I'm a bit of a believer in (my own, I guess) theory that God is a very efficient being - He doesn't actually do, or even have to do, a lot of the work himself. To illustrate: It's common for people to refer to God as our Creator. Yet, how many humans, going by the Genesis account, did he actually create? Only two - and one was formed starting from material from the other. Today there's 6 billion-plus humans, and God created only two. Humans have multiplied and diversified all on their own by means of the ability (God-given if you will) to reproduce and adapt.
Another example may be the formation of stars. Simplistically speaking, we know that stars often form from material brought together by natural (again, God-given if you will) forces such as gravity, and then ignited into a nuclear furnace when their mass reaches a certain point, normally refered to as Jupiter-masses. I doubt God needs to actually do much of the work. He gets the credit by believers, of course.
So it is perhaps with the evolution. Species can diversify, at times quite rapidly, all on their own. God would only need to create a few species, perhaps in a burst of creative activity, then take a vacation and let natural selection take over. In the case of the Flood, I can see no other explanation other than rapid evolution, for the present diversification of life on earth....if one is to believe the Flood account as presented in Genesis. A big if...