Twelver Shi'i Islam is totally dominating the Iranian society, not only as creed, but also with its impact on the political system.
Although Iran political structure is a republic system, it may seem different from other similar political systems. Iran political system's origin and roots are the reason beyond such a uniqueness.
There is a vastly extended network of rivers in Iran most of which seasonally are filled with water. Some permanent rivers run from the Alborz or the Zagros to the Caspian Sea, Persian Gulf and Oman Sea.