Francken, F.

Van den Eynde, D.

Van Lancker, V.

Open Marine Archive

149 
 
Application of a large dataset of sediment transport parameters: variability in 
sediment transport in the HBMC area 
 
Francken Frederic
*1
, Van den Eynde Dries
1
, Van Lancker Vera
1 
*
Presenting author: frederic.francken@naturalsciences.be 
1 
Royal Belgian Institute of Natural Sciences, Operational Directorate Natural Environment, Suspended Matter 
and Seabed Monitoring and Modelling Group, Gulledelle 100, 1200 Brussels, Belgium 
Introduction 
Distinguishing naturally- from anthropogenically-induced variability of the seabed is very difficult, as the range 
of natural variation is hard to quantify. Mostly, variations are described locally, using in-situ depth data (e.g., 
Van Lancker and Jacobs, 2000; Lanckneus et al., 2002; Degrendele et al., 2010; Roche et al., this volume), or are 
derived from newly acquired current and turbidity data. Still, in many cases the regional context is missing, and 
sound interpretations on the driving forces are not possible. Nevertheless the quantification of both naturally 
and man-made changes are needed for the definition of acceptable thresholds for alterations to the seabed 
(e.g., aggregate extraction, Van Lancker et al., this volume). Also, to assess the recovery potential of impacted 
areas after extraction, a critical parameter within Europe’s Marine Strategy Framework Directive (MSFD), 
natural system variability needs to be quantified. This can be approached through statistical analyses of long-
term databases on seabed evolution (cf. Dalyander et al. 2013). For the Belgian part of the North Sea, a 12-year 
long hindcast (1999-2010) on the main sediment transport parameters (i.e., bottom stress, bottom geometry, 
total load and bottom evolution) was therefore produced (Francken et al., 2014) and has now been expanded, 
and applied to case studies for validation. 
In this case study we evaluate the natural variability of the total load sediment transport from a long-term 
database, as it directly impacts the bottom morphology. 
 
Material and methods 
Model data 
Results from a subset (2012-2014) of the 16-year long hindcast (1999-2016) were used to assess the variability 
of sediment transport in the Hinder Banks. Purpose was to provide regional context to sediment processes in 
the monitoring area HBMC, being a subarea of the aggregate sector 4C (see Roche et al., this volume).   
Wave hindcasts for the period were obtained using the Simulating Waves Nearshore (SWAN) wave model 
(Holthuijsen et al., 1993; Booij et al., 1999), a third generation phase-averaged wave model, suited for 
modelling waves in shallow water. The model calculates in time and space, the generation of waves, their 
propagation and shoaling, non-linear wave-wave interactions (quadruplets and triads), white-capping, bottom 
friction and depth-induced wave breaking. The wave model was coupled with the results from a hydrodynamic 
model, to account for current refraction and for the influence of the changing water depth on the waves. The 
model runs on a grid resolution of about 750 m x 750 m. The boundaries for the wave model were obtained 
from two larger scale WAM models (WAMDIG, 1988) covering the entire North Sea. Detailed information on 
the wave modelling can be found in Fernández (2011) and Van Lancker et al. (2012). The currents and water 
elevations were obtained from two-dimensional hydrodynamic models (Ozer et al., 1996; Yu et al., 1990). A 
finer resolution model, using the same grid as the wave model, was set up for the Belgian Part of the North 
150 
 
