This question is about how a soil's water uptake behaves once it can no longer take in any more water, and what happens to the leftover water in that state.
- Infiltration: this is the rate water soaks into the ground. It starts high on dry soil and drops as the soil wets up, flattening out near a small constant value once the soil is saturated. It does not keep rising, so this option is wrong.
- Runoff: once the soil cannot absorb more water, any extra water supplied has nowhere to go except across the surface. The longer the soil stays saturated during rain, the more water piles up as runoff, so this quantity keeps growing. This is the correct choice.
- Porosity: this is simply the share of a soil's volume that is empty space between the grains. It is set by the soil's texture and structure, not by whether the pores happen to be full of water right now, so it stays fixed.
- Permeability: this measures how easily water can move through the connected pore network. Like porosity, it depends on the physical arrangement of grains and pores, and does not change just because the soil has stayed saturated for a while.
Runoff is the only quantity among the four that keeps climbing over time once the soil is fully saturated, so option (B) is correct.
Let's summarize:
- Infiltration falls to a low steady rate on saturated soil, it does not rise.
- Porosity and permeability are built-in soil properties that do not respond to saturation state.
So runoff is what increases over time on fully saturated soil.