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Antwerpen, Belgium

van Maren D.S.,Deltares | van Maren D.S.,Technical University of Delft | Winterwerp J.C.,Deltares | Winterwerp J.C.,Technical University of Delft | And 5 more authors.
Continental Shelf Research

A new container dock in the Port of Antwerp, the Deurganckdok, was recently constructed in a location close to the Estuarine Turbidity Maximum (ETM) of the Scheldt River. In order to minimise sedimentation in the new dock, a Current Deflecting Wall (CDW) willbeconstructed. The aim ofthis paper isto assess the effect of the CDW on exchange flows and sediment fluxes. Determining this effect requires (1) understanding and reproduction of the sediment dynamics close to the Deurganckdok, and (2) accurate reproduction of the exchange flows between the dock and the Scheldt, and the effect of the CDW thereon. The sediment dynamics close to the Deurganckdok are dominated by a high concentration suspension (near-bed concentrations around 1 g/l) which is advected along the dock by the tidal currents. The sediment concentration is limited by the supply of sediment rather than the flow velocity. Most sediment will temporarily settle from suspension around slack tide. Hence, flood and ebb sediment concentrations are comparable, although the ebb and flood velocities are asymmetric. The peak sediment concentration occurs at the left or right bank of the Scheldt River, depending on the clockwise and counter-clockwise residual cross-channel currents. Exchange flows between the dock and the Scheldt are mainly a combination of horizontal eddies and salinity-driven flows, with velocities around 0.4 m/s. Most sediment enters the dock in a near-bed horizontal eddy, occurring around HW. The main effect of a CDW is a deflection of this sediment patch towards the river, reducing the sediment influx into the dock. The estimated reduction of siltation by the CDW is 18%. Alternative CDW configurations also reduce sedimentation in the dock, but less than computed with the design CDW. © 2010 Elsevier Ltd. Source

Winterwerp J.C.,Deltares | Winterwerp J.C.,Technical University of Delft | Wang Z.B.,Deltares | Wang Z.B.,Technical University of Delft | And 3 more authors.
Ocean Dynamics

This is Part II of two papers on man-induced regime shifts in small, narrow, and converging estuaries, with focus on the interaction between effective hydraulic drag, fine sediment import, and tidal amplification, induced by river engineering works, e.g., narrowing and deepening. Paper I describes a simple linear analytical model for the tidal movement in narrow, converging estuaries and a conceptual model on the response of tidal rivers to river engineering works. It is argued that such engineering works may set in motion a snowball effect bringing the river into an alternative steady state. Part II analyses the historic development in tidal range in four rivers, e.g., the Elbe, Ems, Loire, and Scheldt, all in northwest Europe; data are available for many decades, up to a century. We use the analytical model derived in Part I, showing that the effective hydraulic drag in the Ems and Loire has decreased considerably over time, as anticipated in Part I. We did not find evidence that the Upper Sea Scheldt is close to its tipping point towards hyperturbid conditions, but risks have been identified. In the Elbe, tidal reflections against the profound step in bed level around Hamburg seem to have affected the tidal evolution in the last decades. It is emphasized that the conceptual picture sketched in these papers is still hypothetical and needs to be validated, for instance through hind-cast modeling of the evolution of these rivers. This will not be an easy task, as historical data for a proper calibration of the models required are scarce. © 2013 Springer-Verlag Berlin Heidelberg. Source

Decrop B.,Ghent University | De Mulder T.,Ghent University | Toorman E.,Catholic University of Leuven | Sas M.,IMDC
Journal of Environmental Engineering (United States)

Numerical simulations of the sediment-air-water buoyant jet released through the hopper dredgers' overflow shaft have been performed. The release of sediments into the marine environment due to skimming the excess water from the dredging vessel's hopper can lead to increased turbidity and adverse effects on the adjacent environment. Base-case simulations have been validated using in situ field observations. Simulations have been performed using the large-eddy simulation technique, which allows including the effect of large turbulent structures on the sediment dispersion. The complex nature of the flow field poses challenges for numerical simulations, such as the presence of propeller jets and three different phases: water, sediment, and air bubbles. The model has been applied to simulate the effect of a so-called environmental valve, which reduces air inclusion. This valve has been used in the past, but its efficiency as a function of the boundary conditions was never analyzed before. It is shown in this article that this type of valve can be very effective in reducing the generated turbidity, but only under given combinations of dredging speed, sediment concentration, overflow shaft diameter and overflow-stern distance. © 2015 American Society of Civil Engineers. Source

Latif A.,Hashmat Medical and Dental College HMDC | Farhan M.A.,IMDC
Medical Forum Monthly

Objective: To study the presentation of varicose veins of lower limbs, treatment in our patients; and to see the causes of recurrent varicose veins at Islam Medical College, Sialkot, Pakistan. Study Design: Observational and descriptive study. Place and Duration of Study: This study was carried out at the Department of Surgery, Combined Military Hospital, Sialkot; from June 2007 to August 201 O.Department of Surgery, & Islam Teaching Hospital, Sialkot from September 2010 to September 2013. Materials and Methods: Adult patients referred by general practitioners with varicose veins of lower limb were included in the study. Data of sixty seven patients with varicose veins of lower limb was collected from June 2007 to September 2013. Patients were distributed in four groups depending upon the surgical procedures carried out. Full detailed history, examination, and investigations were done. Results of treatment were assessed by regular follow up. Data of only those patients was included who could complete follow up for at least 6 months. Results: Out of 67 patients included in our study, 25 cases were having recurrence; 8(32%) was recurrent cases from pervious surgeries from somewhere else and 17(68%) cases were diagnosed with recurrence after surgery at our hospitals. So, the incidence of recurrence in our cases exclusive remained to be 29%. Failure or recurrence in "Ligation" only was 38.5%, in ligation and reverse stripping was 30.7%, stab avulsions was 44.44% and in patients who underwent ligation, reverse stripping and stab avulsions was 12.5% after follow up of minimum 6 months. The patients are still on followup and the percentages are likely to increase with time as varicosities could be obvious. The anomalous double great saphenous veins, neovascularisation or missed tributaries of great saphenous vein during surgery and deep venous thrombosis before and after surgery were the most observed finding of recurrence. The recurrence of varicose veins was more in leg only as compared to both leg and thigh. Conclusion: Saphenofemoral ligation with below knee stripping and stab avulsions combined has the least frequency of recurrence, while Trendlenberg operation alone has the highest. Source

Gysens S.,Agency for Maritime and Coastal Services MDK | De Rouck J.,Ghent University | Bolle A.,IMDC
Proceedings of the Coastal Engineering Conference

The coastal town Ostend in Belgium has his sea wall far in the sea. For this reason, the protection of the town against storms is difficult. A harbor is situated in the city, with the harbor entrance close to the most important sea wall. Integration of harbor constructions and coastal protections schemes is necessary. Source

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