New method for monitoring soil water infiltration rates applied to a disc infiltrometer

Disc infiltrometers commonly use low-capacity water-supply reservoirs made of small diameter tubes. This reservoir geometry allows accurate measurements of water levels, but makes it necessary to stop the infiltration measurements to refill the water-supply reservoir when long-term infiltration experiments are conducted. The purpose of this study is to determine if a double Mariotte system provides accurate infiltration rate data from disc infiltrometer. To this end, infiltration rates (Q) is calculated from the head losses (ΔHT) produced by the water flowing along a flexible silicone pipe that connects a high-capacity water-supply reservoir and the disc of the infiltrometer. The method was calibrated in the laboratory using 2- and 3-mm internal diameter (i.d.) and 50- and 100-cm-long silicone pipes by comparing the measured ΔHT with the corresponding theoretical values, for different Q measured from the drop in water level in the water-supply reservoir. This method was next applied to field conditions, where the infiltration rates (at four supply pressure heads in five different soils) measured from the water-level drop in the water-supply reservoir of a double Mariotte disc infiltrometer (using 2- and 3-mm-i.d. and 100-cm-long silicone pipes) were compared with the corresponding values calculated from ΔHT measured in the Mariotte tube. An excellent correlation was found in the laboratory experiment between the calculated and the measured ΔHT (r2 = 0.99), and between Q measured from the water-supply reservoir and that calculated from the measured ΔHT (r2 = 0.99). In the field experiments, excellent correlation was shown between the infiltration rates measured from the water-level drop in the water-supply reservoir and the corresponding values calculated from the ΔHT measured in the Mariotte tube. This correspondence indicated that this method would be a consistent alternative to the standard procedure used in the disc infiltrometry technique.