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Bedforms evolution in the Vistula River mouth during extreme flood event, southern Baltic Sea

Lisimenka Aliaksandr, Kubicki Adam, Kałas Maciej

Oceanologia

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2022

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No. 64 (1)

212--226

EN

Results of bathymetric surveys conducted to examine changes of sand dunes geometry in the Vistula River mouth before, during and after the extreme flood event are presented. A total of 2076 dunes were analysed based on a series of bed elevation profiles obtained along the centreline of about 3.3 km length. Low-steepness dunes characterized by the mean lee-side slopes milder than β<10° are fully dominant at low flows. In contrast, at high hydrology, nearly 50% of dunes indicate β>10°. Dune height and length are substantially out of phase with progressive changes of water discharge exposing a well-pronounced anti-clockwise hysteresis. Distinct behaviour of dune dimensions reflected in increasing of dune steepness H/λ of about 3-fold and decreasing of about 4-fold were observed during rising and falling discharges, respectively. The bed roughness due to dunes presence showed changes of about 10-fold during the both of limbs and is found to be in range of about kdunes=(1/5÷3/5)Hmean. At the mesoscale region, spectra followed sufficiently by the ‘–3 power law’ for low hydrology, with steeper spectrum slopes close to ‘–4’ during moderate and high water discharges. With the development of the flood, potential of flow separation phenomena was increased of about 9-fold, from 2.2% at the flood beginning phase up to 20% at the flood peak. The obtained results could be used for the improvement of the hydraulic numerical models in sand-bed rivers to predict bedforms evolution, flow resistance and turbulence as well as water levels for proper river system management during flood events.

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Bedload transport in the Vistula River mouth derived from dune migration rates, southern Baltic Sea

Lisimenka Aliaksandr, Kubicki Adam

Oceanologia

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2019

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No. 61 (3)

384--394

EN

In this paper, bedload sediment transport to the Baltic Sea in the main Vistula River mouth (Przekop Wisły) is estimated. For the first time in this area, investigations were performed based on the non-invasive measurement techniques with the using of hydroacoustic tools. Repeated bathymetric surveys were carried out using a multibeam echosounder for the period with hydrological conditions close to that of the long-term mean annual water discharge. Quantification of the bedload transport, as a main factor for the subaqueous Vistula delta development, involved applying the bedform tracking technique, and estimating the dune celerity by analysing the cross-correlation functions of bed elevation profiles (BEPs). The BEPs were obtained along two transects of 500 m in length situated in two different morphological parts of the river mouth — in the “shallow” and in the “deep” sites located upstream and downstream of the submerged sandbar, respectively. Contrarily to previous observations, the bedload transport was found to take place constantly. Moreover, a significant difference in a character of dune migration between the two sites of the investigated area was determined. The “shallow” dunes migrate 7 times faster (0.022 m/h) than the “deep” ones (0.003 m/h). Estima-tion of the daily bedload transport towards the Baltic Sea revealed values about 40.9 t/day and 8.4 t/day for “shallow” and “deep” sites, respectively. This result can probably indicate that a significant portion of sediments (ca. 80%) transported by the river during average hydrological conditions is deposited temporarily on the submerged sandbar, causing its growth.

3

The Vistula Canal, the state after 120 years of activity

Lisimenka A., Wróblewski R., Nowak J., Rudowski S., Kałas M., Szefler K.

Biuletyn Instytutu Morskiego w Gdańsku

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2015

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Vol. 30, No. 1

164--166

EN

During the catastrophic flood caused by the ice dam in 1840, a new river mouth was created. Nevertheless some series of floods were observed in the next years. In order to facilitate of river waters run-off, the artificial crosscut was performed in 1891-1895 years. The artificial channel was opened in 31st of March 1895. Since, at the time of continuous exploitation of the channel, high effectiveness of the engineering project which is unique in the world scale has been confirmed. A permanent flood hazard for Gdansk city and adjacent lowland areas has been receded. Since this time, the external delta is being formed by acumulation of bed-loaded sediment that is transporting by the river. Consequently free run-off of the river water is reducing due to the external delta growing. During the years 2009-2014, detailed monitoring researches of the Vistula Canal as well as the Vistula River External Delta have been performed. The obtained results constitute a basis for the evaluation of flood risk in the area, as well as for prognosis of morphological changes of the Vistula River External Delta and sand supply to the Gulf of Gdansk. The state of the Vistula River mouth canal is briefly presented after 120 years of its history.

PL

Podczas katastrofalnej powodzi w 1840 roku doszło do utworzenia nowego ujścia, tak zwanej Wisły Śmiałej. W ciągu kolejnych lat nadal jednak wystepowały sytuacje powodzie. Podjeto wiec decyzję o wykonaniu odpowiedniego przekopu dla zapewnienia skutecznej ochrony przeciwpowodziowej. Przekop został otwarty 31 marca 1895 roku. Podczas kolejnych lat użytkowania Przekopu Wisły jego skuteczność została potwierdzona. Rumowisko piaszczyste wynoszone przez rzekę, składane przy jej ujsciu, zaczeło formowac stożek ujściowy – tak zwana zewnetrzną deltę.W miarę jej wzrostu następuje jednak zmiejszanie możliwości swobodnego spływu wód. W latach 2009-2014 przeprowadzono szczegółowe badania monitoringowe Przekopu Wisły i delty zewnętrznej. Uzyskane wyniki stanowią podstawę do oceny stanu przekopu i jego mozliwosci zapewnienia swobodnego spływu, wraz z prognozą zmian delty zewnetrznej i szacowniem ilosci dostarczanego materiału piaszczystego do Zatoki Gdańskiej.