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Abstract

The Tisza River is the largest tributary of the Danube in Central Europe, and has been subjected to various human interventions including cutoffs to increase the slope, construction of levees to restrict the floodplain, and construction of groynes and revetments to stabilize the channel. These interventions have altered the natural morphological evolution of the river. The aim of the study is to assess the impacts of these engineering works, employing hydrological surveys of 36 cross sections (VO) of the Lower Tisza River for the years of 1891, 1931, 1961, 1976 and 1999. The changes in mean depth and thalweg depth were studied in detail comparing three reaches of the studied section. In general, the thalweg incised during the studied period (1891-1931: 3 cm/y; 1931-1961: 1.3 cm/y and 1976-1999: 2.3 cm/y), except from 1961-1976 which was characterized by aggradation (2 cm/y). The mean depth increased, referring to an overall deepening of the river during the whole period (1891-1931: 1.4 cm/y; 1931-1961: 1.2 cm/y; 1961-1976: 0.6 cm/y and 1976-1999: 1.6 cm/y). The thalweg shifted more in the upper reach showing less stabile channel, while the middle and lower reaches had more stable thalweg. Although the cross-sections subjected to various human interventions experienced considerable incision in the short-term, the cross-sections free from direct human impact experienced the largest incision from 1891-1999, especially along the meandering sections.

Abstract

Bahr Youssef (B.Y) is a semi-natural branch canal connecting the River Nile with Fayoum depression, in the desert immediately to the west of the Nile Valley, about 92 kilometers southwest of Cairo, for irrigation purposes of El-Minya, El-Fayoum, Bani-Swif, and Giza governorates. The area served by Bahr Youssef reaches about 850.000 feds in the Middle Egypt, out of 1.650.000 feds served by the Ibrahimeya carrier canal, which branches from the River Nile's at Assiut barrage, and extends northward for 55 kilometers, until Dayrut city. In Dayrut; “Ibrahimeya” canal bifurcates into seven carrier canals, (Bahr Youssef is one of them,) through Dayrut Group of regulators. Bahr Youssef suffers from, meandering phenomenon, in many reaches, occurred with all its harmful and destructive effects. As meanders are the direct result of erosion-deposition processes occur in such flatty reaches with hydraulically unstable sections, our effort here is directed for studying the existing geometric, and hydraulic conditions of some representative reaches of Bahr Youssef, to evaluate the size of the problem through intensive field measurements, and to verify the available predicting techniques and theories by comparison with the obtained measured values. Introducing an acceptable, effective and easy method, which can be used for an accurate estimation of the meandering phenomenon, is the main objective of this study. This was achieved through reviewing and assessment of the available predicting techniques, and evaluating their liability, validity, and suitability through the comparison with the field collected measurements.

Abstract

Various direct human impacts changed the hydro-morphology of the Danube during the last centuries. The aims of the present study are (1) to analyze the water regime of the Danube River using the data of Mohács gauging station (1900-2013), and (2) to study the channel development (1952-2014) in connection with water regime changes and human impacts at a section near Bogyiszló (upstream of Mohács). According to the results the height of low water stages decreased by approx. 136 cm (1.2 cm/year), and new, high record flood stages were measured too. The discharge values appertaining to the same low water stages doubled, thus nowadays almost twice as much water flows through the cross-section of the channel at a given stage as at the beginning of the studied period. As the duration of low stages increased, the sandbar development intensified, thus the channel became narrower (by 48% at some places) and deeper thalweg evolved. Therefore, a smaller cross-section for flood-waves evolved, affecting the height of flood. These changes affect shipping, as due to riverbed incision and decrease of low water stages, the lowest shipping water level has to be set repeatedly at lower stages. Besides water extraction from the channel will have difficulties, thus irrigation and industrial cooling water supply will be limited in the future.

Abstract

In intramontane landscapes shaped by glacial-interglacial cycles, the most rapid changes during the proglacial/paraglacial phases may be amplified by catastrophic mass-wasting. Herein, we describe the Last Glacial Maximum (LGM) to Holocene development of a catchment in the Northern Calcareous Alps wherein intense proglacial/paraglacial sedimentation and descend of a rock avalanche persistently modified drainage and sediment dispersal.

