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16
Fluvial Imprints in Flysh Valley Bottoms—
Topľa and Ondava Valleys
MilošRusnák, Anna Kidová, Milan Lehotský, and Ján Sládek
Abstract
The central part of Ondavskávrchovina upland represents
a medium-altitude and moderately dissected relief with
narrow elongated valleys. The Topľa and Ondava rivers
are the main axis of flysch valleys and their flat bottoms
are modelled by dynamic river processes acting upon thin
layers of Quaternary sediments. They bear a record of all
historical changes of the channel pattern, from a wide
wandering gravel-bed wild river to a narrow and sinuous
channel. Both rivers are characterized by distinct bank
erosion, resulting in bank movement and bank retreat
within meander bends. From an economic point of view,
erosion of arable land and grassland is a negative
consequence of channel migration. Vice versa, from an
ecological point of view we can consider bank erosion as
a natural process that leads to the increase of geo- and
bio-diversity of the riparian landscape. Nowadays, ‘green
approaches’are applicable in the river management,
aiming to eliminate technical interventions in the river
basins and allowing for free channel migration. All these
processes create valuable ecosystems with natural flood
regime and floodplain forest.
Keywords
Flysch Gravel-bed rivers The Ondava River The
Topľa River Bank erosion
16.1 Introduction
The north-eastern part of Slovakia is formed by the
Palaeogene flysch sequence of sedimentary rock (sand-
stones, claystones and conglomerates), cropping out to the
north parts the Klippen Belt. Geological setting of this area
conditioned typical upland relief developed upon less or
medium-resistant flysch rock formation, moderately to
sharply dissected with incised river valleys filled by Qua-
ternary deposits, and reflecting monotonous bedrock lithol-
ogy. Valleys bottom are reshaped by fluvial processes and
create interesting fluvial and cultural landscapes modelled by
river systems. River morphology is modified at different
spatial taxonomy levels (from basin to channel unit) and
sensitive to dynamic events caused by intrinsic variability or
external human pressure and flood impact. River behaviour
adapts to the complex interaction of erosion and accretion
mechanisms (Brierley and Fryirs 2005). Freely migrating
and dynamic rivers are strongly affected by changing natural
conditions in industrial Europe and altered with increasing
human pressure on the landscape. Anthropogenic modifica-
tion, grade-control structures and channelization resulted in
channel narrowing, transformation and incision along many
rivers in Europe (Brierley and Mum 1997; James 1997;
Rădoane et al. 2013; Scorpio et al. 2018;Škarpich et al.
2013;Wyżga et al. 2016b; Ziliani and Surian 2012). It was
pointed out that alteration of sediment supply by gravel
extraction (Hajdukiewicz et al. 2017; Korpak 2007; Marston
et al. 2003; Surian and Rinaldi 2003;Wyżga et al. 2016a)
and afforestation or deforestation (Jefferson and McGee
2013;Liébault et al. 2005; Price and Leigh 2006) are key
factors resulting in channel transformation, narrowing and
expansion rather than flow regime changes (Comiti et al.
2011). Extraordinary floods and their geomorphological
effectiveness are influenced by the actual state of the channel
(Gorczyca et al. 2013; Hajdukiewicz et al. 2016; Hooke
2015; Kijowska-Strugała et al. 2017) and affect short-term
rejuvenation and channel modification.
M. Rusnák(&)A. KidováM. LehotskýJ. Sládek
Department of Physical Geography, Geomorphology and Natural
Hazards, Institute of Geography, Slovak Academy of Sciences,
Štefánikova 49, 814 73 Bratislava, Slovakia
e-mail: geogmilo@savba.sk
A. Kidová
e-mail: geogkido@savba.sk
M. Lehotský
e-mail: geogleho@savba.sk
J. Sládek
e-mail: geogslad@savba.sk
©Springer Nature Switzerland AG 2022
M. Lehotskýand M. Boltižiar (eds.), Landscapes and Landforms of Slovakia, World Geomorphological Landscapes,
https://doi.org/10.1007/978-3-030-89293-7_16
307
Bank erosion of meandering and sinuous channels are
demonstrated by lateral movement and migration of river
bends (Bertalan et al. 2019; Hooke 2003). Interaction
between erosional and depositional processes lead to channel
modification, floodplain creation and construction of riparian
landscape. In this system, high magnitude events lead to
floodplain reworking and restoration of new habitats. The
geomorphological effect of a flood depends on its magni-
tude, frequency and timing, as well as physical characteris-
tics of the river bed and the floodplain (Miller 1990). It is
important to distinguish between the effects of inundation
and those of flood-related erosion (Fuller 2008). Flood
events rework the riparian zone, modify floodplain topog-
raphy and increase landscape heterogeneity. Dynamic
behaviour of sinuous channels and lateral migration in a
form of bank erosion is a natural process (Hooke 2003).
