FREE CEPSCI Erosion and Sediment Control Measures Questions and Answers
What is the primary purpose of Polyacrylamide (PAM) in erosion and sediment control?
Explanation:
Polyacrylamide (PAM) is used in erosion and sediment control primarily as a non-toxic chemical temporary tackifier. It helps to bind soil particles together and reduce erosion by improving soil structure and stability. PAM is also utilized as a flocculant, which aids in sedimentation by causing suspended particles in water to aggregate and settle out, reducing turbidity and sediment transport in runoff.
Where are sediment tubes typically installed to reduce soil erosion and retain sediment?
Explanation:
Sediment tubes are commonly used as erosion control measures in drainage conveyance swales. They serve as ditch checks to slow down the flow of water, allowing sediment to settle out before it leaves the site. By retaining sediment within the swales, sediment tubes help to prevent erosion and reduce the amount of sediment entering stormwater systems or water bodies downstream.
Which of the following best describes erosion control blankets (ECBs)?
Explanation:
Erosion control blankets (ECBs) are temporary Best Management Practices (BMPs) used to prevent soil erosion on construction sites and other disturbed areas. They are typically made of biodegradable materials such as straw, coconut fiber, or synthetic materials, and they hold seed and soil in place until vegetation can become established. ECBs gradually degrade over time, typically lasting between 1 to 3 years, depending on the specific product and environmental conditions.
When should silt fence sediment typically be removed according to erosion control guidelines?
Explanation:
According to erosion control guidelines, silt fences should have their accumulated sediment removed when it reaches approximately 1/3 the height of the fence. This ensures that the silt fence remains effective in trapping sediment and preventing it from washing into adjacent areas or stormwater systems. Prompt removal helps maintain the functionality of the silt fence throughout the construction or disturbance phase.
Sediment control structures such as silt fences most commonly trap sediment by the following means.
Explanation:
Silt fences and similar sediment control structures primarily work by slowing down the flow of water. When water slows down, its ability to carry sediment is reduced, allowing particles of sediment (such as soil, sand, or other debris) to settle out of the water and accumulate behind the structure. This process effectively prevents sediment from being carried away by runoff and helps to protect surrounding areas from sediment pollution.
While silt fences do have openings that can trap larger particles of sediment, their main function is to slow down the velocity of water, which enables sedimentation. They are not primarily designed to prevent erosion or to act as physical barriers for vehicles, although they may serve these secondary functions to some extent depending on their design and placement.
What is a rip rap channel typically used for?
Explanation:
A rip rap channel is a permanent erosion control measure used to prevent soil movement by lining channels or watercourses with large, loose, angular stones. This stone lining is effective in resisting erosive forces from flowing water, such as runoff or streams, thereby stabilizing the channel bed and banks. The use of non-woven geotextile filter fabric or granular underlining further enhances its effectiveness by preventing soil particles from being carried away by water.
The main benefit of using mulches and ECBs is that they:
Explanation:
Mulches (such as wood chips or straw) and ECBs (Erosion Control Blankets) provide instant cover to bare soil upon installation. This immediate coverage helps to protect the soil from rain impact, reduce surface runoff, and prevent erosion before vegetation can become established. It is a critical initial step in erosion and sediment control on construction sites and other disturbed areas.
Unlike vegetation, which takes time to grow and provide cover, mulches, and ECBs offer an immediate solution to stabilize soil and prevent erosion during the early stages of project development. This early protection is essential for maintaining soil integrity and preventing sediment runoff into nearby water bodies or storm drains.
When would a pipe slope drain (PSD) typically be used?
Explanation:
A pipe slope drain (PSD) is used to safely direct water flow down a slope without causing erosion, especially in situations where the slope has not yet been stabilized or where permanent drainage structures are not yet installed. PSDs are designed to manage runoff and prevent erosion by safely conveying water away from sensitive areas until permanent stabilization measures can be implemented. They help to protect soil integrity and prevent sedimentation in nearby water bodies during construction or other land-disturbing activities. Therefore, option C is the correct answer as it accurately describes the primary purpose of a pipe slope drain.
PAM is a chemical that is added to turbulent runoff primarily to achieve the following.
Explanation:
PAM (Polyacrylamide) is a chemical used in erosion and sediment control practices, particularly in controlling sediment in runoff from construction sites or disturbed areas. When added to turbulent runoff water, PAM functions by causing flocculation. Flocculation is the process where small particles in the water aggregate together to form larger particles (called flocs). These flocs are heavier and settle out more readily than individual particles, reducing the turbidity of the water and hence reducing sediment transport. This process helps to clarify the water by promoting the settling of suspended solids, which can then be trapped or filtered out more effectively by sediment control measures such as silt fences or sediment basins.
Why is it important to install a silt fence at the proper distance from the toe of steep slopes?
Explanation:
Installing a silt fence at the proper distance from the toe of steep slopes is critical for effective erosion control. This placement allows the silt fence to capture sediment runoff before it reaches the slope, thereby preventing erosion. Additionally, maintaining a proper distance ensures that there is adequate space behind the silt fence for sediment storage. This sediment can then be periodically cleaned out to maintain the effectiveness of the silt fence over time.
The sediment control structure in the center-right side of the photo above is a:
Explanation:
A rock spillway for a sediment trap is designed to control sediment by allowing water to flow over a constructed barrier of rocks. This structure helps to slow down water flow, allowing sediment to settle out before water continues downstream. It's typically used in areas where sediment control is critical, such as construction sites, to prevent sediment from entering water bodies or stormwater systems.
In the context of erosion and sediment control BMPs (Best Management Practices), a rock spillway for a sediment trap is specifically designed to manage sediment runoff effectively.