Detention time in a sediment basin helps reduce turbidity by allowing sediments to settle before runoff leaves the site. Which statement best supports this?

Detention time in a sediment basin helps reduce turbidity by allowing sediments to settle before runoff leaves the site. Which statement best supports this?

• A. Detention allows sediments to settle from runoff before it leaves the site.
• B. Detention has no effect on turbidity.
• C. Detention increases turbidity by keeping sediments suspended.
• D. Detention only affects the color of water.

Answer: (B)

Detention time in a sediment basin controls how long water sits before leaving the site, giving suspended particles a chance to settle under gravity. This settling removes fine solids from the flow, which directly lowers turbidity—the measure of cloudiness caused by those suspended particles. The statement that detention allows sediments to settle from runoff before leaving the site best captures this mechanism, because it ties the time water spends in the basin directly to the removal of suspended solids and the resulting reduction in turbidity. Ideas that detention has no effect or that it increases turbidity don’t fit the physics of settling, since more time in the basin generally means more particles can drop out of suspension. Detention’s impact isn’t primarily about color, but about reducing suspended solids that drive turbidity.

Detention time in a sediment basin controls how long water sits before leaving the site, giving suspended particles a chance to settle under gravity. This settling removes fine solids from the flow, which directly lowers turbidity—the measure of cloudiness caused by those suspended particles.

The statement that detention allows sediments to settle from runoff before leaving the site best captures this mechanism, because it ties the time water spends in the basin directly to the removal of suspended solids and the resulting reduction in turbidity.

Ideas that detention has no effect or that it increases turbidity don’t fit the physics of settling, since more time in the basin generally means more particles can drop out of suspension. Detention’s impact isn’t primarily about color, but about reducing suspended solids that drive turbidity.