Understanding and preserving this dynamic river system,
laterally unconfined and capable of bank erosion is a chal-
lenge for a society that wishes to protect natural behaviour of
rivers. This is because stream bank erosion on the one side
represents natural hazard that threatens artificial construc-
tions and human activities in the landscape, but on the other
it increases ecological variability and spatial geodiversity of
the riparian zone (Bertalan et al. 2018). Preferred ‘green
approaches’and understanding of river behaviour is essen-
tial to understanding river processes and application of
proper management strategies. Restrictive interventions are
too expensive, lead to increasing river degradation and
support irreversible channel changes (Piégay et al. 1997).
16.2 Regional Settings
The Topľa and Ondava River drain the north-eastern part of
Slovakia (Fig. 16.1). Both streams are located in the Outer
Western Carpathians, in the central part of Ondavská
vrchovina upland, which belongs to the area of the Nízke
Beskydy mountains (Mazúr and Lukniš1978). Geologically,
the area is the result of flysch sedimentation of the Outer
Carpathians, whereas this succession was arranged into three
tectono-lithostratigraphic units of the Magura Group during
the deformation phase (Kováčik et al. 2011; Nemčok et al.
1990). The southernmost part of the study area is marginally
formed by the Krynica unit of proximal deep-marine envi-
ronment, with prevailingly medium to coarse-grained sand-
stones and conglomerates. The right slope of the Topľa
valley is covered by a narrow strip of the Bystrica unit and
the Zlín Formation in “sandstone development”, whereas in
northern parts of the catchment the Beloveža Formation
occurs, formed by thin-bedded claystones and siltstones with
layers of sandstones (fine-rhythmical flysch). Central parts of
the Ondavskávrchovina upland and slopes of the Ondava
valley are formed by the Rača unit with complicated
geological settings and variegated facies content. The
Beloveža formation creates cores of anticlinal structures
(thick-bedded claystones and sandstones) and main central
parts of the catchment are formed by the Zlín Formation with
claystone and sandstone facial developments. In the central
section of the Topľa valley, along the south-western margin
of the Rača unit, the Malcov Formation occurs (grey cal-
careous claystones to siltstones with layers of the
quartz-carbonate sandstone). The valleys of both rivers are
filled with Holocene fluvial sediments (gravels and sandy
gravels) in close genetic relation with proluvial sediments of
alluvial fans. Their thickness ranges between 2 and 8 m
(Harčár1995). The shape of the basins is significantly
extended in the north–south direction with trellis drainage
pattern (main flow with smaller tributaries), where the river
creates the main axis of the landscape in prevailing north–
south direction.
The river landscape was evaluated in two sections of the
eastern Slovakian rivers of Ondava and Topľa. Both repre-
sent in their middle part (6th order stream) gravel-bed
channels, less affected by technical intervention and regu-
lation. The Topľa River springs at the foothill of the Minčol
peak at an altitude 1,015 m a.s.l. in the Čergov Mountains.
With the length of 115 km and 1,506 km
2
basin area, it is the
largest tributary of the Ondava River. The long term daily
average discharge at the Bardejov gauging station is 3.018
m
3
s
−1
with maximal culmination Q
max
= 350 m
3
s
−1
during
aflood event with 100-year recurrence interval (17th May
2010). Flow regime is characterised by high variability of
discharge due to snow melting and intensive rainfall in
summer period. The Ondava River springs at an altitude
546 m a.s.l. at the Slovak-Polish borders and flows for
144.4 km to the confluence with the Latorica River. Its
catchment area is 3,355 km
2
, and the long term average
discharge at Stropkov gauging station is 5.73 m
3
s
−1
, with
maximum 550 m
3
s
−1
(19th July 1974).