During buildup of the LGM, the pre-last glacial Strassberg valley – the trunk valley of this study – was filled with a proglacial fluvio-lacustrine succession. Thereafter, the area became largely buried under the Inn ice stream. During deglacial ice melt, copious sediment was shed from glacially-conditioned mountain flanks. Alluvial fans cut off from their former supply area, and perched in isolated position, result from presumed sediment dispersal across dead ice. Shortly after deglaciation, a ~11 Mm3 rock avalanche detached from a high cliff, overran an opposing mountain ridge, and spread over a lower-positioned plateau. The rock avalanche blocked the Strassberg valley and set the base-level to an intramontane basin that persists until present. A quartz OSL age from a loess drape above the rock-avalanche deposit dates mass wasting prior to 18.77 ± 1.55 ka; so far, this is the oldest age-bracketed post-LGM catastrophic mass-wasting of the Eastern Alps.

After mass wasting, the valley was barred by the rock-avalanche deposit. This, in turn, triggered a westward switch of drainage thalweg and stream incision. The present Strassberg valley is an epigenetic bedrock gorge 1.5 km in length and down to 100 m in depth. A 234U/230Th calcite disequilibrium age of 9 ± 1 ka from cemented talus indicates that most incision took place during the late-glacial to early Holocene. Aside of the large-scale morphology (valleys, ranges) the drainage, the smaller-scale morphology, and the sediment volumes of the study area are mainly coined by proglacial/paraglacial processes and by rock avalanching. Holocene landscape changes are modest and chiefly comprise aggradation of high-positioned scree slopes, colluvial/alluvial redeposition and stream incision, and slope stabilization by reforestation. Our results underscore that intramontane sceneries are mosaics with respect to the age of landforms and that large parts of the landscape still are off geomorphic equilibrium with interglacial conditions.

characteristic as well as micromorphological characteristics of soil in the ecosystem “Kapitanivskiy unhomogeneous forest in the baulk” on the example of slope of the northern exposition and the thalweg of the unhomogeneous forest (in Ukrainian). Optimization and Protection of Ecosystems (pp. 181−191). Simferopol: TNU. Buza, A. K. & Divos F. (2016). Spruce tree fighting back – study of honey fungus infection. Folia Oecologica , 43, 204–207. Chornyy, S.G. & Volosheniuk A.V. (2016). Evaluation of wind erosion protective efficiency No-till technology in southern Ukraine steppe

the main watercourse of the island (the ‘Bauerngrundwasser’) was the thalweg of the River Rhine in AD 1828 ( Fig. 1c ). The excavation pit sampled for this study was located on a median bar of the Rhine braiding system at this date. During the correction works between AD 1828 and 1872, the River Rhine was forced artificially into an easterly direction. This caused a drastic decrease of flood energy and induced an important channel narrowing and disappearance of bars by vegetation overgrowth, as is shown on the maps of AD 1838, 1872 and 1949 ( Fig. 1c ). Prior to the

the main basin extending along the N–S axis, with variable bottom relief with numerous thalwegs and shallow areas, and a very shallow bay extending west from the main basin. Four larger rivers flow into the lake, the largest being Samica Kierska, flowing into the lake in its north-western part. The same river drains the lake, and flows out in its northern part. The shores of the lake are of very variable character – from steep scarps rising a dozen metres above the lake to flat marshy plains extending up to several hundred metres from its shoreline. To the north

( Figs. 5C – 5E ). This GR line is also relatively linear, and thus is a good marker for offset measurement. We obtained a range of displacements from this feature of 60– 70 m, given that the upper part of the GR line has an uncertainty of ~10 m ( Fig. 5E ). Reconstructions of the offset from the three-dimensional surface topography show a best-fit displacement of 65 m. Using this value, the thalweg and eastern margin (or western margin of Fan3) of a dry rill have been reconstructed ( Fig. 5A ). We consider 65 ± 5 m to be a reasonable estimation for the displacement

cross-section of the mires analysed. Sediment cores with intact structure were collected using a Russian D-Sampler. At the Sławięcice 2 site, the analysis included a sequence of deposits collected at a distance of about 10 metres from the thalweg zone in the paleochannel because the record of peat decay was the most visible in that zone (see Wójcicki, 2013 ). It should be noted at this point that the black colour of peat layers can also be related to a high concentration of sulphur compounds (total sulphur >5%). Such a case was identified at the Głogówek site in the