Noah's flood must have been global, not a local flood like some propose.
God promised that he would send no more floods (Gen. 9:8-17), but there
have been many local floods through history. To believe in a local flood
is to say that God broke his promise.
According to the Bible, God promises not to send another flood that
would destroy all life. Since no such flood has occurred, the promise
is kept.
Someone who proposes that Genesis refers to a local flood has already
decided not to interpret the Bible literally, so a non-literal
interpretation of the promise is not an issue. Non-literal
interpretations of the Bible are compatible both with the Bible and
with reality; literal interpretations are scarcely compatible
with the Bible and not compatible with reality.
Further Reading:
Pleins, J. David. 2003. When the Great Abyss Opened. New York:
Oxford.