Problems in the area of geomechanics have a special place in engineering; we deal with nature and are not in complete control of our designs, as is the case for manmade constructions. In the field of groundwater flow, we deal with the additional complication that the properties of the aquifers are hidden to us; we need to do tests to determine both the geometry and the relevant properties of the aquifer system.

Fortunately, compared with other fields of applied mechanics, steady flow of groundwater is governed by a comparatively simple differential equation. The difficulty in solving practical flow problems is the diversity of natural conditions encountered; to deal with this diversity, we categorize groundwater flow problems into types of flow according to the natural conditions under which the flow takes place. We define and discuss these types of flow in this chapter, treating one type of flow in each section.

Many of the natural types of flow are three-dimensional, but can be covered with good approximation by a two-dimensional analysis.We present the approximations for each type of flow, derive the basic equations, present some elementary methods of solution, and apply these to one or more practical problems. The scope of this chapter is limited to homogeneously permeable and isotropic porous media. Where possible, we introduce dependent variables for each type of flow in such a way that the various mathematical formulations are similar, if not identical.

The solution of practical problems may be viewed as a process that consists of three main steps:

1. 1. Simplification of the real problem in such a way that it becomes mathematically tractable, while retaining the important characteristics of the problem

2. 2. Formulation of the physical quantities in terms of abstract variables and functions used in the mathematical description of the problem

3. 3. Determination of the mathematical solution and interpretation of the results in terms of the practical questions to be answered.

We apply this approach to practical problems in each section.

Horizontal Confined Flow

We call a flow horizontal if it takes place only in the horizontal plane; horizontal flow occurs if the vertical component of the specific discharge vector is zero throughout the flow region, i.e., if

Flow is called confinedif the groundwater flows between two impermeable boundaries.