Environmental Engineering Reference
In-Depth Information
Chapter 5
Subsidence Phenomena
5.1. Subsidence caused by water withdrawal
5.1.1
. Introduction
There are several ways in which human activities have caused lowering of the
Earth's surface. One of these, shown in this chapter, is subsidence due to water
extraction from underground strata. This withdrawal generally changes the
hydraulic equilibrium conditions of a rather complex system, represented by
aquifers confined by more or less impermeable strata, called aquitards.
The phenomenon observed is linked with the mechanical interaction between the
solid skeleton (soil) and fluid phases (water in this case, but similar conditions arise
in the presence of gas and oil that will be discussed in Chapter 7). The problem is
usually defined at a regional scale, i.e. horizontal distances of interest are several
orders larger than the thickness of the exploited aquifers and impermeable layers
that make up the system. Such subsidence develops over very long time spans. This
is because the time scale depends on the velocity of water flow, represented by
Darcy's law, and by the exploitation history.
Subsidence phenomena have only recently become of interest to researchers, as
the effects of intense extraction due to industrial and/or agricultural reasons became
