Air Encapsulation During Infiltration

Abstract A series of field and laboratory experiments were performed to measure the effects of air encapsulation within the soil's transmission zone upon several infiltration properties. In the field, infiltration rates were measured using a double‐cap infiltrometer (DCI), and soil‐water contents were measured using time‐domain reflectometry (TDR). Before half of the infiltration experiments, CO 2 was injected through the DCI into the soil to reduce the amount of air encapsulation in the soil's transmission zone. For a gravelly loam as steady infiltration rates were approached, the average volumetric water content was 0.38 cm 3 cm −3 for control experiments and 0.43 cm 3 cm −3 for CO 2 experiments. The average steady infiltration rate was 0.42 cm min −1 for the control experiments compared to 4.40 cm min −1 for the CO 2 experiments. For a sandy loam as steady infiltration rates were approached, the average volumetric water content was 0.43 cm 3 cm −3 for control experiments compared with 0.45 cm 3 cm −3 for CO 2 experiments. The average final infiltration rate was 0.09 cm min −1 for the control experiments compared with 0.42 cm min −1 for the CO 2 experiments. In the laboratory, infiltration experiments were performed using repacked soil columns (15‐cm i.d. by 140 cm long), again using TDR and CO 2 flooding. For a medium sand as steady infiltration rates were approached, the average volumetric water content was 0.29 cm 3 cm −3 for the control experiments and 0.36 cm 3 cm −3 for the CO 2 experiments. The average steady infiltration rate was 0.25 cm min −1 for the control experiments and 1.23 cm min −1 for the CO 2 experiments. For a loam as steady infiltration rates were approached, the average volumetric water content was 0.45 cm 3 cm −3 for the control experiments and 0.50 cm 3 cm −3 for the CO 2 experiments. The average steady infiltration rate was 0.02 cm min −1 for the control experiments and 0.10 cm min −1 for the CO 2 experiments. These results suggest that a significant portion of the total encapsulated air resided in interconnected pores within the soil's transmission zone. For the time scale considered, this residual air caused the effective hydraulic conductivity of the transmission zone to remain at a level no greater than 20% of the saturated hydraulic conductivity of the soil.