Effect of lithology and morphology of high-gradient channels on bed sediments: a case study of the Kobylská Stream (Vsetín highlands, Czech Republic)

High-gradient streams are integral parts of the fluvial systems, which connect the mountainous landscapes with lowland rivers in the sense of water and sediment transport. We analysed downstream grain-size characteristics of bed sediments and sphericity of grains with respect to the local flysch lithology and channel geometry in the 5.4 km long reach of the high-gradient Kobylská Stream (the Vsetín highlands, Outer Western Carpathians, Czech Republic). Results showed a high variability of bed-sediment sizes in the longitudinal course of the Kobylská stream. This condition is given by the occurrence of anthropogenic impact in the studied channel (local bank stabilisations, grade-control structures) and lateral sediment input from the adjacent landslides and bank failures. The lithology of the flysch nappe structure of the basin significantly influenced variations of bed sediment grain-sizes. Different bedrock resistance resulted into inverse correlation between the local river gradient and related bed grain-sizes. Especially the mudstone bedrock layers had significant impact on the fining of bed sediment in the upper steep part of the basin (D50 ≤ 40 mm) and by contrast, sandstone bedrock caused the coarsening of the bed sediment in the middle and lower parts (D50 up to 50 mm) characterised by lower bed gradients.High-gradient streams are integral parts of the fluvial systems, which connect the mountainous landscapes with lowland rivers in the sense of water and sediment transport. We analysed downstream grain-size characteristics of bed sediments and sphericity of grains with respect to the local flysch lithology and channel geometry in the 5.4 km long reach of the high-gradient Kobylská Stream (the Vsetín highlands, Outer Western Carpathians, Czech Republic). Results showed a high variability of bed-sediment sizes in the longitudinal course of the Kobylská stream. This condition is given by the occurrence of anthropogenic impact in the studied channel (local bank stabilisations, grade-control structures) and lateral sediment input from the adjacent landslides and bank failures. The lithology of the flysch nappe structure of the basin significantly influenced variations of bed sediment grain-sizes. Different bedrock resistance resulted into inverse correlation between the local river gradient and related bed grain-sizes. Especially the mudstone bedrock layers had significant impact on the fining of bed sediment in the upper steep part of the basin (D50 ≤ 40 mm) and by contrast, sandstone bedrock caused the coarsening of the bed sediment in the middle and lower parts (D50 up to 50 mm) characterised by lower bed gradients

Conditions of sediment transport and accumulation in man-affected Beskydian rivers: case study of the Morávka and Mohelnice rivers confluence

This paper summarizes results of grain-size distribution of gravel bars and transport conditions in the context of sediment sources in the confl uence area of the Morávka and Mohelnice rivers (Moravskoslezské Beskydy Mts). We deal with a hypothesis that general changes of grain-size distribution of gravel bars are controlled by disconnection in sediment flux in the Morávka River and, by contrast, that higher sediment delivery is related to the Mohelnice river basin. The second focus is the evaluation of fluvial transport parameters of a channel influenced by control works and sediment mining. Bed load transport research was conducted with the application of BAGS (Bedload Assessment for Gravel-bed Streams) spreadsheet-based program. Sediment analysis of the channel confluence showed limited sediment supply character indicated by coarser sediment delivery from the Morávka River. This fact is related to the effect of hungry water caused mainly by the Morávka Reservoir. On the other hand, the Mohelnice River displayed trends of relatively higher sediment delivery without potential disconnectivities in sediment flux. Results of this analysis brought an insight into a potential scheme of the future development of the studied reaches. We suppose preservation of recent trends in case of the occurrence of signifi cant changes in land use or watershed management.This paper summarizes results of grain-size distribution of gravel bars and transport conditions in the context of sediment sources in the confl uence area of the Morávka and Mohelnice rivers (Moravskoslezské Beskydy Mts). We deal with a hypothesis that general changes of grain-size distribution of gravel bars are controlled by disconnection in sediment flux in the Morávka River and, by contrast, that higher sediment delivery is related to the Mohelnice river basin. The second focus is the evaluation of fluvial transport parameters of a channel influenced by control works and sediment mining. Bed load transport research was conducted with the application of BAGS (Bedload Assessment for Gravel-bed Streams) spreadsheet-based program. Sediment analysis of the channel confluence showed limited sediment supply character indicated by coarser sediment delivery from the Morávka River. This fact is related to the effect of hungry water caused mainly by the Morávka Reservoir. On the other hand, the Mohelnice River displayed trends of relatively higher sediment delivery without potential disconnectivities in sediment flux. Results of this analysis brought an insight into a potential scheme of the future development of the studied reaches. We suppose preservation of recent trends in case of the occurrence of signifi cant changes in land use or watershed management