16.3 Fluvial Dynamics on Valleys Floor:
Channel Planform Evolution by Old
Aerial Images
The last decades of channel evolution are recorded by his-
torical maps and aerial photographs taken from the begin-
ning of twentieth century, which show significant channel
pattern modifications (Fig. 16.2). Both rivers flow within
narrow valleys floors and valley slopes create a confined
environment for river processes and landform reorganisa-
tion. The Ondava River valley floor is approximately 1 km
wide, and the floodplain is structured to different vertical
levels, from 0.5 to 2 m height difference. River terraces are
preserved only locally and lateral tributaries created a system
of alluvial fans emerging from side valleys. The Topľa River
308 M. Rusnák et al.
floodplain width is approximately 700–1000 m and on sys-
tems of lower river terraces are preserved in the valley floor.
Historical maps dating back to the middle of the nineteenth
century and aerial photographs point to significant channel
modification and pattern changes (Lehotskýet al. 2013;
Rusnák2010; Rusnák and Kidová2018; Rusnák and
Lehotský2014a,b). During the last seventy years lateral
dynamics and the numbers of branch channels within the wide
gravel plains of maximum width of 226.4 m in the Ondava and
456.7 m in the Topľa River decreased. Gravel-bed rivers have
gradually changed from lateral unstable systems with high
extent of gravel bar accumulation to simple meandering and
sinuous channels with concentrated flow (Fig. 16.3). An
average channel width in studied section decreased from
62.1 m in 1949 to 37.2 m in 2009 (Topľa) and from 87.6 m to
39.9 m (Ondava). Overall, the Ondava channel area decreased
from 116 ha (1949) to 54 ha (2009), whereas the respective
values for the Topľa River are 258 ha and 147 ha. The most
significant changes from the point of view of geomorphology
are those in gravel bar area, which drastically dropped in the
studied period from 76 to 17 ha (Ondava) and from 149 to
53 ha (Topľa). Historical maps and aerial photographs pro-
vide direct and indirect evidence of landscape evolution and
human impact. Relatively sparsely vegetated area around the
river channel was used for agricultural purposes or for grazing.
After channel modification and lateral movement accompa-
nied by channel narrowing, newly deposited parts in the form
of gravel bars were transformed to a floodplain covered solely
with woodland. Riparian forest stabilisation was supported by
the process of agricultural collectivisation and subsequent
land management resulted in gradual abandonment of small
plots in the close vicinity of river channels (Fig. 16.4.).
Fig. 16.1 Topľa and Ondava valleys with their sinuous channel
patterns of the dynamic river system. Location of the study area in
Slovakia (a); main tectonic units of the Western Carpathians in
Slovakia: 1—Flysch belt, 2—Pieniny Klippen belt, 3—
Inner-Carpathian Paleogen, 4—Tatra-Fatra belt of core mountains, 5
—Vepor belt, 6—Gemer belt, 7—Neogene volcanics and 8—Neogene
basins; topography of the Topľa and Ondava River basins (b) and
general situation of channels in the valley reaches analysed in detail (c,
d)
16 Fluvial Imprints in Flysh Valley Bottoms—Topľa and Ondava Valleys 309
Fig. 16.2 Various sources record the channel pattern evolution of the
Topľa River over more than two centuries. An old map produced by the
Second Austrian Military Surveys conducted in the second half of the
eighteenth century (a, 1839), historical aerial photographs from 1949
(b) and current channel position in 2013 (c) (orthophoto: EUROSENSE
Slovakia, Historical orthophoto: GEODIS SLOVAKIA, s r. o.,
EUROSENSE, s r. o. and Topographic institute BanskáBystrica)
