A river in the Southwest carrying sediment
Rivers carry sediment, particles of soil and rock, in varying amounts. Rivers that run muddy red or milky white contain more sediment than those that appear clear. Free-flowing "wild" rivers contain more sediment than those that have been dammed, since dams capture the heavy particles behind them.
Sediment in rivers comes from different sources. It may be soil washed away by storm runoff or material broken up by rivers as they slowly carve away at the sides of their channels and riverbeds. Whatever the source, sediment transported by rivers is eroded from one place and is deposited in another, causing the creation of different landforms.
Flood Plains
Flood plains may be wide, and the sediment deposited in them can create rich farmland. Levees are often built to contain this natural process and prevent flooding of cities and towns. However, most levees aren't built to contain an exceptional "100 year" flood.
River Terraces
River terraces rise step-like from the edges of a flood plain. They are remnants of former flood plains. Terraces may be evenly paired in height, but they will be more uneven if the river flowed gradually and its channel meandered around.
Sand and Gravel Bars
Gravel bars in the Waiho River in New Zealand
Sand and gravel bars are often formed in "braided" rivers, in which multiple channels cut their way across a valley floor. Many of the world's largest rivers have braided courses in their lower reaches. Sediment may form islands between channels, which may then be covered by vegetation and even trees.
Deltas
Deltas appear at river mouths, where a river joins the ocean. As a river's course flattens out as it approaches sea level, the water slows and sediment begins settling to the bottom, creating a large, fan-shaped area of material. Deltas contain other landforms, such as sand bars, spits and tidal flats.
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