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1

Laboratory study of suspended sediment dynamics over a mildly sloping sandy seabed

Stachurska Barbara, Staroszczyk Ryszard

Oceanologia

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2019

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No. 61 (3)

350--367

EN

This paper presents the results of laboratory measurements of suspended sediment movement induced by regular non-linear water waves propagating over a mildly sloping sandy seabed covered with ripples. The measurements conducted in a water flume were carried out by applying the technique of particle image velocimetry (PIV). The aim of those experiments was to investigate near-bed velocities of sediment particles under controlled surface wave conditions. In particular, horizontal and vertical profiles of sand grain velocities were measured, and some comparisons between the measured and theoretically-predicted quantities were carried out. A number of selected wave cases were examined, for which the Ursell number ranged from 18 to 39, and the sediment grain mobility numbers varied between 12 and 26. For these flow conditions, the near-bed layer of intense sediment grain movements had a thickness of about 2-3 ripple heights. The maximum horizontal sediment velocities measured over ripple crests were about twice as large as those over ripple troughs. Vertical sediment velocities above ripple crests and troughs were similar, amounting to about 1/4 to 1/3 of horizontal velocities over ripple crests. The detailed quantitative results obtained in the flume can help validate other experimental techniques and can be useful in testing numerical models for simulating surface wave-induced sediment dynamics.

2

The history of the sedimentation processes and heavy metal pollution in the Central Danube Delta (Romania)

Begy R. C., Kelemen S., Simon H., Tănăselia C.

Geochronometria

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2018

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Vol. 45, no. 1

97--106

EN

The aim of this study was to investigate the effects of the Iron Gates (IG) hydroelectric power station on the Danube Delta sediment dynamics, and to assess the heavy metal concentrations and pollution in a typical Central Danube Deltaic lake. Eight sediment cores were analysed. The total 210Pb content was measured with 210Po using alpha spectrometry, and the supported 210Pb (226Ra) and 137Cs were measured by gamma spectrometry. The age depth model was derived by applying the 210Pb dating method, and for the calculation of the ages and the sedimentation rates the CRS model was used. The sedimentation rates can be divided into four periods:1940–1972, 1972–1980, 1972–1989 and 1989–2013. In the case of Lake Iacob in the first period, the average sedimentation rate was 0.418 g/cm2y, while in the second it slowly decreased to 0.376 g/cm2y. In the third period, the sedimentation fell to 0.209 g/cm2y, which means the retention of 27.3% of the sediment by the IG dam. In the case of Lake Isac the changes were more visible: in the first period the average sedimentation rate was 0.446 g/cm2y, while in the second it decreased to 0.197 g/cm2y, which means a 42.35% retention of sediment. In the last period, in both cases, a high increase in the sedimentation rate is shown: 0.677 g/cm2y for Lake Iacob and 0.715 g/cm2y for Lake Isac. The heavy-metal concentrations for As, Co, Cr and Ni show decreasing and Hg increasing tendencies, while Cd and Pb show constant values of 310 ± 12 ppb and 9 ± 1 ppm respectively.

3

Extended models of sedimentation in coastal zone

Selezov I.

Vibrations in Physical Systems

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2014

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Vol. 26

243--250

EN

Construction of a generalized hyperbolic model of sediment dynamics predicting a sediment evolution on the bottom surface with a finite velocity is presented. The transport equation is extended with introducing a generalized operator of flux change and a generalized operator of gradient. Passing to the convenient model is a singular degeneration of extended model. In this case the results are obtained in the class of generalization solutions. Some expressive examples of constructions of hyperbolic models predicting a finite velocity of disturbance propagation are presented. This problem is developed starting from Maxwell (1861). His approach in the theory of electromagnetism and the kinetic theory of gases is commented. A brief review on propagation of heat and diffusive waves is presented. The similar problems in the theory of probability and diffusion waves are considered. In particular, it was shown on the microscopic level for metals that the conservation law can be violated.

4

Natural radioactivity of coastal sediments as tracer in dynamic sedimentology

Thereska J.

Nukleonika

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2009

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Vol. 54, No. 1

45-50

EN

Natural radioactivity of coastal sediments could provide interesting information on sediment dynamics. Natural radioactivity measurements were performed in two areas of the Adriatic Sea littoral of Albanian cost, in the gulfs of Durres and Vlora, where complex studies were carried out in the framework of the maintenance of existing Durres harbour and the design of a new harbour in Vlora. Dynamic mapping of the gamma total radioactivity at the sea bottom sediment was carried out using a 2" × 2" NaI probe. Radiometric data were converted to lithological map, and the sand and silt distribution configuration was interpreted in terms of sediment transport. The obtained results have shown that the natural radioactivity of sediments provides qualitative data about the sediment dynamics. This cost-effective method is recommended to be used as complementary to other tracer techniques for sediment transport in coastal engineering investigations.