Canals in ash basins can increase sedimentation by which mechanism?

• A. decreasing flow velocity
• B. increasing salinity
• C. increasing retention time
• D. reducing water depth

Answer: (C)

Sedimentation is driven by how long the water stays in the basin—the hydraulic residence time. Canals in ash basins extend the flow path or add storage, so water remains there longer. That extra time lets suspended ash particles settle out under gravity, increasing sedimentation. So the mechanism is increasing retention time because it directly controls the opportunity for particles to drop out. While slower flow can help, and other factors like salinity or depth changes, do not directly describe the main driver here.