ABSTRACT
Saturated regions may occur in the vadose zone as perched ground water and possibly as water-table mounds. Perched ground water develops at the interface between regions of varying hydraulic conductivity, e.g., a coarse zone overlying a finer-textured zone (Everett et al., 1984, Wilson and Schmidt, 1979), while water-table mounds develop above a regional water table. Perched systems are underlain by unsaturated sediments. Figure 31.1 shows the growth of perched ground water and a water-table mound in stratified alluvium during a recharge event in the Santa Cruz River, an ephemeral stream near Tucson, Arizona (Wilson and Schmidt, 1979). The two regions were separated by an unsaturated transmission zone which remained at a water content sufficient to transmit vertical leakage from the perched system into the water table mound. Piezometers in both regions manifested positive pressures, yielding water samples. Elsewhere in this book, Schmidt discusses perched ground-water systems in more detail. Water content profiles obtained in a neutron access tube during flow in the Santa Cruz River, December, 1967, showing perched water and a water table mound (after <xref ref-type="bibr" rid="ref31_29">Wilson and Schmidt, 1979</xref>; Courtesy of the American Water Resources Association). https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780203752524/4944dc30-7a88-4095-9b59-93e6ffefeae6/content/fig31_1.tif"/>
