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• Morphological alteration of the Dráva as the result of human impact

  58-75

  Tímea Kiss

  Gábor Andrási

  Péter Hernesz

  Views:

  113

  The Croatian-Hungarian border section of the Dráva River has been undisturbed for almost a century, and it is characterised by unique fluvial morphology (braided pattern and islands) supporting rich habitats and wildlife. However, during the last decades human impact became more and more intensive. Between 1975 and 1989 three water reservoirs were built on the Croatian section of the river, just 16 km from the beginning of the border-section, altering the hydrology and the sediment characteristics of the river. On a local scale cut-offs, revetments and groynes were built. The aim of the study was to evaluate the effect of these human interventions. As the result of the alteration of the hydrology the channel pattern of the Dráva has been changing from braided to meandering, though on the upstream meandering part the territory and number of islands increased due to the drop of water stages. A cut-off and a groyne influenced only the morphology of a short section. As the result of the cut-off braided pattern became more pronounced, and the groyne caused intensive channel aggradation and gave way to lateral island development.

• Land use changes and their effect on floodplain aggradation along the Middle-Tisza River, Hungary

  1-10

  Tímea Kiss

  Andrea Sándor

  Views:

  77

  Land-use changes and their effect on overbank sediment accumulation were investigated on the floodplain of Middle-Tisza River. Military survey maps (1783, 1860, 1883 and 1890) and aerial photos (1950, 1965, 1980 and 2000) were used to evaluate land-use changes and to calculate the vegetational roughness of the area. To determinate the rate of overbank sedimentation sediment samples were collected from a pit, the grain-size, content of organic matter, heavy metal content (Pb, Cu, Zn, Ni and Cd) and pH were measured. Until 1950 meadows and pastures were typical on the floodplain, gallery-forest was along the river, the oxbow-lake and the artificial levee. Notable landuse changes were detected in the second half of the 20th century, as the aerial photo taken in 1965 shows extensive forestry in the area. These land-use changes affected the average vegetational roughness, as it has been doubled since the disappearance of grasslands. Land-use changes highly affect the aggradation, as the increased roughness decreases the flood velocity on the floodplain, causing accelerated aggradation. Using Pb marker horizons and grain-size changes the studied sediment profile was compared to dated profiles (Braun et al. 2003), thus, the sediment accumulation rate could be determined for the periods of 1858-1965 and 1965-2005. According to our measurements the accumulation rate was doubled since 1965, very likely in connection with the doubled vegetational roughness.

• Bedload transport measurements on the Maros river, Hungary

  37-41

  Tímea Kiss

  Gabriel J. Amissah

  Gábor Mezősi

  Károly Fiala

  György Sipos

  Views:

  176

  Sediment transport is a vital component in hydrological and fluvial geomorphological studies, however, the temporal and spatial changes in sediment fluxes, and the efficiency of bedload samplers are rarely analysed, as bedload measurements are quite difficult. The aim of the present study is to measure the bedload transport of the sand-bedded Maros River (Hungary) at low stages using the Helley-Smith bedload sampler. In order to understand the variability in the bedload transport, the water stage and discharge across the channel section were also measured. The variability of the bedload was caused by an active in-channel bar and translational sediment pulses. The created bedload transport rating curve could be applied just below 300 m3/s water discharge thus further measurements are needed to evaluate the bedload transport of higher discharges.

• Active point bar development and river bank erosion in the incising channel of the lower Tisza river, Hungary

  13-28

  Gabriel Jonathan Amissah

  Tímea Kiss

  Károly Fiala

  Views:

  233

  The development of point-bars and bank erosion are critical near-bank processes, as they indicate the sediment and hydraulic regime of a river system, thus, they refer to the equilibrium conditions of a channel. However, throughout history, rivers have been modified for various benefits which change the development of point-bars and the rate of bank erosion. In the Lower Tisza River (Hungary), river regulations influenced the channel and floodplain development, altering the natural fluvial processes. The aim of the research was to determine the rate of near-bank processes and to make trajectory for future river evolution to support future engineering works. The bank erosion and point-bar development at human-influenced and freely meandering sections of the Tisza River were monitored since 2011. Behind a collapsed revetment, the bank erosion rate was 0.6 m/y, while at a freely meandering section it was 2.3 m/y. The studied point-bars are located in revetted and freely meandering sections. Their surface eroded within the period. These intensive erosional processes refer to an incising meandering channel, which must be considered during future planning of in-channel structures (e.g. revetments, bridges), thus, geomorphic methods must be considered in any river engineering scheme.