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What type of sampler is designed to collect sediments being transported along the bottom of a stream or river?
Which device measures cloudiness to estimate the concentration of suspended sediments?
How do Acoustic Doppler Current Profilers estimate sediment transport?
What is a primary function of gravel traps in sediment measurement?
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What type of sensors measure light scattering caused by suspended particles?
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Which of the following factors does NOT influence soil erosion?
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What are the primary erosive agents responsible for soil erosion by water?
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Which of the following best describes the interaction of raindrop impact and overland flow in soil erosion?
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What is essential for selecting methods of estimating soil erosion?
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Which of the following is NOT one of the four interactive erosion sub-processes?
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What is the primary focus of a qualitative observation regarding soil erosion?
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Which method of estimating soil erosion is likely employed for broader scale applications?
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What determines the rate at which a soil erosion study will be undertaken?
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What is the primary natural force responsible for soil erosion mentioned in the content?
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Which of the following is NOT classified as a primary cause of soil erosion?
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What distinguishes accelerated erosion from natural soil erosion?
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How is soil erosion by water primarily initiated on a small scale?
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What is geological erosion primarily caused by?
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Which term describes erosion caused by human activities that disrupt the natural balance of soil formation?
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In the context of sediment transport, which factor enhances sediment yield from erosion?
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What is the term for the vertical distribution of sediments during sediment transport?
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Which feature indicates concentrated overland flow that may have replaced sheet flow?
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What do exposed E horizons typically look like in comparison to the surrounding soil?
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What indicates soil loss when certain rocks are found on the surface?
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How do exposed roots indicate erosion?
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What do pedestals indicate about surrounding soil?
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What distinguishes direct measurements from passive measurements in studying erosion?
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What is a primary characteristic of debris dams?
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Which method of obtaining information about erosion is described as time-consuming but most accurate?
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What defines rill erosion?
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Which variable is NOT part of the formula for rill detachment rate?
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What effect does critical shear (τc) have on rill erosion?
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How does gully erosion differ from rill erosion?
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Which factor does NOT affect the rate of gully erosion?
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What is hydraulic shear (τ) a function of?
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Which of the following statements regarding sediment transport capacity (Tc) is correct?
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What is the main distinguishing feature of a rill compared to a gully?
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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.
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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.
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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.
