CESSWI Erosion Control BMPs 3 — Questions and Answers
Question 1: An inspector observes that fiber rolls installed on a slope have gaps larger than 1 inch between the roll and the soil surface. What problem does this create?
- Runoff bypasses the roll by flowing underneath rather than being slowed (Correct answer)
- The roll will decompose faster than intended
- Sediment will accumulate above the roll too quickly
- The roll will shift upslope during rain events
Correct answer: Runoff bypasses the roll by flowing underneath rather than being slowed
Gaps beneath fiber rolls allow runoff to channel under the device, bypassing its flow-retarding function entirely.
Question 2: Which of the following is a key advantage of biodegradable erosion control blankets over plastic netting blankets?
- They do not need to be removed and will not entangle wildlife (Correct answer)
- They provide greater tensile strength on steep slopes
- They are less expensive to purchase and install
- They suppress weed growth more effectively
Correct answer: They do not need to be removed and will not entangle wildlife
Biodegradable blankets decompose naturally, eliminating wildlife entanglement hazards and the labor cost of removal after vegetation establishes.
Question 3: A temporary seeding BMP specifies using annual ryegrass. What is the PRIMARY purpose of annual ryegrass in this application?
- Rapid germination and cover to protect soil until permanent species establish (Correct answer)
- Long-term soil stabilization and permanent ground cover
- Nitrogen fixation to improve soil fertility
- Deep-rooting to prevent slope mass failure
Correct answer: Rapid germination and cover to protect soil until permanent species establish
Annual ryegrass germinates quickly, providing fast interim ground cover to protect disturbed soil until slower-establishing permanent species take hold.
Question 4: What is the recommended maximum ponding depth behind a rock check dam in a drainage swale?
- 1.5 feet (Correct answer)
- 3 feet
- 0.5 feet
- 5 feet
Correct answer: 1.5 feet
Rock check dams are typically designed to limit ponding to approximately 1.5 feet to prevent overtopping damage and upstream saturation.
Question 5: During a post-storm inspection, an inspector finds that a silt fence has been undermined by concentrated flow. What does this indicate about the original BMP design?
- The silt fence was placed in a concentrated flow path where it should not have been used (Correct answer)
- The fabric selection was incorrect for the soil type
- The fence posts were installed too deep
- The fence needed to be doubled for this application
Correct answer: The silt fence was placed in a concentrated flow path where it should not have been used
Silt fences are designed for sheet flow only; placement in concentrated flow areas is a fundamental design error that leads to failure.
Question 6: Which erosion control BMP is MOST appropriate for protecting a freshly graded cut slope in a semi-arid climate where irrigation is not available?
- Bonded fiber matrix (BFM) hydraulic mulch (Correct answer)
- Standard straw wattle with native seed
- Open-weave textile erosion control blanket
- Polyethylene sheeting
Correct answer: Bonded fiber matrix (BFM) hydraulic mulch
BFMs create a continuous bonded matrix that protects soil and retains moisture to support seed germination even in dry conditions without irrigation.
Question 7: According to SWPPP requirements, how soon after rain events must a CESSWI-level inspection of erosion controls be conducted?
- Within 24 hours after a 0.25-inch or greater rain event (Correct answer)
- Within 72 hours after any measurable precipitation
- Once per week regardless of rain events
- Only after rain events exceeding 1 inch
Correct answer: Within 24 hours after a 0.25-inch or greater rain event
Most Construction General Permits require inspection within 24 hours following a qualifying storm event (typically ≥0.25 inch) to assess BMP performance.
CESSWI Erosion Control BMPs 3
An inspector observes that fiber rolls installed on a slope have gaps larger than 1 inch between the roll and the soil surface.
What problem does this create?