Groundwater is a valuable and vital resource. Water covers over 70% of the earth's surface and although less than 5% of this water is defined to be groundwater, it is the largest source of freshwater which is vital to all life. The natural superior quality of groundwater as well as the reliability of its supply makes it a resource to be valued. Groundwater supplies must be studied and analyzed to efficiently use the resource without exploiting the source.
When evaluating a groundwater site for the construction of a possible well, the negative effects of the pumping must be weighed against the benefits of the yield of water from the well. Drawdown or the decline in hydraulic head is an important consequence in the consideration of a well site as it can indicate a lowered water level that outweighs the benefit of the well; an unacceptable change to the hydrologic cycle; or an adverse effect on other wells tapping the same aquifer.
This paper will first develop the theory behind the calculation of the drawdown cone or cone of depression in the potentiometric surface around a potential well. The empirical law, Darcy's Law is discussed first to set the foundation for the analysis of groundwater flow. Since groundwater flow is essentially three dimensional through the void spaces in the formations under the surface of the earth, Section 2.2 will derive the 3-dimensional form of Darcy's Law that forms the foundation for the drawdown equations.
A simple model of the hydraulic head drawdown as a mathematical boundary-value problem will be developed in Section 3. In conclusion, Section 3.1 presents an analytical solution in the form of the Theis Equation in the specific example of the drawdown in a confined aquifer of a non-steady flow.
The appendices contain detailed discussions of topics mentioned throughout the paper as well as a glossary. Code for a program written in Matlab that plots the drawdown versus the radial distance of a cone of depression is also included.