Your last para summed it all up for me, that is. Were not dealing with standing or ponding water, were actually dealing with water table being high. In Corpus Christi, where I once resided, they have many homes built along intercostal waterways leading out to the bays which lead out to the gulf. Their homes were built up much higher than yours apparently is. They were almost on stilts. Anyway, when people get more and more complacient about hurricanes and rising water, the under neath part of the home becomes a new addon.
As others have stated, the water will still be there and always will be there, all you can do is to raise the ground above the water table more. This can be done with more and more sand.
I did assist a friend of mine in Rockport, Texas do just this same thing.