What is the meaning of "ka'Ned"?
Rashi: It refers to height. Targum Onkelos of "Nitzevu Chemo Ned" (Shemos 15:8) is Kamu ch'Shur.
Radak: It is a mound or pile, like "Chemo Ned Nozelim" (Shemos 15:8). Hashem gathered all the water in the world to one place, and there was dry land. If not, only fish could survive!
Where are the "Otzaros"?
Rashi: They are under the ground.
Radak: It is as if the Tehomos are in storehouses and cannot leave - "Samti Gevul la'Yam Chok Olam v'Lo Ya'avenhu" (Yirmeyah 5:22).
Malbim: The water is in the sea and in Tehomos (underground). The majority went up in vapors and is on top of the Raki'a, suspended via Hashem's word. It says "Nosen" (present tense), for He does so constantly via Hashgachah.