The effect of land reclamations and sediment extraction on ...The effect of land reclamations and sediment extraction on the suspended sediment concentration in the Ems Estuary D.S

Marine Geology xxx (2016) xxx–xxx

MARGO-05427; No of Pages 11

Contents lists available at ScienceDirect

Marine Geology

j ourna l homepage: www.e lsev ie r .com/ locate /margo

The effect of land reclamations and sediment extraction on thesuspended sediment concentration in the Ems Estuary

D.S. van Maren a,b,⁎, A.P. Oost a,c, Z.B. Wang a,b, P.C. Vos d

a Deltares, Dept. of Coastal and Marine Systems, P.O. Box 177, 2600 MH Delft, The Netherlandsb Delft University of Technology, Faculty of Civil Engineering and Geosciences, The Netherlandsc Utrecht University, Dept. Phys. Geography, P.O. Box 80115, 3508 TC Utrecht, The Netherlandsd Deltares, Dept. Applied Geology and Geophysics, P.O. Box 85467, 3508 AL Utrecht, The Netherlands

⁎ Corresponding author at: Deltares, Dept. of Coastal an2600 MH Delft, The Netherlands.

E-mail address: [email protected] (D.S. van M

http://dx.doi.org/10.1016/j.margeo.2016.03.0070025-3227/© 2016 The Authors. Published by Elsevier B.V

Please cite this article as: vanMaren, D.S., et ain the Ems Estuary, Marine Geology (2016),

a b s t r a c t
a r t i c l e i n f o
Article history:Received 13 August 2015Received in revised form 21 February 2016Accepted 8 March 2016Available online xxxx

Natural sediment sinks have been removed in many estuaries and tidal basins, and the resulting loss in accom-modation space likely led to an increase in the suspended sediment concentration (SSC). The effect of land rec-lamations and changes in other sediment sinks on SSC has been investigated using the Ems Estuary as a well-documented example. Coastline reconstructions and stratigraphic observations in the Ems Estuary, on theDutch–German border, have been used to quantify the long-term (centennial) changes in sediment sinks.These data indicate that approximately 2–3 · 106 dryweight tons of fine-grained sediments annually accumulat-ed in the estuary from the end of the 16th century up to the beginning of the 20th century. In the 20th centuryand especially from 1960 to 1994, large amounts of sediment were dredged and removed from the Ems Estuary.Since the 1990s, sediment removal rates through dredging activities sharply decreased, while available monitor-ing data show that on average SSC in the estuary increased during this period. The potential impact of sedimentsinks on SSC has been investigated using a simple mass balance and a complex numerical model. Both method-ologies indicate that the reduction in sediment sinks lead to an increase in suspended sediment concentration ofseveral 10s ofmg/l averagedover the estuary. The numericalmodel also resolves the spatial variation in changingsuspended sediment concentrations, suggesting that locally the increasemay exceed 100mg/l. Thiswork revealsthat a decrease in accommodation space for fine-grained sediments by land reclamations or by reducing fine-grained sediment extraction will lead to an increase in suspended sediment concentrations, and provides meth-odologies to estimate the impact of interventions on SSC of estuaries and tidal basins.

© 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license(http://creativecommons.org/licenses/by/4.0/).

Keywords:Land reclamationsSuspended sediment concentrationCoastal geologyTurbidity increaseNumerical modelEms Estuary

1. Introduction

Natural estuaries and tidal basins have extensive sub-, inter andsupratidal flats in which fine-grained sediments accumulate throughvarious mechanisms (van Straaten and Kuenen, 1957; Postma, 1961,1967). Depending on sediment supply, sediment demand and localphysical conditions, tidal flats can accumulate at a faster rate than rela-tive sea level rise (RSLR). Rates of infill vary spatially, with largest sedi-mentation rates typically occurring in the sheltered parts of estuariesand tidal basins. In such areas subtidal flats may change into intertidalflats, which in turn may become supratidal salt marshes, influencingthe suspended sediment dynamics in several ways. First the ratio ofsubtidal to intertidal area influences tidal dynamics (Friedrichs andAubrey, 1988). Thus, basin infilling will affect suspended sediment con-centrations (SSC) in the estuary. Secondly, land reclamations influence

dMarine Systems, P.O. Box 177,

aren).

