On the Great Flood of Noah, the Church teaches exactly what the Bible teaches….
“In the six hundredth year of Noah’s life…the springs of the great deep burst forth, and the floodgates of the heavens were opened. And rain fell on the earth forty days and forty nights. For forty days the flood kept coming on the earth, and as the waters increased they lifted the ark high above the earth. The waters rose and increased greatly on the earth, and the ark floated on the surface of the water. They rose greatly on the earth, and all the high mountains under the entire heavens were covered. The waters rose and covered the mountains to a depth of more than twenty feet. The waters flooded the earth for a hundred and fifty days.” Genesis 7: 11-24
Jesus speaks of the flood in Matthew 24:37-39:
“As it was in the days of Noah, so it will be at the coming of the Son of Man. For in the days before the flood, people were eating and drinking, marrying and giving in marriage, up to the day Noah entered the ark; and they knew nothing about what would happen until the flood came and took them all away. That is how it will be at the coming of the Son of Man.”
II Peter 3:3-7:
”…But they deliberately forget that long ago by God’s word the heavens existed and the earth was formed out of water and by water. By these waters also the world of that time was deluged and destroyed.”
*Catechism of the Catholic Church * no. 1219
“The Church has seen in Noah’s ark a prefiguring of salvation by Baptism, for by it “a few, that is, eight persons, were saved through water”:
The waters of the great flood
you made a sign of the waters of Baptism,
that make an end of sin and a new beginning of goodness.
"The covenant with Noah after the flood gives expression to the principle of the divine economy toward the “nations”, in other words, towards men grouped “in their lands, each with [its] own language, by their families, in their nations”. no. 56
Details of the flood (e.g. its coverage, when it took place) are questions for science, not theology. For further information on the flood I recommend the following sites:
Commentary on Genesis by Father William Most: