River deposition

False-colour Landsat image of the Lena Delta with many branching distributaries and islands. — Landsat's view of the Lena Delta, 2000. Distributaries spread sediment into the Arctic Ocean. The image combines infrared and red bands.

A suggested lesson sequence

Use these stages at your own pace. Pause for students to sketch, compare observations or lead part of the demonstration.

01
Observe
Locate the inner bank and point bar.
Open Observe
02
Tinker
Compare overbank flow and a delta; change the separate settling experiment.
Open Tinker
03
Explain
Why can a river erode its outer bank while depositing sediment on the inner bank?
Open Explain
04
Check
Choose an answer and explain your reasoning. Each question includes feedback.
Open Check

Rehearse with the model

The same scene and controls as the lab. Load it when you are ready; use Start projector for the full classroom view.

Before the lesson

Explain where rivers deposit sediment and compare the formation of point bars, natural levees and deltas.

Open the model before the lesson and choose a view that makes the important feature easy to see. Drag to rotate, and use the on-screen controls to change one variable at a time. The Controls panel explains the available keyboard shortcuts.

Pause the animation at a useful moment. Ask students what should happen next, then play it to test their explanation.

Guide the demonstration

Locate the inner bank and point bar.

Compare overbank flow and a delta; change the separate settling experiment.

Discuss a common misconception

“A river deposits all its sediment as soon as the water slows down.” Deposition depends on the ability of the flow to keep particular particles moving. Coarser material often settles or stops first as transport capacity falls, while finer particles may remain suspended farther downstream. Sediment size, turbulence, water depth and incoming supply all affect the result.

Build the explanation

Sediment is deposited when transport conditions no longer keep it moving. Inner bends, floodplains and river mouths create different settings for sorting and storing sediment.

Compare overbank flow and a delta; change the separate settling experiment.

The separate settling experiment describes small quartz spheres in still water; river turbulence and flocculation can change their behaviour.

Teaching notes

Distinguish sediment accumulation in a delta from processes operating in a tidal estuary.

Locate inner-bank deposition and outer-bank erosion correctly when interpreting a meander.

Explain that levees can form naturally during floods as well as being built or enlarged by people.

Check understanding

Open Check for 4 questions. Ask students to explain their choice before revealing the answer.

Return to the opening photograph. Ask students to identify one visible feature and explain which part of the model helps account for it.

Look more closely

Use these observations to connect the vocabulary to features students can identify.

Slip-off slope

The muddy Ucayali River winds through forest in Peru, with abandoned bends beside the active channel. — Ucayali River, Peru, photographed from the ISS. Meander migration leaves cut-offs and abandoned channels across the floodplain.

Read the definition

Levée

A raised embankment separates floodwater from farmland beside the Mississippi at Hannibal, Missouri. — Mississippi levee at Hannibal, Missouri, 20 June 2008. This engineered embankment limits inundation; natural levees instead build up from repeated overbank deposition.