Geoscience Reference
In-Depth Information
hydrological processes occurring in stored water is
very important.
In this chapter two major stores of water are
described: water beneath the earth's surface in the
unsaturated and saturated zones; and snow and ice.
Inflow
Outflow
Storage
Figure 4.1 Illustration of the storage term used in the
water balance equation.
WATER BENEATH THE EARTH' S
SURFACE
water in or around planet earth (see Table 1.2,
p. 6). The majority of this is either in snow and ice
(particularly the polar ice caps) or groundwater.
For many parts of the world groundwater is a major
source of drinking water, so knowledge of amounts
and replenishment rates is important for water
resource management. By definition, stored water is
slow moving so it is particularly prone to contami-
nation by pollutants. The three 'Ds' of water pollu-
tion control (dilution, dispersion and degradation;
see Chapter 7) all occur at slow rates in stored water,
making pollution management a particular prob-
lem. When this is combined with the use of these
waters for potable supply, an understanding of the
One way of considering water beneath the earth's
surface is to divide it between the saturated and
unsaturated zones (see Figure 4.2). Water in the
saturated zone is referred to as groundwater and
occurs beneath a water table . This is also referred
to as water in the phreatic zone .
Water in the unsaturated zone is referred to as soil
water and occurs above a water table. This is some-
times referred to as water in the vadose zone .
In reality all water beneath the surface is
groundwater, but it is convenient to distinguish
between the saturated and unsaturated zones and
maintain the terminology used by other hydrolo-
gists. As shown in Figure 4.2, there is movement
Soil water (unsaturated)
Groundwater (saturated)
Figure 4.2 Water stored beneath the earth's surface. Rainfall infiltrates through the
unsaturated zone towards the saturated zone. The broken line represents the water table,
although, as the diagram indicates, this is actually a gradual transition from unsaturated to
fully saturated.
Search WWH ::




Custom Search