Impacts of gravel-bed rivers transformation on fluvial ecosystems and human society: Examples from the Czech flysch Carpathians

Abstract

In the last centuries, gravel-bed rivers in developed countries have undergone rapid changes in channel morphology. The most serious problems include channel transformation related to progressive channel narrowing, incision or bed sediment coarsening. The main reasons for transformations were connected to the human interventions, which affected water and sediment fluxes in the basins. This paper summarizes contemporary research activities focused on these negative effects of channel transformations in the Czech flysch Carpathian rivers (the Morávka, the Olše and the Ostravice draining the highest mountainous areas of the Beskydy Mts). As the result of channel transformations, progressive changes in fluvial ecosystem were observed. The initial phytosociological survey demonstrates a higher biodiversity in the floodplain along the preserved multi-thread river channel than along the deeply incised channel in the Morávka River basin. Our observations of aquatic communities demonstrated that the channel transformation connected with incision and coarsening of bed sediments negatively affected fish or lamprey populations in the studied rivers. Regulation, damming and incision of channels caused changes of hydrological regime linked with gradual drying of floodplain. Additionally, a large set of hydraulic structures, bridges or weirs were affected by undercutting and progressive destruction in the Ostravice, Olše and Morávka River basins, which is assigned to increased transport capacity of regulated channels together with decreased sediment supply from mountainous parts.

Full text

Impacts of gravel-bed rivers transformation on
fluvial ecosystems and human society:
Examples from the Czech flysch Carpathians
Václav Škarpich1,*, Miroslav Kubín2, Tomáš Galia1, Stanislav Ruman1, and Jan Hradecký1
1Department of Physical Geography and Geoecology, Faculty of Science, University of Ostrava,
Chittussiho 10, 71000 Ostrava, Czech Republic
2Protected Landscape Area Administration Beskydy, Nádražní 36 756 61 Rožnov pod Radhoštěm,
Czech Republic
Abstract. In the last centuries, gravel-bed rivers in developed countries
have undergone rapid changes in channel morphology. The most serious
problems include channel transformation related to progressive channel
narrowing, incision or bed sediment coarsening. The main reasons for
transformations were connected to the human interventions, which affected
water and sediment fluxes in the basins. This paper summarizes
contemporary research activities focused on these negative effects of
channel transformations in the Czech flysch Carpathian rivers (the
Morávka, the Olše and the Ostravice draining the highest mountainous
areas of the Beskydy Mts). As the result of channel transformations,
progressive changes in fluvial ecosystem were observed. The initial
phytosociological survey demonstrates a higher biodiversity in the
floodplain along the preserved multi-thread river channel than along the
deeply incised channel in the Morávka River basin. Our observations of
aquatic communities demonstrated that the channel transformation
connected with incision and coarsening of bed sediments negatively
affected fish or lamprey populations in the studied rivers. Regulation,
damming and incision of channels caused changes of hydrological regime
linked with gradual drying of floodplain. Additionally, a large set of
hydraulic structures, bridges or weirs were affected by undercutting and
progressive destruction in the Ostravice, Olše and Morávka River basins,
which is assigned to increased transport capacity of regulated channels
together with decreased sediment supply from mountainous parts.
1. Introduction
Gravel-bed rivers are defined as channel reaches with coarse sediment material on bed and
banks and typically with large discharge variation, which affects sediment material
movement in river network [1, 2]. Their occurrence is characteristic for montane and
upland valley and mountain foreland area [3]. During the 20th century, the most serious
problems of gravel-bed rivers transformation were widely studied around the globe [4, 5,
*
Corresponding author: vaclav.skarpich@osu.cz
© The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative Commons
Attribution License 4.0 (http://creativecommons.org/licenses/by/4.0/).
E3S Web of Conferences 40, 02005 (2018) https://doi.org/10.1051/e3sconf/20184002005
River Flow 2018

6]. The researches focused on the identification of channel pattern changes, which were
accompanied by progressive channel narrowing, river bed incision or bed sediment
coarsening [4, 5, 6]. The main reasons for these changes were related to the sediment
movement and impediments (buffers, barriers and blankets) to sediment movement in the
fluvial system by so-called disconnectivities [7].