. This is an open access article under

l., The effect of land reclamatiohttp://dx.doi.org/10.1016/j.m

the cross-shore distribution of hydrodynamic energy because the tidalprism is reduced and the cross-shore profile generally becomes steeper.A reduction of the tidal prism leads to smaller tidal flow velocities in thetidal channels, thereby promoting sediment deposition. In wave-dominated environments, seaward encroaching embankments lead tosteeper cross-shore profiles. The resulting increase in hydrodynamic en-ergy reduces deposition of fine-grained sediment in the Wadden Seaforeshore (Flemming and Nyandwi, 1994) and possibly lead to increas-ing suspended sediment concentrations (Dellwig et al., 2000).

Thirdly, a decreasing tidal basin size increases SSC through a de-crease in storage capacity for fine-grained sediments. Sub- to supratidalflats are effective sediment sinks (Nichols, 1989), and more sedimentdeposits in basins with an intact tidal flat–salt marsh sequence than inbasins where salt marsh areas have been reclaimed (e.g. Pedersen andBartholdy, 2006). Fine-grained sediment that does not deposit remainsin suspension, and unless amechanismexists to efficiently transport thefine sediment offshore, the SSC should increase until export equals im-port. Surprisingly, relations between the loss of natural sediment sinksand changes in SSC in the estuary or tidal basin have not yet been

the CC BY license (http://creativecommons.org/licenses/by/4.0/).

ns and sediment extraction on the suspended sediment concentrationargeo.2016.03.007

http://creativecommons.org/licenses/by/4.0/

http://dx.doi.org/10.1016/j.margeo.2016.03.007

mailto:[email protected]


http://creativecommons.org/licenses/by/4.0/

http://www.sciencedirect.com/science/journal/00253227

www.elsevier.com/locate/margo


2 D.S. van Maren et al. / Marine Geology xxx (2016) xxx–xxx

established, even in a qualitative sense. Thismay bebecause inmanyes-tuaries and tidal basins land reclamations have been gradual (coveringperiods of decades to centuries) whereas for many estuarine systemsdecadal SSC observations are rare (Fabricius et al., 2013). Even more,any response in SSC to loss of sediment sinks is obscured by parallelhuman-driven developments, which may have larger short-term im-pacts (such as channel deepening and dredging activities; van Marenet al., 2015a, 2015b). Sediment sinks can be quantified by summationof the individual sediment contributions (e.g. Morton et al., 2000) or ag-gregated estimators such as cores (Nichols, 1989; Beets and van derSpek, 2000), seismics (Sha, 1990) or bathymetric maps (Elias et al.,2012). For many estuaries and tidal basins, the historical coastline evo-lution is well known and becoming increasingly accurate (e.g. Beets andvan der Spek, 2000; Vos and Gerrets, 2004; Vos, 2015), providing infor-mation to estimate historic sediment sinks.

An estuary of which the basin size changes are well known and forwhich detailed paleo-reconstructions are available, is the Ems Estuary(Vos and Knol, 2015). The SSC in the Ems Estuary has been increasingin the past decades (de Jonge et al., 2014; van Maren et al., 2015a),and the reasons for this increase are under debate. The expandingports necessitated deepening of the central channels of the estuaryand regular maintenance dredging. In this way, the port of Emden ex-tracted 1.8 · 106 tons/year of fine sediments over a 30-year period (alltons are dry weight) as part of maintenance dredging. van Maren et al.(2015a) suggest that ending the sediment extraction around 1990was the main driver for the increase in SSC in the past decades. Theyalso hypothesize that the loss of sedimentation areas resulting fromlarge-scale land reclamationsmay have had a similar effect on estuarineSSC as sediment extraction through dredging.

This paper aims to quantify themain historical sediment sinks in theEms Estuary over the past centuries, and relate these sinks to changes inestuarine SSC. In Section 2, we describe the historical development inthe Ems Estuary, including changes in suspended sediment concentra-tion and extraction rates in the past decades. The sediment sinks inthe past centuries are quantified in Section 3. Using two differentmeth-odologies, the sediment sinks are related to changes in estuarine SSC inSection 4. The implications of sinks for SSC in estuarine systems in gen-eral are discussed in Section 5.

