Genesis 8:4

And the ark rested in the seventh month, which is the month of Nisan, in the seventeenth day of the month, upon the mountains of Qadron; the name of the one mountain is Qardania, and the name of the other mountain Irmenia; and there was builded the city of Armenia in the land of the east.

AND THE ARK RESTED IN THE SEVENTH MONTH, ON THE SEVENTEENTH DAY OF THE MONTH. Rashi wrote: “From here you may infer that the ark was submerged in the water to a depth of eleven cubits.” This he wrote on the basis of the calculation written in his commentaries, and it is so found in Bereshith Rabbah. But since in certain places Rashi minutely examines Midrashic traditions and for the same verses also takes the trouble to explain the simple meanings of Scripture, he has thus given us permission to do likewise for there are seventy ways of interpreting the Torah, and there are many differing Midrashim among the words of the Sages. And so I say that this calculation which they have mentioned does not fit into the language of Scripture unless we bear with that which explains And the ark rested in the seventh month as referring to that day mentioned above [in Verses 2-3] when the rain was withheld and the waters receded from the earth and decreased continually. [This interpretation of the seventh month is] unlike the counting of the second month mentioned in the beginning of the section, [which Rashi explains there as being “the second month” of the creation calendar], and unlike the counting stated at the end of the section [in Verse 13: in the first month, which Rashi similarly explains as being “the first month” of the creation calendar]! And how is it possible that in the second verse Scripture should immediately retract [from using the withholding of the rain as a reference point for counting] and state, until the tenth month, and proceed to another reference point, counting it, as Rashi explains, as the tenth month with reference to the coming of the rains!
The evidence Rashi brings from the submergence of the ark in the waters is no proof for he attributes an equal decrease of water to each of the days — namely, a cubit every four days — and it is known in nature concerning the decrease of water that a great river which decreases at first a cubit every four days will at the end decrease four cubits in a day. Thus according to this calculation of Rashi, on the first day of the month of Ab the tops of the mountains were seen, and on the first day of Tishri the earth dried. Thus in sixty days the waters decreased the entire height of the high mountains consisting of many thousands of cubits, [surely a greater rate than four cubits a day, as Rashi would have it]! Besides, when Noah sent forth the dove on the seventeenth day …

ותנח התבה בחדש השביעי, this is the month of Sivan being the seventh month counting from the end of the rain descending which occurred in Kislev. Even though, as we know, the rains had begun to fall in the month of Marcheshvan, the Torah speaks here of a count beginning in Kislev seeing that the end of the rains and the end of the ark floating around have something in common in terms of stages of the deluge ending.
על הרי אררט, perhaps those were the tallest mountain range, or it happened that the ark was in that region on the day in question. At any event, the mountain range of Ararat is one of the highest mountain ranges that we know of. What is clear is that lower mountain ranges on earth did not become visible to people in the ark until the tenth month. The meaning of the line is that the process of the waters diminishing continued progressively until at the beginning of the tenth month the tops of the mountains became visible. These “mountains” were actually only hills. The process continued unabated. The “tenth” month mentioned here was the month of Av, seeing it was the tenth month counting from the month during which the rains had started, Marcheshvan.