Hurricane George’s flood threat to New Orleans
Transcript of Hurricane George’s flood threat to New Orleans
World TradeCenter: 13.4 fee
ClaiborneAvenue:0.5 feet
Lake Pontchartrain levee:14.5 feet above sea-level
METAIRIE RIDGE
HarrisonAvenue:-3.6 feet
FilmoreAvenue:-4.9 feet
Robert E. LeeBoulevard:-3.5 feet
Lake PontchartrainBroadStreet:-0.3 feet
CarrolltonAvenue:-1.2 feet
Base ofI-610:-2.8 feet
Cemeteries atCity Park Ave.: 3.9 feet
Mississi21.4 fee
Normal lake level:1 foot above sea level
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Surge crashes inlandwith high wind-drivenwaves on top
FRENCH QUARTERMID-CITYLAKEVIEW
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CANAL BLVD.CANAL STREET
Jeff DavisParkway:-1.8 feet
GalvezStreet:0.6 feet
RampartStreet:2.3 feet
BourbonStreet:2.5 feet
NavarreAvenue:1.9 feet
PolkStreet:-4.6 feet
JewelStreet:0.9 feet
Over 8 feet
4-8 feet4-8 feet
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No floodingat UNO
Intracoastal Waterway
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Much of the area is belowsea-level, creating a natural“bowl.” Storm surge simplyfollows the law of gravityand meanders to thelowest points.
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KEY:5 feet or more above sea-level0 to 5 feet above sea-level0 to -5 feet below sea-level-5 feet or less below sea-level
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EXPLAININGTHE BOWL
When a hurricane even stronger than Georges hits New Orleans, Lake Pontchartrain — a foot higher than sealevel — will be the city’s biggest threat. Surge water from the Gulf of Mexico, topped by towering waves, willswell the lake above levees and cause widespread flooding. A look at average surge levels by category, comparedto a cross-section of the city known as “the bowl”:
CITY BELOW THE SEA
Surge and wavesat low tide*
HurricaneCategory
7 feet
14 feet
24 feet19 feet
9 feet12345
Effect on New OrleansLake Pontchartrain’s levees stop the low-level surge
Levees stop bulk of surge, but waves could cause considerable flooding
Entire city submerged including Mississippi River leveesLevees topped, causing catastrophic flooding
Levees stop the surge, but some waves could find their way over
SL IDELL
MANDEV ILLE
Note: Figures correspond to maximum surge heights, plus Lake Pontchartrain’s +1 sea-level. High tides could add as much as 2 feet, and the surge level could rise even higher in some spots on the lake’s shore. Elevations are approximate. Source: LSU’s Louisiana Water Resources Research Institute, Army Corps of Engineers, staff research
Over 8 feetOver 8 feet
Dry land onMetairie Ridge
UNDER
Approximate floodingdepth corresponds tosatellite image above
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Approximatediameter ofhurricane’s eye
New Orleans most recently dodged catastrophicflooding in 1998, when Hurricane Georges cutacross the Gulf of Mexico on a beeline to themouth of the Mississippi River. As half thepopulation fled, the storm veered tothe east and made landfall in Mississippi.The hurricane caused flooding inSt. Bernard Parish and also pushedwaves from Lake Pontchartrainup against its south shore levees,leaving many to ponder:What if?
IF GEORGES HADN’T TURNED
5 ST. CHARLES SUBMERGEDHere, water in the lake would reachheights of 3-8 feet above normal, spillinginto wetlands and towns in St. Charlesand St. John parishes. The water wouldbe deepest near the river levees.
6 GRAVITY’S GATEWAYRelentless winds from the stalled hurricanepush a dome of water 14 feet above sealevel at the levee. The model says that waterwould top low levees and floodwalls andmove east into Jefferson and Orleansparishes. Jefferson Parish officials say someareas would be sandbagged to 10 feet butprotection would be lower near the river.
7 FILLING THE BOWLWith the storm stalled, water continues to pourinto Jefferson and Orleans, filling the bowl withas much as 8 feet of water until it reachesnatural ridges or the Mississippi River levees.
90°W 89°W 88°W
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Gulf of Mexico
ModelGeorgespath
Sept. 26 at 4 a.m.
ActualGeorgespath
50 miles
1 THE MODELA computer model designed by LSUscientists Joseph Suhayda and VibhasAravamuthan and used by governmentagencies to prepare evacuation plans showswhat would have happened if Georges hadnot turned. This scenario assumes that thestorm continued on the track and intensityforecast by the National Hurricane Centeron Saturday, Sept. 26, 1998, at 4 a.m. In themodel, Georges intensifies to a Category 3with 115-mph winds when it makes landfalljust west of the mouth of the Mississippi.During the next two days, it moves slowlynorthwest, weakening to a Category 1 andstalling over eastern New Orleans.Here’s what would happen ...
4 LAKE LEVEES HOLDWinds on the west side wouldpush water against thehurricane-protection levees.
3 SLIDELL SOAKEDLarge parts of Slidell wouldbe inundated, but the waterswould recede rapidly with nolevees to contain them.
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Gulf of Mexico
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Clockwise high-pressure winds
Counter-clockwisehurricanewinds
Windspushingwaterinto lake
Easterly winds in advance of the storm would pumpwater from Lake Borgne and from Breton andChandeleur sounds into Lake Pontchartrain, raisingthe lake’s surface by 5 feet.
2 PUMPED UP LAKE
ELEVATIONS
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KEY:Surge water flowWind directionModel hurricane track