Circular Isobaric Cavity in Descending Unsaturated Flow

Two-dimensional flows near cavities were studied by superposition of the Philip solution for an isobaric cylindrical cavity in an infinite unsaturated soil and vertical infiltration. Depending on the radius of the cavity and the intensity of the net infiltration, the cavity irrigates the surrounding soil forming a plume of seeping moisture (source regime), drains the descending infiltration forming a capture zone (sink regime), or admits water through its upper section and releases water through its bottom (dipole regime). The separatrices, i.e., the lines, which divide the incoming, outgoing, and passing-by portions of the flow, were found. For the dipole regime, the values of flow rates through the admitting and releasing sections of the cavity and streamlines were calculated. The supercritical flow regime is characterized by a permeable blunt upstream section of the cavity and watertight downstream segments. For elongated cavities, this regime was modeled as a combination of a permeable isobaric segment and a part of the adjacent separatrice. Analogies with saturated flows in confined aquifers near a circular constant head boundary and with contaminant transport from a circular isoconcentric source were discussed.