• Explain why saturated flow is faster than unsaturated flow. Saturated flow 1 is water movement driven by the pull of gravity through soil pores that are mostly saturated by water, meaning at water contents above field capacity 1. Because the pores are mostly filled by water, the rate of saturated flow depends on the size of the pores. The larger the pores, as in a sandy soil, the more rapidly water flows under saturated conditions. Unsaturated flow 1 is water movement driven by capillary forces (the so-called matric potential) through soil pores that are mostly empty, meaning at water contents below field capacity. Because the pores are mostly empty, the rate of unsaturated flow is very slow. You can easily imagine that water in a thin film coating an empty pore will move more slowly than water in a filled pore.