Department of Earth and Environmental Sciences, University of Waterloo, Waterloo, Ontario, Canada, N2L 3G1.
Ground Water. 2010 Jan-Feb;48(1):59-67. doi: 10.1111/j.1745-6584.2009.00606.x. Epub 2009 Jul 31.
The point velocity probe (PVP) is a device that can measure groundwater velocity at the centimeter scale, and unlike devices that measure velocity within well screens, the PVP operates while in direct contact with the porous medium. Because of this feature, it was postulated that the PVP could be effective in measuring velocity within the capillary fringe. This hypothesis was tested using a laboratory flow-through cell filled with a medium-fine sand from Canadian Forces Base Borden. The cell was constructed to simulate conditions such that the PVP was positioned from 2.5 cm below the water table to 79 cm above the water table. As the water table was lowered, the PVP gave highly consistent values of velocity over the range equivalent to 2.5 cm below the water table to 44 cm above the water table, the approximate extent of the capillary fringe. The average measured velocity was 11.3 cm/d +/- 11.6%, somewhat higher than that calculated based on the measured discharge through the cell (7.5 cm/d +/- 5.5%). With a further decline in the water table there was a progressive decrease in the measured velocity values, consistent with the declining hydraulic conductivity as the sand material drained. Readings could not be made beyond about 57 cm, where the water content was approximately 75% of saturation. These experiments showed that the PVP is capable of measuring groundwater velocity within the saturated zone above the water table and possibly into the unsaturated zone. Currently, this is the only instrument available with this capability.
点速度探头 (PVP) 是一种能够以厘米为单位测量地下水速度的设备，与测量井内水流速度的设备不同，PVP 在直接与多孔介质接触时进行测量。由于这一特点，有人假设 PVP 可以有效地测量毛管带内的水流速度。为了验证这一假设，研究人员使用加拿大武装部队博登基地的中细砂填充的实验室渗流池进行了测试。该渗流池的设计旨在模拟 PVP 从地下水面以下 2.5 厘米到地下水面以上 79 厘米的位置的条件。随着地下水位的下降，PVP 在地下水面以下 2.5 厘米到地下水面以上 44 厘米的范围内给出了高度一致的速度值，这大致相当于毛管带的范围。测量得到的平均流速为 11.3 厘米/天±11.6%，略高于根据通过渗流池测量的流量（7.5 厘米/天±5.5%）计算得出的流速。随着地下水位的进一步下降，测量的流速值逐渐下降，这与砂质材料排水时水力传导率下降是一致的。读数不能超过大约 57 厘米，因为在这个位置的含水量约为饱和含水量的 75%。这些实验表明，PVP 能够测量地下水面以上饱和带内的地下水速度，并且可能测量到非饱和带。目前，这是唯一具有这种能力的仪器。
