The downward movement of water into soil and rock formations. Infiltration capacity is exceeded if the volume of rain falling is greater than the rate at which infiltration can take place. Effective infiltration is a term used to describe infiltration which increments groundwater. Once in the upper soil layers, further downward movement is sometimes described as percolation. Infiltration can occur as saturated or as non-saturated flow and rates can be very slow in some soil materials. Percolation is usually used to describe saturated flow infiltration.
See also Percolation.