False-colour Landsat image of the Lena Delta with many branching distributaries and islands.

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Preparing the 3D view

Preparing lighting and the first complete frame…

Model scale

600 × 400 m conceptual reach. relief ×5. sediment symbols enlarged.

Inner-bank point bar within a curved channel. Flow tracers move downstream; the selected bar is not growing.

How to read these results

Separate settling experiment: 40 μm quartz spheres settle at 1.44 mm/s in still 20 °C fresh water; at 0.1 m/s horizontal transport through 2 m depth, distance ≈ 139 m. Turbulence and flocculation are excluded.

River deposition

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

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Why it happens

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.

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Landsat's view of the Lena Delta, 2000. Distributaries spread sediment into the Arctic Ocean. The image combines infrared and red bands.

Try a comparison

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

Reading the result

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

A common misunderstanding

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.

Cases

Exam language

Slip-off slope

The gently sloping inner bank of a river bend, where sediment tends to accumulate as a point bar. It contrasts with the steeper outer cut bank. Both develop as the bend migrates and its flow redistributes sediment.

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

Cut bank

The eroding outer bank of a river bend, where the faster part of the flow commonly approaches the bank. A steep face or exposed roots can reveal active erosion. Deposition often occurs on a point bar across the channel.

Levée

A raised bank beside a river, either built naturally by overbank sediment deposition or constructed to reduce flooding. Also written levee.

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Mississippi levee at Hannibal, Missouri, 20 June 2008. This engineered embankment limits inundation; natural levees instead build up from repeated overbank deposition.

Floodplain

Relatively flat land beside a river that is shaped by channel migration and flood deposition and may be inundated when the river overflows.

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The South Fork Stillaguamish River in flood. Water spreads beyond the usual channel when discharge exceeds channel capacity.

Delta

A body of sediment built where a river enters a sea or lake and deposits enough material to accumulate. Distributary channels often cross its surface.

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Landsat's view of the Lena Delta, 2000. Distributaries spread sediment into the Arctic Ocean. The image combines infrared and red bands.

Estuary

A partly enclosed coastal water body where freshwater meets and mixes with seawater, influenced by tides.

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NASA Landsat observation of the Thames estuary. The tidal river widens towards the North Sea; pale water reveals suspended material and shallow coastal water.

Helicoidal flow

A secondary, spiral-like circulation within a river bend, superimposed on the downstream current. Near-bed movement helps transfer sediment towards the inner bank, while strong flow near the outer bank promotes erosion. The pattern varies with channel shape and discharge.

Process0.40EnvironmentGrain diameter40 μm