Question

Which one of the following increases over time when the soil is fully saturated?

• A. Infiltration
• B. Runoff
• C. Porosity
• D. Permeability

Hint:

Once soil cannot absorb more water, incoming water has to go somewhere. Think about what happens to the excess.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question asks which quantity keeps growing with time once a soil has already reached full saturation, meaning every pore space in it is filled with water.

Step 2: Key Concept:
Infiltration is the rate at which water enters the soil surface. It is high when soil is dry and keeps falling as the soil fills up with water, settling near a low, roughly steady rate once the soil is saturated, it does not keep climbing. Porosity is the fraction of open space between soil grains, a fixed geometric property of the soil that does not change just because water is filling it. Permeability, also called hydraulic conductivity, depends on how well connected the pore spaces are, another fixed material property of the soil that stays essentially constant once the soil is already saturated. Runoff is the part of rainfall or applied water that cannot soak in and instead flows across the surface.

Step 3: Detailed Explanation:
As a storm continues on already saturated ground, the soil has no more spare pore space to take in extra water, so its infiltration rate stays pinned near its lowest value instead of rising. Since less and less of the incoming water can enter the ground, more of it is forced to move over the surface as runoff, so runoff keeps building up with time on saturated ground. Porosity and permeability belong to the soil grains and structure themselves, not to how wet the soil currently is, so neither of them grows just because the soil stays saturated for longer.

Step 4: Final Answer:
Runoff is the quantity that increases with time once the soil is fully saturated, so the correct option is (B). Infiltration actually falls to a steady minimum rather than rising, ruling out (A). Porosity, option (C), and permeability, option (D), are fixed properties of the soil material and are not affected by how long the soil stays saturated.