The impact of disposal of fine-grained sediments from maintenance dredging works on SPM concentration and fluid mud in and outside the harbor of Zeebrugge

The amount of sediments to be dredged and disposed depends to a large part on the suspended particulate matter (SPM) concentration. Tidal, meteorological, climatological, and seasonal forcings have an influence on the horizontal and vertical distribution of the SPM in the water column and on the bed and control the inflow of fine-grained sediments towards harbors and navigation channels. About 3 million tons (dry matter) per year of mainly fine-grained sediments is dredged in the port of Zeebrugge and is disposed on a nearby disposal site. The disposed sediments are quickly resuspended and transported away from the site. The hypothesis is that a significant part of the disposed sediments recirculates back to the dredging places and that a relocation of the disposal site to another location at equal distance to the dredging area would reduce this recirculation. In order to validate the hypothesis, a 1-year field study was set up in 2013–2014. During 1 month, the dredged material was disposed at a new site. Variations in SPM concentration were related to tides, storms, seasonal changes, and human impacts. In the high-turbidity Belgian near-shore area, the natural forcings are responsible for the major variability in the SPM concentration signal, while disposal has only a smaller influence. The conclusion from the measurements is that the SPM concentration decreases after relocation of the disposal site but indicate stronger (first half of field experiment) or weaker (second half of field experiment) effects that are, however, supported by the environmental conditions. The results of the field study may have consequences on the management of disposal operations as the effectiveness of the disposal site depends on environmental conditions, which are inherently associated with chaotic behavior.

[1]  V. Ernstsen,et al.  Formation and entrainment of fluid mud layers in troughs of subtidal dunes in an estuarine turbidity zone , 2013 .

[2]  D. S. van Maren,et al.  The impact of channel deepening and dredging on estuarine sediment concentration , 2015 .

[3]  R. Adriaens.  Neogene and Quaternary clay minerals in the southern North Sea , 2015 .

[4]  Carl T. Friedrichs,et al.  Size and settling velocities of cohesive flocs and suspended sediment aggregates in a trailing suction hopper dredge plume , 2011 .

[5]  A. D. Vethaak,et al.  Environmental impact and recovery at two dumping sites for dredged material in the North Sea. , 2003, Environmental pollution.

[6]  M. Baeye,et al.  Mine burial in the seabed of high-turbidity area—Findings of a first experiment , 2012 .

[7]  A. J. Mehta,et al.  Understanding fluid mud in a dynamic environment , 1991 .

[8]  R. Kirby.  Minimising harbour siltation—findings of PIANC Working Group 43 , 2011 .

[9]  E Garnacho,et al.  Ecological consequences of dredged material disposal in the marine environment: a holistic assessment of activities around the England and Wales coastline. , 2006, Marine pollution bulletin.

[10]  J. Winterwerp,et al.  The effect of dock length on harbour siltation , 2009 .

[11]  D. Roelvink,et al.  Observation and modeling of the storm-induced fluid mud dynamics in a muddy-estuarine navigational channel , 2014 .

[12]  B. Nechad,et al.  Weather and climate induced spatial variability of surface suspended particulate matter concentration in the North Sea and the English Channel , 2012 .

[13]  E. Toorman,et al.  Large-eddy simulations of turbidity plumes in crossflow , 2015 .

[14]  Michael Fettweis,et al.  Evaluation of in situ and remote sensing sampling methods for SPM concentrations, Belgian continental shelf (southern North Sea) , 2011 .

[15]  P. Larcombe,et al.  Estimating the spatial distribution of dredged material disposed of at sea using particle-size distributions and metal concentrations. , 2009, Marine pollution bulletin.

[16]  J. Robbens,et al.  Synthesis report on the effects of dredged material disposal on the marine environment ( licensing period 2010-2011 ) , 2011 .

[17]  T. Kanellopoulos,et al.  A screening procedure for selecting the most suitable dredged material placement site at the sea. The case of the South Euboean Gulf, Greece , 2013, Environmental Monitoring and Assessment.

[18]  Weather and climate related spatial variability of high turbidity areas in the North Sea and the English Channel , 2012 .

[19]  Erwan Garel,et al.  Monitoring estuaries using non-permanent stations: practical aspects and data examples , 2011 .

[20]  Rolf Riethmüller,et al.  On the morphological long-term development of dumped material in a low-energetic environment close to the German Baltic coast , 2009 .

[21]  S. Henson.  Slow science: the value of long ocean biogeochemistry records , 2014, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences.

