First of all, I never want to “get rid of or ignore” any part of the Scriptures. There is value for me in every part of it (even in those boring genealogies 
). So whether a point is made allegorically, poetically, or historically, that point is still part of teachings inspired by the Holy Spirit!
Secondly, there are consistent ways to discern the intended teaching of a particular text. Most importantly, you have to take into account that the original audience at whom most parts of the Bible were directed were people from an Ancient Near-Eastern civilization. This process is not about getting rid of anything. On the contrary, it is about developing an understanding that takes us deeper into the text and into the teaching.
Thirdly, I believe that the (local) flood was a real event and Noah an actual person. I don’t interpret the flood account allegorically. However, as Jesus makes clear in His explanation in Luke 17:26, the actual sense of the flood account is that is foreshadows the End of Times, essentially preparing humanity for it.
As I said before, my position does not entail that Jesus was all knowing on every single topic imaginable. This is in accordance with the doctrine of kenosis: the self-emptying of the Son of God in the flesh. Jesus didn’t know when the End of Times would come (Mark 13:32). Similarly, He could have had a different impression of the natural history of the world. No problem. It didn’t affect the point of His teachings in any way: “I am the Way, the Life, and the Truth.”