James. 1 Unnavigable river, 710 mi (1,143 km) long, rising in central N.Dak. and flowing across S.Dak. to the Missouri River at Yankton, S.Dak. Jamestown Dam on the river is an irrigation and flood control unit of the Missouri River basin project of the U.S. Bureau of Reclamation. The James is also known as the Jim River or the Dakota River. 2 River, 340 mi (547 km) long, formed in W central Va. by the union of the Jackson and Cowpasture rivers and winding E across Va. to enter Chesapeake Bay through Hampton Roads. One of Virginia's chief rivers, it is navigable for large ships to Richmond, c.100 mi (160 km) upstream; Norfolk, Newport News, and Portsmouth are large ports at its mouth. Its chief tributaries are the Appomattox and Chickahominy rivers. The James's upper course flows through scenic gorges in the Blue Ridge Mts. and the Piedmont; waterfalls and rapids provide power. English colonists founded Jamestown on the lower river in 1607. During the Civil War, Union forces used the river in vain attempts to capture Richmond (see Peninsular campaign; Seven Days battles).