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This study examines the long-term impact of water management and navigation modifications on the hydromorphology of the lower Elbe River in Czechia. The research focuses on gravel-sand bars, which are remnants of the river's natural morphology. The analysis revealed a significant shift in the hydromorphological quality of the river, evaluated using a morphological quality index and historical data. The study analysed morphological and grain-size parameters of selected gravel-sand bars, as well as daily flow data. The results show a significant reduction in channel width and maximum average daily flows, leading to lower disturbance frequencies of the bars. The analysis suggests that close-to-natural processes affect the development of the bars but are influenced by artificial modifications. The findings indicate the need for restoration measures, which are discussed in this paper. [ABSTRACT FROM AUTHOR]

Riparian vegetation reflects the current conditions and the dynamics of streams. The floodplain vegetation along the watercourse of the Morávka River was subject to study in this project. In some reaches, the river has the natural character of an anabranching gravel-bed stream; in contrast, other Morávka R. reaches are incised into the bedrock. These cases were used to assess potential changes in vegetation conditions as evidence of negative processes taking place in the gravel-bed streams of the Beskydy Mts. The results demonstrate a higher biodiversity in the floodplain along the anabranching river channel. In contrast, the floodplain along the incised river channel shows low biodiversity values. Redundancy analysis was used to determine the relationships between plant species composition, distance from the main channel and relative elevation from the mean water level of the main channel. In addition, the results show a higher degree of change in plant species composition on the floodplain along the incised river channel. The analysis of floodplain groundwater fluctuations shows a decreasing trend in the annual maximum groundwater level.

The stepped-bed system, with a step-like longitudinal profile, is typical morphology in steep headwater streams. These systems are created by a series of coarse sediments or instream wood (steps with supercritical flows) interspaced with finer material (forming pools with subcritical flows). In the case of well-developed steps and pools, the resulting channel-reach morphology is referred to as “step-pool” morphology. In this study, we identify a previously undescribed type of step-pool formation, the “foliaged step-pool”, in the high-gradient Stoligy Stream of the Moravskoslezské Beskydy Mountains. The defining feature of this formation is the significant presence of leaves in the step structure. The geometry of the steps and pools was measured and the parameters that characterise the distribution, amount and function of leaves acting in these areas were defined. Statistical results showed differences between non-foliaged and foliaged step-pool formations, in which the latter showed a significant increase in storage level, influencing the channel’s hydrodynamics. Particle-size analyses demonstrated that foliaged step-pool formations had finer sediment in the pools, which indicates that there are differences in sediment transport processes between foliaged and non-foliaged formations. These results offer new insights into stepped-bed and step-pool morphology, providing directions for further research on small streams in deciduous forested regions.

Charakter dnových sedimentů v říčních systémech obvykle odráží probíhající fluviální procesy a dynamiku transportu sedimentů. Naše metodika byla založena na měření největších valounů a balvanů uvnitř aktivního koryta a sledování velikostních změn v rámci podélného profilu beskydského pramenného toku. Výsledné trendy indexu velikosti klastů reflektují charakter donášky sedimentů do korytových segmentů a současné korytotvorné procesy. Největší balvany byly pozorovány v korytových úsecích se silnou interakcí svahových a fluviálních procesů a mírné hrubnutí sedimentů bylo pozorováno v zahlubujících se úsecích dolní části studovaného podélného profilu toku. Naopak zjemňování dnových sedimentů bylo typické pro přechodnou zónu mezi korytovými úseky přimknutými ke svahům a úseky nacházejícími se na proluviálním kuželu, kde se spíše projevovala agradace materiálu.

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.

We present a comparative study of large wood (LW) mobility in two steep channels (0.06