310 M. Rusnák et al.
16.4 Bank Erosion Hazards and Riverbank
Undercuts
North-eastern Slovak rivers have remained unaffected by
human intervention and technical bank stabilisation, which
still allows for lateral migration, bank erosion and investi-
gation of dynamic behaviour (Fig. 16.5.). Erosion hazard
was evaluated by digitalisation of the channel position from
the end of 1949. An active channel was defined based on the
location of permanent vegetation that marks the boundary
between the stabilised floodplain and active channel with
flow fluctuations and ongoing in-channel processes (gravel
accumulation and bank undercutting). In GIS environment it
was possible to calculate the processes of erosion and
deposition by superposition of channel positions in different
time snapshots (Lehotskýet al. 2013). Erosion is understood
as replacement of former floodplain areas by river channels,
and deposition is recorded by areas of the former channel
incorporated into the floodplain by sediment accumulation
and vegetation stabilisation (continuous vegetation cover).
From the middle of the twentieth century both rivers
eroded an area of 351 ha, as measured in reaches between
Bardejov to Giraltovce (length of 40 km) and from Stropkov
to Domaša waterwork reservoir (13 km). The intensity of
this process is 5.85 ha y
−1
, which translates into erosion of
1104 m
2
of valleys floor in one year for every kilometre of
the river. In both rivers during the second half of the
twentieth century the process of deposition prevailed, being
1.5 times higher that process of erosion (accumulation of
524 ha).
Results of bank erosion and deposition processes include
the lateral shift of a river channel (Fig. 16.6). In meandering
and sinuous rivers this led to gradual movement of bends by
cliff erosion during flood events. The average shift of the
Ondava river channel in the period from 1949 is 2.68 m per
year and 1.91 m y
−1
for Topľa River. Moreover, during
flood events the lateral displacement of a channel can have
Fig. 16.3 Planform evolution of the Ondava river from 1949 to 2009 in a meandering (a) and sinuous (b) channel section with historical position
of channel plotted as for 2009
16 Fluvial Imprints in Flysh Valley Bottoms—Topľa and Ondava Valleys 311
reach up to 400 m. In these cases, the main process of
channel re-location is avulsion, often occurring at meander
necks and leading to meander cut-off. The dynamics of lat-
eral migration is influenced mainly by the distribution and
variability of discharge. In the monitored section an increase
of bank erosion was recorded during intensive floods in the
period 2002–2010. During the period of more frequent
floods floodplain erosion dramatically increased, from
13,619 m
2
y
−1
to 21,740 m
2
y
−1
(Rusnák and Lehotský
2014b). The flood events of 1–2-year recurrence interval do
not have destruction effect, but lead to the stabilisation of the
system and support vegetation succession (Corenblit et al.
2007; Gurnell et al. 2016; Opperman et al. 2010). On the
contrary, frequent floods (high magnitude floods in Topľa
and Ondava River in 2004, 2005, 2006, 2008 and 2010) led
to intensive destruction and collapse of river banks and
in-channel gravel bar accumulation.
These dynamic changes are demonstrated in the section
near the village of Hrabovec, where the gravel bar area in a
2 km long reach increased from 5.7 ha in 2002 to 16.2 ha in
2009 due to intensive flood events (see Fig. 16.5I.). Frequent
flood occurrence has led to significant channel pattern
changes and river could not stabilize themselves by intro-
ducing vegetation. The meandering river pattern and its
tendency towards lateral migration is controlled by the
magnitude of discharge. On the Ondava river one can
observe stabilisation of the meander belt, individual meander
migration and point bar deposition with an increase of sin-
uosity index (from 1.34 to 1.57) in the period with low
magnitude discharges in the 1990s (Rusnák and Lehotský
2014b). Floods in 2004, 2006 and 2008 led to the straight-
ening of the channel, meander cut-off and abandonment of
channel arms (Fig. 16.5b). Consequently, sinuosity
decreased to 1.41.
Several authors (Bertoldi et al. 2009; Hickin and
Sichingabula 1988) emphasized the role of bank full dis-
charge (relatively low but long duration floods) in bank
erosion. In highly dynamic gravel-bed rivers of the flysch
Carpathians, as pointed out by Lehotskýet al. (2013), low
magnitude floods are responsible for the formation of river
bed, its planform and relatively slow bank erosion associated
with overall behaviour of the channel and helicoidal flow in
the river bends. By contrast, high magnitude flows lead to
sudden and disastrous bank erosion, channel pattern
destruction and partial rejuvenation of stream with gravel bar
expansion, destruction of old habitats and creation of new
ones.
