There are some difficult questions if flood account is true:
1) 8.7 million species to be loaded in 7 days
2) Complete burden fallen on the lone righteous family (the wicked died within minutes)—something that should not happen when God Almighty directs matters
3) Flood did not cleanse the earth permanently, soon earth filled with violence again
4) China’s history remained untouched by Noah’s flood
5) Jesus had totally different picture about Noah’s flood and the reasons that led into it (Mat 24:36)