Geology Reference
In-Depth Information
5.4.2 Renewable water resources: surface and groundwaters
Despite their relative scarcity (see Table 5.3), renewable water resources in the form
of lakes, streams
2
, rivers and groundwater play an important role in the maintenance
of life. They are the main suppliers of freshwater including that needed in the
agricultural and industrial sectors. Many rivers are avenues of transportation and
can be dammed to provide hydropower. They may also have a great scenic and
recreational value.
The mean renewable global water resources are estimated at 42,785 km
3
/year,
which varies with space and time. Table 5.7 presents the continental distribution
and availability of water resources. Such information is based on a water balance
approach by Shiklomanov (1999), who provided data for 51 countries. Other com-
prehensive publications are the early works of L'vovich (1979), Gleick (2000) and
the World Resources Institute (WRI, 2000). By absolute value, the largest water
resources are those of Asia and South America. The smallest are in Europe and
Australia and Oceania.
Table 5.7 Renewable water resources and potential water availability by continent (Shiklo-
manov, 1999)
Continent
Area,
M km
2
Water
resources,
Water
availability,
1000 m
3
/year
km
3
/year
Average
Max
Min
per
km
2
per
capita
Asia
43.5
13,510
15,008
11,800
311
3.92
South America
17.9
12,030
14,350
10,320
672
38.2
North America
24.3
7,890
8,917
6,895
324
17.4
Africa
30.1
4,050
5,082
3,073
134
5.72
Europe
10.46
2,900
3,410
2,254
277
4.23
Australia and Oceania
8.95
2,404
2,880
1,891
269
83.7
The World
135
42,785
44,751
39,775
317
7.6
5.4.2.1 Stream, river and lake waters
The nature of aqueous solutions, produced or modified by weathering is determined
by several factors including chemical controls such as solubility and interface reac-
tions, as well as environmental aspects such as climate, geology and the hydrological
cycle. The chemical solutions derived from weathering may mix with water bodies
that have not been involved directly. In turn, the mixed waters may be modified
by further reactions such as a natural cation exchange with clay or other mineral
phases or by anthropogenic activities. There is therefore a great variation in the
concentrations of dissolved materials in lakes, streams and rivers. Nonetheless an
extensive amount of available data allowed Livingstone (1963) to estimate the mean
composition of world river water (see Table 5.8).
2
A stream is defined as a body of water that carries rock particles and dissolved substances and
which flows down a slope along a clearly defined path.
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