The Flood was a global flood. There is now so much evidence for it, it's amazing people still deny it happened.
Remember that Jesus confirmed the Flood:
But as the days of Noe were, so shall also the coming of the Son of man be. For as in the days that were before the flood they were eating and drinking, marrying and giving in marriage, until the day that Noe entered into the ark, And knew not until the flood came, and took them all away; so shall also the coming of the Son of man be.
- Matthew 24:37-39 (KJV)
Don't let the Atheists deceive you. Broad is the road to destruction.
Knowing this first, that there shall come in the last days scoffers, walking after their own lusts, And saying, Where is the promise of his coming? for since the fathers fell asleep, all things continue as they were from the beginning of the creation. For this they willingly are ignorant of, that by the word of God the heavens were of old, and the earth standing out of the water and in the water: Whereby the world that then was, being overflowed with water, perished: But the heavens and the earth, which are now, by the same word are kept in store, reserved unto fire against the day of judgment and perdition of ungodly men.
- 2 Peter 3:3-7 (KJV)
They willfully 'forget', because their lives function "better" without God, e.g. it allows them to live a wicked life without being judged, so they'll firmly defend that point of view.
If you have the time (6-7 hours), have a look at these YouTube movies.
The Global Flood (Part 1 of 6) - Noah's Ark and the Animals
The Global Flood (Part 2 of 6) - Historical Evidence and Mechanism
The Global Flood (Part 3 of 6) - Geology 101
The Global Flood (Part 4 of 6) - Geological Evidence
The Global Flood (Part 5 of 6) - Fossil Evidence
The Global Flood (Part 6 of 6) - Erosion Evidence
If you don't have time, have a look at these YouTube movies.
If you prefer to read articles, consider this one.