The combination of dynamic river behaviour and active
use of landscape generates problems related to floodplain
destruction. From economic point of view destruction of
farmland areas is a negative phenomenon. According to the
Decree No. 38/2005 the monetary loss resultant from
floodplain erosion along the Topľa River was estimated for €
29,924.02 (Rusnák et al. 2016). Identifying unstable reaches
Fig. 16.4 Digitised aerial photographs from the second half of the
twentieth century point to the creation of a riparian belt along the Topľa
River. Land cover classes: 1—water, 2—gravel bar, 3—meadow, 4—
shrubs, 5—forest, 6—arable land, 7—garden, 8, 9—urban area, 10—
building, 11—road, 12—gravel mining
312 M. Rusnák et al.
and potentially at risk is important for effective river man-
agement. Bank erosion is a naturally occurring process and
‘green approaches’are nowadays applied in management,
leading to elimination of technical interventions in river
basins and allowing for free channel migration in a certain
area where it does not threaten human activity. As pointed
out by Piégay et al. (1997), active interventions into the
channels are expensive and create spiral effect that leads to
degradation and increased flood risk, whereas bank erosion
is in most cases a psychological effect, affecting river sec-
tions in less valued areas than settlements or farmland.
16.5 Valleys Floor Reworking: Power
of River
The energy of river during a flood event is transformed to
valley floor re-modelling by erosion-accumulation phases of
channel pattern evolution. A characteristic feature of mean-
dering rivers are cutoffs of meander bends. Archive aerial
photographs show long-term meander bend evolution near
the village of Stropkov from a narrow and straight channel,
where township flood defence walls and embankments built
Fig. 16.5 Dynamic changes of channel planform reflected by bank
erosion and changes of channel planform of the Topľa River south from
Bardejov (I.); avulsion channel creation on the Topľa River near the
village of Dubinnéduring flood events in 2010 (II.) and meander cutoff
near the village Porúbka (III.). Example of avulsion channel formation
in the meander neck during the flood in 2010 near Stropkov (the
Ondava River) (a); abandoned channel in the meander loop near the
village Breznica (Ondava) after meander neck cutoff (b); erosion of
arable land with part of winter crops planted before winter 2010/2011
(c; Topľa, photo: April 2012); erosion of arable land in the meander
loop above the village Lomné(d; Ondava) and erosion of Pleistocene
terraces near the village of Kurima with height 6 m and 580 m length
of eroded bank (e; Topľa). Reproduced from Rusnák and Lehotský
(2014a)
16 Fluvial Imprints in Flysh Valley Bottoms—Topľa and Ondava Valleys 313
in the 1960s. During flood events in 2010 a chute cutoff
channel was formed inside the meander neck, with the length
of 450 m and 150 m wide (Fig. 16.7). The first flood cul-
minated on 17 May (254 m
3
s
−1
) and was followed 18 days
later with 220 m
3
s
−1
(Rusnák et al. 2019). The evolution of
the chute cutoff was monitored by drones and
UAV-photogrammetry (Unmanned aerial vehicle). After
initial reconnaissance by means of field work the first
monitoring campaign started on 15 June 2012, followed by
the collection of second set of images on 1 April 2014 and
the final imaging was performed on 18 July 2014. Overall,
712 images were processed during campaigns. Meander
neck cutoff was enforced by headcut gully formation on the
floodplain and erosion of topsoil cover. It was also demon-
strated that a high-accuracy digital elevation model is
important for precise evaluation of the morphological effects
of floods.
UAV technology enables one to produce high resolution
models with 1–2 cm resolution, that capture chute channel
morphology in great detail (Fig. 16.8.). A part of the former
meander loop in its position from 2009 is clearly identifiable,
with a gradual extension in the direction of water flow. In the
central part the original floodplain surface is well-preserved
between two main headcut gullies, buried by a thin sandy
layer several centimetres in thickness and progressively
destroyed by anthropogenic gravel mining. The gravel pits
are identifiable throughout the all study area and retreat bank
cliff was observed. The avulsion channel bend was slowly
shifted laterally by 7.5 m in the monitored period of
24 months.