2. Historical development of the Ems Estuary

The Ems Estuary, situated on the Dutch–German border (Fig. 1), isan estuary which has undergone large anthropogenic changes in thepast decades to centuries (overview in Table 1). Up to the middleages, the land surrounding the Ems Estuary was primarily composedof peat land with a surface level well above extreme high water levels.With increasing habitation of the area, the land was drained for agricul-tural purposes. The area subsided as a result of the drainage, and dikeswere built to protect the land from being flooded from as early as1000–1100 AD onwards (Oost, 1995; Ey, 2010) to form a continuousdike ring in the 13th century (Vos and Knol, 2015). Thesemodificationsmade the area even more susceptible to compaction, lowering the landsurface to levels below mean sea level. Dyke collapses occurred inDollard Bay as early as 1277 and continued in the 14th, 15th and early16th century. In 1509 AD the flooding of Dollard Bay reached its largestextent, enlarging the embayment to some350km2 (Vos andKnol, 2015;see Fig. 1). It led to wide spread removal of the peats, and subsequentsubsidence of the remaining peats due to the weight of sediments de-posited on top of them, and oxidation and compaction. By sedimenta-tion on top of the peats the area changed from subtidal to supratidal.

In the following centuries, land was gradually reclaimed from thesea (see Fig. 1). Since 1650, the total size of the Ems Estuary betweenEmden and Eemshaven decreased by 40% (from 435 to 258 km2:Herrling and Niemeyer, 2007); the combined intertidal and supratidalarea decreased from 285 to 156 km2. Infilling is mostly of marine origin(the Wadden Sea or North Sea); the sediment load carried by the Ems

Please cite this article as: vanMaren, D.S., et al., The effect of land reclamatioin the Ems Estuary, Marine Geology (2016), http://dx.doi.org/10.1016/j.m

River or local rivers is very small (van Straaten, 1960). As of at leastthe 16th century, the tidal channels in the Ems Estuary were organizedas distinct ebb- and flood channels (van Veen, 1950). Since the beginningof the 19th century the main ebb channel has degenerated and most ofthe estuary was transformed into a single-channel system (see Fig. 1 forcurrent conditions). The exact mechanisms for this transformation arenot fully understood, but are probably related to (a combination of) thereduction in tidal prism of Dollard Bay (Gerritsen, 1952) and deepeningof the central channels for shipping and sediment disposal in thedegenerating channel.

Human interventions accelerated in the past 50 years with the con-struction and extension of three ports (Eemshaven, Delfzijl and Emden)and a shipyard (Papenburg). Deepening of the access channels influ-enced the tidal regime (Chernetsky et al., 2010; Herrling et al., 2014;van Maren et al., 2015b) and estuarine circulation (van Maren et al.,2015a) and requires regular maintenance dredging.

The sediment concentration in the Ems Estuary has significantly in-creased in this period (Fig. 2). The annual change in SSC is computed byfitting a parameterised regression model (van den Boogaard et al.,2006) to the SSC observations, separating periodic variations from themulti-year trend (see Vroom et al., 2012 for details). The error bars indi-cate the 95% uncertainty interval around the observed SSC series, com-puted using a resampling technique (Efron and Tibshirani, 1993). Thedata show that in the 20 year period, the sediment concentration in-creased significantly with 0.7 to 4 mg/l per year, varying per station.The annual increase is largest for stations with a high sediment concen-tration, resulting in an increase in SSC between 0.5 to 3% per year (withthe upper bound of 3% corresponding to a doubling of SSC within24 years).

Multiple mechanisms are probably responsible for the increase inSSC in the estuary, operating concurrently. Dredging was consideredto be the major source for increasing turbidity by de Jonge (1983). DeJonge et al. (2014) hypothesize that channel deepening works mayhave modified transport mechanisms or exposed erodible sediment,thereby increasing SSC, or that offshore sediment supply increased.The lower Ems River (draining into the Ems Estuary) becamehyperturbid in the past decades (probably as a result of deepening;Winterwerp et al., 2013; van Maren et al., 2015b), which may have animpact on turbidity in the Ems Estuary (de Jonge et al., 2014). vanMaren et al. (2015a) suggest that dredging and disposal within theEms Estuary has a smaller impact on SSC than the concurrent deepeningof the tidal channels (leading to increased SSC levels because estuarinecirculation is strengthened), but that the largest contributor to changingsediment concentrations is the loss of sediment sinks. On the short term(decades) the main change in sediment sinks was related to sedimentextraction through dredging works, but over longer timescales (centu-ries) infilling of tidal embayment is probably important. Therefore thehistorical sediment sinks in the Ems Estuary, and in particular in theDollard area where changes were most extensive, are quantified inmore detail in the next section.

