Understanding KATRINA 8/29/05 One-hour presentation delivered 9/30/05 at Montana State University William Locke Bozeman, MT http://www.nnvl.noaa.gov/hurseas2005/Katrina1215z-050829-4kg12.jpg

On promontories, not bays 2 category 5s, 7 cat. 4s Hurricanes are not uncommon occurrences along the Gulf and Atlantic coast. They typically strike promontories rather than bays or inlets. Since 1950, there have been two Category Five storms and seven Category Four storms. Hurricane Katrina made Gulf Coast landfall on August 29th, 2005, as a Category Four storm. http://www.nhc.noaa.gov/gifs/hur5005.jpg

History (1900-1996) http://www.nhc.noaa.gov/pastall.shtml Percent per year probability (historical) per 50-mile (80 km) coastline South Florida = most frequent South Texas and Miss. Delta = second Katrina Rita Most of the coastal areas hit by recent (2004-5) hurricanes have a historical expectation of a direct hit every 7-20 years and of a Category 3+ hit every 15-50 years (the lifetime of a noncommercial structure. Most of the coastal areas hit by recent (2004-2005) hurricanes have a historical expectation of a direct hit every seven to twenty years. They also have a historical expectation of Category Three hit every fifteen to fifty years, which happens to be within the lifetime of a noncommercial structure. Hurricanes hit South Florida most frequently, followed by South Texas and the Mississippi River Delta region.

Hurricane history Named storms Hurricanes Cat. 3+ http://www.nhc.noaa.gov/gifs/atlhist_lowres.gif Named storms Hurricanes follow cycles longer than ENSO, and anthropogenic global change is not evident in hurricane frequency (in fact, 1970-200 was the strongest hurricane drought in the period of observation. About 100 hurricanes, typhoons, and tropical storms occur globally each year, with ten (plus or minus five) in the Atlantic region. These cycles tend to be longer than El Nino/Southern Oscillation. There has been an increasing number of hurricanes since 1995. There are several possible interpretations of this increase in Atlantic hurricane activity, including natural climatic cycles and warmer ocean temperatures in the North Atlantic. Hurricanes Cat. 3+

Hurricane history But – see http://wind.mit.edu/~emanuel/anthro2.htm Named storms In fact, 1970-200 was the strongest hurricane drought in the period of observation. But – hurricane intensity may be increasing (see Emanual reference). Hurricanes Cat. 3+

Miss. delta Sea level? Lake Pontchartrain Lake Borgne SW Pass Although the Mississippi River runs to SW Pass, it is at ~2 feet a.s.l. through New Orleans, with sea level (or lower) on all sides. SW PASS http://www.mpcnetwork.com/marinersinfo/charts/gm/2neworleans.gif

Mississippi delta in flood Note: Sediment to Gulf 1,000,000 ton/day Flooded outer delta Dry diked areas Vegetation/land use on natural levees Bayou Lafourche Natural levees naturally breach to enable flooding of wetlands (see the outer delta) – where heightened and maintained they starve the backswamp areas of sediment. http://jan.ucc.nau.edu/~rcb7/MissDelta.jpg

Topography of New Orleans Much of north N.O. lies well below sea level Sea water gains access through canals An uneasy truce is maintained by ~350 miles of levees. Follows slide 8 – “Mississippi Delta in flood”. Natural levees, “reclaimed land along Lake Pontchartrain, and extent of local subsidence are evident. From Brian Hayes (2005), American Scientist, v. 93, p. 496-499 [original map from Louisiana State University]

Natural levees Result from multiple floods Extend 2+ km from river channel Are poorly engineered! Natural levees are composed of massive-to-layered sand and finer sediment – not well-designed to prevent leakage, piping (erosion from within) and failure. Rivers rarely stand above the backswamp (but New Orleans is unusual). Levees can be either natural or man-made. Man-made levees are constructed to prevent flooding on the land adjacent to the river. Natural levees are built by floodwaters depositing sediment along the river banks. They can extend more than two kilometers from the river channel. Natural levees do not protect rivers from large flooding events because they are built by frequent (five to twenty year) recurrent floods. Levees can, however, protect from most ocean-based flooding.

