Answer :
To understand the relationship between the speed at which water flows and the size of material it can carry, we can refer to the Hjulström Curve, which illustrates how particle size and stream velocity interact. Here’s the detailed explanation:
1. Introduction to the Hjulström Curve:
- The Hjulström Curve is a graph that shows the relationship between the particle size of sediments (in cm) and the velocity of the water flow (in cm/s) required to erode (lift), transport (move), and deposit (settle) those particles.
2. Key Observations from the Data:
- When looking at the data, various particle sizes are mentioned (boulders, cobbles, pebbles, sand, silt, and clay), along with their corresponding diameters in centimeters.
- Similarly, stream velocities in cm/s are given, which are needed to either erode, transport or deposit these particles.
3. Explanation of the Relationships:
- Erosion:
- Larger particles like boulders and cobbles require much higher velocities to be eroded due to their greater mass. As the particle size decreases to sand, silt, and clay, the velocity required for erosion decreases. However, for very fine particles like clay, the velocity required again increases slightly due to the cohesive forces between these tiny particles.
- Transportation:
- Water can transport particles of varying sizes once they are lifted into the flow. The velocity needed to keep particles in transport is generally lower than the velocity needed to erode them.
- Larger particles like boulders and cobbles remain in motion only when the stream velocity is high. Smaller particles like sand can be transported by moderate velocities, and even lower velocities can transport fine particles like silt and clay.
- Deposition:
- As the flow velocity decreases, the stream loses its capability to carry larger particles first, causing them to settle out of the water column. Hence, boulders and cobbles are the first to be deposited as velocity decreases.
- With further reduction in velocity, pebbles and sand grains start to settle out. The finest particles, silt, and clay, remain suspended in the water at very low velocities and only settle when velocity is extremely low.
4. Summary of the Relationship:
- Faster flowing water can carry larger particles.
- As water flow slows down, it can no longer sustain the transport of larger particles, which then settle to the bottom.
- Very fine particles like clay remain suspended even in very slow-moving water due to their low settling velocity and cohesive properties.
By observing these patterns, we understand that the size of sediment particles that water can carry is directly related to the flow velocity:
- Higher velocities are needed to pick up and transport larger particles.
- As velocity decreases, the capability to transport particles also decreases, leading larger particles to be deposited first followed by smaller particles.
This relationship is critical in understanding sediment transport in rivers and streams and managing erosion and sedimentation in natural water bodies.
1. Introduction to the Hjulström Curve:
- The Hjulström Curve is a graph that shows the relationship between the particle size of sediments (in cm) and the velocity of the water flow (in cm/s) required to erode (lift), transport (move), and deposit (settle) those particles.
2. Key Observations from the Data:
- When looking at the data, various particle sizes are mentioned (boulders, cobbles, pebbles, sand, silt, and clay), along with their corresponding diameters in centimeters.
- Similarly, stream velocities in cm/s are given, which are needed to either erode, transport or deposit these particles.
3. Explanation of the Relationships:
- Erosion:
- Larger particles like boulders and cobbles require much higher velocities to be eroded due to their greater mass. As the particle size decreases to sand, silt, and clay, the velocity required for erosion decreases. However, for very fine particles like clay, the velocity required again increases slightly due to the cohesive forces between these tiny particles.
- Transportation:
- Water can transport particles of varying sizes once they are lifted into the flow. The velocity needed to keep particles in transport is generally lower than the velocity needed to erode them.
- Larger particles like boulders and cobbles remain in motion only when the stream velocity is high. Smaller particles like sand can be transported by moderate velocities, and even lower velocities can transport fine particles like silt and clay.
- Deposition:
- As the flow velocity decreases, the stream loses its capability to carry larger particles first, causing them to settle out of the water column. Hence, boulders and cobbles are the first to be deposited as velocity decreases.
- With further reduction in velocity, pebbles and sand grains start to settle out. The finest particles, silt, and clay, remain suspended in the water at very low velocities and only settle when velocity is extremely low.
4. Summary of the Relationship:
- Faster flowing water can carry larger particles.
- As water flow slows down, it can no longer sustain the transport of larger particles, which then settle to the bottom.
- Very fine particles like clay remain suspended even in very slow-moving water due to their low settling velocity and cohesive properties.
By observing these patterns, we understand that the size of sediment particles that water can carry is directly related to the flow velocity:
- Higher velocities are needed to pick up and transport larger particles.
- As velocity decreases, the capability to transport particles also decreases, leading larger particles to be deposited first followed by smaller particles.
This relationship is critical in understanding sediment transport in rivers and streams and managing erosion and sedimentation in natural water bodies.
