Reason for the Mabul being a flood of Water

An explanation as to why God brought a Mabul upon the world and drowned all civilization in water is possibly as mida keneged mida for their sins. Water as we know represents "Chesed". Chesed brings things together as opposed to Fire which represents "Din". Fire breaks things down and  separates them into their basic elements while water is typically a bonding agent. The aveira of the Dor hamabul was "Nizkakim Lishe'aynum minum-Mishkav Zachar. There was an abundance of  zima in the world. Civilization's attitude was to  love indiscriminately, they even loved animals. The medrash says that the Dor Hamabul were the first generation that sanctioned mishkav Zachar by instituting a "Ksuva Lizachar". They affected animals to the point where animals were cohabitating with other species other than their own. Znus in the Torah is called "Chesed" which is really misplaced Love. Love has to be channeled correctly. Indiscriminate love is destructive.

The other aveira of Dor Hamabul  of "Gezel" is always described as "Chamas" as in "Vatimaleh Ha'aretz Chamas" and 'ki malah Ha'aretz Chamas. "Chamas" is translated as  "Chatofin" in the Targum. The Torah is not referring to private Gezel where people are stealing from each other but rather institutionalized stealing where the strong take from the weak. Grabbing by force of the law such as in Sdom where legal stealing was their way of life. When the strong government steals from the producers to redistribute their private property to others that they feel is politically expedient is called "Chamas". When those in power take from the weak to redistribute the wealth it is  usually done in the name of social justice. Again this is a misplaced act of Chesed. Sdom would steal from visitors and distribute to citizens. They had a rationalization. They were doing Chesed to those that needed it most.

וַיִּרְא֤וּ בְנֵי־הָֽאֱלֹהִים֙ אֶת־בְּנ֣וֹת הָֽאָדָ֔ם כִּ֥י טֹבֹ֖ת הֵ֑נָּה וַיִּקְח֤וּ לָהֶם֙ נָשִׁ֔ים מִכֹּ֖ל אֲשֶׁ֥ר בָּחָֽרוּ:

This was another example of the powerful taking advantage of the week. The powerful decided who should be married to whom and who should love whom. Private citizens were not allowed to make those decisions. For sure there was a rationale to that too. This was the sin of the Dor Hamabul

The punishment was "Mida Keneged Mida". Water which symbolizes chesed when it is doled out in measure became a flood. The Gemara says that one of the Chasadim of God is that when it rains no raindrop touches the other. If the raindrops combined they would flood the world. A flood happens when water which usually creates growth combines unnaturally and instead of acting as a constructive force becomes the ultimate destructive force. A flood is water becoming a destructive force which symbolizes the ultimate perversion of "Chesed".