Overland flow occurs when

Overland flow occurs when

• A. Evaporation dominates rainfall
• B. The soil is completely saturated
• C. Rainfall is less than the soil's infiltration capacity
• D. Rainfall exceeds the soil's infiltration capacity

Answer: (D)

Overland flow is surface runoff that happens when rainfall cannot infiltrate the soil quickly enough. The infiltration capacity is the maximum rate at which the soil can absorb water given its properties and current moisture. When rainfall intensity exceeds that capacity, the excess water stays on the surface and runs off, producing overland flow. If rainfall is lighter than the infiltration capacity, all the water can infiltrate with no surface runoff. The soil being fully saturated is another way runoff can occur, but it relates to a different mechanism (saturation excess) rather than the infiltration-rate limit being exceeded. Evaporation-dominated rainfall doesn’t produce overland flow.

Overland flow is surface runoff that happens when rainfall cannot infiltrate the soil quickly enough. The infiltration capacity is the maximum rate at which the soil can absorb water given its properties and current moisture. When rainfall intensity exceeds that capacity, the excess water stays on the surface and runs off, producing overland flow. If rainfall is lighter than the infiltration capacity, all the water can infiltrate with no surface runoff. The soil being fully saturated is another way runoff can occur, but it relates to a different mechanism (saturation excess) rather than the infiltration-rate limit being exceeded. Evaporation-dominated rainfall doesn’t produce overland flow.