What Rivers Carry & Deposit: Sediment, Rocks & Organic Matter
Rivers are Earth's great transporters. As they flow, they erode, carry, and deposit materials—shaping landscapes and ecosystems.
What They Carry (Load)
| Load Type | Particle Size | Transport Mode | Examples |
|---|
| Dissolved Load | Ions/molecules | In solution | Calcium, bicarbonate, silica, salts |
| Suspended Load | Clay, silt, fine sand (<0.062 mm) | Held in water column | Muddy water color; most load by mass |
| Bed Load | Sand, gravel, cobbles, boulders | Rolling, sliding, saltation (bouncing) | Channel bed material; moves during floods |
| Organic Matter | Variable | Suspended or floating | Leaves, wood, algae, carcasses |
Controls on Transport
- Velocity: Faster flow = larger particles carried (Hjulström curve).
- Discharge: More water = more power.
- Sediment Supply: Landslides, bank erosion, tributaries.
- Channel Shape/Slope: Steep, narrow = high energy.
What They Deposit (Landforms)
- Channel Bars: Point bars (meander inside), mid-channel bars.
- Floodplains: Fine sediment (overbank deposition) — fertile farmland.
- Alluvial Fans: At mountain fronts (sudden slope drop).
- Deltas: At mouth (velocity drops to zero) — distributary networks.
- Natural Levees: Coarse sediment along banks during floods.
Impacts
- **Positive:** Soil fertility, habitat creation, aquifer recharge, navigation.
- **Negative:** Channel aggradation (flood risk), reservoir siltation, habitat smothering, pollutant transport.
River sediment is the architect of lowlands and deltas—cradles of civilization.
Wanderlust World