Method to estimate water storage capacity of capillary barriers

This paper presents a method to estimate the additional storage capacity derived from the presence of a capillary break or barrier beneath a soil layer used in a surface cover system. The method involves first estimating the suction head profile in the soil layer at breakthrough. Then, using a relationship between suction head and water content (i.e., the moisture characteristic function), the corresponding water content profile is derived. Integrating the water content over the depth of the soil layer yields the total water in the layer from which the the net storage capacity can be determined. Good agreement was obtained between the water storage claculated using this method to those derived from numeric simulations. Example calculations illustrate the influence of the overlying soil texture, thickness, and the water entry head of the coarse layer on the storage capacity of a capillary barrier system. The paper also discusses how the moisture characteristic curve provides insight into the expected storage capacity for a soil in a capillary barrier configuration.