Environmental Engineering Reference
In-Depth Information
new branches and cutting off the old channels and the other is cutting off the
meanders and creating oxbow lakes. Between the active river channel and the old
channels, wetlands, bogs or fens may occur.
Mountain Rivers
The unaffected
flow of the mountain rivers in their alluvial channels may naturally
result in the formation of an incised channel, a stable channel or a channel domi-
nated by accumulation (e.g., braided system). Stable and accumulation liable
channels occupy the longest river segments with good conditions to form wetted
areas or wetlands. Yet the most adequate conditions can be observed in alluvial
parts of the rivers as they create the whole network of new branches and often shift
main channels creating old ones (Gorczyca et al. 2011 ). While the bigger slope is
the characteristic trait of mountain rivers as well as narrow valleys, wetlands are
strictly connected with three factors, namely: the nature of
fl
fluvial processes taking
place in the river channel (Stru ż y ń ski 2014 ;Wy ż ga et al. 2010a ), human and animal
activity (K
fl
onowska-Olejnik and Radecki-Pawlik 2000 ), trees transported by the
river current during
ł
ga and Zawiejska 2005 ; Faustini and Jones 2003 ;
Radecki-Pawlik et al. 2011 ). Consequently, the incision of the mountain river
channel may easily cause the disappearance of wet areas near the river channel.
fl
oods (Wy
ż
5.2.2 Fluvial Processes in Regulated Rivers
Until the XXI century, rivers were regulated mostly with the technical methods.
These trends led to narrowing and deepening of the river channels and narrowing of
the
flood channel. Main stream in regulated rivers had been forced to be as narrow
as the bank enforcements. Within so-called hydraulically favourable channels, the
fl
fl
floods. However, it has to be remem-
bered that even in regulated, straight channels, the
flowing water reaches high energies during
fl
fluvial processes exist. Such kind
of regulations leads to the decrease of the transported material and to the appearance
of the so-called
fl
in which bed degradation predominate. Regulated
rivers cannot create wetlands, which
hungry rivers
finally tend to be degraded and used for human
purposes. Bed incision processes caused the increase of channel capacity, so rivers
started intensively drain their valleys.
Lowland Rivers
The process of meandering initiation is well recognized and found often in regu-
lated rivers (Leopold and Wolman 1960 ; Kitanidis and Kennedy 1984 ) (Fig. 5.2 ).
The thalweg movement is connected with the secondary currents. The same ten-
dency can be observed in straight, regulated channels.
The aerial picture of the regulated lowland river, which is presented below,
shows a distribution sand bars placed at an alternate angle (Fig. 5.3 ). This indicates
non-homogeneous
flow velocity distribution within the subsequent cross-sections.
The presented riverbed forms move but sustain after frequent spring or summer
fl
fl
floods. Regulated rivers are often separated from their valleys with the use of
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