MODEL CALCULATIONS FOR EXTRACTION OF SOIL-WATER BY CERAMIC CUPS AND PLATES

A numerical method is developed with which the flow of moisture towards suction units in soil can be evaluated. For a number of selected problems the unsaturated moisture flow equation is solved twice: for radial flow towards a suction plate or suction cup; for vertical downwards flow under the same conditions, but without a suction unit in the soil. The calculations are performed for a flat soil without a plant cover. It is found that even for little vacuum, large differences may exist between the seepage rate as determined from a suction unit as compared to the seepage rate of the unextracted soil.