3. Reconstruction of historical sinks

3.1. Infill of Dollard Bay

The most extensive land reclamations in the Ems Estuary took placein Dollard Bay (Fig. 1). Mainly fine-grained sediments deposited inDollard Bay from the 16th century onwards, transforming subtidalflats into intertidal flats and subsequently into supratidal marshes.Once the marshes were high enough they would be reclaimed. Uponcompletion, the reclamation works were archived, providing historicalrecords with areal size and date of completion. These records allow areconstruction of the evolution of the size of Dollard Bay (Fig. 3). Thisreconstruction reveals that the rate of reclamation in theDollard is fairlyconstant over the period 1550 to 1924 (Fig. 3), but decreased slightlyafter 1800. We therefore assume the reclamation rate to be constant



Fig. 1.Map of the Ems Estuary (top right) with the three main ports of Eemshaven, Delfzijl, and Emden and the shipyard Papenburg (in blue). Locations S1 to S8 denote SSC observations(see Figs. 2 and 7). The largest coastline changes took place in Dollard Bay, detailed in the lower panel (adapted from Esselink et al., 2011 after de Smet andWiggers, 1960). The line A–Bshows the transect location in Fig. 4. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

3D.S. van Maren et al. / Marine Geology xxx (2016) xxx–xxx

in two distinct periods based on a linearfit for each period: 6.5 · 105m2/year between 1550 and 1800 and 3.3 · 105 m2/year between 1800 and1924. After 1924, the size of Dollard Bay remained approximatelyconstant.

The cumulative area of reclaimed land ΔA can be converted to achange in sediment volume ΔV by multiplying ΔA with the depth ofthe deposits Hd. For Dollard Bay, Hdcan be inferred from historicalcross-sectional profiles based on corings (Vos and Knol, 2015; seeFig. 4). Accumulation of muddy subtidal and intertidal deposits on top


of the (partially) eroded peaty substrate and underlying strongly con-solidated clays provide a clear time marker for sediment accumulation.These existing peat and consolidated clay depositswere fairly uniformlyeroded and – due to later sediment deposition – compressed to a depthof 5 m below present-day chart datum. At other areas the depositionmight have been less: in the order of 2.5 m. A range of Hd = 2.5 to5m accumulating from 1509 onwards provides an average vertical sed-iment deposition rate around 0.5–1mper century, which is much fasterthan local RSLR (0.2 to 0.25 mm/year; e.g. Jensen et al., 1990; Töppe,



Table 1Time chart of the hydro-geomorphologic factors influencing changes in historic sedimentsinks.

Period Description

±1000–1509 Lowering of the bed level of peatlands due to drainage, resultingin regular floodings and development of Dollard Bay

1509–1924 Reclamation of large parts of Dollard Bay1800–present Degeneration of an ebb channel (the ‘Bocht van Watum’),

probably in response to the reduction of the size of Dollard Bay1950–present Construction of ports and deepening of tidal channels1960–1994 Extraction of fine sediment from the port of Emden and

its approach channel1990–present Extraction of fine sediment from the lower Ems River

Fig. 3.Cumulative area of reclaimed land inDollard Bay (ΔA), based on sizes of the poldersand theirmoment of empolderment. TheR2 of the regressionfit is 0.98 in theperiod 1550–1800 and 0.99 in the period 1800–1924.


1993). In equilibrium tidal basins, infill rates are comparable to RSLRwhereas deviations usually result from active river deltas or human in-terventions (Nichols, 1989). The rapid infilling of Dollard Bay thereforereflects thenon-equilibrium conditions resulting fromanthropogenical-ly induced bed level subsidence. Using a vertical accretion range of 2.5to 5 m, ΔV is estimated at 1.6–3.2 · 106 m3/year over the period 1550to 1800, and to 0.8–1.6 · 106 m3/year between 1800 and 1924 (Dollardreclamations in Table 2).

