand the subsidence and sea level rise risks.



Subsidence on the Michould Fault (added April 20, 2006)

A study by Roy Dokka of the Department of Civil & Environmental Engineering, Louisiana State University and submitted as testimony to the Subcommittee on Water Resources, Committee on Transportation and Infrastructure, places significant blame for recent subsidence on the Michould Fault, a normal fault that trends beneath the eastern portion of New Orleans. Dokka demonstrates that a portion of the city known as "Michould" has an unusual subsidence rate (see illustration below) and that at least 50% of this subsidence can be blamed on the Michould Fault. Dokka's testimony transcript is only about ten pages long and is not extremely difficult reading: Effect of Subsidence on Flood Protection Options and Water Resources Planning in the Gulf Coast


Image from House Testimony
Michould Fault Shown as "MF" - note subsidence adjacent to fault.


Levee System Security:

New Orleans is protected by an extensive levee system. One breach of this system without warning could result in a tremendous loss of life. In the past, commercial and residential development has been allowed in close contact with the levees. This arrangement makes the levee system vulnerable to terrorist attack. Preventing such an event should be a key element of any redevelopment plan.

In the event of an attack or other sudden failure, everyone in the city must know how to evacuate. Residents are easy to educate but commuters and thousands of visitors present a more challenging problem. Emergency exit routes, signage and communications must be developed and maintained well enough to prevent a small number of confused evacuees from producing life-threatening delays.


The Bottom Line on Rebuilding New Orleans:

The data presented above clearly shows the following:

  • Hurricanes will repeatedly impact New Orleans
  • Sea level is rising and reduces the effectiveness of any levee system over time
  • The city is subsiding and this also reduces levee effectiveness
  • The current levee system is vulnerable to terrorist attack at many points

A proper redevelopment plan must center around safety and sustainability considering all of the above items. Short term economics and determination to rebuild can be admired but lives and a sustainable future are much higher priorities. In addition, more dialogue is needed on who should foot the bill. It is humane to provide financial assistance to those who suffered losses as a result of Hurricane Katrina. However, looking forward, perhaps the money spent on future development and losses should come from those who choose to use such risky land? Perhaps the costs of maintaining the levee system could be generated through taxes on real estate and tourism and those who hope to be reimbursed for future flood damage should have adequate insurance coverage.

Hobart King
Geology.com publisher
January 12, 2006


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