Sediment Basin and Trap Design Flashcards

What is the primary purpose of a temporary sediment basin on a construction site?

Answer: To capture and retain sediment-laden runoff, allowing sediment to settle out before water is discharged

Temporary sediment basins trap stormwater runoff and hold it long enough for suspended sediment to settle to the bottom before the clarified water is released through a controlled outlet.

A sediment basin is typically required for drainage areas exceeding:

Answer: 5 acres

Most regulatory guidance requires a sediment basin when the drainage area exceeds 5 acres, where the volume of runoff exceeds the practical capacity of smaller BMPs like sediment traps.

The wet storage volume in a sediment basin is designed to:

Answer: Hold the accumulated sediment load between cleanout events

Wet storage volume is the portion of the basin below the permanent pool level that accumulates settled sediment between cleanout operations.

The outlet structure of a sediment basin should be designed to:

Answer: Release water slowly from the upper portion of the pool where the water is clearest while retaining the sediment-laden lower water

Outlet structures should discharge from near the water surface where the water is clearest, retaining the deeper, sediment-laden water and allowing sediment to settle before discharge.

Surface area is critical in sediment trap design because:

Answer: Larger surface area allows more particles to settle per unit time by lowering the overflow rate

Surface area is the key design parameter for sediment settling because larger surface area relative to flow rate lowers the overflow rate and increases the proportion of particles that settle out.

When should a temporary sediment basin be cleaned out?

Answer: When sediment accumulation reaches 50% of the designed wet storage volume

Sediment basins should be cleaned out when accumulated sediment reaches approximately 50% of the wet storage volume to maintain hydraulic capacity and sediment removal efficiency.