The Catholic Church does not have an "official" position on the literal interpretation of the Old Testament (including the great flood narration). Whether they are literal or not has no bearing on whether the lesson they impart is true. Catholics are free to understand them as literal or not. The Church only insists that the Bible is inspired and inerrant and that what it teaches is the truth.
Just because there is no official position on the literal interpretation doesn't mean that Catholics can interpret scriptures to mean anything they want. Catholic interpretation should always be within the boundaries laid down by the church. These boundaries are most importantly guided by church tradition. Careful attention must be paid to the actual meaning intended by the authors, in order to render a correct interpretation. The Roman Catholic Church holds that the authority to declare correct interpretation rests ultimately with the church through its magisterium.src Catholics believe that the teaching authority (Magisterium) of the Catholic Church (headed by the Pope) has a God-given mission to interpret and teach both Scripture and Tradition.
Just a footnote about the question you referred to: that is about Card. Joseph Ratzinger's position on evolution and is not an official dogmatic teaching of the Church.