Which way to the ocean? Miss. R. is twice as long (half as steep) as shortcuts via the Atchafalaya R. or Lake P. Mississippi Atchafalaya The Mississippi River has aggraded (built up) through New Orleans in order to maintain the slope necessary to transport its sediment load all the way to SW Pass. http://www.ssec.wisc.edu/~gumley/modis_gallery/images/MississippiDelta_20040127_1940_1000m.jpg

Mississippi River deltas Sea level stable for ~6000 yr Delta front moves as river avulses Average duration <1000 yr Modern delta for ~1300 yr Time for a change! Based on radiocarbon dating of previous late Holocene (last 6000 years) deltas, the present distributary could/should have been abandoned in the last 300 years in favor of a more efficient route to sea level. The Mississippi River Delta has been moving laterally over the last 6,000 years as the river migrates across the delta region. The river typically remains in one spot for less than 1,000 years. During that time sediments build a delta. Once the delta is significantly above sea level, the river channel will migrate to a shorter, more direct route to the ocean. Then the river builds a new delta and the cycle continues. However, the modern delta has remained in place for about 1,300 years. Based on radiocarbon dating of previous late Holocene deltas, the present distributary could/should have been abandoned in the last 300 years in favor of a more efficient route to sea level. The present Mississippi River channel is twice as long and half as steep as shortcuts via the Atchafalaya River or Lake Pontchartrain. If the river were to seek these new courses, then the Mississippi would not flow through New Orleans. The course has been engineered to remain in its present channel and to continue to flow through New Orleans. Much of the damage sustained in Louisiana was due not only to the storm, but also to the unique physiographic setting of New Orleans. Although the Mississippi River enters the Gulf at the South Pass, the river is only about two feet above sea level as it flows through New Orleans. The land surrounding the Mississippi River through New Orleans is at sea level, or lower, on all sides. http://www.uwgb.edu/dutchs/graphic0/geomorph/missdlt.gif

Recent sediment thickness Greatest near edge of shelf [max. ~ 100 m] Can’t restore wetlands Can’t armor coast Can compact and subside (1-10 mm/yr)! S.L.  1-3 mm/yr N.O. -8’ to 15’ “above” sea level. http://coastal.er.usgs.gov/LA-subsidence/figure2.html Modern deposition occurs near the edge of the continental shelf. Thick young sediment accumulations (warm colors) compact and subside rapidly. Areas of older sediment subside more slowly, but are thousands of feet thick, thus have significant remain subsidence (N.O. = star).

Levee history & failure Overtopping Seepage through/under the levee Not protection - postponement Courtesy USACOE Levees are continually enlarged, but they must be widened (consuming development land) and the weight increases their local subsidence. In only rare settings (e.g., St. Louis), levees can resist any foreseeable event. New Orleans is NOT such a place. http://web.umr.edu/~rogersda/flood_hazards/Should%20I%20Trust%20That%20Levee.htm

Katrina http://www.ssd.noaa.gov/GOES/katrina.html Katrina was both huge and powerful – the well-formed eye is typical of category 4+ storms. The linked animation nicely displays the rapid weakening of the storm immediately before and after landfall. http://www.ssd.noaa.gov/GOES/katrina.html

Sea-surface temperatures Note extremely warm water Shallow coastal waters commonly lack cold layers Warm sea water is the fuel for hurricanes. The evaporation of abundant water from the ocean allows condensation in the storm, releasing the latent heat stored since evaporation, thus fueling continued storm power. Rita overran a cold eddy (more common over deeper water than the northern Gulf of Mexico). Image courtesy NASA-JPL

Katrina by strength and warnings Tropical depression Tropical storm Hurricane 1 Hurricane 2 Hurricane 3 Hurricane 4 Hurricane 5 The track of Katrina was normal and generally followed predictions. The point of landfall was accurately estimated almost three days prior (see linked animation) – before that time, it had been predicted to turn north sooner and impact the Florida Panhandle. http://www.nhc.noaa.gov/archive/2005/KATRINA_graphics.shtml

Katrina winds Data (from NOAA Katrina archive) show slow progression to category 5 intensity, then rapid weakening before and during landfall. Minimum pressure (898 mb) is equivalent to average conditions at an elevation of about 1 km, and is among the five lowest ever recorded in the Atlantic.

Katrina modeled rainfall Note max. EAST of track of storm eye Same for wind The right-front quadrant of a hurricane is commonly the most powerful, because rotational winds and steering winds are summed. This effect as the storm passed is evident in the accumulated storm rainfall.

Hurricane Structure Cyclonic (CCW) winds >74 mph Right side = storm wind + forward motion Left side = storm wind – forward motion Biloxi N.O. Waveland The same concept, in theory here, explains the devastation along the Mississippi coast. New Orleans escaped the brunt of the storm winds.

Storm surge Key variables Can exceed 8 m (25’) in worst case scenario Onshore winds Central pressure State of the tide Configuration of the coast Can exceed 8 m (25’) in worst case scenario Storm surge components include the factors shown here plus the configuration of the coast, which can funnel wind and water into enclosed bays. Katrina, although missing New Orleans to the east, may have followed almost the worst-case path for storm surge NE of the delta.

Katrina comes ashore [Surviving] tide gauges Most tide gauges were destroyed (I have heard no formal estimate of storm surge at Waveland, although 30-35 feet (9-10 m) has been estimated). Open-ocean storm surge was “only” 6 feet at SW Pass.

