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MEANDERS

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As it flows around a bend, river water cuts away the bank on the outside of the bend and drops sand and mud on the inside. This makes the bend more pronounced, so over time its winding course may become a series of exaggerated loops, or meanders. Sometimes a loop is cut off to become an “ox-bow lake”, seen here (centre left) as the River Amazon flows through rainforest in Peru, South America.

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VALLEYS AND GORGES

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As a river flows down from its upper course, the water

usually erodes a winding V-shaped valley through the land. Some rivers pass through steep-sided gorges,

like Tiger Leaping Gorge on the River Yangtze

in China. Gorges are often created

by the collapse of limestone cave

systems that once concealed

underground rivers.

LOWER COURSE

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When rivers reach the lowlands they flow more slowly, but carry more water. If they are not controlled they tend to flood each year, spilling over their banks and swamping the landscape. The floodwater leaves layers of

fine silt, which build up to form a floodplain of deep, fertile soil. This makes excellent farmland. Here the Willamette River flows across its floodplain in Oregon, USA.

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ESTUARIES AND DELTAS

At the coast, fresh river water meets the salt water that pushes upriver at high tide. As a result, the river drops mud particles, building up the mudflats of an estuary. If the river flow is more powerful than the flow of the tide, the flats extend out from the shore to form a wide flat area with many outlet channels, known as

a delta. This view from space shows the delta of the River Niger as it meets the sea in Nigeria.

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