A similar pattern of channel changes was also recorded in the rivers draining the Czech
part of flysch Carpathians [8, 9, 10, 11]. This paper presents channel transformations in a
wider context of ecosystem changes and water resources structures. A number of
detrimental feedback effects of transformation of the Czech Carpathian rivers have been
identified, e.g. decreasing biodiversity, destruction of fish and lamprey habitat, landscape
drying or destruction of man-made constructions (as weirs or bridges).
2. Channel transformations and their effect on riverine
ecosystems in the Czech Carpathian rivers
Transformations of rivers draining the Czech part of Carpathian were studied in the
Ostravice, Morávka [8, 9, 10] and Olše [11] River basins. The contemporary state of rivers
in the Czech Carpathians has been particularly affected by human impact starting at the
beginning of the 16th century during the so-called Wallachian colonisation of the
mountainous area. Extensive deforestation to clear pastureland and supply the demand for
wood disrupted the original state of channels. The deforestation and probably effect of
Little Ice Age intensified sediment supply to the river network and subsequently
development of multi-thread channel reaches, which had been developing from the end of
the Last Glacial period [9]. The change in basin management related to the change in
human lifestyles from the beginning of the 20th century brought new afforestation and thus
an initiation of deficit in sediment supply for multi-thread reaches. Industrial development
related to increased demands for large amounts of water (construction of valley dams,
weirs), which caused the acceleration of the above-mentioned processes and the blockage
of sediment transport. In result, channels were transformed from originally multi-thread
river pattern with intensive sediment transport to single-thread river pattern often incised
into the bedrock [8, 9, 10, 11].
Effect of channel transformation on riverine plant ecosystems was studied in the
Morávka River basin [12]. The research was conducted with phytosociological survey of
plant species composition from phytosociological relevés in the transversal profiles in the
floodplain. They were conducted in the floodplain with (i) the single-thread bedrock-
incised channel and (ii) the preserved multi-thread channel. The Shannon-Wiener [13] and
Simpson's [14] indices of biodiversity for the analysis of species distribution was evaluated.
In the context of the importance of vegetation response to channel-floodplain conditions,
the following environmental variables were selected as response variables for the analysis:
phytosociological relevé distance from the main channel with flowing water, and relative
elevation of a phytosociological relevé from the water level in the channel. The channel
effect on the riparian vegetation conditions was evaluated by using multivariate data
analysis of detrended correspondence analysis (DCA) and redundancy analysis (RDA).
The results showed that different plant habitat conditions occur in the incised channel
reach and in the multi-thread channel reach [12]. The analysis of the Shannon-Wiener and
Simpson's indices demonstrated a larger variety of habitat conditions in the floodplain area
along the multi-thread river channel (see fig. 1). Multivariate analysis confirmed that
incision processes of channel cause a more rapid change in the plant community
composition with increasing distance from the main channel. This suggests that
groundwater conditions could be affected by the river incision through the gradual relative
sinking of water level in the river channel – relative to the floodplain level [12].
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E3S Web of Conferences 40, 02005 (2018) https://doi.org/10.1051/e3sconf/20184002005
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6]. The researches focused on the identification of channel pattern changes, which were
accompanied by progressive channel narrowing, river bed incision or bed sediment
coarsening [4, 5, 6]. The main reasons for these changes were related to the sediment
movement and impediments (buffers, barriers and blankets) to sediment movement in the
fluvial system by so-called disconnectivities [7].
A similar pattern of channel changes was also recorded in the rivers draining the Czech
part of flysch Carpathians [8, 9, 10, 11]. This paper presents channel transformations in a
wider context of ecosystem changes and water resources structures. A number of
detrimental feedback effects of transformation of the Czech Carpathian rivers have been
identified, e.g. decreasing biodiversity, destruction of fish and lamprey habitat, landscape
drying or destruction of man-made constructions (as weirs or bridges).
