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Using Large-Scale Lysimeter to Monitor Dynamic Soil Hydraulic Properties:Dynamic Capillary Pressure, Velocity, and Celerity
unsaturated zone,water retention curve,wetting front,old-new water interaction,
|Publication Year :||2021|
The unsaturated soil is a complex porous media system, and the soil hydraulic properties are easily affected by its complex structure and observation scale. In recent years, small-scale sandbox experiments have confirmed the influence of dynamic effects on the water retention curve, but it has not yet been clarified whether it is affected by the observation scale. In this study, we control the soil moisture change rate inside the large lysimeter by the different boundary pressure conditions. And the tensiometer and time domain reflectometry (TDR) were used to measure the water retention curve during the dynamic and static drainage and imbibition processes. The experimental results show that the shallow soil layer during the dynamic drainage process can retain a higher volumetric water content than during the static process, which is so-called dynamic effect of capillary pressure. But this effect decreases with the soil depth. On the other hand, the soil water velocity and celerity of the unsaturated soil are considered to significantly affect the interaction between the new and old water (infiltration water and residual water), the rainfall-runoff mechanism and the solute transport in the unsaturated zone. The relevant mechanism has yet to be clarified. We used the changes in water content and soil temperature to detect the wetting front movement during the infiltration and the influence of boundary conditions. This study also observed that the water content of the wetting front decreases under the air-confined condition. The soil temperature data shows that the hot water (new water) signal observed from the upper sensors mostly overlaps with the water content change signal, but the hot water signal in the middle and deep area lags behind the cold water (old) signal. It implies that when the wetting front moves, the ratio of new and old water at different depths is significantly different. At the same time, the old water celerity can reach more than twice the velocity of the new water. The abovementioned findings will help quantify the observation scale influence on dynamic capillary pressure and further clarify the flow velocity and celerity of soil water in the unsaturated zone.
|Appears in Collections:||生物環境系統工程學系|
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