[22]  M. Baeye,et al.  Seasonal variation in concentration, size, and settling velocity of muddy marine flocs in the benthic boundary layer , 2015 .

[23]  P. Hir,et al.  Application of the continuous modeling concept to simulate high-concentration suspended sediment in a macrotidal estuary , 2000 .

[24]  R. Spanhoff,et al.  Massive Sedimentation Events at the Mouth of the Rotterdam Waterway , 2000 .

[25]  J. Vanlede,et al.  A geometric method to study water and sediment exchange in tidal harbors , 2014, Ocean Dynamics.

[26]  J. Winterwerp.  Reducing Harbor Siltation. I: Methodology , 2005 .

[27]  J. Winterwerp.  Stratification effects by fine suspended sediment at low, medium, and very high concentrations , 2006 .

[28]  Y. C. Agrawal,et al.  Instruments for particle size and settling velocity observations in sediment transport , 2000 .

[29]  Peter D. Thorne,et al.  A review of acoustic measurement of small-scale sediment processes , 2002 .

[30]  Jamie Oliver,et al.  Natural turbidity variability and weather forecasts in risk management of anthropogenic sediment discharge near sensitive environments. , 2004, Marine pollution bulletin.

[31]  P. Régnier,et al.  Nutrient dynamics and phytoplankton development along an estuary-coastal zone continuum: A model study , 2011 .

[32]  Y. Li,et al.  Fluid mud in the wave-dominated environment revisited , 2000 .

[33]  Jason C. S. Yu,et al.  Hydro-meteorological influences and multimodal suspended particle size distributions in the Belgian nearshore area (southern North Sea) , 2012, Geo-Marine Letters.

[34]  V. Lancker,et al.  Changes of sedimentological patterns and morphological features due to the disposal of dredge spoil and the regeneration after cessation of the disposal activities , 2008 .

[35]  Rainer Reuter,et al.  Towards continuous long-term measurements of suspended particulate matter (SPM) in turbid coastal waters , 2009 .

[36]  T. Kessel,et al.  Wave-induced liquefaction and flow of subaqueous mud layers , 1998 .

[37]  P. Barker,et al.  The opening of Drake Passage , 1977 .

[38]  S. Geoffrey Schladow,et al.  Using laser diffraction data to obtain accurate particle size distributions: the role of particle composition , 2010 .

[39]  H. D. Vriend,et al.  Sand–mud morphodynamics in a short tidal basin , 2004 .

[40]  R. Simonini,et al.  Effects of long-term dumping of harbor-dredged material on macrozoobenthos at four disposal sites along the Emilia-Romagna coast (Northern Adriatic Sea, Italy). , 2005, Marine pollution bulletin.

[41]  S. D. Smith,et al.  The effects of dredge-spoil dumping on a shallow water soft-sediment community in the Solitary Islands Marine Park, NSW, Australia. , 2001, Marine pollution bulletin.

[42]  S. Bolam.  Impacts of dredged material disposal on macrobenthic invertebrate communities: A comparison of structural and functional (secondary production) changes at disposal sites around England and Wales. , 2012, Marine pollution bulletin.

[43]  J. C. Agunwamba,et al.  Potential effects on the marine environment of dredging of the Bonny channel in the Niger Delta , 2012, Environmental Monitoring and Assessment.

[44]  V. Van Lancker,et al.  Sediment mobility in response to tidal and wind-driven flows along the Belgian inner shelf, southern North Sea , 2011 .

[45]  Sabine Schmidt,et al.  Turbidity in the fluvial Gironde Estuary (southwest France) based on 10-year continuous monitoring: sensitivity to hydrological conditions , 2015 .

[46]  Matthias Baeye,et al.  Monitoring the effects of disposal of fine sediments from maintenance dredging on suspended particulate matter concentration in the Belgian nearshore area (southern North Sea). , 2011, Marine pollution bulletin.

[47]  P. Thorne,et al.  An overview on the use of backscattered sound for measuring suspended particle size and concentration profiles in non-cohesive inorganic sediment transport studies , 2014, CSR 2014.

[48]  P. Hill,et al.  Single-grain, microfloc and macrofloc volume variations observed with a LISST-100 and a digital floc camera , 2006 .

[49]  E. Toorman.  Modelling of turbulent flow with suspended cohesive sediment , 2002 .

[50]  J. Maa,et al.  Estimation of high-resolution sediment concentration profiles in bottom boundary layer using pulse-coherent acoustic Doppler current profilers , 2011 .

[51]  Arun Kumar,et al.  Continuous measurement of suspended sediment concentration: Technological advancement and future outlook , 2015 .