What is the primary technique for removing sediment from runoff?

Detention and settling is the primary technique for removing sediment from runoff due to its effectiveness in allowing particles to settle out of the water column. This method involves creating a temporary storage area, such as a detention basin, where stormwater can accumulate. When water slows down in this area, heavier sediment particles settle to the bottom due to gravity, thereby reducing the amount of sediment that flows into downstream water bodies.

This technique is widely employed in stormwater management practices because it not only captures sediments but can also reduce other pollutants contained within the runoff. By allowing sediment to settle, the quality of the water that is eventually discharged or infiltrated can be significantly improved. This process is natural and can be part of both engineered systems and natural landscapes.

In contrast, while other methods such as direct filtration, mechanical sifting, and chemical treatment have their own applications in removing certain pollutants, they are not as effective for sediment removal as detention and settling. Direct filtration usually targets smaller particles and does not have the capacity for large sediment volumes. Mechanical sifting may be impractical for large-scale runoff management. Chemical treatment typically involves additives to alter properties of pollutants rather than physically removing sediment. Thus, detention and settling stands out as the most effective and commonly used method for managing