If we look to Catholic Tradition, we will see the evidence solidly behind a historical Flood. As the Catholic Encyclopedia says, "The Deluge is referred to in several passages of Scripture as a historical fact; the writings of the Fathers consider the event in the same light, and this view of the subject is confirmed by the numerous variants under which the Flood tradition lives in the most distant nations of the earth...the Bible story concerning the Flood has never been explained or understood in any but a truly historical sense by any Catholic write. It would be useless labour and would exceed the scope of the present article to enumerate the long list of Fathers and Scholastic theologians who have touched upon the question. The few stray discordant voices belonging to the last fifteen or twenty years are simply drowned in this unanimous chorus of Christian tradition." Isn't it interesting that in the view of the Catholic Encyclopedia, the patristic and Scholastic support for the historicity of the Flood is so universal as to make it a "useless labour" to enumerate them all! I guess that settles the question of whether or not it is part of Catholic Tradition! Fundamentals of Catholic Dogma is silent on the issue as it is on many historical topics (except for the question of Genesis 1).
As to whether or not the Flood was universal, we do not necessarily have to believe that it was geographically universal (that it covered the entire earth), but we must adhere to the belief that it was anthropologically universal (that it destroyed all men). Some of the Fathers defends a geographically universal Flood, but they do not defend it vigorously and often express reservations about its universality. However, all of the Fathers admit that the Flood wiped out all of mankind, and Sacred Scripture confirms this; the reality seems to be that at such an early time in history, mankind was confined to only a small portion of the earth. This was the portion destroyed by the Flood.
Interesting is the Catholic Encyclopedia's assertion that the existence of other Flood myths in the world proves the reality of the event: "The historicity of the Biblical Flood account is confirmed by the tradition existing in all places and at all times as to the occurrence of a similar catastrophe. F. von Schwarz enumerates sixty-three such Flood stories which are in his opinion independent of the Biblical account."
These alternate Flood myths have always fascinated me; they occur in such divergent places in the globe that they seem to leave no other explanation than that Flood legends are part of the universal patrimony of mankind, and hence harken back to an anthropologically universal event that objectively happened.
Algonquin Indian: Long ago, when men had become evil, the powerful serpent Maskanako came and fought with them. The serpent brought the snake-water rushing, spreading everywhere, destroying everything. Then the waters ran off, and the great evil went away through a cave.
Assyria: The gods agreed to cleanse the earth of humanity, but Utnapishtim was warned by the god Ea in a dream. He and some craftsmen built a large boat (one acre in area, seven decks) in a week. He then loaded it with his family, the craftsmen, and "the seed of all living creatures." The waters of the abyss rose up, and it stormed for six days. The waters covered everything but the top of the mountain Nisur, where the boat landed. Seven days later, the waters had receeded enough for the people to emerge. Utnapishtim and his wife were given immortality and lived at the end of the earth.
Babylonians: Three times (every 1200 years), the gods were distressed by the disturbance from human overpopulation. The gods dealt with the problem first by plague, then by famine. Both times, the god Enki advised men to bribe the god causing the problem. The third time, Enlil adivsed the gods to destroy all humans with a flood, but Enki had Atrahasis build an ark and so escape. Also on the boat were cattle, wild animals and birds, and Atrahasis' family. After the flood, the gods regretted their action, and Enki established barren women and stillbirth to avoid the problem in the future.
Caddo Indians (Arkansas): Four monsters grew large and powerful until they were high enough to touch the sky. One man heard a voice telling him to plant a hollow reed. He did so, and it quickly grew very big. He, his wife, and pairs of all good animals entered the reed. Waters rose to cover everything but the top of the reed and the heads of the monsters. Turtle destroyed the monsters by digging under them and uprooting them. The waters subsided, and winds dried the earth.
Chinese Flood Myth: A 22-year-long flood, caused by the water god Gong Gong, drove people to mountains and treetops. The supernatural hero Gun dammed up the waters with Growing Soil stolen from heaven.
Kammu (northern Thailand) Flood Myth: A brother and sister, warned of the upcoming flood by a mouse, sealed themselves inside a drum, and emerged again after the flood receded. They looked far and wide for mates, but they were the only survivors. A malcoha cuckoo sang to them, "brother and sister should embrace one another." They slept together. After seven years, the child was born as a gourd. A little later, hearing noises from the gourd, they burnt a hole in its shell, and people of the different races came out, first Rumeet, then Kammu, Thai, Westerner, and Chinese.
Flood Myth of the Maya: The gods used a flood to destroy the wooden people, an early imperfect version of humanity.
Flood Myth of New Hebrides (South Pacific): Tilik and Tarai, who lived near a sacred spring where they were making the land, discovered that their mother had been urinating in their food. They exchanged the food and ate hers. In anger, she rolled away the stone which had confined the sea, and the sea poured out in a great flood.
Roman: Jupiter, angered at the evil ways of humanity, resolved to destory it. He was about to set the earth to burning, but considered that that might set heaven itself afire, so he decided to flood the earth instead. With Neptune's help, he caused storm and earthquake to flood everything but the summit of Parnassus, where Deucalion and his wife Pyrrha found refuge. Recognizing their piety, Jupiter let them live and withdrew the flood. Deucalion and Pyrrha, at the adivce of an oracle, repopulated the world by throwing stones behind them; each stone became a person.
Scandinavia: Oden, Vili, and Ve fought and slew the great ice giant Ymir, and icy water from his wounds drowned most of the Rime Giants. The giant Bergelmir escaped, with his wife and children, on a boat. Ymir's body became the world we live on.
Toltecs: One of the Tezcatlipocas (sons of the original dual god) transformed himself into the Sun and created the first humans to show up his brothers. The other gods, angry at his audacity, had Quetzalcoatl destroy the people, which he did with a flood. The people became fish.
Zoroastrian: After Ahura Mazda has warned Yima that destruction in the form of winter, frost, and floods, subsequent to the melting of the snow, are threatening the sinful world, he proceeds to instruct him to build a vara, 'fortress or estate,' in which specimens of small and large cattle, human beings, dogs, birds, red flaming fires, plants and foodstuffs will have to be deposited in pairs.""Beneath this earth there is water everywhere."
There was once a time when the Hebrew Flood story was explained away as a cultural borrowing from the older and more advanced Babylonian civilization to the East. But in modern times, with so many Flood stories from every corner of the earth, is it still feasible to believe that they all "borrowed" them from each other? Wouldn't the more reasonable explanation be that humanity is collectively recalling an event that actually took place in the distant years of its infancy? This seems obvious to me.