Experimental Study of Phreatic Evaporation at Different Depth of Groundwater Table

The process of day average change of phreatic evaporation in bare field at different depth of groundwater table showed that there was a large evaporation ability in summer season,next to in spring and autumn season,the less in winter season.Phreatic evaporation tends to decrease with the increase of depth of groundwater table.The accumulative phreatic evaporation decrease with increase of depth of groundwater table,the relationship of these can be described with power function.There was coincident relation with phreatic evaporation and water surface evaporation by E20 in small depth of groundwater table,when the increase of depth of groundwater table and water surface evaporation ability,the slope of curve decrease gradually.The effect of precipitation on bare field phreatic evaporation main perform two aspect,when the precipitation occur,the atmosphere evaporation ability tend to zero,the precipitation supply to soil water and weaken the capillary effect and decrease of field water evaporation.