ABE 66 PPT 4

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Questions and Answers

What type of sampler is designed to collect sediments being transported along the bottom of a stream or river?

Depth-Integrating Sampler

Acoustic Doppler Current Profiler

Bed Load Sampler (correct)

Turbidity Sensor

Which device measures cloudiness to estimate the concentration of suspended sediments?

Turbidity Sensor (correct)

Gravel Trap

Helley-Smith Sampler

Optical Backscatter Sensor

How do Acoustic Doppler Current Profilers estimate sediment transport?

By detecting light scattering from particles

By measuring the velocity of water (correct)

By measuring the temperature of the water

By collecting sediment samples directly

What is a primary function of gravel traps in sediment measurement?

To capture bed load particles Signup and view all the answers

What type of sensors measure light scattering caused by suspended particles?

Optical and Laser Sensors Signup and view all the answers

Which of the following factors does NOT influence soil erosion?

Water temperature Signup and view all the answers

What are the primary erosive agents responsible for soil erosion by water?

Rainfall and runoff Signup and view all the answers

Which of the following best describes the interaction of raindrop impact and overland flow in soil erosion?

They work together to cause soil erosion. Signup and view all the answers

What is essential for selecting methods of estimating soil erosion?

Objective-based criteria Signup and view all the answers

Which of the following is NOT one of the four interactive erosion sub-processes?

Filtration by vegetation Signup and view all the answers

What is the primary focus of a qualitative observation regarding soil erosion?

Visual inspection for indicators of erosion Signup and view all the answers

Which method of estimating soil erosion is likely employed for broader scale applications?

Soil erosion modeling Signup and view all the answers

What determines the rate at which a soil erosion study will be undertaken?

The duration of the study Signup and view all the answers

What is the primary natural force responsible for soil erosion mentioned in the content?

Water Signup and view all the answers

Which of the following is NOT classified as a primary cause of soil erosion?

Urban development Signup and view all the answers

What distinguishes accelerated erosion from natural soil erosion?

It is typically caused by human activities. Signup and view all the answers

How is soil erosion by water primarily initiated on a small scale?

Through the action of rainfall Signup and view all the answers

What is geological erosion primarily caused by?

Natural processes involving water Signup and view all the answers

Which term describes erosion caused by human activities that disrupt the natural balance of soil formation?

Accelerated erosion Signup and view all the answers

In the context of sediment transport, which factor enhances sediment yield from erosion?

Human-induced land disturbance Signup and view all the answers

What is the term for the vertical distribution of sediments during sediment transport?

Sediment stratification Signup and view all the answers

Which feature indicates concentrated overland flow that may have replaced sheet flow?

Rills or gullies Signup and view all the answers

What do exposed E horizons typically look like in comparison to the surrounding soil?

They appear as white patches. Signup and view all the answers

What indicates soil loss when certain rocks are found on the surface?

Exhumed rocks Signup and view all the answers

How do exposed roots indicate erosion?

They show what should be buried is exposed. Signup and view all the answers

What do pedestals indicate about surrounding soil?

Soil has been eroded around them. Signup and view all the answers

What distinguishes direct measurements from passive measurements in studying erosion?

Direct measurements involve collection and weighing of materials. Signup and view all the answers

What is a primary characteristic of debris dams?

They catch sediment from upstream erosion. Signup and view all the answers

Which method of obtaining information about erosion is described as time-consuming but most accurate?

Direct measurements Signup and view all the answers

What defines rill erosion?

The detachment and transport of soil by a concentrated flow of water. Signup and view all the answers

Which variable is NOT part of the formula for rill detachment rate?

Sediment transport capacity (Tc) Signup and view all the answers

What effect does critical shear (τc) have on rill erosion?

It is the shear below which soil detachment is negligible. Signup and view all the answers

How does gully erosion differ from rill erosion?

Gully erosion results in ephemeral channels that cannot be obliterated by tillage. Signup and view all the answers

Which factor does NOT affect the rate of gully erosion?

Air pressure in the area Signup and view all the answers

What is hydraulic shear (τ) a function of?

The specific weight, hydraulic radius, and hydraulic gradient. Signup and view all the answers

Which of the following statements regarding sediment transport capacity (Tc) is correct?

Tc can be defined as Bτ^{1.5}. Signup and view all the answers

What is the main distinguishing feature of a rill compared to a gully?

Rills can be obliterated by normal tillage operations. Signup and view all the answers

Study Notes

Direct Sampling

Sediment Transport and Suspended Load Samplers: Devices like depth-integrating samplers or point-integrating samplers are used to collect suspended sediment at various depths.
Bed Load Samplers: Specialized devices placed on the bed of a stream or river to collect sediments that are being transported along the bottom (e.g., Helley-Smith sampler).

