What process prevents water from forming runoff?

Runoff can be thought of as the water that flows over the surface of Earth after a precipitation event or after excessive water application to an area (say, through irrigation). The water present on the surface of Earth after a precipitation and/or irrigation event has two pathways: it can either flow over the surface of Earth, forming runoff, or infiltrate below the earth's surface (where it may ultimately reach the groundwater, depending on a number of factors).
Thus, it is infiltration that may prevent water from forming runoff. If soil is saturated, then excess water will form runoff; otherwise, water is likely to infiltrate the soil until the surface becomes completely saturated. Soil has empty spaces, known as pores, between its particles. These pores can get filled with water, and once they are saturated, the excess water has nowhere to go but form runoff.
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