Contradiction with Genesis 7:24
Genesis 7:24 states that the waters prevailed upon the earth for 150 days, but Genesis 8:5 states that the waters decreased continually until the 10th month, at which point the tops of the mountains were seen, suggesting an earlier reduction.
Genesis 7:24: And the waters prevailed upon the earth an hundred and fifty days.
Contradiction with Genesis 8:4
Genesis 8:4 says the ark rested in the 7th month on the mountains of Ararat, yet Genesis 8:5 suggests the waters continued to decrease after this point, even though the ark had already come to rest.
Genesis 8:4: And the ark rested in the seventh month, on the seventeenth day of the month, upon the mountains of Ararat.
Contradiction with Genesis 7:19-20
Genesis 7:19-20 claims that all high hills and mountains were covered, contrasting with Genesis 8:5 which indicates the tops of the mountains were visible in the 10th month.
Genesis 7:19-20: And the waters prevailed exceedingly upon the earth; and all the high hills, that [were] under the whole heaven, were covered.