THE EXTENSION OF THE THEIS EQUATION FOR NATURAL BOUNDARY CONDITIONS FOR THE DETERMINATION OF HYDROGEOLOGICAL PARAMETERS BY A LONG-TERM PUMPING TEST

摘要

The solution of the partial differential equation for nonsteady groundwater flow near a well is known as the THEIS equation. To get a unique solution, you have to define suitable boundary and initial conditions. Up to now a homogeneous, infinite aquifer has been required. Both the natural gradient of the groundwater and the influence of surface waters were disregarded. If you consider a well in a natural aquifer and near surface waters, the piezometric level h follows from the superposition of the local radially symmetric THEIS-solution with the steady and nonsteady influence of the surface waters and the natural gradient of the groundwater. A new method is presented, which incorporates these enlarged boundary conditions into an improved THEIS equation. This formula can be solved numerically by the method of coefficient determination. With it, the important parameters T (transmissivity) and S (storage-coefficient) can be determined for the classification of the aquifer.