In Situ Hydraulic Conductivity at Four Hillslope Locations in a Closed Drainage System

Virtually no information has been published concerning the hydraulic properties of large acreages of till plain soils associated with “Potholes” in Northcentral United States and Canada. The objectives of this research were to measure and compare in situ hydraulic conductivities and selected soil physical properties at several depths in four soil profiles on a till plain in southeastern North Dakota. In addition, theoretical hydraulic conductivity values were calculated and compared with the in situ conductivities. Unsaturated soil hydraulic conductivity vs. depth was measured in situ at four sites on a toposequence developed from a glacial till. Water was allowed to infiltrate the soil at each site and the soil surface covered to prevent evaporation. During the ensuing drainage periods soil water pressure was monitored with triplicate tensiometers at each of six depths. These depths were not arbitrary as in previously reported studies but were selected on the basis of soil morphology. Soil water characteristics, determined on triplicate 7.6‐ by 7.6‐cm cores taken from the same depth as the tensiometer cups, were used in conjunction with the soil water pressure data to compute hydraulic conductivities. Hydraulic conductivity generally increased with depth to about 90 cm. Below this depth, hydraulic conductivity tended to decrease. In addition, hydraulic conductivity values at each depth for each site were computed by the Green and Corey Method. When the matching factor was selected from the midpoint of the measured hydraulic conductivity range, the conductivities computed by Green and Corey's method compared favorably with those measured in situ .