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Vadose zone
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<p>The vadose zone (from the <a href="/facts/Latin/pM3Kge85">Latin</a> word for "shallow"), also termed the unsaturated zone, is the part of Earth between the land surface and the top of the <a href="/facts/Phreatic_zone/LF6xDSV5">phreatic zone</a>, the position at which the groundwater (the water in the soil's pores) is at atmospheric pressure. Hence, the vadose zone extends from the top of the ground surface to the <a href="/facts/Water_table/2j0VD0lF">water table</a>. </p><p>Water in the vadose zone has a <a href="/facts/Hydraulic_head/qLTjjWLn">pressure head</a> less than <a href="/facts/Atmospheric_pressure/wJLMSaVG">atmospheric pressure</a>, and is retained by a combination of <a href="/facts/Adhesion/NuVQPk4z">adhesion</a> (<i>funiculary groundwater</i>), and <a href="/facts/Capillary_action/aa60yQ32">capillary action</a> (<i>capillary groundwater</i>). If the vadose zone envelops <a href="/facts/Soil/5Ddpr3QM">soil</a>, the water contained therein is termed <a href="/facts/Soil_moisture/N9Yo068u">soil moisture</a>. In fine grained soils, capillary action can cause the pores of the soil to be fully saturated above the water table at a pressure less than atmospheric. The vadose zone does not include the area that is still saturated above the water table, often referred to as the <a href="/facts/Capillary_fringe/p9tAuJca">capillary fringe</a>. </p><p>Movement of water within the vadose zone is studied within <a href="/facts/Soil_physics/Jkl25Abd">soil physics</a> and <a href="/facts/Hydrology/Xh727cnE">hydrology</a>, particularly <a href="/facts/Hydrogeology/4HEanFa0">hydrogeology</a>, and is of importance to <a href="/facts/Agriculture/TGztqzJs">agriculture</a>, <a href="/facts/Contaminant/RC0L7KRy">contaminant</a> transport, and <a href="/facts/Flood_control/rf0476SJ">flood control</a>. The <a href="/facts/Richards_equation/EE1JgC0v">Richards equation</a> is often used to mathematically describe the flow of water, which is based partially on <a href="/facts/Darcy%2527s_law/VP9uYnyy">Darcy's law</a>. <a href="/facts/Groundwater_recharge/el8C40xD">Groundwater recharge</a>, which is an important process that refills aquifers, generally occurs through the vadose zone from precipitation. </p>