Overland flow occurs when infiltration capacity is exceeded.

• A. Excess rainfall
• B. Infiltration capacity being exceeded
• C. Infiltration capacity being exceeded by rainfall
• D. Evaporation losses

Answer: (B)

Overland flow happens when water from rainfall cannot enter the soil fast enough. The soil can absorb water only up to a certain rate, called its infiltration capacity. When rainfall pushes water onto the land faster than that capacity, the soil becomes saturated at the surface and the excess water cannot infiltrate, so it flows over the land as surface runoff. That fits best with the idea that overland flow is triggered by the infiltration capacity being exceeded. While heavy rainfall contributes to the situation, the key mechanism is surpassing the soil’s infiltration limit, not just the rainfall amount alone. Evaporation losses reduce how much water is available but do not cause runoff.