Sculpting the Landscape

Sculpting the Landscape. . The Missouri flows free for 59 miles below Gavins Point Dam and for 39 miles below Fort Randall Dam. These sections of the national recreational river provide glimpses of the once undammed, unchannelized river that played a major role in America's settlement and commerce., Because the Missouri loses elevation about one foot for every mile, the waters do not pick up much speed. Instead of cutting straight down through the valley, the river winds, or meanders, around high spots, solid rock, and resistant soils. Behind the dams, the waters slow even more and dump their loads of sand and dirt., Below the dams, the relatively clear waters erode the sandy riverbanks and capture new loads of sediment. As shown below, the river sculpts the landscape in many ways., 1 Meanders form as riverbanks bounce the river's energy back and forth. Water flows faster around the outside of a bend (arrow). This force erodes the outer channel, while slower water deposits sediments on the inside of a turn., 2 Wetlands may be created during major floods if the river slices a new channel through the banks of a meander and diverts most of the water from the meander., 3 Snags are dead trees that have fallen into the river. They may have been toppled by the river cutting into the banks, or felled by beavers, old age, disease, or other natural causes. When the current hits a snag, it deposits sediment on the downstream side., 4 Oxbow lakes may form if the water table is high and fills meanders that have been cut off and left dry by the river's main channel. They look like crescents from above., 5 Islands develop when the river divides and follows both the older, deeper channel and the newer, shallower channel around a piece of land. In some places the river may use both channels only during floods., 6 Sandbars are created when fast-moving waters lose their energy moving downstream and dump loads of soil picked up from the river bottom and banks.