Water velocity dramatically affects deposition: as water velocity decreases, deposition increases.
Here's a more detailed explanation:
When water slows down, it loses energy and its ability to carry sediment. This loss of energy causes the sediment to settle out of the water column and deposit. The relationship between water velocity and the size of particles that can be transported is crucial in understanding deposition.
- High Velocity: High water velocity allows the water to carry larger and heavier particles such as gravel, sand, and even boulders. Little to no deposition occurs.
- Decreasing Velocity: As water velocity decreases, the largest and heaviest particles settle out first. This is because they require more energy to stay suspended in the water.
- Low Velocity: At very low water velocities, even the smallest particles, such as silt and clay, will eventually settle out. This often occurs in still water environments like lakes or the backwaters of rivers.
The following factors contribute to the slowing of water velocity and subsequent deposition:
- Expansion of Channel: When a river or stream flows out of a narrow channel and into a wider area (like a floodplain), the water spreads out, reducing its velocity.
- Obstructions: Obstacles such as vegetation, rocks, or debris in the water can slow the flow and promote deposition around them.
- Changes in Gradient: A decrease in the slope (gradient) of a river channel reduces the water's speed.
- Entering Standing Water: When a river flows into a lake or ocean, the sudden decrease in velocity causes significant deposition, often forming deltas.
Here's a table summarizing the relationship:
| Water Velocity | Sediment Carrying Capacity | Deposition Rate | Particle Size Deposited |
|---|---|---|---|
| High | High | Low | Large (gravel, sand) |
| Moderate | Moderate | Moderate | Sand, silt |
| Low | Low | High | Silt, clay |
| Very Low | Very Low | Very High | Clay |
Therefore, deposition is inversely proportional to water velocity. The slower the water moves, the more sediment it drops.
