Sustainable Water Management - Sustainable Practices in Geoenvironmental Engineering - page 75

(ICWE, 1992). In other words, water is essential for these three categories. Note that the
use of the term environment is meant to include the life-supporting functions of ecosys-
tems, as discussed in Chapter 1.

3.2.1 Hydrological Cycle

Although it is convenient to think in terms of essentially two primary sources of drinking
water—surface water and groundwater (aquifer and soil porewater)—it is more useful
to bear in mind the total hydrological cycle when one wishes to consider (a) the need for
water for life-support systems and (b) the impact of mankind on the sources of water. The
hydrological cycle relects the constant or continuous movement of water within the earth,
on the earth, and in the atmosphere, as shown in Figure 3.2.
Beginning with the ocean and other surface water bodies—such as rivers, ponds, and
lakes—together with open land surfaces, we can identify these processes as (a) evapora-
tion and condensation, (b) evapotranspiration, (c) precipitation, (d) iniltration (percola-
tion) from ground surface into subsurface, (e) groundwater (subsurface water) discharge
into land receiving waters and oceans, (f) discharge from rivers, and (g) surface runoff. It
is necessary to note that the terms iniltration and percolation are quite often used to mean
the same event, i.e., entry of water into the ground surface from water on the surface, either
from precipitation or from ponded water, or other similar sources. Direct anthropogenic
interference in the natural hydrological cycle occurs most often in processes such as inil-
tration and runoff, for example, in the quality of the water that iniltrates into the ground
and also the quality of the runoff that enters the receiving waters.

Clouds

Precipitation

Evapotranspiration

Terra firma

Aquifers and
groundwater

Evaporation

Ponds,
lakes,
rivers, etc.

Oceans

Subsurface water discharge

FIGURE 3.2
Sketch of basic elements and processes in the hydrological cycle. Percolation from surface into subsurface is not
shown in the sketch.