Republican, river, c.420 mi (680 km) long, formed in S Nebr. by the junction of the North Fork and Arikaree rivers. It is joined by the South Fork at Benkelman and flows E across the rolling grasslands of Nebraska and SE across Kansas to join the Smoky Hill and form the Kansas River at Junction City. Its broad channel traverses a rich agricultural region. The river is included in the Missouri River basin project. Many dams and reservoirs have been built for flood control, irrigation, and power.