Sediment Control BMPs Flashcards
6 cards from real CESSWI practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Sediment Control BMPs flashcards as text
An inspector observes a rock check dam in a channel with a 4% grade. The crest of the downstream dam is at the same elevation as the toe of the upstream dam. Sediment has accumulated to approximately half the height of the downstream dam. What is the most appropriate action for the inspector to recommend?
Answer: Remove the accumulated sediment from the upstream side of the dam.
Regular maintenance is crucial for the effectiveness of check dams. Sediment should be removed when it accumulates to one-half of the dam's height to restore ponding capacity and prevent sediment from being washed downstream in subsequent storm events.
A CESSWI is inspecting a large construction site (over 10 acres) with significant grading. Which of the following sediment control BMPs is most appropriate for managing sediment-laden runoff at the primary discharge point for a large drainage area?
Answer: A sediment basin designed to detain runoff and allow sediment to settle.
Sediment basins are specifically designed to handle runoff from large drainage areas (typically 5 to 100 acres) by creating a temporary pond that allows sediment to settle out before the water is discharged from the site. Silt fences, inlet protection, and fiber rolls are typically used for smaller drainage areas or as secondary controls.
During a site inspection, you notice a silt fence has been installed in a swale where concentrated flow is expected. The fabric is bulging and there is evidence of undercutting. What is the fundamental issue with this installation?
Answer: Silt fences are not intended for use in areas of concentrated flow.
Silt fences are designed to intercept and detain sheet flow, not concentrated flow. When placed in ditches, swales, or other areas of concentrated flow, they are likely to fail due to the high velocity and volume of water, leading to undercutting and collapse. Check dams or other channel-specific BMPs should be used in these areas.
Which of the following is a critical maintenance requirement for all storm drain inlet protection devices?
Answer: Ensuring the device is removed as soon as the contributing drainage area is stabilized.
Inlet protection is a temporary BMP. It is crucial to remove the device once the surrounding area is permanently stabilized to prevent it from becoming a long-term source of concentrated flow or a blockage in the storm drain system.
A site superintendent plans to use straw bales as the primary perimeter sediment control measure. As a CESSWI, what advice should you provide?
Answer: Advise against using straw bales due to their high failure rate and suggest alternatives like silt fence or fiber rolls.
Straw bale barriers have a high failure rate. They are prone to rotting, being displaced by runoff, and allowing water to flow around or underneath them. Professional guidance often recommends avoiding their use in favor of more reliable and effective BMPs such as silt fences, compost filter socks, or fiber rolls.
According to the NPDES Construction General Permit (CGP), when must sediment be removed from a sediment basin?
Answer: When sediment storage capacity has been reduced by 50% (i.e., it is half full).
Standard maintenance protocols for sediment basins and traps require that accumulated sediment be removed once it has reached 50% (or one-half) of the design volume. This ensures the basin has adequate capacity to function properly during the next storm event.