Time filter

Source Type

Vandenbohede A.,Ghent University | Lebbe L.,Ghent University | Adams R.,International Marine and Dredging Consultants IMDC | Cosyns E.,West Vlaamse Intercommunale WVI | And 2 more authors.
Journal of Environmental Management | Year: 2010

In dune slacks a close coupling exists between changes in the hydrology and changes in species composition and vegetation structure. Consequently, there is a need to underpin nature restoration projects not only with ecologically relevant knowledge but also with scientifically sound hydrogeological data. In this paper, this necessity is illustrated through a study of the Flemish Nature Reserve 'The Zwindunes and Zwinpolders' (Belgian coastal plain) as an example. The management plan for the nature reserve suggests rewetting part of it to enhance its ecological value. The groundwater aspect was studied by means of field observations and mathematical modelling. First, fresh water head observation showed a mean groundwater flow from the nature reserve to the adjacent polder. Secondly, groundwater quality was studied with borehole measurements and water samples, resulting in a map of the fresh-salt water distribution and of water types. All available information was then put together in a density dependent groundwater flow model. The aim of this model was the description of current flow and fresh-salt water distribution and to simulate the impact of three possible rewetting scenarios. Rewetting will be accomplished by the infiltration of water in a depression, different lay-outs for which are considered. A zoomed in flow model based on a regional model was used to incorporate both local scale, which is of importance to ecology, and the larger scale, which determines general groundwater flow and fresh-salt water distribution. This modelling indicated differences between scenarios and was used to decide on the best rewetting strategy. © 2010 Elsevier Ltd.


Roose F.,Flemish Ministry of Mobility and Public Works | Sas M.,International Marine and Dredging Consultants IMDC | Meersschaut Y.,Flemish Ministry of Mobility and Public Works
Proceedings WODCON XX - Congress and Exhibition: The Art of Dredging | Year: 2013

In August 2011 the Current Deflecting Wall (CDW) was realized at the entrance of the tidal dock 'Deurganckdok' in the port of Antwerp, Belgium. Equipped with container terminals, Deurganckdok can receive vessels with a draught of 13,10m independent of the tide. Due to its position in a stretch of the Schelde estuary with salinity gradients near the estuarine turbidity maximum, Deurganckdok is subject to siltation. Accumulation of fine-grained cohesive sediments in the dock runs up to 1 million m3 annually and requires regular maintenance dredging. During the early stages of preliminary investigations for Deurganckdok (1997-1999), the Current Deflecting Wall (CDW) was selected as a measure to reduce sedimentation. The design was adapted to function in an environment with salinity gradients during the feasibility research (2001-2004), which included physical and numerical modelling, supported by field measurements. Initial calculations predicted a reduction of 10-20% in sediment accumulation. In the final phase of investigations (2005-2007), state-of-the-art numerical models were calibrated with field measurements to enhance sediment accumulation predictions under a range of boundary conditions. In this paper the results are summarized of the preliminary investigations that have led to the design of the Current Deflecting Wall (CDW). © 2013 WODA.


Manning A.J.,University of Plymouth | Van Kessel T.,Deltares | Melotte J.,International Marine and Dredging Consultants IMDC | Sas M.,International Marine and Dredging Consultants IMDC | And 3 more authors.
Continental Shelf Research | Year: 2011

