Erosion Control BMPs Flashcards

An inspector observes a stockpile of soil on a construction site that will be inactive for the next 21 days. Which of the following erosion control BMPs is MOST appropriate to prevent wind and water erosion from the stockpile?

Answer: Applying a soil tackifier or covering with a tarp.

Applying a soil tackifier binds the soil particles together, while covering with a tarp provides a direct physical barrier against wind and rain. A silt fence is a sediment control measure, not an erosion control measure for the pile itself. A diversion dike protects the pile from upslope runoff but doesn't prevent erosion from the pile's surface. Compaction can reduce infiltration but is not the primary method for preventing surface erosion on a temporary stockpile.

On a 2:1 slope where vegetation needs to be established, which Rolled Erosion Control Product (RECP) would be most suitable to protect the seed and soil until the vegetation takes root?

Answer: An erosion control blanket made of straw or coconut fiber.

Erosion control blankets (ECBs) made of natural fibers like straw or coconut are specifically designed to protect seed and soil on slopes, slow water velocity, and promote germination. A lightweight netting alone offers minimal protection. A TRM is typically for high-flow channels or permanent reinforcement, which is more than needed for establishing simple vegetation. Loose straw mulch is less effective on a steep 2:1 slope and would likely require netting or tackifier to hold it in place.

A construction site plan calls for the use of check dams in a newly constructed drainage swale. What is the primary function of these check dams?

Answer: To reduce the velocity of water flow, preventing channel erosion.

The main purpose of a check dam is to reduce the velocity of concentrated stormwater flow within a channel or swale. By slowing the water, it reduces its erosive energy, which helps prevent scouring and gullying of the channel bed and banks, and allows some sediment to settle out.

Which of the following is a key limitation when using standard mulching (e.g., loose straw) for erosion control?

Answer: It can be ineffective on slopes steeper than 3:1 without anchoring.

Loose organic mulches like straw can be easily displaced by wind or heavy runoff on steep slopes. Therefore, their effectiveness is limited on slopes steeper than 3:1 unless they are properly anchored with methods like crimping, netting, or applying a tackifier.

During a site inspection, you notice a hydroseeding mix is being prepared. The contractor is adding a plant-based, glue-like substance to the slurry. What is the purpose of this additive?

Answer: To act as a tackifier to bind seed and mulch to the soil.

The substance being added is a tackifier. Tackifiers are used in hydroseeding mixtures to act as an adhesive, binding the seed, mulch fibers, and soil particles together. This is crucial for preventing the seed and mulch from being washed or blown away, especially on slopes, ensuring good seed-to-soil contact for germination.

Which statement accurately describes the primary difference between a sediment trap and a sediment basin?

Answer: Sediment basins are generally larger and designed for larger drainage areas (typically >5 acres) than sediment traps.

The primary distinction between sediment traps and basins is the size of the drainage area they serve. Sediment traps are smaller and typically used for drainage areas of 1 to 5 acres. Sediment basins are larger, more engineered structures designed to handle runoff from larger areas, often 5 to 100 acres, and may include more complex outlet structures like risers.