Katrina storm surge (model hindcast) http://hurricane.lsu.edu/floodprediction/katrina32/images/katrina32.JPG It missed New Orleans Max. impact on Miss. Coast Funneling? This is the most accurate synthesis available of the storm surge. Note the effect of the levees maintaining the river outlet and of E and NE winds wrapping around the storm.

Flooding at New Orleans Observed at Miss. River gauge Not (quite) to flood stage ~12 foot storm surge Big sigh of relief as storm passed but… On the river gauge the water level peaked 1.5 feet below the crest (and about two feet higher than at Baton Rouge, 75 miles upstream!). Observer reports suggest that the dike system (about 350 miles long) was only overtopped at one location along an industrial canal. However – it failed in several localities as well.

Images courtesy NASA The 17th street canal (on the left) apparently failed through buckling of a vertical “wing wall” atop the actual earthen levee. Lake Pontchartrain lies to the north

Images courtesy NASA The 17th street canal apparently failed through buckling of a vertical “wing wall” atop the actual earthen levee – the breach is highlighted at left. Flooded areas are dark (compare to previous slide). Note that this slide is an animated combination with the previous one

Images courtesy NASA Downtown New Orleans with the Superdome at center and the Mississippi River at right.

Images courtesy NASA Note flooding up to and slightly past the Superdome and the extent of the unflooded natural levee along the river. The old parts of town, including the French Quarter, lie largely along the levee.

Damage (courtesy of USGS) Biloxi http://coastal.er.usgs.gov/hurricanes/katrina/ Selected images of damage (link mounts continuous images) in the NE quadrant of the storm. Some structures resisted the wind and waves (although lower floors were devastated), but poorly engineered major structures and all private housing was essentially eliminated. Pass Christian Biloxi

Most intense http://www.nhc.noaa.gov/pastall.shtml Rank Hurricane Year Category at landfall Minimum Pres. (mb) Minimum Pres. (in) 1 (FL Keys) 1935 5 892 26.35 2 Camille (MS, SE LA, VA) 1969 909 26.84 3 Andrew (SE FL, SE LA) 1992 922 27.23 4 (Indianola TX ) 1886 925 27.31 (FL Keys, S TX) 1919 927 27.37 6 (Lake Okeechobee FL) 1928 929 27.43 7 Donna (FL, Eastern U.S.) 1960 930 27.46 8 (New Orleans LA) 1915 931 27.49 Carla (N & Cent. TX) 1961 10 LA (Last Island) 1856 934 27.58

Costliest http://www.nhc.noaa.gov/pastall.shtml Rank Hurricane Year Category Damage 1 Andrew (SE FL, SE LA) 1992 5 26.5 2 Charley (SW FL) 2004 4 15 3 Ivan (AL/NW FL) 14.2 Frances (FL) 8.9 Hugo (SC) 1989 7 6 Jeanne (FL) 6.9 Allison (N TX) 2001 TS 8 Floyd (Mid-Atl & NE) 1999 4.5 9 Isabel (Mid-Atlantic) 2003 3.4 10 Fran (NC) 1996 3.2

Deadliest (through 1996) http://www.nhc.noaa.gov/pastall.shtml RANKING HURRICANE YEAR CATEGORY DEATHS 1. TX (Galveston) 1900 4 8000+ 2. FL (Lake Okeechobee) 1928 1836 3. FL (Keys)/S. TX 1919 600 4. NEW ENGLAND 1938 3 5. FL (Keys) 1935 5 408 6. AUDREY (SW LA/N TX) 1957 390 7. NE U.S. 1944 8. LA (Grand Isle) 1909 350 9. LA (New Orleans) 1915 275 10. 11. CAMILLE (MS/LA) 1969 256

Who’s to blame? Individuals who assumed risk, then didn’t listen and follow instructions New Orleans, for not having a real evacuation plan The Corps of Engineers, for a century and more of false promises and wasted billions FEMA et al., for not recognizing the scope of the impending disaster Congress, for not funding adequate maintenance/upgrades of levee system The human toll was enormous and relief is required. However – it didn’t have to happen, and should never reoccur. If there is one entity most responsible for the destruction, I blame the USACOE, which has encouraged development of inappropriate regions (albeit at local demand) throughout its history. Neither the Army (“win at all costs”) nor engineers (“with enough funding I can do it”) are necessarily good managers of natural systems.

What do we do about it? Abandon New Orleans? Rebuild New Orleans only along the natural levees? Rebuild, but zone/plan undersea areas for only unoccupied ground floors? Rebuild and raise the levees? Rebuild A rational examination might suggest that rebuilding a city below sea level in a hurricane-prone location with a rapidly retreating coastline is not a good idea!. But who ever said humans are rational?

In summary…