Wyniki wyszukiwania - Biblioteka Nauki

1

Usage of an empirical equation for determination of mean sediment diameter in beds of small mountain rivers

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Lenar-Matyas A. , Wolak A.

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tom nr IV/2

1513--1527

EN

Knowledge of properties of materials deposited in beds of small reservoirs is important, as it can be used for a range of analytic works, concerning river rehabilitation and river management and other similar undertakings. Usually the one property - the d50 value can be obtained using in-situ measurements using sieves but in most cases of preliminary, large scale research may not be feasible. In this paper the Osuch empirical formula for determination of standard sediment grain sizes of d50 is presented. Besides the original formula an improved method of assessing of the slope value for that formula is proposed, which may greatly improve the usefulness of the original, unmodified method. The calculation results are then compared with the in-situ measurements done on many samples taken from the Trzebuńka dam reservoir. The dam was recently partially removed and partially rebuilt, so there was an unique and easy access to wide strata of different layers of sediments, accumulated across many years of dam operation in the exposed bed of partially emptied reservoir. Additionally, the Ratomski formula for riverbed slope determination near dams was used as a reference. The mentioned methods taken together can be used for preliminary analysis before significant works are to be done. The results are quite encouraging and can be a starting point for further method refinement.

2

The studies on check dam restoration effectiveness

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Łopuszek M.

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2018

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tom nr IV/1

1071--1085

EN

A check dam is a hydraulic structure, which is constructed in order to limit river sediment transport. A sedimentation reservoir is created upstream from the body of the dam, where river sediment is constantly accumulated. These structures were constructed starting in the early 20th century in upstream parts of mountain streams in the Polish part of the Carpathian Mountains. At present, the reservoirs of most check dams are already fully filled with sediment and the impact of these structures on the ecosystems of streams is unfavorable. Moreover, the dams that have not been renovated are in poor technical condition. In the paper two cases of check dam lowering and restored is discussed and the one hypothetical case of gradual check dam lowering is presented and discussed as well. The cases of Krzczonówka and Trzebuńka, where the method of removing sediment from reservoirs was different, showed that the sudden change of „established” hydrodynamic conditions for decades is not favorable for the stream. The results of hypothetic simulation of gradual check dam lowering for the case of Isepnica Stream leads to the conclusion that lowering the construction of check dam and removing sediment from its reservoir in a way that does not have a drastic impact on the hydrodynamic balance of the stream channel is possible. However, as it was shown in the case of Isepnica Stream, it is very complicated task.

3

Analysis and Modeling the Streambed Evolution after the Check Dam Restoration: the Case of Krzczonówka Stream

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Łapuszek M.

Journal of Ecological Engineering

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2019

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tom Vol. 20, nr 1

188--196

EN

In the Upper Vistula Basin, series of check dams are located on almost each of mountain stream. These streams are strongly affected by the presence of dams that disrupt the sediment movement in the channel. Moreover, the check dams are in poor technical condition. The current study focuses on the Krzczonówka Stream, a left-bank tributary of the Raba River, where restoration works were undertaken in 2014 involving lowering of a check dam. The aim of the project was the continuity of the stream corridor for fish migration restoration. This paper aims to provide an analysis of the streambed evolution and a numerical analysis of the impact of check dam lowering and removal of sediment, previously accumulated upstream under the geomorphologic conditions in the studied stream after three years of project execution. A 1D sediment transport model was employed to estimate the areas of erosion and deposition throughout the river course. The calculations show that the thickness of the deposited sediment ranged from 0.20 up to 0.91 m at 1.5 km of the reach. The layer thickness deposited form 2.1 to 1.75 km of the reach, is rather thin; subsequently, the layer thickness increases and the highest values are reached at the area of 1.35 – 1.7 km. The local erosion is observed in 1.1 km of the reach. It is very important to note that the identified erosional and accumulation tendencies are the same at corresponding cross sections measured as calculated based on the model. This also provides a practical form of model validation. Additionally, the stream channel evolution on the base on low annual water stages in Krzczonów gauging station, located downstream the dam, indicates that the bottom has increased in this section by about 50 cm. The comparison of cross-sectional geometry in years of 2015–2016 (after flood event) shows that the stream channel moved in the transverse direction (bank erosion and deposition) and the streambed level has changed slightly. Currently, the stream channel does not seem to be in a state of hydrodynamic equilibrium. Thus, further field measurements will try to indicate when this balance is achieved.

4

Identify runoff generation patterns of check dams and terraces and the efects on runoff: a case study

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Chen Y. , Jian S. , Wu Q. , Hu C. , Soomro S.-e. h.

Acta Geophysica

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2022

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tom Vol. 70, no 2

819--832

EN

Over the past 50 years, China has implemented a series of ecological construction projects in the Loess Plateau that have significantly decreased the runoff and sediment from the Yellow River, and it plays an important role in check dams and terraced fields. In this study, the hydrological characteristics of check dams and terraces are used to distinguish their runoff generation pattern. Combined with different runoff generation patterns, runoff generation models were built, and quantitative analysis was conducted on the runoff reduction situation of check dams and terraced fields. Chenggou River Basin, in the Loess Plateau Zhuli River System's second tributary, was selected as an example for analyzing quantitatively the influence of check dam and terraced fields on the runoff production process. Twenty-nine rainfall-food events from 2013 to 2017 were used to evaluate the effect of the runoff generation model, and the results showed that the built model could well simulate the runoff generation in the basin with many check dams and terraces in which runoff relative error of the model was less than 10%. The effect of check dams and terraces on runoff was studied by setting different scenarios. The results show that the dam system can intercept over 50% of the runoff yield of the basin. Terraced fields can enhance the water storage capacity of the basin and reduce the runoff of the basin, and intercept over 10% of the runoff yield of the basin.