Bereishit 6:14
עֲשֵׂה לְךָ תֵּבַת עֲצֵי-גֹפֶר קִנִּים תַּעֲשֶׂה אֶת-הַתֵּבָה וְכָפַרְתָּ אֹתָהּ מִבַּיִת וּמִחוּץ בַּכֹּפֶר
Aseh lecha tevat atzei-gofer kinim ta'aseh et-hatevah vechafarta otah mibayit umichutz bakofer
Make yourself an ark of gopher wood. The ark should be divided into compartments. Caulk the inside and outside with pitch.
"Gopher" is an especially light weight kind of wood. Onkelos translates the word as a kind of cedar-wood. G-d instructed Noach to make for himself an Ark out of this well-known wood and to bring into it two specimens, male and female, f all the domestic and free roaming animals in order to keep these species alive as well as seven pairs of each of the pure species of birds in order for some to serve as sacrifices after the deluge. G-d informed Noach beforehand that he was going to bring the deluge in order to wipe out all flesh on earth which had the breath of life in it.
Noach knew there was a need for only ten righteous people in order to ensure the survival of the world as it was. He based this tradition on the ten directives G-d employed to create the universe. He reasoned that if there were indeed ten righteous people alive at that time G-d would not have instructed him to prepare for the deluge by building the Ark. Under the prevailing circumstances, only eight people had been commanded to enter the Ark - Noach, his wife, his three sons and their respective wives, proof that at that time there were already no ten righteous people left on the earth. (Avraham had also stopped praying when he realized that there were fewer than ten good people in Sedom.) Seeing that there were no ten good people left on earth it was clear to him that the generation did not merit survival on account of the remaining eight good people. Under the circumstances, the most that G-d was willing to do was to save Noach seeing he was the first member of the tenth generation of mankind. G-d accommodated Noach by also saving his immediate family. The fact that Avraham himself did not bother to implore G-d to save the city of Sedom for the sake of few than ten righteous people proves that Noach cannot be faulted for not having prayed when told to tke only seven additional human beings into the Ark with him. In fact, Noach was not even allowed to pray when he knew here were fewer than ten good people. In addition, as opposed to the people of Sedom, the people at the time of Noach had been given 120 years warning. The people of Sedom had not been given any kind of warning by G-d prior to Avraham being informed of their impending doom. G-d is not in the habit of decreeing doom unless the potential victims had been warned (Yuma 81).
6:15
וְזֶה אֲשֶׁר תַּעֲשֶׂה אֹתָהּ שְׁלֹשׁ מֵאוֹת אַמָּה אֹרֶךְ הַתֵּבָה חֲמִשִּׁים אַמָּה רָחְבָּהּ וּשְׁלֹשִׁים אַמָּה קוֹמָתָהּ
Vezeh asher ta'aseh otah shelosh me'ot amah orech hatevah chamishim amah rachbah ushloshim amah komatah
This is how you shall construct it: The ark's length shall be 300 cubits, its width 50 cubits, and its height 30 cubits.
G-d commanded Noach the measurements of the Ark. When one considers the many types of species Noach had been asked to bring into the Ark, these measurements appear to be totally insufficient. In fact, according to the number of species of animals and birds in our world today, even ten times as many Arks of that size would not be able to accommodate them all. There can therefore be no doubt that the entire operation was possible only by means of G-d's miraculous intervention. G-d demonstrated to Noach and his family that even a physically small space can accommodate a great number of creatures when G-d so decrees it.
There was an additional reason why G-d had commanded Noach to spend 120 years of his life to build the Ark even when G-d could have had a number of other alternatives once He had decided to invoke miracles. He had hoped that when people would watch the vast amount of time and energy which Noach and his sons put into constructing this huge Ark that he must have known what he was doing, and that at least some people would take his warning of the impending deluge to heart to repent and change their lifestyle. If they would nonetheless ignore such warnings they were obviously irredeemable sinners and would deserve whatever G-d decreed for them.
7:4
כִּי לְיָמִים עוֹד שִׁבְעָה
Ki leyamim od shive'ah
For in another seven days.
