CPESC Erosion Control Methods & Techniques 4 — Questions and Answers
Question 1: When designing a vegetated swale for erosion control, the most critical hydraulic parameter to verify is that:
- The swale length exceeds 200 feet to maximize treatment
- Flow velocity during the design storm does not exceed the permissible velocity for the lining material (Correct answer)
- The swale width-to-depth ratio is exactly 3:1
- Longitudinal slope is maintained at exactly 2% throughout
Correct answer: Flow velocity during the design storm does not exceed the permissible velocity for the lining material
Permissible velocity limits ensure the swale lining material (grass, rock, etc.) is not scoured or damaged during storm events.
Question 2: A CPESC professional inspects a construction site after a 2-inch rain event and finds silt fence with ponded water 18 inches deep. The appropriate response is to:
- Remove the silt fence since it is impeding drainage and causing flooding
- Document that the silt fence is functioning correctly and retaining sediment
- Assess whether overflow or failure occurred and repair any damaged sections (Correct answer)
- Replace fabric with a higher-permeability material to reduce ponding
Correct answer: Assess whether overflow or failure occurred and repair any damaged sections
Some ponding behind silt fence is expected, but inspection should verify the fence held, no overflow occurred, and damage is repaired promptly.
Question 3: Which RUSLE factor accounts for the management and conservation practices used on a field?
- K factor (soil erodibility)
- C factor (cover-management)
- P factor (support practice) (Correct answer)
- LS factor (slope length and steepness)
Correct answer: P factor (support practice)
The P factor in RUSLE represents the ratio of soil loss with a specific support practice (contour farming, terracing, strip cropping) to straight-row farming.
Question 4: Bioengineering techniques such as live stake plantings are most appropriate for:
- Actively eroding streambanks where root establishment can stabilize soil (Correct answer)
- Steep slopes greater than 2:1 where conventional seeding has failed
- Areas with chronic drought that prevent survival of woody cuttings
- Temporary erosion control during the construction phase only
Correct answer: Actively eroding streambanks where root establishment can stabilize soil
Live stakes of willow and other species root quickly in moist streambank soils, providing long-term biological stabilization of eroding banks.
Question 5: The purpose of a construction entrance/exit stabilization pad is to:
- Provide a permeable surface to allow rainwater infiltration near site access
- Reduce tracking of mud and sediment from construction sites onto public roads (Correct answer)
- Create a buffer between the construction site and adjacent wetlands
- Direct stormwater runoff away from active construction areas
Correct answer: Reduce tracking of mud and sediment from construction sites onto public roads
Stabilized construction entrances use coarse aggregate or other materials to knock mud off vehicle tires before they exit onto public roads.
Question 6: When seeding disturbed areas in late fall in the northern US, the recommended approach is often to use:
- High seeding rates of warm-season grasses that will germinate in spring
- Dormant seeding with cool-season species that will germinate after winter (Correct answer)
- Hydromulch without seed to protect soil until spring seeding
- Annual ryegrass at double rate to achieve full winter coverage
Correct answer: Dormant seeding with cool-season species that will germinate after winter
Dormant seeding places cool-season grass seed that remains dormant through winter and germinates with spring moisture and temperature, providing early cover.
Question 7: Which property of soil most directly determines its erodibility (K factor in RUSLE)?
- Soil color and organic matter percentage only
- Texture, structure, organic matter content, and permeability (Correct answer)
- Compaction level measured by standard proctor test
- Cation exchange capacity and nutrient levels
Correct answer: Texture, structure, organic matter content, and permeability
The K factor integrates soil texture, structure, organic matter, and permeability to quantify how easily soil particles are detached and transported.
CPESC Erosion Control Methods & Techniques 4
When designing a vegetated swale for erosion control, the most critical hydraulic parameter to verify is that: