The Diyala River is 275 miles long, rising as the Sirvan River in NW Iran and
flowing SW through the Zagros Mts. into E Iraq, where it enters the Tigris
River S of Baghdad. The Diyala is unnavigable, but its valley is an important trade
route between Iran and Iraq. A dam on the lower Diyala provides flood control
and irrigates the area NE of Baghdad.