How do soil type and soil moisture affect infiltration rate and runoff generation?

How do soil type and soil moisture affect infiltration rate and runoff generation?

• A. Coarse textures (sand) infiltrate quickly; fine textures (clay) infiltrate slowly; high soil moisture reduces infiltration capacity and increases runoff.
• B. Fine textures infiltrate quickly; coarse textures infiltrate slowly.
• C. Soil moisture has no effect on infiltration.
• D. Infiltration rate is constant regardless of soil texture.

Answer: (A)

Soil texture and soil moisture together set the infiltration rate and the likelihood of runoff. Texture controls pore size and connectivity: sandy soils have large, well-connected pores that allow water to drain rapidly, so they exhibit high infiltration rates. In contrast, clayey soils have tiny pores and more tortuous pathways, which slow water entry and result in low infiltration rates. When rainfall continues or the soil surface is already wet, the soil’s infiltration capacity drops because pores are near full and capillary suction decreases; as infiltration capacity is exceeded, water begins to pond and surface runoff increases. If the soil becomes fully saturated, infiltration essentially stops and most incoming water becomes runoff. That’s why the statement about coarse textures infiltrating quickly and fine textures infiltrating slowly is correct, and why high soil moisture reduces infiltration capacity and promotes runoff. Other options misstate the relationship by suggesting rapid infiltration in fine textures, or claiming soil moisture has no effect and that infiltration rate is constant.

Soil texture and soil moisture together set the infiltration rate and the likelihood of runoff. Texture controls pore size and connectivity: sandy soils have large, well-connected pores that allow water to drain rapidly, so they exhibit high infiltration rates. In contrast, clayey soils have tiny pores and more tortuous pathways, which slow water entry and result in low infiltration rates. When rainfall continues or the soil surface is already wet, the soil’s infiltration capacity drops because pores are near full and capillary suction decreases; as infiltration capacity is exceeded, water begins to pond and surface runoff increases. If the soil becomes fully saturated, infiltration essentially stops and most incoming water becomes runoff.

That’s why the statement about coarse textures infiltrating quickly and fine textures infiltrating slowly is correct, and why high soil moisture reduces infiltration capacity and promotes runoff. Other options misstate the relationship by suggesting rapid infiltration in fine textures, or claiming soil moisture has no effect and that infiltration rate is constant.