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  • Author: Tímea Kiss x
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Hydrological and Morphological Changes of the Lower Danube Near Mohács, Hungary

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.

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Characteristics of Point-Bar Development under the Influence of a Dam: Case Study on the Dráva River at Sigetec, Croatia

Abstract

Before the extensive engineering works the Dráva River had braided pattern. However in the 19-20th centuries river regulation works became widespread, thus meanders were cut off, side-channels were blocked and hydroelectric power plants were completed. These human impacts significantly changed the hydro-morphology of the river. The aim of the present research is to analyse meander development and the formation of a point-bar from the point of view of indirect human impact. Series of maps and ortho-photos representing the period of 1870-2011 were used to quantify the longterm meander development, rate of bank erosion and point-bar aggradation. Besides, at-a-site erosion measurements and grain-size analysis were also carried out. As the result of reservoir constructions during the last 145 years floods almost totally disappeared, as their return period increased to 5-15 years and their duration decreased to 1-2 days. The channel pattern had changed from braided to sinuous and to meandering, thus the rate of bank erosion increased from 3.7 m/y to 32 m/y. On the upstream part of the point-bar the maximum grain size is 49.7-83.4 mm and the mean particle size is 7.6 mm, whilst on the downstream part the maximum grain size was only 39.7-39.9 mm and mean sediment size decreased to 6.1 mm. Due to the coarse sediment supply and the decreasing stream energy the point-bars develop quickly upstream and laterally too.

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Assessment of nutrient content of tomato hybrids for processing

Abstract

We have tested the refraction of 6 cultivars of open-field tomatoes. In our work, we have tested the nutritional values of tomato cultivars harvested at different times. Our aim was to answer the question as to which cultivar fulfils the requirements for processing under given circumstances. During harvest time, we also measured the ratio of yellow and red pigments. The trial was conducted in Kecskemét, Hungary, on the trial field of NAIK ZÖKO, in open-field conditions. The refraction measurement was done on weighted tomato, which was then ground to juice and then measured on a tabletop refractometer. The 6 tested cultivars Brix% were measured at 5 different harvest dates, and then the average refraction of the harvest was analysed. The most suitable cultivar for processing was found to be Solerosso.

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Grain Size Distribution of Stabilised Aeolian Dune Sediments in Inner Somogy, Hungary

Abstract

In Inner Somogy the former researches concluded that the grain size of stabilised aeolian dunes decreases from north to south fitting to grain size distribution of the alluvial fan the dunes were built of and to the prevailing wind. However, the trend is not so evident, if considering the dune types and sand moving periods. The aim of this paper is to analyse the grain size distribution trends from the point of view of (1) different dune classes, (2) OSL age and (3) general morphological characteristics of the region. During the analysis the grain size distribution of 345 samples from 17 cores (120-300 cm in depth) was determined, and 15 OSL samples were dated. According to the results, the material of simple forms and level 1 dunes (these are the lowest dunes on the surface of the alluvial fan) becomes finer southward, in accordance with the structure of the alluvial fan and prevailing wind direction. Similar trend applies for level 2 dunes (which were formed on the top of level 1 dunes), but it does not apply for level 3 dunes, which are situated on the top of other dunes. It seems that the grain size is inversely proportional to the size of a dune and its age, thus younger and smaller dunes have coarser and less well sorted material. The sediments of the oldest, large parabolic dunes are the finest, younger, medium size parabolic forms have fine material, and the youngest hummocks contain the coarsest sand. The decreasing grain size towards south is the most apparent along longitudinal residual ridges, while within parabolic dunes the wings contain finer material than their elevated head.

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Modelling the Hydrological Effects of a Levee Failure on the Lower Tisza River

Abstract

Along the Lower Tisza River (Hungary) the water level of the floods reached new record stages in 1998 and 2006, resulting in 80 cm increase in the peak flood level since the “great flood of 1970”. Due to the gradual weakening of the levee-system caused by the several long-lasting floods, the question has arisen, that as in case of a levee breach or failure how would it modify the hydrological parameters of the river. The aim of the research is to create a hydrological model to analyse the effects (as stage reduction, slope and stream power) of two different levee breaches: one happening before the peak of the flood and another at the time of the flood level. The simulated levee breaching happened on the Tisza River at Mindszent, and the data-set of the 2006 flood was used for the modelling (at that time no levee failure happened in Hungary, and it was the greatest flood in history).

In the simulation the levee was broken at a point, where the channel is very close and intensively eroding, thus there is a real risk of a levee failure. If the levee would be broken a well defined area (reservoir) would be flooded, surrounded by the secondary levees and the rim of the high floodplain. During the simulation the HEC-RAS 4.1. ArcGIS 10.1 and HEC-GeoRAS software were applied.

The greatest changes in the hydrology of Tisza occurred in the cross section where the levee breached, though the effects propagated upstream and downstream too. Due to the water outflow from the Tisza the greatest stage reduction effect was 1.54±0.1 m. The slope conditions changed too, as it increased from 4 cm/km to 6.5 cm/km in the upstream reach, while downstream of the failure point it decreased from 3.5 cm/km to 1.9 cm/km. At the same time the stream power increased from 4 W/m to 5.5 W/m in the upstream section, while it decreased from 3.5 W/m to 1.5 W/m in the downstream reach. Comparing the results of the simulations at different stages (one at the highest stage and one at 1.0 m lower stage) it seems that the hydrological parameters did not change considerably (1%), though in a case of a levee failure at higher the reservoir reached the maximal water level sooner, though less water was stored in it, as the fall of the river was continuous

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Centurial Changes in the Depth Conditions of a Regulated River: Case Study of the Lower Tisza River, Hungary

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.

