Here was an interesting question that was asked last week by Jeff Masters (of weather underground) about the devastating flooding that took place in New Orleans from Hurricane Isaac. This just 7 years after Hurricane Katrina nearly wiped the city completely off the map.
Did the new $14.5 billion upgrade to the New Orleans levee system cause
worse flooding elsewhere? Whenever a new levee or flood control structure is
created, you make someone else’s flood problem worse, since the water has to go
somewhere. Where did the water that was stopped by the new $1.1 billion, 1.8
mile-long Lake Borgne flood barrier on the east side of New Orleans go? Did it
flow south and contribute to the overtopping of the levees near Braithwaite? Or
did it go north and contribute to the 36 hours of storm surge in excess of 5′
observed along the Mississippi coast at Waveland? I posed this question to NHC’s
storm surge expert Jaime Rhome, and he said it was impossible to know without
doing detailed storm surge modeling studies.
Let’s bring this a little closer to home and use the barrier islands of southern New Jersey as an example here. Suppose for a second a flood wall was built in front of Sea Isle City, but only Sea Isle City and no other shore town. When a storm surges, it’s pushing ocean water inland. That ocean water continues to pile up or around or go where ever it has to go until the storm finally weakens and lets it back out to sea. So what do you think is going to happen in this example if a sea wall is built?
Think about what happens when you build a sand castle on the beach. You decide to build a little protective wall in front of the castle to stop the waves from ruining your creation. Well what happens when the waves coming up? At first they hit the sand wall and they retreat. However, as the tide gets higher and higher, more and more water hits your little protective sand wall and starts wrapping around it because the ocean won’t let it back out to sea. The same thing happens with the flood wall or levee. The levee may have protected Sea Isle City from serious flooding, but now that water that would have originally flooded Sea Isle has piled up on the north and south ends of the island, making the flooding worse for the towns of Avalon and Strathmere that sit on either side. Yet had the wall not even been built in the first place Sea Isle City would have been flooded like everyone else, but the flooding in Avalon and Strathmere would not have been as severe.
The problem for New Orleans is that it sits below sea level and a levee system must be built or the Gulf Of Mexico will swallow the city up completely. Up until the past ten years it seemed as if the levee system had done a great job. However, I think what has happened now is up until the past 10 years the levee system had never truly been tested by “Mother Nature”. Now it has, and now the city of New Orleans is seeing the reasons why it’s not a good idea to build a city that sits below sea level when it actually sits right next to the sea!
The storm surge expert from the National Hurricane Center said that it was impossible to determine for sure if the new levee system made the flooding worse without doing detailed storm surge modeling studies first. So it may be quite a while before this question is answered. But when you take a closer look at the areas that were flooded during Hurricane Katrina versus the areas that were flooded this time around by Hurricane Isaac, taking in to consideration the similar tracks, the idea makes sense.
Just thought this was interesting.