Sediment also accumulated on the bed of the present-day DollardBay (A = 100 km2), but not sufficient to be reclaimed. The thicknessof these deposits is slightly less than the deposits in the reclaimedareas (see Fig. 4), with Hd typically 2 to 4 m. There is no informationavailable on the infill rates over the period since 1550 (as provided byland reclamation records), and therefore it is assumed that depositionrates are constant in time. Accretion is assumed to have continueduntil 1960 (i.e. ΔHd = 0.5–1 cm/year) resulting in ΔV = 0.5 to1 · 106 m3/year (Dollard infill in Table 2).

In order to determine the impact of reclamations on SSC,ΔV need tobe converted to a change in mass of fine-grained sediment ΔM bycorrecting for the mud fraction fmud, the mineral content fmin, and thedry density ρdry:

ΔM ¼ f mud f minρdryΔV: ð1Þ

Mud deposits of several metres thick and centuries old are heavilyconsolidated. A best estimate for the dry density ρdry is 1.25 tons/m3

Fig. 2.Annual change (including 95% uncertainty interval) in sediment concentration C (inmg/l/year) as a function of the sediment concentration C in 2010 for stations S1, S6, S7 andS8 (see Fig. 1 for location). The SSC observations are a 20-year time series ofwater samplescollected1mbelow thewater surface once or two timespermonth at the same tidal stage.


(Puls et al., 1997; Dellwig et al., 2000) representing very consolidatedmud deposits or more recent mixed sand–mud deposits. Sediment de-positing in the present-day Dollard is very fine-grained, with fmud typi-cally between 0.6 and 0.9 in the shallow subtidal and the intertidalareas, but lower and more variable (fmud = 0.3–0.7) in the channels(Fig. 5). The organic content of these recent deposits is 1–5%: theminer-al content fmin is therefore approximated to be 0.98. Since the spatialdetail of these present-day observations is much larger than in the sed-iment cores, they are used as a proxy for the mud content of sedimentdeposited in Dollard Bay. Using these values, ΔM decreases from 1.2–3.5 · 106 tons/year (1550–1800) to 0.6–1.8 · 106 tons/year between1800 and 1924 (Dollard reclamations in Table 2).

The Dollard channel infill is more sandy than the intertidal deposits:fmud of present channel deposits varies between 0.3 to 0.7 (Fig. 5). Usingthe samemethodology and uncertainty as for the Dollard reclamations,this leads to a ΔM between 0.2 and 0.9 · 106 tons/year from 1550 to1960 (Table 2).

3.2. Infill of channels in the Ems Estuary

The decrease of the size of the Dollard (and other areas) reduced theflow velocities in the tidal channels of the Ems Estuary, leading to netaccumulation in these channels. Most of the fine-grained sediment de-posited in the Bocht van Watum, a degenerate tidal channel where onaverage 5 m deposited between 1985 and 2005 (van Maren et al.,2015a). The total sediment volume deposited in this tidal channel(using bathymetric maps of 1985 and 2005) is 20.4 · 106 m3 of sedi-ment, equivalent to 1 · 106 m3/year. The mud content of these depositsis around 50% (see Fig. 5), and assuming a dry bed density ρdry of1000 kg/m3 (being a fairly recent deposit) the annual sink of fine-grained sediment is around 0.5 · 106 tons (Table 2).

The infilling of this channel began early in the 19th century andwithin 150 years, the channel width decreased from ~2 km to severalhundred metres (maps in Gerritsen, 1952). A large part of the channelwas originally up to 10 m deep. Using an average reduction in widthof 1500 m and in depth of 8 m, 180 · 106 m3 deposited in the 15 kmlong channel. The mud content is assumed lower (fmud =0.2–0.4; typi-cal value for present-day active tidal channels, see Fig. 5) and is morecompact than the present-day channel deposits (similarly to theDollard, we assume ρdry is 1250 kg/m3), resulting in an annual sedimentsink of 0.2–0.4 · 106 tons (Table 2).



