A system of drainage classification devised by the Soil Conservation Service of the US Department of Agriculture. The most porous soil in this classification system is said to be excessively drained, in which water is removed from the soil very rapidly. In contrast, is the least porous soil, classified as very poorly drained, in which water is removed from the soil so slowly that the water table remains at or near the surface most of the time.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.