CESSWI Erosion & Sediment Control Principles 3 — Questions and Answers
Question 1: What is the primary function of a check dam installed in a drainage swale on a construction site?
- To filter sediment-laden runoff through a permeable barrier
- To reduce flow velocity and promote sediment deposition within the swale (Correct answer)
- To divert runoff away from the swale entirely
- To increase channel capacity during large storm events
Correct answer: To reduce flow velocity and promote sediment deposition within the swale
Check dams slow water velocity within the swale, encouraging sediment to settle out before runoff reaches a receiving water body.
Question 2: Under the RUSLE model, increasing the slope length (L factor) while keeping all other factors constant will have what effect on predicted soil loss?
- Soil loss decreases because flow is more distributed
- Soil loss remains unchanged because slope length is offset by gradient
- Soil loss increases because longer slopes accumulate more runoff (Correct answer)
- Soil loss decreases because longer slopes have lower gradients
Correct answer: Soil loss increases because longer slopes accumulate more runoff
Greater slope length allows runoff to accumulate and gain erosive energy, resulting in higher predicted soil loss when other RUSLE factors are held constant.
Question 3: Which cover practice provides the most immediate and effective temporary erosion protection on a freshly graded slope?
- Hydroseeding with annual ryegrass
- Installation of erosion control blankets (ECBs) (Correct answer)
- Application of straw mulch crimped into the soil
- Construction of rock check dams at the slope toe
Correct answer: Installation of erosion control blankets (ECBs)
Erosion control blankets provide immediate physical protection by absorbing raindrop energy and holding soil particles in place from the moment of installation.
Question 4: A site inspector observes clear water flowing through a silt fence while turbid water pools behind it. What does this indicate about the silt fence's performance?
- The silt fence is failing because it is not retaining enough water
- The silt fence is functioning correctly by filtering sediment from the runoff (Correct answer)
- The silt fence fabric is too impermeable and should be replaced
- The ponded water indicates that the fence will soon be overtopped
Correct answer: The silt fence is functioning correctly by filtering sediment from the runoff
Clear water passing through while turbid water ponds behind indicates the silt fence fabric is trapping sediment particles as intended.
Question 5: Which soil texture is generally considered the most erodible under typical rainfall conditions?
- Clay
- Gravel
- Silt loam (Correct answer)
- Coarse sand
Correct answer: Silt loam
Silt loam soils have high erodibility because silt particles are easily detached by raindrop impact and transported in suspension with minimal cohesion.
Question 6: A SWPPP calls for a concrete washout area to be located at least how far from storm drains, open ditches, and water bodies under typical EPA guidance?
- 25 feet
- 50 feet (Correct answer)
- 100 feet
- 200 feet
Correct answer: 50 feet
EPA's Construction General Permit guidance and most state standards require concrete washout facilities to be located at least 50 feet from storm drains, ditches, and surface waters.
Question 7: During a dry-season inspection on a site with established temporary seeding, an inspector finds bare patches with rill formation. What is the MOST appropriate corrective action?
- Install additional silt fences downslope of the bare areas
- Reseed the bare areas and apply erosion control blankets to protect them (Correct answer)
- Grade the rills flat and compact the soil surface
- Construct a sediment basin at the base of the slope
Correct answer: Reseed the bare areas and apply erosion control blankets to protect them
Reseeding and applying ECBs addresses both the immediate erosion risk and the underlying lack of vegetative cover causing the bare patches.
CESSWI Erosion & Sediment Control Principles 3
What is the primary function of a check dam installed in a drainage swale on a construction site?