Sea, which was coupled with a lower resolution model for the entire West-European Continental Shelf. 
Atmospheric data (wind speed at 10 m height above sea level), were obtained from the United Kingdom 
Meteorological Office.  
Currents and waves were used by the sediment transport model MU-SEDIM (Van den Eynde et al., 2010), 
calculating the total load, under the influence of the local hydrodynamic conditions. The MU-SEDIM model was 
improved in the framework of this project to include a more time effective method for calculating the 
combined wave-current bottom stresses, using the method of Soulsby and Clarke (2005). A new 
implementation for the calculation of the bottom geometry (ripple height and ripple length), which is 
important for the calculation of the total bottom roughness (including skin bottom roughness, bottom 
roughness from bedload and form bottom roughness), was executed based on Soulsby and Whitehouse (2005). 
The model calculates the current and wave generated ripples and takes into account their time evolution. The 
total load is then calculated using the Ackers-White formulae (Ackers and White, 1973), adapted for waves by 
Swart (1976, 1977). Model output resulted in 30 minutes time step sediment transport parameters (bottom 
stress, bottom geometry, total load and bottom evolution) on a 750 m grid resolution. 
Statistical analysis 
Yearly averages of the X and Y vectors of the total load were calculated at every grid node. The same routine 
was also used for every season, i.e., winter (January-March), spring (April-June), summer (July-September) and 
autumn (October-December), but is adaptable to cover any desired period. See Francken et al. (2014) for more 
details on the analysis. 
Results and discussion 
The results from the yearly averaging of the total load in the HBMC area are presented in Figure 1. 
Comparing the mean transport in 2012, 2013 and 2014 (Figure 1) it is clear that the depth-averaged sediment is 
mostly NE-directed. Most striking is the magnitude of transport along the SE flank of the Westhinder sandbank, 
but also the local variation in the Hinder Banks region. In the northern part of the study area, the general 
transport direction is mainly SW-directed, except for 2014 where the mean transport was near zero. In this 
year, NE-directed transport dominated on average over the whole area. 
To investigate the underlying reasons for this distinct year-to-year variability in total load sediment transport, 
all data was regrouped into seasonal averages and cross-related to atmospheric data coming from the 
measuring pile at the Westhinder Bank (MOW7) (Meetnet Vlaamse Banken, Agentschap Maritieme 
Dienstverlening en Kust). Averaged wind speed at 10m above the sea surface and averaged wind direction 
were combined in wind roses and compared to the total load sediment transport in the Figures 2 to 5. 
Figures 2 and 3 show for 2013 overall predominant winds blowing from the SW and less frequent and less 
strong winds blowing from the NE, which is a normal regime for the Belgian part of the North Sea (Meetnet 
Vlaamse Banken). However, in winter, winds were predominantly blowing from the NE sector and were much 
stronger than in spring and summer. They were often equally strong than the SW winds that occurred less 
frequent. This had a clear effect on the total load. In the northern part of the area, as well along the deeper 
southern part of the Oosthinder sandbank, the mean transport was directed S to SW. In autumn, SW sector 
winds were predominant, but showed a large spread. Almost no wind came from the NE sector. This resulted in 
a predominant SW to NE oriented total load transport. 
The next two figures (Figs. 4 and 5) show the wind roses and averaged total load sediment transport for the 
four seasons of 2014. 
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Figure 1: Yearly (2012-2013-2014) averaged direction of the total load sediment transport in the region of the Hinder Banks. HBMC area is shown in red. 
 
152 
 
 
Figure 2: Seasonal averaged total load sediment transport and wind roses for winter and spring 2013. 
 
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Figure 3: Seasonal averaged total load sediment transport and wind roses for summer and autumn (fall) 2013. 
 
154 
 
Figure 4: Seasonal averaged total load sediment transport and wind roses for winter and spring 2014. 
 
155 
 
Figure 5: Seasonal averaged total load sediment transport and wind roses for summer and autumn (fall) 2014. 
 
156 
 
Figure 4 shows the winter of 2014 characterised by strong and very frequent winds blowing from the W and 
SW sector. Almost no wind originated from the N or the NE. The effect on the average total load transport 
direction is obvious. The global transport over the entire study area was SW-NE oriented. Spring and summer 
showed comparable patterns as in 2013. Both winds from the SW and NE sectors, giving rise to the same 
transport patterns as the previous year. Autumn 2014 again showed winds predominantly blowing from the W 
and SW sector, showing strong winds and wide spread. 
It is clear that the winter of 2014 differed from the one of 2013. Model results show a distinct overall transport 
from the SW to the NE, which is at least partly explained by the meteorological conditions at that time. For the 
validation of the model results, measurements were sought on the depth and morphological evolution in the 
area. To this end FPS Economy, Continental Shelf Service provided a set of monitoring data (multibeam 
datasets) of the HBMC area on a 1m by 1m grid, for the years 2012 – 2014, each year containing two datasets.   
In the SW part of the monitoring area a 2D profile was selected for the analysis of the morphological evolution 
(Figure 6).  
 
