Porosity factors that control the hydraulic conductivity of soil-saprolite transitional zones

Slowly permeable transitional horizons separate soil and saprolite, but these horizons cannot be identified easily in the field. The objectives of this study were to determine why the soil-saprolite transitional zone (BC and CB horizons) is slowly permeable, and to evaluate ways for identifying it in the field. Two saprolite deposits were studied in the North Carolina Piedmont. At each site, saturated and unsaturated hydraulic conductivities (K_sat and K_unsat) were measured for major horizons. Volume fractions of water-conducting pores were also compared with the changes in hydraulic conductivity with depth. Horizon mean K_sat values at both sites ranged from virtually 0 to approximately 3 cm h^-1. The lowest K_sat values (