Capillary losses from ground water

A method is presented for estimating the discharge of ground water by evapotranspiration of water rising from the water table by capillarity. ‘Potential capillary water loss’ is defined as a measure of the ability of the capillary interstices of a soil to raise water from the water table to the ground surface. Published equations describing soil‐moisture movement and published graphs relating capillary conductivity and capillary potential are used to derive expressions of the relation between ‘potential capillary water loss’ and depth to the water table in a given soil. On the basis of these theoretical relationships, graphs are drawn that show how the depth to the water table affects the ability of a particular soil to raise water to the ground surface under given conditions. The application of these methods is discussed in relation to the estimation of ground‐water losses by capillary rise, the determination of potential evapotranspiration, and the analysis of soil‐tank data. Their essential agreement with empirical profiles of capillary potential obtained in soil tanks demonstrates their usefulness.