Environmental Engineering Reference
In-Depth Information
basis for a hypothesis that land reclamations may play a positive environmental role
providing the environment is transformed by human activity.
You have to remember that wildlife in Poland almost never feel the excess water.
Even disastrous
floods were mostly favourable or at least neutral to the natural
environment. In most situations the increased amount of water is favourable for
nature in agriculturally used areas. There are few situations when decreasing
amount of water is bene
fl
cial in cultivated areas. This is because, historically, the
introduction of crop species under Polish conditions required decreasing the soil
moisture in habitats. Grasses from cereal group are the steppe species,
”
meadow grasses are the species from dry ground habitats and tuber crops consist in
part of species from the subtropical zone.
A plant dies of oxygen de
“
noble
cit in soil and not of water excess. It also dies of water
de
cit but not of the excess of oxygen. It means that the amount of oxygen in root
zone is important during drainage and water availability for plant roots is important
during irrigation. Most grass species signi
cant as the source of fodder develop
optimally at air content in the root zone in the range of 8
12 % per volume
(Szuniewicz
1979
). Such air content corresponds to ground water levels given in
Table
6.1
understood as the distance between water table and land surface. Esti-
mating these depths is an effect of laborious experimental studies of the generations
of Polish meadow and soil specialists.
Data from Table
6.1
show that, for most grassland habitats in Poland, the
optimum ground water level is ca. 0.5 m beneath the land surface. In the last
decades, ground water in these habitats has declined in the middle of the growing
season to one or more metre, which had a detrimental effect particularly for
meadows situated on shallow non-peat soils.
To continue deliberations on stereotypical formulations which sometimes carry
misleading contents, it is worth thinking of the notion of
-
fl
flood. According to
traditional de
flood is a transitory hydrological phenomenon consisting in
the rise of river waters which, after exceeding bankfull level, causes the inundation
of large areas
nition,
fl
river valleys, near-shore or depression areas which leads to mea-
sureable social and material losses. Water rising is a high river water level which
leads to over
—
fl
ow and
fl
flooding the river valley. The reasons of
fl
floods are of two
kinds: either
flood control facilities do not play their role or social and material
goods are situated by man in a place exposed to
fl
fl
flooding. Considering water rising
Table 6.1 Optimum and extreme for plant survival levels of ground water in soils for grasses
grown on permanent lowland grasslands (Szuniewicz et al.
1992
)
Soil conditions
Optimum (and extreme) depths of ground water [m]
Poorly decomposed peat
0.80 (0.35
-
1.10)
Medium decomposed peat
0.65 (0.35
0.95)
-
Medium and strongly decomposed peat
0.55 (0.30
0.85)
-
Strongly decomposed peat
0.35 (0.25
-
0.60)
Shallow non-peat soils
0.35 (0.25
0.50)
-
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