Figure 6: Digital elevation model of the HBMC area in 2012. Superimposed (south) is a profile along which depth 
data were extracted for comparison in time. Data courtesy FPS Economy, Continental Shelf Service. 
Depth (m) 
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Figure 7: 2D profiles extracted from the digital elevation model time series. Dark blue and orange are profiles in 
2012, yellow and purple in 2013, green and light blue in 2014. 
Figure 7 shows the time series of the selected 2D profile. The dunes at the beginning of the profile (deeper 
water parts) show a yearly progressive migration. Most striking is the migration of the very large dune at the 
NE extremity of the profile, being located nearest to the top of the sandbank. The position of the dune was 
quasi stable in the years 2012 and 2013, but clearly a large bedform migration occurred at the end of 2013, 
beginning 2014 (winter 2014). In a period of several months, the top of the dune shifted for 80m in a NE 
direction and reduced in height. This testifies that also in the offshore area, dunes have dynamic behaviours 
and respond to changing hydro-meteorological conditions.    
 
Conclusions 
The previously created on-demand queryable sediment transport database (spanning 1999 – 2010) was 
expanded with four more years (2011 – 2014). From this, a subset (2012 – 2014) was selected to study 
variations in the total load sediment transport in the hinder Banks region. At first sight aberrant model output 
could at least be partially explained by deviant atmospheric conditions and the effects were validated by time 
series of a digital terrain model of the HBMC monitoring area in the aggregate sector 4C. Future applications 
are wide-spread and can include the estimation of the regeneration or recovery potential of the seabed, based 
on the natural deposition character of the area. It will also provide insight into the areas that are naturally 
more erosive, hence more vulnerable to the impact of human activities. With direct relevance to Europe’s 
Marine Strategy Framework Directive, future work will concentrate also on the development of envelopes of 
natural variability, critical to distinguish naturally- versus anthropogenically-induced sediment dynamics. 
 
  
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Acknowledgements 
Financial support for this study was provided through the project ZAGRI, a continuous monitoring programme, 
paid from the revenues of marine aggregate extraction activities. Wave analyses, KULeuven, were performed in 
the framework of BELSPO QUEST4D (SD/NS/06B) project. This work contributes also to the Brain.be project 
TILES (Transnational and Integrated Long-term marine Exploitation Strategies), funded by BELSPO under 
contract BR/121/A2/TILES. FPS Economy, Continental Shelf Service is acknowledged for making their 
monitoring datasets of the HBMC area available to us. 
 
