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📘 How rivers change course overnight

You stand beside a river at dusk: faster water is eroding the outside bank while slower water deposits sand and gravel on the inside. Most migration is too slow for one visit—until a flood reaches the floodplain and makes a quiet change sud

4
lessons
~20 min
to learn
Adults
level
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What you’ll learn

  1. A river is always editing its banksExplain how erosion and deposition move meanders across a floodplain.Outer-bank erosion and inner-bank deposition make a river bend migrate while leaving clues in bars and old channels.
  2. When high water opens a shortcutDistinguish neck and chute cutoffs and connect them to overbank flow.Floodwater can turn a weak low route across a bend into a shorter active channel.
  3. Avulsion is a different kind of jumpDefine avulsion and explain how sediment and paleochannels influence a new route.Avulsion shifts a river to another floodplain position, often through a self-reinforcing contest among routes.
  4. After the channel movesPredict hydraulic, ecological, and human consequences of channel change.A new channel and an abandoned loop continue adjusting, creating habitat and hazards after the first flood.

Questions this course answers

Why does a meander usually migrate?

Faster outer-bend flow erodes the cut bank while slower inner-bend flow deposits a point bar.

What can begin a neck cutoff?

High water can cross the meander neck and enlarge a gully into a shorter channel.

How is avulsion different from ordinary meander migration?

Avulsion relocates the channel across the floodplain rather than moving continuously along its old centerline.

Why can a cutoff keep enlarging after the first flood?

A shorter route can increase local slope, allowing later flows to scour and reshape the new bed.

What is a paleochannel?

Paleochannels are traces of former channels and can sometimes guide later floodwater.

What does an oxbow lake preserve?

An oxbow is an abandoned loop whose crescent shape records an earlier course.

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