Bed sediments and geomorphological processes in high-gradient streams based in flysch of the Moravskoslezské Beskydy Mts.

Lithology of bed sediments in high-gradient streams may aff ect grain-size parameters and, thus, bed morphology and sediment transport dynamics. Flysch character of bedrock with alternation of resistant sandstones and less-resistant claystones influenced geomorphic processes and bed sediments in Beskydian headwater channels. Generally, claystone members supplied streams by higher amounts of relatively fi ner clastic material. On the contrary, channels located in sandstone members (e.g., Godula Member) were prone to occurrence of exposed bedrock due to signifi cantly lower sediment supply, except channel-reaches with evidence of debris-fl ow activity. Obtained trends of evaluated grain-size parameters (D90 and nominal index) in the stream longitudinal profi les pointed up on infl uence of claystone ratio in bed sediments and a character of sediment inputs. Signifi cant presence of claystones in bed sediments of selected streams led to decrease in D90 percentile and nominal index Dn of bed surface material. On the other hand, sandstone sediment supply in high-gradient streams underlaid by the middle part of the Godula Member did not show downstream coarsening or fi ning of bed sediments within stream longitudinal profi les and higher values of grain-size parameters were observed. Lithology of bed sediments in high-gradient streams may affect grain-size parameters and, thus, bed morphology and sediment transport dynamics. Flysch character of bedrock with alternation of resistant sandstones and less-resistant claystones influenced geomorphic processes and bed sediments in Beskydian headwater channels. Generally, claystone members supplied streams by higher amounts of relatively finer clastic material. On the contrary, channels located in sandstone members (e.g., Godula Member) were prone to occurrence of exposed bedrock due to significantly lower sediment supply, except channel-reaches with evidence of debris-flow activity. Obtained trends of evaluated grain-size parameters (D90 and nominal index) in the stream longitudinal profi les pointed up on influence of claystone ratio in bed sediments and a character of sediment inputs. Significant presence of claystones in bed sediments of selected streams led to decrease in D90 percentile and nominal index Dn of bed surface material. On the other hand, sandstone sediment supply in high-gradient streams underlaid by the middle part of the Godula Member did not show downstream coarsening or fining of bed sediments within stream longitudinal profiles and higher values of grain-size parameters were observed

Stream-bed sediments as indicators of sediment sources in flysh areas

The character of bed sediments reflects fluvial processes and the dynamics of material transport in fluvial (dis)continuum systems. The approach in this study was based on the measurement of the five largest boulders located within a channel, and on the observation of changes in their size in the longitudinal profi le of headwater streams Kobylská and Pulčínský potok. All three axes (dimensions) of the five largest boulders were measured at 10 ± 1m intervals of the longitudinal profile. The resulting trends in a particle-size index reflect the character of sediment delivery into the channel segment. The largest boulders were observed in channel sections with a strong interaction of slope processes. But local lithological conditions affect changes of the mean value of the particle-size index of the largest boulders. The role of slope processes can be accentuated by the presence of uniform sandstone lithology of the studied bed particles. In the lithology built by claystone layers the role of slope processes has problematic identification. The main reason is erodible character of claystone layers which affects sediment supply of finer particles from adjacent slopes into the channel segment.The character of bed sediments reflects fluvial processes and the dynamics of material transport in fluvial (dis)continuum systems. The approach in this study was based on the measurement of the five largest boulders located within a channel, and on the observation of changes in their size in the longitudinal profi le of headwater streams Kobylská and Pulčínský potok. All three axes (dimensions) of the five largest boulders were measured at 10 ± 1m intervals of the longitudinal profile. The resulting trends in a particle-size index reflect the character of sediment delivery into the channel segment. The largest boulders were observed in channel sections with a strong interaction of slope processes. But local lithological conditions affect changes of the mean value of the particle-size index of the largest boulders. The role of slope processes can be accentuated by the presence of uniform sandstone lithology of the studied bed particles. In the lithology built by claystone layers the role of slope processes has problematic identification. The main reason is erodible character of claystone layers which affects sediment supply of finer particles from adjacent slopes into the channel segment

