Environmental Engineering Reference
In-Depth Information
Table 3.1
Freshwater reservoirs on
the land.
Mass (10
15
kg)
Reservoir
Proportion (%)
Ice sheets
26,200
80
Groundwater
6,200
19
Lakes, fresh water
126
0.4
Lake Baikal
22
Great Lakes, North America
32
East African lakes
36
Lakes, brackish water
105
0.4
Caspian Sea
80
Soil, unsaturated zone
150
0.5
Rivers
2
Potential distribution on the surface
of the theoretical flow region
Fig. 3.3
Groundwater flow systems
in a homogeneous subsoil after
Toth (1963). Higher order systems
lie nested within lower order
systems. Reproduced by permission
of American Geophysical Union.
where deep permeable layers exist in almost flat
landscapes, can be very complex. Toth (1963) devel-
oped the concept of nested systems (Fig. 3.3) where
small flow systems are embraced by larger systems.
These systems may differ considerably, not only in flow
rates but - depending on the chemical composition
of the soil strata - also in water chemistry.
of rivers and lakes where wetlands can occur under
any climate but it is also true in groundwater-fed
systems in climates where there is a precipitation
surplus on a yearly basis. During wet periods the
groundwater stock is replenished and this water can
sustain wetlands in large areas during dry periods.
Such groundwater-fed mires once covered substantial
areas (Succow & Joosten 2001; see Chapter 9 in this
volume). Today the hydrological balance is changed
in many wetlands by human activities but, interest-
ingly, this sometimes leads to an increase in wet areas
instead of the more commonly observed decrease.
Loucks (1990) presents the case study of the Columbia
wetland where the amount of upwelling groundwater
was more than tripled due to the creation of a cool-
ing lake near a power plant.
Transport of water by water flows
Inhabitants from temperate latitudes often forget that
the most relevant substance transported by water flow
is water! Of course this is highly relevant in arid
regions but it can also be of significant importance
for the survival of wetlands during dry periods in more
humid areas. This is clearly the case along the fringes
