Great letter, very logical and respectful.
I also sent a similar letter once. They answered, if there is a contradiction between science and the bible, they would believe the bible.
Why are there many flood myths globally?
At the end of the ice ages (around 10000 - 8000 years ago) the sea level rose dramatically. There were many local floods worldwide, as the ice melt and the sea level rose more than 100 metres.
Very interesting is the work of scientists Pitman and Ryan, who proved, that about 8000 years ago the Bosporus broke and the mediterranian flooded into the black sea. This might have been the root of the middle eastern flood stories.