School of Geography and Earth Sciences, McMaster University, Hamilton, ON, Canada.
Ground Water. 2013 Jan-Feb;51(1):41-50. doi: 10.1111/j.1745-6584.2012.00915.x. Epub 2012 Feb 9.
Water table fluctuations continuously introduce entrapped air bubbles into the otherwise saturated capillary fringe and groundwater zone, which reduces the effective (quasi-saturated) hydraulic conductivity, K(quasi), thus impacting groundwater flow, aquifer recharge and solute and contaminant transport. These entrapped gases will be susceptible to compression or expansion with changes in water pressure, as would be expected with water table (and barometric pressure) fluctuations. Here we undertake laboratory experiments using sand-packed columns to quantify the effect of water table changes of up to 250 cm on the entrapped gas content and the quasi-saturated hydraulic conductivity, and discuss our ability to account for these mechanisms in ground water models. Initial entrapped air contents ranged between 0.080 and 0.158, with a corresponding K(quasi) ranging between 2 and 6 times lower compared to the K(s) value. The application of 250 cm of water pressure caused an 18% to 26% reduction in the entrapped air content, resulting in an increase in K(quasi) by 1.16 to 1.57 times compared to its initial (0 cm water pressure) value. The change in entrapped air content measured at pressure step intervals of 50 cm, was essentially linear, and could be modeled according to the ideal gas law. Meanwhile, the changes in K(quasi) with compression-expansion of the bubbles because of pressure changes could be adequately captured with several current hydraulic conductivity models.
水位波动会不断将被困的气泡引入原本饱和的毛细带和地下水位带，从而降低有效（准饱和）水力传导率 K(quasi)，进而影响地下水流动、含水层补给以及溶质和污染物的迁移。这些被困的气体将随着水压的变化而容易发生压缩或膨胀，就像水位（和大气压）波动时所预期的那样。在这里，我们使用沙柱进行实验室实验，定量研究水位变化高达 250 厘米对被困气体含量和准饱和水力传导率的影响，并讨论我们在地下水模型中考虑这些机制的能力。初始被困空气含量在 0.080 到 0.158 之间，相应的 K(quasi)值比 K(s)值低 2 到 6 倍。施加 250 厘米的水压会导致被困空气含量减少 18%至 26%，从而使 K(quasi)相对于初始（0 厘米水压）值增加 1.16 到 1.57 倍。在压力步长为 50 厘米时测量的被困空气含量的变化基本上是线性的，可以根据理想气体定律进行建模。同时，由于压力变化导致气泡的压缩-膨胀而引起的 K(quasi)变化，可以通过几种现有的水力传导率模型来充分捕捉。
