Applying Research to Practical Use for Hurricane Katrina Homeowners
I have studied the effects of Hurricane Katrina for the past year (including considerable on-the-ground field research) and have developed a number of techniques to help to determine what happened to dwellings during Hurricane Katrina. These and other techniques helped me to follow the destructive paths of Hurricane Katrina’s powerful wind and water. My findings indicate that many houses were destroyed by water while others were destroyed by wind. However, vast numbers of dwellings were destroyed by both wind and water. Determining the direction that the wind hit your property versus the direction that the water hit, is very important to demonstrate that wind damaged your property during Hurricane Katrina.
The initial major flooding direction was a wind-driven event that hit the shore line from the Southeast, and the initial damage could have been from the wind or wind-driven water. This type of wind event is due to the normal circulation pattern of hurricanes. It is necessary to follow the wind damage out of the flooding area to see if your property may have been damaged by the wind before the flooding hit. See the tracking techniques below on how to do this. The other major direction of impact flooding was from the Southwest due to storm surge, with water flow being hindered by the land. Damage from other directions, other than the Southeast and the Southwest, may indicate that property may have been hit with a downburst. Determining the time of this event as it relates to the flooding is very important. See that geological techniques may help in the determining of the event order.
How do you determine if your house was affected by wind, wind and water, or just water? The following tracking techniques can be invaluable to your understanding of what happened to your property. You would start by drawing a map of your property and your neighborhoods with a properly oriented North arrow. Use a good compass or obtain a US Geological Survey 7.5-minute topographic map that shows the direction of North relative to your house/street: www.topozone.com. Select a scale (for example, 1 inch equals 100 feet) and place the scale on your map so that it will be readable for your area of study. Do measurements with a tape rule if possible, to keep the map consistent with the scale you’ve selected. Also, take photos of all observations to document your findings in the field.
Start at your foundation or foundation wall. On your map, mark the direction that the vertical reinforcing re-bars are bent, if they are exposed. Draw and orient each scratch mark observed on the foundation floor or walls of the building. Notate the number of scratch marks and calculate the orientation of the majority. The next step is to take an inventory of trees around your property. Did they fall or not? If they did not fall, place a small circle on your map. For trees that fell, draw a small line on your map showing the direction that the trees fell. Now place a circle where impact scars are observed on larger trees; leave alone if no impact scars are observed. Look down the ‘fall line from the downed trees. Do you see other trees that fell in the same or similar direction? If so, mark the lines on the map.
The next step is to look at neighboring properties. Follow the lines of force that you observed on your property and compare those lines to what you see in the neighborhood. Do you see similar lines of force in the same orientation (to within maybe 20 degrees)? If so, mark the location and orientation of these forces on your map. Continue to look at the tress and the damage to other properties and document your observations as you move along. Do you now see a reinforcing pattern of force lines in the immediate area or do you see force lines that are predominantly oriented in different directions? Mark your observations on your map. Use additional sheets of paper to make your map in order to keep the scale readable. Continue the map survey as long as you are on safe ground. Safety is paramount! Do not trespass and watch for hazards wherever you are walking. If possible, you may decide to drive around your neighborhood and look to see if your observation of force vectors can be reinforced at a larger, more regional, scale.
The Geological Principle of Relative Dating can be used determine relative age or order of events that took place during Hurricane Katrina, by showing that different layers were deposited at different times. Try to keep in mind the direction of flooding in your area; compare the flooding direction to sedimentary deposits. It is best to think of the debris as sedimentary deposits even though you are dealing with parts of houses, cloth from clothes, along with normal mud, sand and tree sediment. If you see two or more different directions, document by taking pictures and have a professional investigate because it is possible to determine a relative time line of the events that happened at your property from the debris and sediment deposits.
How might you interpret all of this data once it is collected? Professional help could be invaluable, but you can make an initial assessment yourself. If the re-bars are bent by forces coming from the Southwest (or, conversely, they are pointing towards the Northeast), they were most likely the result of a storm surge hit from the Southwest. If the re-bars are bent by forces coming from the Southeast (pointing toward the Northwest) the resulting force could have been from wind, wind driven waves, or just rising water damage. If you have scratch marks on the foundation floor, the marks may indicate that something was pushed over by wind. However, if the observed force direction was from the Southwest, it most likely resulted from the storm surge and quickly rising water. If the force direction is predominantly from the Southeast, it could be wind or water related and you should have a professional look at it. If you have observed multiple force vectors that appear to be almost radial in direction, or oriented in a direction that differs from the vectors discussed herein, this may indicate you were hit either directly by a downburst or one of the straight-line winds that develop from it. Evidence of multiple force directions in a single area may indicate changing wind patterns over the evolution and movement of the storm.
Some other things to look for, and this is where you may need the help of an engineering professional, include determining if the hurricane straps that hold the roof onto the house have been bent. Such damage might indicate that the roof experienced damage due to high winds. If the roof experienced high winds, the roof would have had an uplift during which the roof was held on by the hurricane straps. Yet the roof may have been damaged or have a gap between the studs the roof line check both the leeward and windward. If this is the case than your house experienced hurricane-level damaging winds. Holes in the roof also may indicate an upward lift. If your house experienced upward lift, it is very likely that the entire house was under wind stress.
If you have computer access, go to: http://ngs.woc.noaa.gov/katrina/ and look at the NOAA Hurricane Katrina Air Photos. When you get to your property location, click on the picture (see button on the right side bottom of the screen) for a close up of your area. Find your property and look for confirmation of the lines that you just drew on your map. Do the force directions observed on the photo and your map match? Look at the larger region using the photos. Do you find reinforcement of the downdrafts, straight-line winds, or predominant storm-force winds observed on your property? If you find that your observations on the ground and the observations ‘in the air suggest that wind force may have significantly impacted your home, have your results evaluated by an independent (not-related to your insurance company) professional.
You should also ask for the engineers complete report, because wind speeds vary greatly and the top winds ‘speeds record are different from the estimated winds speeds for your area. Good luck in your quest.
By Geologist David Jungblut and Environmentalist Joseph Hockreiter