2. Channel transformations and their effect on riverine
ecosystems in the Czech Carpathian rivers
Transformations of rivers draining the Czech part of Carpathian were studied in the
Ostravice, Morávka [8, 9, 10] and Olše [11] River basins. The contemporary state of rivers
in the Czech Carpathians has been particularly affected by human impact starting at the
beginning of the 16th century during the so-called Wallachian colonisation of the
mountainous area. Extensive deforestation to clear pastureland and supply the demand for
wood disrupted the original state of channels. The deforestation and probably effect of
Little Ice Age intensified sediment supply to the river network and subsequently
development of multi-thread channel reaches, which had been developing from the end of
the Last Glacial period [9]. The change in basin management related to the change in
human lifestyles from the beginning of the 20th century brought new afforestation and thus
an initiation of deficit in sediment supply for multi-thread reaches. Industrial development
related to increased demands for large amounts of water (construction of valley dams,
weirs), which caused the acceleration of the above-mentioned processes and the blockage
of sediment transport. In result, channels were transformed from originally multi-thread
river pattern with intensive sediment transport to single-thread river pattern often incised
into the bedrock [8, 9, 10, 11].
Effect of channel transformation on riverine plant ecosystems was studied in the
Morávka River basin [12]. The research was conducted with phytosociological survey of
plant species composition from phytosociological relevés in the transversal profiles in the
floodplain. They were conducted in the floodplain with (i) the single-thread bedrock-
incised channel and (ii) the preserved multi-thread channel. The Shannon-Wiener [13] and
Simpson's [14] indices of biodiversity for the analysis of species distribution was evaluated.
In the context of the importance of vegetation response to channel-floodplain conditions,
the following environmental variables were selected as response variables for the analysis:
phytosociological relevé distance from the main channel with flowing water, and relative
elevation of a phytosociological relevé from the water level in the channel. The channel
effect on the riparian vegetation conditions was evaluated by using multivariate data
analysis of detrended correspondence analysis (DCA) and redundancy analysis (RDA).
The results showed that different plant habitat conditions occur in the incised channel
reach and in the multi-thread channel reach [12]. The analysis of the Shannon-Wiener and
Simpson's indices demonstrated a larger variety of habitat conditions in the floodplain area
along the multi-thread river channel (see fig. 1). Multivariate analysis confirmed that
incision processes of channel cause a more rapid change in the plant community
composition with increasing distance from the main channel. This suggests that
groundwater conditions could be affected by the river incision through the gradual relative
sinking of water level in the river channel – relative to the floodplain level [12].
Fig. 1. A – Shannon-Wiener index and B – Simpson's index of phytosociological relevés in the study
area of the Morávka River floodplain (reprinted from [12]).
In the last several decades, the flysch Czech Carpathian rivers showed changes of
hydrological conditions. Originally, they were characterised by high discharge variation,
e.g. for the Ostravice River it was approximately 1:2,000 between minimal and maximal
discharges and for the Morávka River 1:4,000 [15]. Constructions of the Šance (built on the
Ostravice River in years 1964-1969), the Morávka (built on the Morávka River in years
1961-1967) valley dams and partially the Morávka-Žermanice Canal (in the Morávka River
basin) which diverts the water flow into the neighbouring Lučina River basin, caused the
decrease in the frequency and magnitude of flood discharges (see fig. 2B). Similarly, the
analysis of groundwater detected hydrological conditions changes of the floodplain which
is gradually drying out in the Morávka River basin (see fig. 2A) [12].
Fig. 2. A – Maximum annual groundwater levels in the years 1963–2008 at the VO 0096 – Nižní
Lhoty drill well gauging station, cross symbols (+) = maximum annual groundwater levels, solid line
= five point running mean, dashed line = linear trend; B – Cumulative distribution of annual
maximum discharge of the Morávka River at the Raškovice gauging station; cross symbols (+) =
cumulative distribution of annual maximum discharge (reprinted from [9, 12]; data source: Czech
Hydrometeorological Institute).
3. Fish and lamprey communities affected by channel
transformation and related hungry water effect
The channel transformations of the gravel-bed rivers within Czech part of Carpathians
resulted in changes of flow hydraulics and it brought a new set of boundary conditions for
erosion, transport and deposition processes [10, 11]. Generally, increased flow velocity in
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transformed channels and hungry water effect related with coarsening of bed sediments of
the studied rivers affected habitat for fish communities [16].
