Mean velocities and boulder transport during Tahoe-age floods of the Truckee River, California-Nevada

Boulders and gravel bars in Truckee River glacial outwash deposits indicate discharges and velocities far greater than those of the present river. Collapse of unstable glacier dams near Lake Tahoe's outlet would have been necessary to release quickly the large volumes of water that produced the above features. Flood velocities and tractive forces are estimated by the size of observed boulders. It is concluded that a tractive force of 20 to 30 lb per sq ft was sufficient to move the largest boulder, measuring 40.20.10 feet above ground surface, in a 40 to 80-ft-deep flood moving nearly 30 fps on a slope of 0.007