The muddy Ucayali River winds through forest in Peru, with abandoned bends beside the active channel.

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Preparing the 3D view

Preparing lighting and the first complete frame…

Model scale

Long-profile relief ×12. channel breadth enlarged.

Relative discharge 0.70×. Increasing discharge raises the water level within the fixed channel. Play to follow the downstream flow.

River long profile

Follow a river from source to mouth and explain how its gradient, channel shape and flow change downstream.

Drag to rotate. Hold Ctrl and scroll to zoom, or pinch on a touch screen.

Why it happens

A river’s long profile usually becomes gentler downstream. Channel shape, water supply and sediment change along its course, helping explain why steep valleys and broad floodplains occur in different reaches.

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Ucayali River, Peru, photographed from the ISS. Meander migration leaves cut-offs and abandoned channels across the floodplain.

Try a comparison

Raise Discharge and compare stage and wetted margins. Play follows water downstream without eroding the fixed channel.

Reading the result

The channel shape stays fixed while the water level changes; the displayed wet margins are an illustration rather than a mapped flood extent.

Film

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The film stays paused until you play it.

How Rivers Shape the Landscape: Crash Course Geography #23 — Crash Course.

A common misunderstanding

A river’s upper, middle and lower courses are separate kinds of river.

These terms describe reaches along one river system. Gradient, channel form, discharge and sediment can change downstream, often gradually and with local interruptions. They help compare patterns along a long profile, but they do not divide every river into three sharply bounded sections.

Cases

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