The thing is, you can't disprove anything. You can say, "oh, it's impossible to separate an ocean so a nation can walk across," but how can you disprove God's acts? Doesn't it say, "with God, all things are possible..."?
Well this seems a little confused.
It is perfectly true that an omnipotent God could do anything, but that doesn't mean we can't tell what he has or hasn't in fact done. He could have made the whole world bright pink, but we can be sure that he didn't.
Hence, arguments against various aspects of the Bible don't rest on a claim that God couldn't do such-and-such a thing (the Flood, for example) but on the fact that the evidence shows that he didn't.