What is sediment transport?

Sediment transport or Soil transport is the movement of solid particles, usually due to the combination of gravitational forces acting on the sediment, and the movement of the liquid at which the sediment enters. Soil erosion occurs in natural systems where the particles are sandstones (sand, rocks), mud, or clay; the liquid is air, water, or ice; and the gravitational force that works to move particles to the landing surface. Sediment transportation or soil migration due to the movement of liquids occurs in rivers, lakes, lakes, oceans, and other bodies of water as a result of currents and waves. Transportation is also caused by glaciers as they flow, and to places on earth under the influence of wind. Soil erosion due to gravity alone is possible in most sloping areas, including hills, scarves, cliffs, and the continental shelf — the continental boundary of the slope.

Sediment transport is important in the fields of sedimentary geology, geomorphology, civil engineering, hydraulic engineering, and natural engineering. Sediment transport information is often used to determine if erosion will occur, the magnitude of this erosion or demolition, the site of sediment deposition, and the time and distance at which it will occur.

Mechanism

Following are some mechanisms of sediment transport:

• Aeolian- Aeolian or eolian is the name for the transport of soil by air.
• Fluvial- In geology, visual geography, and sedimentation or sediment transport, fluvial processes are related to water flowing in natural systems. These include open channels like rivers, streams, per glacial flows, strong floods, and glacial floodplains.
• Coastal- Coastal sedimentation or sediment transport occurs along with coastal areas due to the movement of waves and currents.
• Glacial- As glaciers move over their beds, they stabilize and move objects of all sizes. Glaciers can carry the largest sediments, and glaciers usually contain a large number of glacial erratic’s, many of them a few feet wide.
• Hillslope- In hillslope sediment transport, various processes transmit regolith downslope. These include: Crawling on the ground, Throwing a tree, Soil movement by shaking animals.
• Debris flow- Lots of material is transported in the flow of debris, highly concentrated mud mixtures, layers up to the size of rocks, and water. Debris flow moves as the granary flows down the high mountain valleys and washes away. Because they carry sediment as a granular compound, their modes of transport and strength are formed differently from those of flexible systems.

Initiation of motion

Stress balance

In order for the liquid to begin transporting the sediment currently resting on the surface, the boundary (or bed) of the sheer pressure caused by the liquid must exceed the critical shear stress when starting the movement of the ammunition in the bed. This basic condition for starting a movement can be written as follows:

${𝜏}_B={𝜏}_C$

Where,

• ${𝜏}_B$= Bed shear stress
• ${𝜏}_C$=Critical shear stress

Sediment Transport rate

Formulas for calculating the sediment transport rate are present in the moving sediment in a few different flow phases. These formulas are often divided into bed load, suspended load, and washing load. They can also sometimes be divided into bedding and laundry.

Bed Load

The load on the bed moves by rolling, sliding, and jumping (or adding salt) over the bed, and it moves at a fraction of the speed of the liquid flowing. Beds loading is generally thought to constitute 5-10% of the total soil load in a stream, making it less useful in terms of large balance. However, the load on the bedding material (bed load and part of the fixed load that includes the bedding material) is often dominated by bed load, especially in rocky rivers. This load of bedding material is the only part of the sediment load that interacts with the bed. Since bed load is an important part of that, it plays a major role in controlling channel morphology.

Meyer-Peter Müller and derivatives

The Meyer-Peter and Müller transport formulas, developed in 1948, were designed for fine-grained stone in about eight transport hubs. The formula uses the above non-dimensionalization of shear stress,

$d=\frac{SD}{K_1{({d^1}_{90}/6)}^{3/2}}$

Where,

• d = Sediment size in armor 
• S = Channel slope 
• $K_1$= Constant (= 0.19 when D in feet and 0.058 when D in meter) 
• n = Lower channel density or coefficient of Manning 
• ${d^1}_{90}$= Bed material size when 90% of the material is good

Suspended load

The suspended load is carried in the lower and middle parts of the flow and travels for the greater part of the stream flow rate. A common feature of the fixed sediment concentration in the flow is given in the Rouse Profile. This feature works for a situation where the saturation of the sediment at a certain height above the bed can be measured.

Bed material load

The load on the bed material includes the bed load and part of the fixed load found on the bed.

That all of these formulas cover a wide range of sand sizes and two of them are made only of sand is that they occur in rivers that live in sand and are usually transported simultaneously as a bed and a fixed load.

Wash load

The wash load is carried inside the water column as part of the flow, so it goes with the average speed of the mainstream. The concentration of the wash load is almost the same in the water column. This is explained by the case of the end member when the Rouse number is equal to 0 (i.e. the stopping speed is much lower than the turbulent mixing speed), which results in the prediction of the exact concentration profile of the material.

Total load

Some authors have tried to make the total amount of sediment carried in water. These formulas are mostly designed for sand, (depending on the conditions of the stream or flow) and can usually be carried as both a bed load and a fixed load in the same area or on the beach.

Context and Applications

Sediment transport or soil transport is used to solve many environmental, geotechnical, and geological problems. Measuring soil movement or sediment transport is important for coastal engineering. Various erosion or sediment deposition machines are designed to measure soil erosion or sediment transport for various flow depths.

This topic is important for professional exams in both undergraduate and graduate studies and in particular:

• Bachelors of Technology in Civil Engineering
• Masters of Technology in Civil Engineering
• Bachelors in Science in Earth Science
• Masters in Science in Earth Science

Practice Problem

Q 1. Basic method of sediment transport?

1. Drag the force against the velocity of flow
2. Drag the force towards it where it flows
3. Free movement of suspended particles
4. The applied energy of water on the surface

Correct Answer: b

Correct Explanation: If this force on the bed particles exceeds the force opposed to its movement then, the bed particles will begin to move to lead to sediment transport.

Q 2. On what factor does the movement of load on the bed depend?

1. Velocity of flow
2. Flow depth
3. Suspended particle
4. Surface velocity

Correct Answer: a

Correct Explanation: The load on the bed rests on the lower layers of the water flow. So, it depends on the velocity of flow.

Q 3. What is the minimum amount of shear pressure required to move sediment?

1. Velocity ratio
2. Critical shear stress
3. Critical stream velocity
4. Drag force on suspended particles

Correct Answer: b

Correct Explanation: The minimum amount of shear pressure required to move sediment is critical shear stress.

Q 4. What are the kinds of sediment load-

1. Sediment particles load, Bed load
2. Sediment yield load, Bed load, Suspended load
3. Bed load, Dissolved load, Suspended load
4. Bed load, Depth integrated load

Correct Answer: c

Correct Explanation: The load on the bed moves by rolling, sliding, and jumping over the bed, and it moves at a fraction of the speed of the liquid flowing. The suspended load is carried in the lower and middle parts of the flow.

Q 5. What kind of energy is needed to stabilize suspended particles in flowing water?

1. Gravel bed force
2. Sediment transport force
3. Force of turbulence
4. Gravity force

Correct Answer: c

Correct Explanation: Suspended load is sediment load, force of turbulence causes this suspension, which is generated by the flow of channel during sediment transportation.