Low magnitude discharges after 2010 allowed for vege-
tation stabilisation and rapid vegetation succession with
grass formation and shrubs, almost exclusively Salix spp.,
covered the central part of the chute channel up to the height
Fig. 16.7 Chute cut-off avulsion channel formation in the meander neck during a flood event in 2010 (a) and geomorphological effect of the flood
in the upper part (b), lower part (c) and panoramic view of general situation (d)
16 Fluvial Imprints in Flysh Valley Bottoms—Topľa and Ondava Valleys 315
of 4 m (Fig. 16.9). Vegetation has increased erosion resis-
tance and stabilized the river system by sediment trapping,
slowly leading to floodplain transformation. Finally, the flat
floodplain was transformed to a new highly structured sur-
face with higher geodiversity and former agriculture plots
were replaced riparian forest.
16.6 River and People: Questions in Rivers
Management
Since the prehistoric times, the Nízke Beskydy Mountains
were typified by a forested hilly landscape, with sporadic
evidence of settlements and hence, archaeological findings
(Beňko 1985). The oldest traces of settlements are from the
Stone Age and point to the transport function of this terri-
tory, being associated with the movement of rare hunting
groups at the end of the Ice Age. Archaeological findings
point to settlements in this region from the late Stone Age
(Eneolithic—2500—1800 years BC) onward, but archaeo-
logical discoveries are only sporadic. Important development
of this area started in the Middle Ages, due to German
colonisation associated with the development of trade. Riv-
ers valleys had a transport function, acting as corridors
connecting Poland and Hungary. In the fourteenth century,
the town of Bardejov became a centre of trade with Poland
and gained the status of a royal town in 1376 as a centre of
north-eastern Slovakia. The surrounding areas still preserved
the natural character and were later affected by the so-called
Wallachian colonisation at the beginning of sixteenth cen-
tury, leading to livestock breeding, grazing and deforestation
with agriculture activities confined to valley floor.
The main landscape changes are related to industrialisation
and collectivisation during the second half of the twentieth
century. Floodplain reworking and replacement of eroded
arable land by gravel deposition with rapid vegetation suc-
cession in this period led to extensive afforestation in distinct
contact with river. A continuous complex of floodplain forest
spreading along both flood-affected channels was included in
the network of protected sites the NATURA 2000 in 2004.
Both rivers create axis of the protected area as an important
migratory biocorridors for birds and the nesting places for
avifauna. The varying geodiversity is affected by river mor-
phological changes and floods, directly connecting with high
biodiversity. Floodplain-channel connection is controlled by
water stage fluctuations and discharge regime unaffected by
technical infrastructure. Flooding with maximal discharges
results from spring snowmelt and may also occur in summer
Fig. 16.8 Digital elevation model (DEM from July 2014) of chute cutoff avulsion channel and details of TIN model accuracy (a), solid TIN
model (b), texture 3D model (c) and shaded relief of DEM (d,e)
316 M. Rusnák et al.
months due to extreme rainfall events. Protected areas are
accompanied by the willow, ash, poplar and alder (so-called
soft-wood floodplain forest), complemented by wet meadows
and in-channel vegetation, especially Myricaria germanica.
The development of floodplain forest is dependent on effective
distribution of floods spilled over the floodplain and active
in-channel bar deposition. Unique species of European sig-
nificance have been recorded in the area, including birds such
as Alcedo atthis, Ciconia ciconia, Ciconia, nigra, Picus canus,
Egretta alba, mammals, especially beavers and otters (Castor
fiber, Lutra lutra), amphibians (Bombina variegate), inver-
tebrates (Vertigo angustior) and fish. The nest cavities were
usually found on vertical cliffs of undercut banks
(Fig. 16.10.), reflecting the importance of geomorphological
processes in the riparian landscape.