Fig. 4. Schematized cross-sectional N–S profiles in Dollard Bay (see Fig. 1 for location of transect), in 1750 and 2000. The sediment types are an interpretation of the stratigraphic units inthe original figure by Vos and Knol (2015). Chart datum (CD) is approximately the present-day mean sea level. The mud-layer which formed after the flooding of the Dollard (around1500) has its base on 5 m below MSL. The bay gradually filled in with marine mud: initially with muddy sub to intertidal sediments, followed by tidal marsh deposits. Marshland wasreclaimed with dikes gradually encroaching in the seaward direction (see Fig. 1 for a spatial distribution).


Similar rates of infill may have occurred elsewhere in the estuary butespecially the morphological changes in the more seaward parts of theestuary are less well known. However, this area is more sand-dominated and the tidal volume decrease due to changes in DollardBay was rather slow. Therefore it is assumed that in the outer estuary,reductions inmud deposition rates were too small to significantly influ-ence long-term changes in SSC.

3.3. Dredging activities

Between 1960 and 1994, 5.1 · 106 m3/year was dredged from theport of Emden (1.5 · 106 m3/year) and fairway (3.6 · 106 m3/year)and brought on land (sediment extraction in Fig. 6). Another5 · 106m3 of sediment was dredged and subsequently dispersedwithinthe estuary (data fromMulder, 2013). Approximately 1.5 · 106m3 of theextracted sediment was sand: the remaining 3.6 · 106 m3/year ismud. Since 1994, sediment is no longer dredged from the port ofEmden, but regularly re-aerated, thereby preventing consolidation.The resulting poorly consolidated bed remains navigable, and conse-quently the port no longer requires maintenance dredging (Wurptsand Torn, 2005). At the same time, sediment dredged from the approachchannel to Emden is no longer extracted but dispersed in the estuary.The density of the poorly consolidated sediment currently dredgedfrom the approach channels to Emden is 500 kg/m3 (Mulder, 2013),

Table 2Conversion of annual change in volume ΔV to change inmassΔM in the Dollard basin, using thlamations is computed for two periods (because of a variable ΔV, see Fig. 3), whereasΔM resultthe bandwidth in the uncertainties.

Area Period Areal size Accretion

Dollard reclamations 1550–1800 ΔA = 6.5 · 105 m2/year Hd = 2.5–5Dollard reclamations 1800–1924 ΔA = 3.3 · 105 m2/year Hd = 2.5–5Dollard infill 1550–1960 A = 1 · 108 m2 ΔHd = 0.5–1 cm/yEms channel infill ±1800–1985 A = 2.25 · 107 m2 ΔHd = 4 cm/yearEms channel infill 1985–2005


providing a measure to convert historic extracted sediment volumesto mass. Using this density, on average 1.8 · 106 tons of fine-grainedsediment was annually extracted from the port of Emden and its accesschannel between 1960 and 1994. Sediment was also extracted before1960, but these quantities cannot be quantified in as much detail as inFig. 6. Köthe et al. (2003) estimate that on average 1 · 106 tons/yearwas extracted from the estuary between 1924 and 1960 to raise thebed level of polders.

Sediment is still extracted from the lower Ems River. Since theearly 1980s, the yearly dredged volume in the lower Ems River isdisposed on land and has been steadily increasing from around0.2 · 106 m3/year before the 1993 deepening (Krebs and Weilbeer,2008) to 1.5–2 · 106 m3/year (~0.8 · 106 tons/year) since 1993(Weilbeer and Uliczka, 2012). The dredged sediment was initiallysandy, but is now predominantly muddy (Krebs and Weilbeer, 2008).The rapid increase in extraction from the lower Ems River was probablyrelated to its deepening (van Maren et al., 2015b), although stoppingextraction from the Emden area may have also played a role.