Following the recent completion of the Deurganckdok (DGD) tidal dock in the Port of Antwerpen, Belgium, the Flemish government commissioned a programme of field surveys with the aim to identify potential changes in sediment properties. A significant feature of the Lower Sea Scheldt (LSS) is the presence of a turbidity maximum zone (TMZ) with depth-averaged suspended particulate matter (SPM) concentrations between 50 and 500 mg l -1. This paper highlights aspects of the findings of the suspended sediment properties measured during HCBS1 (conducted in February 2005 prior to DGD construction) and HCBS2 (September 2006 when the dock was open and in operation) surveys, including data comparison. Floc size (D) and settling velocity (W s) spectra were measured nominally 0.6 m above the estuary bed every 10-20 min (turbidity dependent), using derivatives of the INSSEV instrument. This instrument permitted the accurate calculation of the following floc properties: effective density, dry mass, porosity and mass settling flux (MSF). To characterise the corresponding near-bed hydrodynamics, the turbulence was measured by a 3-D Acoustic Doppler Velocimeter and the turbidity monitored by an array of Optical Backscatter Sensors. All measurements were conducted for runs of 8-10 h in duration. HCBS1 was conducted during neap tides in the winter, predominantly during the ebb phase, whilst HCBS2 experienced spring tides in the autumn with sampling generally on the flood. It is therefore important to note that only limited comparison between surveys and the different HCBS locations is possible. Even so, the survey revealed that, following construction of the DGD, turbidity was an order of magnitude higher in the DGD, than in the upper and lower Scheldt Estuary. It was also noted that that the DGD macrofloc fraction settled at W smacro = 5.3 mm s -1 in the TMZ, which was 1.4 and 3.2 mm s -1quicker than the fastest settling macrofloc population observed in the LSS during the winter at neap tides and late summer at spring tides, respectively. The HCBS surveys have highlighted the important role of low density macroflocs in the mass settling flux within the dock. At peak concentration in the DGD produced a MSF of 13.2 g m~ 2 s -1; over an order of magnitude greater than observed within the HCBS1 TMZ. Within DGD the time series MSF of 30,200 mg m~ 2 s -1, was five times the MSF observed at the dock entrance, and 19 times the MSF observed in the Scheldt estuary outside the dock (HCBS2_SS). Over 70% of the total MSF occurred during the TMZ passage through the dock on the flood. The weaker currents present in the dock, particularly on the ebb, when combined with a near continual abundance of fast settling macroflocs, will tend to trap sediment in the basin, whilst near-bed turbulence damping will reduce the level of bed erosion in DGD. The sedimentation in the dock is stimulated by a significantly less turbid supply of cohesive sediment present in the Scheldt Estuary. It is proposed that the construction of a passive structure, such as a current deflecting wall, may reduce sediment entering the open tidal dock. © 2010 Elsevier Ltd.


Zimmermann N.,International Marine and Dredging Consultants IMDC | Buitrago S.,International Marine and Dredging Consultants IMDC | Gullentops C.,International Marine and Dredging Consultants IMDC | Blanckaert J.,International Marine and Dredging Consultants IMDC
Proceedings of the International Conference on Fluvial Hydraulics, RIVER FLOW 2014 | Year: 2014

In a consulting environment, applications at the engineering-research interface occasionally require to develop model prototypes. Unfortunately limitations in programming knowledge often mean that these extensions are not easily reusable. This paper evaluates the potential of a Matlab framework to considerably simplify the development of new prototype models while keeping some of the characteristics that make a model attractive. Some of the basic concepts underlying Environmental Modelling Frameworks (EMFs) are used to define an architecture allowing engineers to easily couple and reuse model components. The benefits of such an architecture are shown with an implementation of a hydro-logical model, and the computation speed and limitations of the proposed approach are evaluated with an implementation of the non-linear shallow water equations. © 2014 Taylor & Francis Group, London.


Broekx S.,Flemish Institute for Technological Research | Smets S.,International Marine and Dredging Consultants IMDC | Liekens I.,Flemish Institute for Technological Research | Bulckaen D.,International Marine and Dredging Consultants IMDC | de Nocker L.,Flemish Institute for Technological Research
Natural Hazards | Year: 2011

The Scheldt is a tidal river that originates in France and flows through Belgium and the Netherlands. The tides create significant flood risks in both the Flemish region in Belgium and the Netherlands. Due to sea level rise and economic development, flood risks will increase during this century. This is the main reason for the Flemish government to update its flood risk management plan. For this purpose, the Flemish government requested a cost-benefit analysis of flood protection measures, considering long-term developments. Measures evaluated include a storm surge barrier, dyke heightening and additional floodplains with or without the development of wetlands. Some of these measures affect the flood risk in both countries. As policies concerning the limitation of flood risk differ significantly between the Netherlands and Flanders, distinctive methodologies were used to estimate the impacts of measures on flood risk. A risk-based approach was applied for Flanders by calculating the impacts of flood damage at different levels of recurrence, for the base year (2000) and in case of a sea level rise of 60 cm by 2100. Policy within the Netherlands stipulates a required minimal protection level along the Scheldt against storms with a recurrence period of 1 in 4,000 years. It was estimated how flood protection measures would delay further dyke heightening, which is foreseen as protection levels are presently decreasing due to rising sea levels. Impacts of measures (safety benefits) consist of delays in further dyke heightening. The results illustrate the importance of sea level rise. Flood risks increased fivefolds when a sea level rise of 60 cm was applied. Although more drastic measures such as a storm surge barrier near Antwerp offer more protection for very extreme storms, a combination of dykes and floodplains can offer higher benefits at lower costs. © 2010 Springer Science+Business Media B.V.

Loading International Marine and Dredging Consultants IMDC collaborators
Loading International Marine and Dredging Consultants IMDC collaborators