whooow that's not good! here in the philippines we had a typhoon last year which caused terrible flooding!
if you have no choice and think that your car will be submerged in the flood, remove the battery right away. if you have time to save your car save it! remove the gauge, computer box your radio, battery and all the electronics that you can take off from the car.
after the flood, have it detailed and checked right away before you start the car.
change oil, oil filter, check plugs, and everything that needs to be checked.