Kelly Susan E, Murdoch Lawrence C
Altamont Environmental Inc., 78 1/2 Patton Ave., Asheville, NC 28801, USA.
Ground Water. 2003 Jul-Aug;41(4):431-9. doi: 10.1111/j.1745-6584.2003.tb02377.x.
The hydraulic conductivity of submerged sediments influences the interaction between ground water and surface water, but few techniques for measuring K have been described with the conditions of the submerged setting in mind. Two simple, physical methods for measuring the hydraulic conductivity of submerged sediments have been developed, and one of them uses a well and piezometers similar to well tests performed in terrestrial aquifers. This test is based on a theoretical analysis that uses a constant-head boundary condition for the upper surface of the aquifer to represent the effects of the overlying water body. Existing analyses of tests used to measure the hydraulic conductivity of submerged sediments may contain errors from using the same upper boundary conditions applied to simulate terrestrial aquifers. Field implementation of the technique requires detecting minute drawdowns in the vicinity of the pumping well. Low-density oil was used in an inverted U-tube manometer to amplify the head differential so that it could be resolved in the field. Another technique was developed to measure the vertical hydraulic conductivity of sediments at the interface with overlying surface water. This technique uses the pan from a seepage meter with a piezometer fixed along its axis (a piezo-seep meter). Water is pumped from the pan and the head gradient is measured using the axial piezometer. Results from a sandy streambed indicate that both methods provide consistent and reasonable estimates of K. The pumping test allows skin effects to be considered, and the field data show that omitting the skin effect (e.g., by using a single well test) can produce results that underestimate the hydraulic conductivity of streambeds.
水下沉积物的水力传导率会影响地下水与地表水之间的相互作用，但考虑到水下环境条件，描述测量水力传导率（K）的技术却很少。现已开发出两种简单的测量水下沉积物水力传导率的物理方法，其中一种方法使用的是类似于陆地含水层中进行的抽水井测试的水井和压力计。该测试基于一种理论分析，该分析使用含水层上表面的恒定水头边界条件来表示上覆水体的影响。现有的用于测量水下沉积物水力传导率的测试分析可能存在误差，因为使用了与模拟陆地含水层相同的上边界条件。该技术的现场实施需要检测抽水井附近的微小水位下降。在倒置U形管压力计中使用低密度油来放大水头差，以便在现场能够分辨出来。还开发了另一种技术来测量与上覆地表水界面处沉积物的垂直水力传导率。该技术使用带有沿其轴线固定的压力计的渗流仪底盘（压力渗流仪）。从底盘抽水，并使用轴向压力计测量水头梯度。来自沙质河床的结果表明，这两种方法都能提供对K的一致且合理的估计。抽水测试允许考虑表皮效应，现场数据表明，忽略表皮效应（例如通过使用单井测试）可能会得出低估河床水力传导率的结果。
