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It rises near Hamadan, in the Zagros Mountains of Iran, where it is known as the Sirvan. It then descends through the mountains, where for some 32 km it forms the international border between the two countries. It finally feeds into the Tigris below Baghdad.
Navigation along the upper reaches of the Diyala is not possible because of its narrow defiles, but the river's valley provides an important trade route between Iran and Iraq.
The river is controlled by a dam on the lower Diyala valley, which controls floods and irrigates the area northeast of Baghdad.
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