some are more or less based on real events. There probably was a great flood at some point around the "time" of Noah. Multiple cultures around the globe report similar instances at roughly the same time. Now did he build a giant boat and have animals go 2 by 2 and that being the first rainbow, no. others are probably complete phooey or true stories that grew legs and went for a walk. Moses: Egypt probably did have a time of plague, locust, frogs etc etc. but it probably wasn't one big event. Water turning to blood, was probably a naturally occurring event where water was turned red, so on and so forth.