论“单位涌水量就是导水系数”成立的特殊条件

针对截取侧向径流的抽水井，兰太权提出一个解释单位涌水量的公式，认为“单位涌水量就是导水系数”(q=T)，并以砂箱试验的结果作为证据。然而，这个等式的推导过程缺少严谨的水动力学基础。砂箱试验的边界条件等价于含有1个或2个定水头边界的矩形承压含水层，单井抽水的稳定流场可以用镜像井点叠加法求解，从理论上表明单位涌水量与导水系数成正比，而比例系数取决于含水层的形状和抽水井的半径。在特定条件下，含水层和抽水井的尺寸可以造成单位涌水量与导水系数相等的情况，兰太权发表于文献中的2组砂箱试验恰好符合这种条件，但并不能证明q=T具有普适性。新的砂箱试验避免了几何尺寸的这种特殊组合，得到了显著偏离q=T的结果。

Discussions on the special conditions satisfying “the Specific Well Yield is the Transmissivity”

To interpret the meaning of the specific capacity of a pumping well capturing lateral groundwater flow, Lan (2007) proposed an equation where the specific capacity is equal to the transmissivity(q=T) and shown evidences from hydraulic tests in sand boxes. However, the derivation of this equation was not on the robust basis of groundwater hydraulics. The boundary conditions of the sand-box tests were equivalent to a rectangular confined aquifer with one or two constant head boundaries. The steady state flow driven by a pumping well in these conditions could be solved with the superposition method on imaging wells. It reveals that the specific capacity is proportional to the transmissivity and the coefficient is subject to the aquifer shape and the radius of the pumping well. In some conditions, q=T could be caused by the special geometric characteristics of the aquifer-well system. The hydraulic tests in sand boxes presented in Lan (2007) just satisfied such special conditions but did not indicate that q=T is generally applicable. New tests in sand boxes without these special geometric characteristics have shown significant different results from the q=T equation.