For example, Brook lamprey (Lampetra planeri), European bullhead (Cottus gobio) and
Alpine bullhead (Cottus poecilopus) belong to protected species and they are listed in the
Red List of threatened species of vertebrates of the Czech Republic [17]. Brown trout
(Salmo trutta) represents a typical fish for Czech freshwaters and it is from the fishing
industry focus economically important fish. The young larvae of Brook lampreys require
river reaches with slow running flow and clay-sand bed substrate (with depth about 30 cm)
[18]. In contrast, adult Brook lampreys (like as Brown trouts) spawn in shallow fast running
flow gravel close to the soft sediment bed reaches. The sand-bed substrate depth about 25
cm armoured gravels (with mean diameter of particle sizes from 5 to 20 cm) and flow
velocity to 0.3 m/s is typical for bullheads [19]. In fact, complexity of habitats [20],
variability of flow velocity of channel reaches [21] and sufficient refugium availability [22]
is necessary for natural development of these fish lamprey species.
Based on the preliminary results of research, habitats of above mentioned fish and
lamprey communities were highly degraded in some channel reaches of the Morávka River
(see fig. 3). The main reasons for degradation of habitats were incision and narrowing of
river reaches, absence of appropriate finer (clay and sand) bed deposits which are
armouring gravel particles on bed and increased flow velocity in channels. Their number
decreased in these reaches. In contrast, numerously- and age-balanced populations of
lamprey and fish species were observed in river reaches with multi-thread channel pattern
with gravel bed armoured by fine sediments and low flow velocities.
Fig. 3. A - Gravels and armouring fine sediments on the channel bed of the Ostravice River; B –
Channel bed of into the bedrock incised reach of the Morávka River (Photo: M. Kubín).
4. Man-made river structures affected by erosion processes of
Czech Carpathian rivers
Negative effects of the transformation of gravel-bed rivers on human society (hydraulic
structures) in Czech flysch Carpathians were visible in number of localities. Especially weir
structures were affected by gradual incision and undercutting. In the Morávka River basin,
the Vyšní Lhoty weir (at 11.38 r. km) built between 1953 and 1964 was gradually affected
by undercutting and headward erosion. The Vyšní Lhoty weir has important function for
society, when it improves water inflow into the adjacent Lučina River basin and Žermanice
water reservoir and helps to decrease flood discharges downstream. The Žermanice water
reservoir has important storage and water supply function for local industry. Firstly, a
protective drop was made under the weir in 1969, followed by a rock chute construction in
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E3S Web of Conferences 40, 02005 (2018) https://doi.org/10.1051/e3sconf/20184002005
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transformed channels and hungry water effect related with coarsening of bed sediments of
the studied rivers affected habitat for fish communities [16].
For example, Brook lamprey (Lampetra planeri), European bullhead (Cottus gobio) and
Alpine bullhead (Cottus poecilopus) belong to protected species and they are listed in the
Red List of threatened species of vertebrates of the Czech Republic [17]. Brown trout
(Salmo trutta) represents a typical fish for Czech freshwaters and it is from the fishing
industry focus economically important fish. The young larvae of Brook lampreys require
river reaches with slow running flow and clay-sand bed substrate (with depth about 30 cm)
[18]. In contrast, adult Brook lampreys (like as Brown trouts) spawn in shallow fast running
flow gravel close to the soft sediment bed reaches. The sand-bed substrate depth about 25
cm armoured gravels (with mean diameter of particle sizes from 5 to 20 cm) and flow
velocity to 0.3 m/s is typical for bullheads [19]. In fact, complexity of habitats [20],
variability of flow velocity of channel reaches [21] and sufficient refugium availability [22]
is necessary for natural development of these fish lamprey species.