In addition to the 120 years which G-d had given mankind to repent and to mend its ways, He now gave them another seven days. Chazal (Sanhedrin 108) say that these seen days were the days of mourning for Metushelach (Noach's grandfather), who had died at 969 years of age. He had lived the life of a righteous man and G-d had held back with bringing on the deluge on his account. This is why the Torah (7:10) wrote the apparently superfluous words, "it was after these seven days that the waters of the deluge were upon the earth."
According to Nachanides the timetable of the deluge ran as follows:
Rain descended on earth for forty days continuously from the date the fountains of the deep broke open. During those forty days the waters on earth rose to a level of fifteen cubits above the highest peaks. At the end of the forty days the rain stopped but the fountains of the deep remained open and the "windows" of heavens also remained open so that the atmosphere was extremely moist. The entire globe was full of water none of which dried off during that period. This condition continued until the end of 150 days after the rain had started falling. At that point G-d made a strong wind blow in the atmosphere and on earth and the fountains of the deep closed. The waters which had flooded earth from below returned to the interior of the earth where they had been before the deluge started. At that point the "windows" of the heavens were closed also and the air of the atmosphere began to dry up. As a result, the level of water on earth became drastically reduced so that the Ark which had previously been about two or three cupbits deep in water managed to "land" on the mountain range of Arrarat. Some 73 days later the tops of the mountains became visible on the first day of the tenth month, i.e. on the first of the month of Tamuz. Another forty days later, on the tenth of the month of Av, the dove left the Ark for good. Another thirty days later Noach removed the cover of the Ark.
8:11
וְהִנֵּה עֲלֵה-זַיִת טָרָף בְּפִיהָ
vehineh aleh-zayit taraf befiha
and here it had torn off an olive leaf with its beak.
Where did the dove find even such a leaf since the destruction of vegetation on earth had been so thorough that Chazal in Bereishit Rabbah 28:3 claim that even the lower millstones had been thoroughly destroyed. This may be based on Iyov 14:19, "the waters wear away even stones." Rabbi Levi (Midrash) claims that the leaf came from Mount Olives in Yerushalayim, seeing the deluge had not touched the Holy Land. He claims that G-d had said to Yechezkel (22:24) "Ben Adam, say to her, 'You are a land that has not been cleansed; she had not been rained upon on the day of fury." The words לא מטהרה (lo metohara - not cleansed) refer to the fountains of the deep beneath the Holy Land not having opened at the time of the deluge, whereas the words לא גשמה (lo gushmah - nor rained upon) mean that no destructive rain fell on the Holy Land during the period of the deluge. Nonetheless, it is fair to assume that the waters of the deluge which had flooded neighboring countries also spilled over into the Holy Land. After all, the Torah testifies that the waters of the deluge "covered all the high mountains beneath the whole sky" (7:19). Seeing that no rain had fallen on the Holy Land which would have uprooted and broken the trees in that land, the waters which spilled over into that land did not have such a destructive effect. It is quite plausible therefore that the dove took the leaf from Mount Olives.
8:14
בְּשִׁבְעָה וְעֶשְׂרִים יוֹם לַחֹדֶשׁ
beshive'ah ve'esrim yom lachodesh
on the twenty-seventh day of that month.
This was the month of Marcheshvan. Earlier the Torah had spoken of "on the seventeenth of the month the fountains of the 'deep' broke open" (7:110, whereas now the Torah says that on the twenty-seventh day of that month the earth had dried out completely. This teaches that the deluge lasted exactly one full solar year (365 days). We know that ordinarily the solar year is 11 days longer than the lunar year, i.e. 12 months. This is why Chazal in Ediyot 2:10 stated that the period during which the people of that generation were judged lasted for 12 months. According to Rabbi Shlomoh ben Aderet we have to add the eleven days of the difference between the solar and the lunar years so as to avoid the Mishnah in Ediyot being in conflict with the Torah. We are also told in that same Mishnah that the judgment of the Egyptians in Egypt (the ten plagues) lasted 12 months and that Iyov's afflictions lasted for 12 months. Finally, the Mishnah states that the judgment experienced by the nations taking part in the final assault on the Jewish people under the kingdoms of Gog and Magog will last for 12 months.
May HASHEM continue to enlighten us with the Light of His Torah.
-Bachya; Chazal