IDENTIFIKACE (DIS)KONEKTIVIT VODNÍCH TOKŮ ZA VYUŽITÍ MAKROGRANULOMETRICKÉ ANALÝZY KORYTOVÝCH SEDIMENTŮ (MORAVSKOSLEZSKÉ BESKYDY)

This paper brings evidence on sediment distribution trends in longitudinal profiles of Beskydian high gradient streams. High gradient streams play an important role in the context of fluvial (dis)continuum as they represent a source of sediment for downstream parts of catchments. The main instrument in the identification of river basin (dis)connectivity was grain-size analysis and fluvialgeomorphological mapping. In addition, bedload material transport force was computed for sections in the vicinity of gauging station. The research comprised the study areas of the Býčinec Basin, the Velký Lipový Basin and the Malá Ráztoka Basin

Peat bog and alluvial deposits reveal land degradation during 16th and 17th century colonisation of the western Carpathians (Czech Republic)

Wallachian (shepherd) colonisation of the upper parts of Carpathians, the second largest mountain range in Europe, provides a unique opportunity to study human-induced ecological changes and subsequent sediment mobilisation within slope and fluvial systems. The Wallachians came to the nearly pristine landscape in the Czech part of the Western Carpathians during the 16–17th Century bringing large scale deforestation and grazing to the upper parts of its ridges. Despite the importance of this event, there is a lack of high-resolution multi-proxy reconstructions to help to decipher the relative influence of anthropogenic and climate factors on this landscape. Here we provide a ca. 2.1 kyr record obtained from a peat bog where, using chronological, sedimentological and pollen analyses, we were able to differentiate between environmental conditions before, during and after colonisation. Prior to colonisation, climate deterioration following the onset of Little Ice Age caused changes in forest composition and erosion events (causing a ~AD 0–1500 gap in the record). Abrupt human-induced deforestation detected in the pollen record, together with the abundant fine-grained minerogenic content of peat deposits between AD ~1640 and AD 1870, correspond to increased runoff and sheet erosion on slopes; enhanced by Little Ice Age climate deterioration. The sedimentary record in alluvial deposits downstream indicates that the colonisation of the mountain slopes in this region not only had a local effect on soil degradation, but it also increased the net aggradation of overbank deposits within valley floors. After reforestation, net aggradation was replaced by river incision into alluvia

Bankfull widths in steep headwaters of the flysch Carpathians

Bankfull widths of steep headwater channels were examined in the Western Carpathian flysch midmountains. The criteria of the top of banks, scoured lines and pre­sence of bank vegetation were helpful in the bankfull width determination. A direct down -stream relationship between the parameters of the bankfull width and the watershed area and a negative downstream relationship between the parameters of the bankfull width and the channel gradient were observed in all examined channels similarly to lower gradient rivers. However, streams based in more resistant sandstone flysch and/or influenced by small debris­flows indicated much less dependence between these parameters. Significant differences in bankfull widths were found when channels of the same watershed areas, but located on leeward and windward hillslopes were compared

Morfologická odezva bystřinných koryt na dlouhodobé zásahy člověka v horských povodích na příkladu Moravskoslezských Beskyd (Česko)

The paper summarizes the history of human interactions with mountain streams on the example of the flysch Western Carpathians, Czechia. These are represented by indirect impacts since the 16th century, mainly corresponding to extensive changes in land use and species composition of forests, and by direct human interventions as timber floating with the removal of instream wood (since the end of the 18th and beginning of the 19th century) and check-dam constructions (since 1906). Mountain streams are very sensitive to changes in sediment supply, hydrological regime or direct interventions and produce a fast morphological response. Thus, hydromorphological assessments and management of mountain streams should take into consideration the contemporary land use at the basin scale in historical perspective, sediment connectivity and the occurrence of instream wood as important elements of stream habitat.21323