1. Settling:
* Reduced Upward Force: The velocity of the fluid is directly related to the upward force it exerts on the suspended particles. As velocity decreases, the upward force also decreases.
* Gravity Takes Over: With reduced upward force, gravity becomes the dominant force acting on the particles. This causes the particles to settle towards the bottom of the fluid.
* Particle Size and Density: The settling rate is influenced by the size and density of the particles. Larger and denser particles settle faster than smaller and lighter ones.
2. Deposition:
* Accumulation: As particles settle, they accumulate at the bottom of the fluid, forming a sediment layer.
* Sedimentation Rate: The rate at which particles settle and deposit depends on several factors, including:
* Fluid velocity
* Particle size and density
* Fluid viscosity
* Turbulence in the fluid
3. Potential for Erosion:
* Critical Velocity: There's a critical velocity below which particles start to settle. If the fluid velocity decreases further, erosion can occur.
* Erosion: If the velocity drops too low, the upward force may not be sufficient to keep previously settled particles suspended. The flow can then pick up the settled particles and transport them again.
Examples:
* Rivers: As a river flows into a wider, shallower area, its velocity decreases, causing sediment to settle out. This can create sandbars and deltas.
* Wastewater Treatment: In sedimentation tanks, the velocity of wastewater is slowed down to allow suspended solids to settle out.
* Wind Erosion: Decreased wind velocity can cause dust particles to settle out, forming dust storms.
In summary: When the velocity of a fluid carrying suspended particles decreases, the particles settle out due to the dominance of gravity. This process leads to deposition, and further decrease in velocity can cause erosion of previously settled particles.