Based on the preliminary results of research, habitats of above mentioned fish and
lamprey communities were highly degraded in some channel reaches of the Morávka River
(see fig. 3). The main reasons for degradation of habitats were incision and narrowing of
river reaches, absence of appropriate finer (clay and sand) bed deposits which are
armouring gravel particles on bed and increased flow velocity in channels. Their number
decreased in these reaches. In contrast, numerously- and age-balanced populations of
lamprey and fish species were observed in river reaches with multi-thread channel pattern
with gravel bed armoured by fine sediments and low flow velocities.
Fig. 3. A - Gravels and armouring fine sediments on the channel bed of the Ostravice River; B –
Channel bed of into the bedrock incised reach of the Morávka River (Photo: M. Kubín).
4. Man-made river structures affected by erosion processes of
Czech Carpathian rivers
Negative effects of the transformation of gravel-bed rivers on human society (hydraulic
structures) in Czech flysch Carpathians were visible in number of localities. Especially weir
structures were affected by gradual incision and undercutting. In the Morávka River basin,
the Vyšní Lhoty weir (at 11.38 r. km) built between 1953 and 1964 was gradually affected
by undercutting and headward erosion. The Vyšní Lhoty weir has important function for
society, when it improves water inflow into the adjacent Lučina River basin and Žermanice
water reservoir and helps to decrease flood discharges downstream. The Žermanice water
reservoir has important storage and water supply function for local industry. Firstly, a
protective drop was made under the weir in 1969, followed by a rock chute construction in
1972 to prevent incision and undercutting [15]. In the year 2005, antierosion measures of
local channel widening have been implemented below the Vyšní Lhoty weir, but
problematic management connected with absence of bed sediment for support of close-to-
natural processes of gravel-bed Morávka River caused total destruction of this antierosive
measures. As the consequence, gradual incision of river reach 1-km long below this
measure took place during the flood in year 2010 [23]. Similarly, the Frýdek weir (at 1.25 r.
km) and the Konečný weir (2.31 r. km) built in the lower river reach of the Morávka River
were destroyed by floods from the reasons of headward erosion and undercutting (the first
one was destroyed in 1949, the latter in the mid-1970s). Also, their destruction negatively
affected originally multi-thread river channel pattern, which has been transformed into the
single-thread channel incised 9 m below the original bed level since the 1970s [9].
Problematics of channel incision and its effect on man-made structures is not only a domain
of weir structures. A large number of bridge constructions at crossing of the river channels
in the Czech flysch Carpathians were destroyed or damaged by undercutting. For example,
some bridges in the Ostravice River basin were repetively repaired several times (see fig 4).
Similarly, bank stabilisation structures, as typical technical approach for river regulation,
are very often damaged by lateral erosion processes.
Fig. 4. A residue of wooden bridge crossing the Ostravice River in Baška near Frýdek-Místek during
the floods in 1960 (Source: Povodí Odry State Enterprise Archives); B – Bridge affected by incision
of the Ostravice River channel in Baška near Frýdek-Místek (Photo: V. Škarpich).
5. Conclusions
Intensive research was realized to detect how the channel transformation of Czech
Carpathian rivers affects fluvial ecosystems and human society [8, 9, 10, 11, 12, 16, 23].
The ecosystem services produced by riverine landscape were significantly degraded. The
decline in river habitat and reduction in functional floodplain resulted in significant
reductions of associated biodiversity, which include impacts on spatiotemporal
heterogeneity, functional processes and species. Also, the transformations of channels
increased financial requirements for water treatment, repair of hydraulic structures (weirs,
dams) or bridges affected by incision of river channel and undercutting. Future river
restoration of Czech Carpathian rivers is necessary to improve the current state. Various
legislative measures to stopping of further river systems degradation were established but
the one of the biggest problem is the potential for river restoration. It is limited by
constraints such as need for flood protection of urban areas, need of water for human
society, density of urbanisation, etc.
Acknowledgement
The study was supported by The Technology Agency of the Czech Republic TAČR: TH02030509
(2017-2019): Risks identification and possibility of support of landscape natural functions in
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landscape protected areas influenced by climate change. Thanks are extended to Aneta Krótka, Radek
Dušek, Tomáš Gwóźdź, Zdeněk Kašpárek, Matěj Horáček, Veronika Kapustová, Vladimír Šala for
their help with fieldwork and data collection.
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