Quote: I thought that I had a good grasp on the High Water Marks. But now I'm slightly confused. The 25.72ft that FrankP mentioned minus the 14ft elevation above sea level at his front yard. Gives me a water depth (surge?) of 11.72ft. Which seems consistant with the damage to his house. Please PM me if I'm missing the math.
No that water mark was a good one. It was the 35 ft one in the Pass that was wrong.
You have the elevation right...14 ft in the front yard, 16 ft at the slab, the 18 foot mark starts a little further back on Frank's property. But the reason the house is gone is mainly due to wave runup and current. It is easy for water to get inside; once water is inside and outside the pressure equalizes and the house will remain standing (like 80% of the homes in Pascagoula which are destroyed inside by being subjected to five feet of salt water, but look almost perfectly normal from the outside). What happens in the velocity zone is that repeated pounding will remove the structure of the home from its footings, and eventually the first floor shifts and quickly collapses. The second floor can sometimes stay mostly together as Frank's did, riding along on top of the water and debris, coming to rest when the water level subsides (as his did, further back from the beachfront). More usually it is just the roof that will stay together.
One thing Stephen Baig mentioned to me was that depending on which elevation reference you use, and how old it is, it might be a little high, because of continuing subsidence along the entire Gulf Coast. FEMA used NAVD 88 as the reference, but they also used LIDAR data from 2004 to do the surge inundation maps. This could be like comparing apples and oranges, but I am not sure. It would be good to find an expert in this area to provide some feedback (anybody know any surveyors?).
Here is more detail on the way the mapping was done:
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