CESSWI Erosion Control BMPs 4 — Questions and Answers
Question 1: What is the purpose of a tracking control BMP such as a stabilized construction entrance?
- Reduce sediment tracked onto public roads by construction vehicles (Correct answer)
- Filter stormwater runoff leaving the site perimeter
- Slow runoff velocity on internal access roads
- Prevent unauthorized vehicle access to the site
Correct answer: Reduce sediment tracked onto public roads by construction vehicles
Stabilized construction entrances use aggregate to dislodge mud from vehicle tires, preventing sediment from being tracked onto public roadways.
Question 2: When is it appropriate to use a slope drain (pipe slope drain) as an erosion control BMP?
- To convey concentrated runoff from the top to the bottom of a slope without causing erosion (Correct answer)
- To intercept sheet flow across a slope face
- To dewater ponded sediment basins
- To protect inlet structures from sediment loading
Correct answer: To convey concentrated runoff from the top to the bottom of a slope without causing erosion
Slope drains (pipe slope drains) safely convey concentrated runoff down steep slopes, discharging at the base with energy dissipation to prevent erosion.
Question 3: A CESSWI inspector finds that an erosion control blanket on a 2:1 slope is not stapled at the recommended density. Which immediate risk does this create?
- Wind and water can lift the blanket, leaving soil exposed underneath (Correct answer)
- The blanket will prevent vegetation from growing through it
- Sediment will accumulate excessively above the blanket
- The blanket will slide upslope during dry periods
Correct answer: Wind and water can lift the blanket, leaving soil exposed underneath
Insufficient stapling allows wind or water to displace the blanket from the soil surface, creating gaps where erosion can occur.
Question 4: What is the primary limitation of using straw mulch alone (without tackifier or netting) on slopes steeper than 3:1?
- Straw will be displaced by wind and runoff velocity on steep slopes (Correct answer)
- Straw decomposes too slowly on steep slopes
- Straw promotes excessive weed growth on steep terrain
- Straw has insufficient thickness to prevent raindrop impact
Correct answer: Straw will be displaced by wind and runoff velocity on steep slopes
On slopes steeper than 3:1, water velocity and wind forces exceed the stability of loose straw, requiring tackifier, netting, or blankets to hold mulch in place.
Question 5: Which vegetative BMP is BEST suited for stabilizing the banks of a constructed drainage channel carrying intermittent high-velocity flows?
- Turf reinforcement mat (TRM) with seeding (Correct answer)
- Temporary seeding with annual grasses
- Hydraulic mulch without seed
- Compost blanket
Correct answer: Turf reinforcement mat (TRM) with seeding
Turf reinforcement mats provide structural reinforcement to established vegetation roots, allowing grass to withstand high-velocity flows that would otherwise erode bare or lightly vegetated banks.
Question 6: An inspector notices that sediment has accumulated to more than one-third of the height of a silt fence. What action is required?
- The silt fence must be cleaned out or replaced to restore sediment storage capacity (Correct answer)
- Install a second silt fence immediately upslope
- The silt fence can remain until it reaches full height
- Remove the silt fence since it has done its job
Correct answer: The silt fence must be cleaned out or replaced to restore sediment storage capacity
When sediment reaches one-third of the fence height, the fence must be cleaned out because further accumulation reduces hydraulic head and risks failure from overtopping.
Question 7: What distinguishes a horizontal slope drain from a standard pipe slope drain?
- A horizontal slope drain runs along the toe of slope to intercept and redirect runoff laterally (Correct answer)
- A horizontal slope drain is installed at a 0% grade
- A horizontal slope drain uses open channels instead of pipe
- A horizontal slope drain does not require outlet protection
Correct answer: A horizontal slope drain runs along the toe of slope to intercept and redirect runoff laterally
Horizontal slope drains (also called diversion ditches or interceptor swales) run along contours at the toe or bench of slopes to intercept and redirect lateral runoff.
CESSWI Erosion Control BMPs 4
What is the purpose of a tracking control BMP such as a stabilized construction entrance?