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Environmental Status of a City Based on Heavy Metal Content of the Tree-Rings of Urban Trees: Case Study at Szeged, Hungary

Abstract

Urban vegetation, especially urban trees could act as ecological archives, as they reflect various elements of their environment. The main aim of the study is to evaluate the spatial and temporal variations of environmental conditions in the city of Szeged (Hungary) based on long-term monitoring of the heavy metal content of tree-rings (soft wood). In general, the living conditions of the urban trees (and other organisms as well) at Szeged was the worst in 2001/05, when the heavy metal pollution was the greatest, therefore the biomass production of the sampled trees decreased. Fortunately, the environmental conditions became better, only there are some points in the industrial area, where the heavy metal pollution of the environment is gradually increases. The temporal change in lead pollution (considerable decline in 2013/17) could be explained by the obligatory usage of lead-free petrol since 1999 and the diversion of through-traffic from the town (2011). The introduction of unleaded petrol had delayed favourable results, as the dust particles containing lead probably circulated in the air for a while before they were gradually become fixed in the soil or they were washed out from the town during heavy rains. The cadmium pollution also declined after the traffic diversion, as it is connected to the usage of brake-linings. Whilst the lead and cadmium content of the tree-rings decreased during the studied decades, the trees accumulated increasing amount of zinc throughout the studied periods, as this element could be up-taken from the ground-water, as the larger the canopy of a tree the denser and deeper its root system is.

Open access
Dating the Holocene Incision of the Danube in Southern Hungary

Abstract

The alluvial development of the Great Hungarian Plain has greatly been determined by the subsidence of different areas in the Pannonian Basin. The temporal variation of subsidence rates significantly contributed to the avulsion and shifting of main rivers. This was the case in terms of the Hungarian Lower Danube when occupying its present day N-S directional course. The considerable role of tectonic forcing is also supported by the presence of different floodplain levels. Although, several channel forms are identifiable on these the timing of floodplain development has been reconstructed up till now mostly by the means of geomorphological analysis, and hardly any numerical dates were available. The main aim of this study is to provide the first OSL dates for palaeo-channels located on the high floodplain surface of the Hungarian Lower Danube, and to determine the maximum age of low and high floodplain separation on the Kalocsa Plain. For the analysis two meanders were sampled close to the edge of the step slope between the two levels. According to the results, the development of the investigated palaeo-meanders could be rapid. The formation of the older meander was dated to the Late Atlantic, while the possible separation of the high and low floodplain surfaces could start in the beginning of the Subboreal Phase.

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Effect of Climate Change on the Hydrological Character of River Maros, Hungary-Romania

Abstract

It is highly probable that the precipitation and temperature changes induced by global warming projected for the 21st century will affect the regime of Carpathian Basin rivers, e.g. that of River Maros. As the river is an exceptionally important natural resource both in Hungary and Romania it is necessary to outline future processes and tendencies concerning its high and low water hydrology in order to carry out sustainable cross-border river management. The analyses were based on regional climate models (ALADIN and REMO) using the SRES A1B scenario. The modelled data had a daily temporal resolution and a 25 km spatial resolution, therefore beside catchment scale annual changes it was also possible to assess seasonal and spatial patterns for the modelled intervals (2021- 2050 and 2071-2010). Those periods of the year are studied in more detail which have a significant role in the regime of the river. The study emphasizes a decrease in winter snow reserves and an earlier start of the melting period, which suggest decreasing spring flood levels, but also a temporally more extensive flood season. Changes in early summer precipitation are ambiguous, and therefore no or only slight changes in runoff can be expected for this period. Nevertheless, it seems highly probable that during the summer and especially the early autumn period a steadily intensifying water shortage can be expected. The regime of the river is also greatly affected by human structures (dams and reservoirs) which make future, more detailed modelling a challenge.

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Constraining the Age of Floodplain Levels Along the Lower Section of River Tisza, Hungary

Abstract

During the Late Pelistocene-Holocene transition the fluvial landscape of the Great Hungarian Plain changed considerably as a consequence of tectonic, climatic and geomorphological factors. Geochronology, and especially luminescence dating, is a very important tool in reconstructing these changes. The present study focuses on the Lower-Tisza region and addresses the timing of the development of different floodplain levels. In the meantime the luminescence characteristics of the investigated alluvial sediments were also assessed, with a special emphasis on the comparison of silty fine grain and sandy coarse grain results, as in the given medium and low energy environment fine grain sediments are more abundant, however, based on the literature, coarse grain samples are more reliable in terms of luminescence dating. Measurements were performed on 12 samples originating from the point bars of two large palaeo-meanders, representing different floodplain levels along the river. Results indicate the applicability of both grain size fractions for dating purposes, though fine grain subsamples overestimate in average by 1.5 ka the ages yielded by coarse grain subsamples. Consequently, fine grain samples can be used for outlining only general trends, and results need to be controlled by coarse grain measurements where possible. Based on the ages received, the upper floodplain was actively formed until 13-15 ka, when incision and the development of an intermediate floodplain level started. The meander on the intermediate flood plain level developed then very actively until 9 ka. As indicated by the received age information the intensity of meander formation could be highly affected by climatic and especially vegetation control. However, reconstruction can be refined later by further sampling and the application of the results of the present paper.

Open access