Measurement Techniques

Turbidity Sensors: Measure cloudiness (turbidity) of water, which can be correlated with suspended sediment concentration.
Acoustic Doppler Current Profilers (ADCP): Measure water velocity and can be used to estimate sediment transport by correlating velocity with sediment concentration.
Optical and Laser Sensors: Devices like optical backscatter sensors (OBS) measure light scattering caused by suspended particles, allowing real-time sediment concentration measurement.
Gravel Traps: Installed to collect transported sediment particles for bed load measurement in controlled environments like rivers.

Soil Erosion

Refers to the detachment and removal of soil particles from the land surface, primarily by the action of water, wind, or other natural forces.
Involves the initial phase where soil particles are loosened and displaced.
Geological Erosion is natural soil erosion by water that includes both soil-forming and eroding processes.
Accelerated Erosion is associated with human disturbances (anthropogenic).

Soil Erosion by Water

A natural process linked to the hydrologic cycle.
On a small scale, soil particles are mainly detached by the impact of rainfall, but at larger scales, other water erosion processes become more dominant.
Factors Influencing Soil Erosion: Land cover, soil physical and chemical properties, raindrops energy, flow velocities and hydraulic properties, cover management, slope, slope length and stiffness, and conservation practices

Mechanics of Soil Erosion

Erosive agents are rainfall and runoff, both detaching and transporting soil particles.
Soil erosion over a land surface is a product of raindrop impact and overland flow.
Four interactive erosion sub-processes: Detachment by rainfall, transport by rainfall, detachment by runoff, and transport by runoff.

Measurement of Soil Erosion

Methods must be objective-based taking into account: Scale, study duration, prediction accuracy, simplicity and complexity, and application.

Methods of Estimating Soil Erosion

Plot-experiment (Field method): Conducted at several locations in a field and results are extrapolated to the entire landscape.
Employing soil erosion models (Soil erosion modeling): Used for applications on a broader scale.

Ways to Obtain Information about Erosion

Qualitative Observations: Involve simple viewing of the land, looking for signs or indicators of erosion.
Indicators of Erosion:
- Rills or gullies reflect concentrated overland flow.
- Exposed E horizons often appear as white patches on hilltops or convex slopes where darker soils are prevalent.
- Exhumed rocks, either boulders or rocks lying loose on the surface, typically indicate soil loss.
- Exposed roots are similar to exhumed boulders.
- Pedestals are the result of items on the surface protecting the underlying soil from raindrop impact.
- Debris dams or traps, comprised of fallen trees and branches, catch sediment eroded from upslope.

Quantitative Observations

Involve collection and measurement.
Types: Direct or passive measurements.
- Most accurate but are more laborious and time-consuming.
- Involve collecting and weighing deposited materials (small setting).
- Involve measuring widths, depths, and lengths of gullies to calculate the volume of material lost (large setting).

Rill Erosion

The detachment and transport of soil by concentrated flow of water.
The predominant form of surface erosion under most conditions.
A function of the flow rate or hydraulic shear of the flowing water, the soil's rill erodibility, and critical shear.
Rills are eroded channels small enough to be removed by normal tillage operations.

Rill Erosion Equation

𝐷𝑟 = 𝐾𝑟 𝜏 − 𝜏𝑐 ( 1− 𝑞𝑠 / 𝑇𝑐 )
- 𝐷𝑟 = rill detachment rate (𝑘𝑔 𝑚−2 𝑠 −1 )
- 𝐾𝑟 = rill erodibility, due to shear (𝑘𝑔 𝑚−2 𝑠 −1 4)
- 𝜏 = hydraulic shear of flowing water (Pa)
- 𝜏𝑐 = critical shear below which no rill erosion occurs (Pa)
- 𝑞𝑠 = rate of sediment flow in the rill (𝑘𝑔 𝑚−1 𝑠 −1 )
- 𝑇𝑐 = sediment transport capacity of the rill (𝑘𝑔 𝑚−1 𝑠 −1 )
- 𝜃 = interrill slope angle (dimensionless)

Gully Erosion

Produces channels larger than rills.
Ephemeral channels that carry water during and immediately after rains.
Gullies cannot be obliterated by tillage.

Factors Affecting the Rate of Gully Erosion

Runoff-producing characteristics of the watershed.
Drainage area.
Soil characteristics.
Alignment, size, and shape of the gully.
Slope in the channel.

Processes Involved in Gully Development

Involve processes that modify soil in a manner that increases erosion.
Involve processes that are initiated by, or dependent on, soil erosion.
Involve processes that are a necessary consequence of gully erosion.

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Description

Explore the various methods used for direct sampling of sediments, including suspended load and bed load samplers. This quiz will cover the equipment and techniques, such as turbidity sensors and Acoustic Doppler Current Profilers, essential in measuring and analyzing sediment transport in aquatic environments.