Most economic activities that take place in the territory of
the Ondavskávrchovina upland are linked to the narrow
valley floors typified by intensive agriculture, relatively
dense population, water demand and the presence of main
transportation lines (roads). River water quality and bank
vegetation habitats are under pressure from urbanized and
agricultural landscape. In-channel bar accumulations are
intensive extracted directly from the main channel and trucks
destroy armoured gravels bed (Fig. 16.11.). Vegetated banks
are excavated by local residents for heating purposes or local
river management authorities to prevent flood risk. Recently,
the main challenge is to manage interventions aimed to
eliminate effects of bank erosion and flooding by “green”
approaches, to minimize negative consequences of direct
technical solutions.
16.7 Conclusions
Rivers are the most dynamic element of the Ondavská
vrchovina upland. Nowadays, active behaviour is the main
imprint that creates and reorganises the landscape with
harmonic interaction throughout villages, farms and agri-
cultural plots. Understanding the dynamics of rivers in their
natural environment allows for predicting further develop-
ment within nature-friendly management. Well-preserved
natural fluvial processes despite human intervention create
an extraordinary aquatic and semi-terrestrial system and the
value of the landscape lies in its high geo- and bio-diversity.
The eastern Slovak gravel-bed rivers are still one of the
less regulated channels that enable for monitoring of
Fig. 16.9 Vegetation succession in chute cut-off avulsion channel in its central part (photo taken 13 October 2014)
16 Fluvial Imprints in Flysh Valley Bottoms—Topľa and Ondava Valleys 317
hydrogemorphological processes and bank erosion. Gradual
erosion and removal of floodplain material, as well as
deposition in the form of gravel bars, generate ever-changing
conditions on the valley floors. However, the most dynamic
reaches achieve lateral shift several hundred metres, and the
average movement is approximately 1 m per year. The
geodiversity of the landscape is enriched by the formation of
vertical cliffs, bank undercutting and abandoned arm
formation. This system is controlled by the occurrence of
floods that have a significant destructive effect perceived as a
natural hazard, but on the other hand, they are essential for
preservation of a dynamic, natural fluvial system.
Acknowledgements The research was supported by Science Grant
Agency (VEGA) of the Ministry of Education of the Slovak Republic
and the Slovak Academy of Sciences; 02/0086/21.
Fig. 16.10 Nest cavities along vertical cliff of undercut banks of the Topľa River
318 M. Rusnák et al.
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320 M. Rusnák et al.
MilošRusnákis a fluvial geomorphologist at the Institute of Geography of
the Slovak Academy of Sciences (Department of Physical Geography,
Geomorphology and Natural Hazards). His research topics are fluvial geo-
morphology, spatial data processing in GIS, UAV data acquisition and
processing, fluvial processes and sediment connections in gravel-bed rivers
and remote sensing applications in rivers and landforms research. He is the
author and co-author of several papers dealing with fluvial system evolution
in the Outer Western Carpathians.
Anna Kidováis fluvial geomorphologist at the Institute of Geography of
the Slovak Academy of Sciences. Her area of research focuses on the
response of river systems to environmental changes, the study of
hydro-morphological processes as well as issues related to measures for the
river management. Since 2018 she is a president of Association of Slovak
Geomorphologists.
Milan Lehotskýis a physical geographer and fluvial geomorphologist at the
Institute of Geography of the Slovak Academy of Sciences. He was many
years head of the Department of Physical Geography, Geomorphology and
Natural Hazards. His research topics are responses of fluvial systems to
environmental changes, sedimentological connectivity, evolution trajecto-
ries, hydromorphology and GIS and remote sensing applications in rivers
and landforms research. He is also working as an external lecturer at the
Department of Physical Geography and Geoecology, the Faculty of Natural
Sciences of the Comenius University in Bratislava.
JánSládek is a geomorphologist at the Institute of Geography of Slovak
Academy of Sciences in Bratislava as well as he works as a professional
UAV operator and beta tester of laser scanner products in private sector. His
research is focused on morphotectonics, morphostructure analysis and flu-
vial landscape monitoring by using of UAVs. The region of his interest
covers Slovak part of Carpathian Mountain Range mainly surroundings of
Turčianska kotlina Basin and other core mountains.
16 Fluvial Imprints in Flysh Valley Bottoms—Topľa and Ondava Valleys 321
