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Aim of research The aim of this research was to analyse an influence of check dams on granulometry of bed sediments in their impact area. Necessary data was obtained during field measurements carried out in May 2017. Sediment was collected using the Wolman’s method. Data collected through this method were used to determine granulometric curves, granulometric parameters and shapes of grains forming riverbed sediment in the region of the studied objects. Material and methods Sediment measurements were carried out below and above the check dams through the Wolman’s method. Grain size curves were then plotted, granulometric and sedimentological parameters were calculated. In addition, grain size and shape were determined using the Sneed and Folk methods. Results and conclusions The number of discoid grain pebbles increased below the dam in relation to the level above the dam. In the material collected below the dam there was a smaller number of spindle-shaped grains than in the material collected above the dam. Above the dam there are larger amounts of finer material than below. This may be related to the retention of even small grains of pebbles in the dam reservoir, in which flow velocity is lower than in the riverbed, thus depositing of carried material. On the other hand, in the lower station, due to the increased water flow velocity, small debris is washed away, and in the bottom of the bed only thick fractions are found.
Aim of the study The paper presents an assessment of capacity of a drop hydraulic structure, which was partially destroyed, and provides a description of slow renaturalization of a riverbed in this area. As a result of damage to the hydrotechnical structure caused by natural processes, some elements detached from the structure were deposited in an energy dissipation basin and in the riverbed downstream of the structure, impeding rock and vegetal debris traffic. These fluvial processes formed a cascade-like structure that led to a change in the regime of water flow through the hydrotechnical structure that was not planned or designed originally. Material and methods Due to partial destruction of the structure, the water flow regime was so drastically altered that it is possible for various species of fish to cross this section of river without any additional constructions like fish passes. Field measurements determined six potential fish migration routes through the damaged structure’s area. Then each fish migration route was evaluated against the possibility for fish to pass through the structure. Results and conclusions The analysis showed that the partly damaged drop hydraulic structure creates favourable conditions for migration of some fish species. It can be concluded that the elements detached from the drop hydraulic structure and deposited downstream should not be removed from the riverbed, because they improve the environmental conditions for aquatic organisms in terms of their migration.
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