The natural or artificial removal of surplus ground- and surface water and dissolved salts from any area in order to enhance crop growth. In the case of natural drainage the excess waters flow from fields to lakes, swamps, streams and rivers. In an artificial system surplus ground- or surface water is removed by means of subsurface or surface conduits, artificial or natural.; Drainage is the removal of excess water from the land surface and/or the upper soil layer to make non-productive wet land productive and wet land more productive.; Removal of excess water to improve agricultural productivity.