Canals in ash basins affect sedimentation by which mechanism?

• A. decreasing turbulence
• B. increasing temperature
• C. increasing retention time
• D. lowering pH

Answer: (C)

The main idea is that sedimentation in ash basins is driven by how long the water, with suspended ash particles, stays in the basin. Canals that create longer flow paths or detention zones increase the hydraulic retention time, giving particles more time to settle out before the water exits. With more residence time, heavier particles settle to the bottom and fines have a better chance to be removed, lowering downstream turbidity. This mechanism is more about time in the basin than about changing temperature or pH or simply altering turbulence, though those factors can affect settling only indirectly. Increasing retention time best explains how canals influence sedimentation.