The formation of an armouring layer can be observed on the base of morphological changs by direct measurements of granulometry (grain diameter generally grows after flood) or by computer simulation of changes of the grain sieve curve. This procedure is based on the Gessler’s analysis of the probability of grain movement, on the basis of the shear stress of the acting water. The critical shear stress is calculated using the Wang function developed for Carpathian streams. The armouring layer is formed by that part of non-cohesive bed material, which is not washed away during the flow. The increase in critical shear stress is due to the increase of the mean diameter dm as small fractions are washed out from the bed. The thickness of the armouring layer is approximately equal to the size of the largest stones of the layer. This process in rivers with natural flow is different from this one below reservoirs; in the former case it takes place at a significant distance below dams. In this case, the armouring layer formation causes bed scouring, linked with a change in the water slope and depth. This scouring may be assumed to be a stochastic process. According to Gessler, ...
Using rivers and mountain streams for economic purposes led to the loss of ecological balance and to the intensification of morphological processes, which in most cases caused erosion as well as the lowering of riverbed. Such changes have made stabilising the river bed and its banks necessary. In our work, on the basis of the analysis of project documentation and the simulations of flood events on several mountain streams, we made an attempt to answer the question: are the river training works enough to let the catastrophic floods pass safely and do they take into account the morphological processes which have a formative influence on the riverbeds? It has been proved that as far as hydraulic structures are concerned, the adjustments that are being planned comply with the requirement of ensuring the required capacity of the river channel. Maintaining the required capacity of the river channel creates the need for constant remedial works. When dimensioning cross-sections with stable bottoms, the width of the river valley is a serious limitation which, in urban environment, does not allow the engineers to design a crosssection of a river channel whose shape would be most efficient one. In case of river channels with moveable ...
The article presents an assessment of the variability of riverbed sediment throughout the Przemsza river course and its main tributaries in relation with the observed disturbances of grain size changes caused by hydro-engineering activity in the channel. Sediment grain size composition in the river channel depends on the hydrodynamic balance and the water flow. In the stable river channel sediment grain size decreases regularly with the river course from the source to the mouth. In the channel where there are sections of anthropogenically modifications, the variation of sediment grain size composition may be irregular in the river course. The article presents the results of measurements and calculations which were made in the following gauging stations: Łysa Góra, Będzin, Sosnowiec, Jęzor, Chełmek non Przemsza river, in Golczowice, Okradzionów, Sławków, Maczki, Niwka on Biała Przemsza river and in Brynica, Kozłowa Góra (above the back of the reservoir Kozłowa Góra and downstream the dam), Szambelnia on Brynica river. The results of studies showes that variability of characteristic diameter of d10 is minimal, while the diameters of d50 and d90 is characterized by significant differences in all the tested gauging stations of Przemsza river and its tributaries. In Brynica river where ...
The analysis of variability of riverbed elevation recorded at three selected gauging cross-sections: Raków, Staszów and Połaniec on Czarna River is presented in the current paper. The studies concern the period of more than fifty year. Focus was on the analysis of the riverbed changes in relation with known anthropogenic activities in the bed of the river. In addition, an analysis of grine size distribution of sediment forming the river channel was examined. The studie was done in order to identify the structure of riverbed, as well as the intensity of sediment movement throughout the ricer course. Czarna river is a left tributary of the Vistula river, at a considerable length, is transformed as a result of technical river channel regultion. At 36+000 km of the river course, Chańcza dam was set. The mouth of Czarna river is located close to the Town of Połaniec. The river channel aspire to shape a new longitudinal profile of hydrodynamic balance in new conditions of fluvial system, by changing its shape in the vertical and horizontal direction. As indicated by river channel observations, changes are very fast after a disturbance, after which they are weakening, and the riverbed reaches again hydrodynamic equilibrium (eg. ...
The analysis of variability of riverbed elevation recorded at three selected gauging cross-sections: Stróża on Raba River and Żywiec and Oświęcin on Soła River is presented in the current paper. The studies concern the period of more than one hundred year. Focus was on the analysis of the river course maintenance in selected gauging stations. Research shows that the river course may change spacially and temporally with varying inensity. In the period of 50 - 100 years, these changes can be slight, but it can be also observed permanent change in the direction of the river channel development. The paper presents the trends of riverbed changes during the long period of time in selected mountain tributaries of the upper Vistula River, which were studied on the basis on the variability of observed mean annual water stages. In the paper there are given the reasons for the observed changes in the river course and channel geometry, which were caused by river regulation relayed on the shortening and narrowing of the river channel or the sediment exploitation. Presented in the article method of assessment of the variability of the river channels level in the long period of time may be the ...
The analysis of variability of riverbed elevation recorded at five selected gauging cross-sections of Nida River, and at three gauging stations of Czarna Nida is presented in the paper. The studies concern the period of 60 - 80 years of observation. The trends of riverbed changes during the study period at the selected gauging stations were calculated based on the variability of observed minimal annual water stages. The reasons for the observed changes in the river course and channel geometry are given. These changes were caused by river regulation consisted of the shortening and narrowing of the river channel. Moreover, grain size distribution analysis in the selected gauging stations of Nida River and characteristic diameter variability of sediments along the river course examination are presented. These analyses were to evaluate the variability of characteristic diameters along the river course in connection with observed changes in cross-sections' geometry. Additionally, to confirm the process of erosion or deposition recognized in the examined river channels, hydrodynamic equilibrium was determined. Three methods were proposed and used: the mean velocity and critical velocity in the main river channel comparison, the stream power value calculation which defines the character of the river channel, and the WWK ...