References: 
Ackers, P. and White, W.R., 1973. Sediment transport: new approach and analysis. Proceeding of the ASCE Journal of Hydraulics Division, 
99(HY11), 2041-2060.  
Booij, N., Ris, R.C. and Holthuijsen, L.H., 1999. A third generation wave model for coastal regions, Part I, Model description and validation. 
Journal of Geophysical Research, 104, C4, 7649-7666. 
Dalyander, S, Butman, B, Sherwood, C.R, Signell, R.P and Wilkin, J.L., 2013. Characterizing wave- and current-induced bottom shear stress: 
U.S. middle Atlantic continental shelf. Continental Shelf Research, 52, 73-86.  
Degrendele, K., Roche, M., Schotte, P., Bellec, V. and Van Lancker V., 2010. Morphological Evolution of the Kwinte Bank Central Depression 
Before and After Cessation of Aggregate Extraction. Journal of Coastal Research, SI51, 77-86. (IF2009: 1.366) 
Fernández, L., Komijani, H. and Monbaliu, J., 2011. Evaluatie van de Belgische oceaanenergie (BOREAS). Deelrapport « waves ». Belgian 
Science Policy, Science for a Sustainable Development, 32 pp. 
Francken, F.; Van den Eynde, D.; Van Lancker, V. (2014). On-demand assessment of spatial and temporal variability of sediment transport 
parameters, Belgian and southern Dutch part of the North Sea, in: De Mol, L. et al. (Ed.) 'Which future for the sand extraction in the 
Belgian part of the North Sea?'. Study day, 20 October 2014, Belgium Pier - Blankenberge. pp. 73-80  
Holthuijsen, L.H., Booij, N. and Ris, R.C., 1993. A spectral wave model for the coastal zone. Proceedings of the 2nd International Symposium 
on Ocean Wave Measurement and Analysis, New Orleans, USA, 630-641. 
Lanckneus, J., Van Lancker, V., Moerkerke, G., Van den Eynde, D., Fettweis, M.,  De Batist, M. and Jacobs, P., 2002. Investigation of natural 
sand transport on the Belgian continental shelf (Beneficial usage of data and geo-environmental techniques - BUDGET). Scientific Support 
Plan for a Sustainable Development Policy. Brussel (B), Federal Office for Scientific, Technical and Cultural Affairs (OSTC) 
(D/2002/1191/28), 104 + 87 pp. Annex. 
Ozer, J., Van den Eynde, D. Ovidio, F., Berlamont, J., Yu, C.S. and Decouttere, C. 1996. Operational Modelling of the Northwest European 
Continental Shelf (OMNECS). Activity Report N° 2 (in Dutch). Report MUMM-KUL/OMNECS/AR02. Management Unit of the North Sea 
Mathematical Models & Catholic University of Leuven, Hydraulics Laboratory. 
Soulsby, R.L. and Clarke, S.,  2005. Bed shear-stresses under combined waves and currents on smooth and rough beds. Report TR 137. HR 
Wallingford, Wallingford, United Kingdom, 42 pp. (http://www.estproc.net/EstProc_library.htm). 
Soulsby, R.L. and Whitehouse, R.J.S., 2005. Prediction of ripple properties in shelf seas. Mark 2 predictor for time evolution. Final Technical 
Report, Prepared for US Office of Naval Research, Contact No. N00014-04-C-0408. Report TR154, HR Wallingford, 40 pp. + App. 
Swart, D.H., 1976. Coastal sediment transport. Computation of longshore transport. The Netherlands, Delft Hydraulics Laboratory, Report 
R968. 
Swart, D.H, 1977. Weighted value of depth of initiation of movement. South Africa, Stellenbosch, Report NR10.  
Van den Eynde, D., Giardino, A., Portilla, J., Fettweis, M., Francken, F. and Monbaliu, J., 2010. Modelling The Effects Of Sand Extraction On 
The Sediment Transport Due To Tides On The Kwinte Bank. Journal of Coastal Research, SI 51, 106-116. 
Van Lancker, V.R.M. and Jacobs, P., 2000. The dynamical behaviour of shallow-marine dunes. In: A. Trentesaux and T. Garlan (Editors), 
Proceedings of the International Workshop Marine Sandwave Dynamics. University of Lille 1 (F), 213-220. 
Van Lancker, V., Baeye, M., Du Four, I., Degraer, S., Fettweis, M., Francken, F., Houziaux, J.S., Luyten, P., Van den Eynde, D., Devolder, M., 
De Cauwer, K., Monbaliu, J., Toorman, E., Portilla, J., Ullman, A., Liste Muñoz, M., Fernandez, L., Komijani, H., Verwaest, T., Delgado, R., 
De Schutter, J., Janssens, J., Levy, Y., Vanlede, J., Vincx, M., Rabaut, M., Vandenberghe, H., Zeelmaekers, E. and Goffin, A., 2012. 
QUantification of Erosion/Sedimentation patterns to Trace natural versus anthropogenic sediment dynamics (QUEST4D). Final Report. 
BELSPO Science for Sustainable Development (D/2012/1191/19), Brussels, 103 pp. + Annex. 
159 
 
WAMDIG: The WAM Development and Implementation Group, 1988. The WAM-model: a third generation ocean wave prediction model. 
Journal of Physical Oceanography, 18, 1775-1810. 
Yu, C.S., Vermunicht, A., Rosso, M., Fettweis, M. and Berlamont, J., 1990. Numerical simulation of long waves on the north-west European 
continental shelf. Part II: model setup and calibration. Techn. Rep., Fac. Appl. Sciences, Dep. Construction, K.U. Leuven, contract 
BH/88/28 with Ministry of Public Health and Environment.  
  


Application of a large dataset of sediment transport parameters: variability in sediment transport in the HBMC area

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