Design for an Automated Tension Infiltrometer

Abstract

Abstract An automated tension infiltrometer useful for a range of water tensions from 0.02 to 0.50 m and for infiltration rates of 1 × 10 −8 to 5 × 10 −4 m s 1 is described. Infiltration rates are calculated from the change in water height in a Mariotte column. Water height is automatically measured by using the difference in tension between two pressure transducers, one installed at the top, and the other at the bottom, of the Mariotte column. Precision of water height measurement using two transducers (SD = 2.2 mm) is increased as compared with height measurements made with only one transducer (SD = 6.2 mm). With only one transducer, much of the measurement error is due to tension fluctuations or “noise” caused by bubbling in the Mariotte column. The new design also incorporates several features used or suggested by other workers. A bubble tower is used for tension regulation, and interchangeable Mariotte columns of different diameters are used to match column volume with expected cumulative infiltration. Advantages of the new device include (i) quick and accurate tension control at low tensions, (ii) improved measurement precision at low flow rates, and (iii) automatic measurement and data collection, which increases measurement speed and eliminates bubbling‐induced variability.