How a River Picks Up Its Load
A river moves sediment—the loose particles of soil and rock—through a mix of rolling and suspension. Gravel and coarse sand tend to bump or roll along the bed, while finer grains can stay aloft in the water. The current’s speed matters, but so does its turbulence: swirling eddies repeatedly lift particles that would otherwise sink.
The river’s load is not simply dirt swept from its banks. It comes from eroding hillsides, exposed riverbeds, and tributaries, and it changes with floods, seasons, and the kind of rock in the watershed. A flood can mobilize grains that ordinary flow leaves in place, briefly turning the channel into a much more powerful transporter.
Where the Cargo Falls
When water slows, its ability to carry sediment falls. The largest, heaviest particles usually settle first; finer material can travel farther before sinking. This sorting builds features such as sandbars, which may shift as later currents cut into them or deposit more material nearby.
At a river’s mouth, the current often spreads into quieter water. Sediment then accumulates in branching channels and shallow deposits, gradually building a delta. The shape and growth of that land depend on how much material the river delivers and how waves, tides, and currents redistribute it.
A Moving Landscape
Because deposition and erosion happen together, a river channel is never just a fixed trench carrying water. It can migrate sideways as one bank wears away and sediment builds on another. That movement reshapes floodplains and can bury, expose, or redirect land over time. The river’s “cargo” is therefore also the material from which new banks, bars, and delta land are made.
