Svasek Hydraulics

Rotterdam, Netherlands

Svasek Hydraulics

Rotterdam, Netherlands

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Radermacher M.,Technical University of Delft | van der Goot F.,Royal Boskalis Westminster N.V. | Rijks D.C.,Royal Boskalis Westminster N.V. | de Wit L.,Svasek Hydraulics
Proceedings WODCON XX - Congress and Exhibition: The Art of Dredging | Year: 2013

One of the potential environmental issues associated with dredging in the marine environment is the increase of suspended sediment concentrations (SSC) by generation and dispersion of sediment plumes. This can be mitigated by source control or the installation of containment barriers like silt screens. This paper focuses on hanging silt screens and describes: (i) The decision process for deployment of hanging silt screens Decisions on the necessity of environmental mitigation measures and subsequently on the viability of silt screen deployment should be made using a receptor-based approach. This starts with the identification of (ecological) receptors and related impact levels, understanding the local environment, checking compatibility with work methods and determining cost and schedule impacts. (ii) Effectiveness of hanging silt screens Local hydrodynamic and morphological circumstances determine the effectiveness of silt screens. Results of extensive numerical modeling tests (3D and 2DH) supported by hands-on experiences from dredging projects are used to describe the effect of hanging silt screens on the distribution of SSC in the water under different conditions. Results show that when deploying silt screens it is important to realize that silt screens are flexible curtains; they do not block the flow. Therefore suspended sediments generated at a dredging project will always pass the hanging screen vertically and/or horizontally. Silt screens can only reduce the distribution of SSC by settling if local hydrodynamic conditions are favourable. (iii) Adaptive management strategies as an alternative for silt screens When local conditions are not optimal for deployment of silt screens, alternative mitigation measures can be used such as adaptive monitoring strategies, to manage SSC around dredging projects. © 2013 WODA.


van Leeuwen B.,Svasek Hydraulics | van Leeuwen B.,University of Twente | Augustijn D.C.M.,University of Twente | van Wesenbeeck B.K.,Deltares | And 4 more authors.
Ecological Engineering | Year: 2010

Mussel beds are known to affect fine sediment dynamics and morphology on mudflat scale, a clear example of ecosystem engineering. Current research into possible ecological engineering applications of mussel beds makes quantitative modeling desirable. In this study a process-based model of the interaction between a young mussel bed and fine sediment was set up for use in the hydrodynamic and morphological model Delft3D-FLOW. The model encompasses the hydraulic roughness of the mussel bed, active capture of suspended sediment by filter feeding and changed bed properties due to biodeposited matter. The mussel bed implementation in Delft3D-FLOW was applied in a test case: a Wadden Sea intertidal mudflat model. It was concluded that a combination of active deposition via filtration and slow down of the flow due to increased roughness leads to high net deposition in the mussel bed. In addition, the ability of young mussels to quickly climb on top of deposited material results in rapid trapping of large amounts of fine sediment. In the wake of the mussel bed, deposition is also high because of reduced flow velocities. The effects of different existing mussel bed patterns were also evaluated. Patchiness and specifically striped patterns cause mussel beds to experience less sedimentation than uniformly covered beds of the same size and may therefore be favorable to mussels. © 2009 Elsevier B.V. All rights reserved.


Radermacher M.,Technical University of Delft | de Wit L.,Svasek Hydraulics | Winterwerp J.C.,Technical University of Delft | Winterwerp J.C.,Deltares | Uijttewaal W.S.J.,Technical University of Delft
Journal of Waterway, Port, Coastal and Ocean Engineering | Year: 2016

When dredging in sensitive environments, efforts have to be made to limit the free dispersal of suspended fine sediment from the dredging spill. The use of hanging silt curtains as an environmental mitigation measure is especially widespread. Despite frequent application, their ability to reduce turbidity levels through vertical diversion of sediment-laden currents remains the subject of debate. This paper addresses a series of laboratory measurements and numerical model simulations to determine the efficiency of hanging silt curtains, defining a new efficiency parameter. The model was validated against the laboratory experiments. Model simulations focusing on vertical diversion of the sediment-laden current suggest that hanging silt curtains do not have a favorable influence on the settling of suspended sediment when applied in crossflow. The diversion of currents underneath the curtain causes flow separation and intense turbulent mixing, which counteracts settling of suspended sediment particles. The results imply that the widespread application of hanging silt curtains should be reconsidered from a physical point of view. © 2015 American Society of Civil Engineers.


Dam G.,Svasek Hydraulics | Bliek A.J.,Svasek Hydraulics
Proceedings of the Institution of Civil Engineers: Maritime Engineering | Year: 2013

Due to the construction of two cross-shore groynes near Waarde in the Western Scheldt estuary, the Netherlands, morphological changes in the area have occurred. A mud flat has developed between the groynes and at the tip of the groynes scour has occurred which has contributed to channel migration. Both the sand and mud fraction have contributed to this change. In this paper a process-based morphological model is presented that can reproduce most morphological changes thanks to the fact that both fractions are taken into account, as well as the interaction between sand and mud. Using the model, 5 years of morphological changes were simulated from the construction of the groynes onwards. The Brier-skill score of the erosion/sedimentation pattern is 0?35, which means that the model has significant skill and can be classified as reasonable. A regression coefficient of 0?66 is found for the observed and modelled mud content in the bed after 5 years, which means that the model can reproduce the mud content reasonably well for most locations. The model can clearly distinguish between a sand- or mud-dominated area.


Dam G.,Svasek Hydraulics | Poortman S.E.,Svasek Hydraulics | Bliek A.J.,Svasek Hydraulics | Plancke Y.,Flanders Hydraulics Research
Proceedings WODCON XX - Congress and Exhibition: The Art of Dredging | Year: 2013

The natural morphological developments of the Western Scheldt and the impact of human activities on these developments are investigated using a process-based morphological model called FINEL2d. The historical period of 1965-2002 is simulated in a T0 scenario including all the human activities that have taken place in that period. Besides this T0 scenario two extreme scenarios are modeled for the same period. The T1 scenario is carried out without any human activities from 1965 onwards. In the T2 scenario regular dredging of the navigational channel takes place, but the dredged material is not distributed back into the Western Scheldt like in the T0 scenario. In this way insight is obtained into how human activities have influenced and will influence the tide in and the morphology of the Western Scheldt. By modeling these different sediment strategies it is concluded that the applied strategy has had a large impact on the morphology of the estuary and tide during this period. The channels have deepened and the tidal flats have increased in the 1965-2002 in the model, because of which the hypsometry of the Western Scheldt has probably has become steeper over the last decades. The results also show significant effects on the propagation of the tide in the estuary. Due to the actual human activities over the past decades the tidal range in the estuary has increased by about 0.4m in Antwerp and accelerated the propagation of the tide with approximately 20 minutes. This corresponds to the observed phase shift in Antwerp over the past decades. The extreme scenario in which all dredged material was removed from the estuary shows that the process of increasing tide levels in the estuary may continue in case that the human activities are intensified. © 2013 WODA.

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