Technical NoteMoisture-pressure dynamics above an oscillating water table

- New sand column data on moisture-pressure dynamics above oscillating water table.
- New data covers a wide range of oscillation frequencies.
- The moisture-pressure loops at low frequencies are hysteretic and tend to follow the static wetting/drying curves.
- The moisture-pressure loops at high frequencies are non-hysteretic but deviate from the static wetting/drying curves.
- The observed dynamics are predicted well by a hysteretic Richards' equation model.

SummaryThis paper presents a sand column dataset on the soil moisture-pressure dynamics above a simple harmonic oscillating water table. A total of 19 experiments were conducted in which all experimental parameters were held constant except for the oscillation period which ranged between 12.25 h down to 10 s. The data show clear evidence of hysteresis at longer oscillation periods where the unsaturated zone has sufficient time to adjust to the water table motion. At shorter periods the contrary exists with the extent of moisture-pressure variations greatly reduced and, for periods less than 15 min, the dynamics become non-hysteretic. The high frequency moisture-pressure loops, although non-hysteretic, do not follow the (non-hysteretic) static equilibrium wetting or drying curves but are consistent with the scanning loops generated by a commonly adopted hysteresis algorithm for numerical solution of the Richards (1931) equation. Thus, the data provides new physical insights behind the need to include hysteresis effects when simulating high frequency water table motions as found by previous researchers.