Drove my Chevy to the levee but the levee wasn't dry!

We were in New Orleans helping to restore the city because of the damaage Hurrican Katrina had. Along the Mississippi River there is a levee which is a concrete wall that holds the water back when it rises. Some levee's are 4 feet high and some closer to 12 feet. Because parts of the city are below sea level, when the water level rises too much it rushes in resulting in a flood. This hurricane brought so much water that the 11 feet of water in the city covered the streets to the roofs of peoples houses bringing the water level to be at sea level.

If the levee is 8 feet high and the town is 10 feet under sea level, how many feet of water will they have if a levee broke or the water overflowed?