3.4. Timeline of sediment sinks

The sediment sinks elaborated in the previous sections aresummarised in Table 3. The total sediment sink has been decreasingfor centuries, but the most abrupt change was realised in the 1990s,

e mud fraction fmud, themineral content fmin, and the dry density ρdry. ΔM for the land rec-ing fromDollard infill is computed for a longer period. The range inΔM is computed using

ΔV (106 m3/year) fmud (–) fmin (–) ρdry (ton/m3) ΔM (106/year)

1.6–3.2 0.6–0.9 0.98 1.25 2.4 (1.2–3.5)0.8–1.6 0.6–0.9 0.98 1.25 1.2 (0.6–1.8)

ear 0.5–1 0.3–0.7 0.98 1.25 0.5 (0.2–0.9)0.9 0.2–0.4 0.98 1.25 0.3 (0.2–0.4)1 0.4–0.6 0.98 1.0 0.5 (0.4–0.6)



Fig. 5.Distribution ofmud (left panel, defined as the volume fractionwith a grain size smaller than 63 μm)and organic content. Sampleswere collectedwith a box core, fromSeptember toOctober 2013. A subsample of the top 10 cm of the box core sample was analysed with a Malvern Mastersizer for grain size distribution, and heated to 400 °C to determine the organiccontent.


when sediment depositing in the approaches to the port of Emden wasno longer brought on land but dispersed within the estuary. More than2 million tons annually deposited in the Ems Estuary before 1990, butdecreased to 0.5 million tons after 1990. The transition around 1990 isless abrupt when also the sinks in the Ems River are considered, but re-mains large. Up to ~1990, the largest sinks were located in the estuary(Dollard, Bocht van Watum, approaches to the port of Emden), butthereafter mostly in the lower Ems River.

4. Impact on SSC

A change in sediment sinks influences estuarine SSC, similar to achange in sediment sources (such as a river or eroding coastline).The impact of sediment sinks and sources on estuarine SSC is esti-mated in two ways: using an aggregated sediment balance model,and using a complex numerical model. With bothmethods, the effectof annually extracting 1.8 · 106 tons on SSC is investigated. This

Fig. 6. Dredging volumes for the Ems Estuary since 1925: sediment extraction (mainly mud)dredging volumes before 1960 are from de Jonge (1983); dredging volumes after 1960 are f(until 2006; after 2006 a constant value of 1.5 · 106 m3 is assumed).


quantity is equal to extractions of mud from the (approaches to)the port of Emden, but also represents loss of sediment sinksresulting from land reclamations.

4.1. Mass balance

The aggregated sediment balance equation for a water body, e.g.of a whole estuary, can be derived from the three-dimensional con-vection–diffusion equation for suspended sediment concentration:

∂c∂t

þ ∂uc∂x

þ ∂vc∂y

þ ∂wc∂z

−∂∂x

εx∂c∂x

� �−

∂∂y

εy∂c∂y

� �

¼ ws∂c∂z

þ ∂∂z

εz∂c∂z

� �: ð2Þ

Such a derivation is not readily available in scientific literature,and therefore included in Appendix A (see also Appendix A for an

in the Ems Estuary and the lower Ems River, sediment dispersal, and sand mining. Totalrom Mulder (2013) for the Ems Estuary and from Krebs (2006) in the lower Ems River



Table 3Summary of estimated sediment sinks ΔM of fine-grained sediment in the Ems Estuary (in 106 tons/year). Deposition in the Dollard Bay is based on shoreline changes and corings (1).Sediment extraction is based on information of volumes on dump sites by Köthe et al. (2003) (2) and dredging data (Fig. 7) (3).The channel infill sediment mass is based on historicalmaps (4) and bathymetric data (5) whereas extraction from the Ems River (6) is derived from Krebs (2006).

ΔM 1550–1800 1800–1924 1924–1960 1960–1985 1985–1994 1994–2015

Dollard reclamations 2.4 (1.2–3.5)(1) 1.2 (0.6–1.8)(1) ~0 ~0 ~0 ~0Dollard infill 0.5 (0.2–0.9)(1) 0.5 (0.2–0.9)(1) 0.5 (0.2–0.9)(1) ~0 ~0 ~0Sediment extraction – 0.1(2) 1(2) 1.8(3) 1.8(3) 0Ems channel infill ? 0.3 (0.2–0.4)(4) 0.3 (0.2–0.4)(4) 0.3 (0.2–0.4)(4) 0.5 (0.4–0.6)(5) 0.5 (0.4–0.6)(5)

Total Ems Estuary 2.9 (1.4–4.4) 2.1 (1.1–3.2) 1.8 (1.4–2.3) 2.1 (2.0–2.2) 2.3 (2.2–2.4) 0.5 (0.4–0.6)Extraction Ems River – – – – – 0.8(6)

Total 2.9 (1.4–4.4) 2.1 (1.1–3.2) 1.8 (1.4–2.3) 2.1 (2.0–2.2) 2.3 (2.2–2.4) 1.3 (1.2–1.4)

Fig. 7. Computed yearly averaged surface suspended sediment concentration (Csurf, in kg/m3) for 2012, without sediment extraction.


explanation of symbols in Eq. 2). The resulting time-varying massbalance for the change in sediment concentration C for a waterbody with volume V is related to the sediment flux into (Sin) andout of (Sout) the system, a sink term Sink (sediment extracted fromor depositing in the water body) and a source term Source (sedimentsupplied to the system).

d VCð Þdt

¼ Sin−Sout þ Source−Sink: ð3Þ

For simplicity, the source and sink terms are combined as SS=Source−Sink. The dynamic equilibrium sediment concentration is the

sediment concentration at which dðVCÞdt ¼ 0. The sediment flux out of

the estuary Sout is equal to the product of tidal discharge and the sedi-ment concentration in the estuary QhC, and therefore Eq. (3) becomes.

Sin þ SS ¼ Sout ¼ QhC: ð4Þ

In which Qh is an average tidal discharge (m3/s). Assuming that thesediment influx remains unchanged (ΔSin=0), a change in the sourcesor sinks results in a change in the sediment concentration level:

ΔC ¼ ΔSSQh

: ð5Þ

It is noted that the change of the dynamic equilibrium concentrationis independent of the volume of the water body V. However, V does in-fluence the period to achieve new dynamic equilibrium (see Eq. (3)).The measured concentrations (Fig. 2) reflect this transitional period aswell: after 20 years the cumulative increase is 15 to 80 mg/l. Using achange in SS of 1.8 · 106 tons/year (and usingQh=2500m3/s) the sed-iment concentration increase according to Eq. (5) is about 22.5 mg/l.This suggests that the estuary-averaged increase in SSC as a result ofstopping sediment extraction at Emden is 22.5 mg/l since 1990. Thisreasonably corresponds with Fig. 2, although the data also reveal a pro-nounced along-estuary variation in SSC. Such spatial variations cannotbe resolvedwith a simple mass balance, and therefore we subsequentlyquantify sinks with a complex numerical model. The rate at which thesediment concentrations changes depends on the volume of the basinV, and cannot be quantified with Eq. (5) — also here numerical modelsare needed.

4.2. Numerical model

The model is setup using the Delft3D software and covers the EmsEstuary including the lower Ems River, parts of the Wadden Sea, and asmall section of the North Sea (see Fig. 7). A hydrodynamic model,forced by river flows, wind-induced waves (using the SWAN wavemodel), and tides was calibrated against a large amount of water level,salinity, and flow velocity observations (see van Maren et al., 2015afor details). A sediment transport model has been setup incorporatingthe effect of the buffering of fine sediments in the seabed, applyingthe algorithms developed by van Kessel et al. (2011a). These algorithms


are coupled offline with the hydrodynamics, and have proved robustformulations to model the sediment dynamics in the North Sea (vanKessel et al., 2011a), the Western Scheldt (van Kessel et al., 2011b),Singapore (van Maren et al., 2014) and the Ems Estuary (van Marenet al., 2015a). This model distinguishes two bed layers: an upper layer(S1) which rapidly accumulates and erodes, and a deeper layer (S2) inwhich sediment accumulates gradually and is only eroded during ener-getic conditions (spring tides or storms). This S2 layer represents asandy layer inwhichfine sediment accumulates during calm conditions.When the bed shear stress exceeds a critical value the sandy layer be-comes mobile, and fine sediment that infiltrated earlier into this layeris slowly released. Most sediment is stored in this S2 layer; S1 repre-sents the thin fluff layer consisting of mud, which rapidly erodes, char-acteristic for fine-grained estuarine environments. Siltation in the threeestuarine ports and approach channels is computed by the model, andsediments depositing in these ports are disposed on their allocateddumping grounds or brought on land (extraction).

The hydrodynamic model is run for one full year (2012), providinghydrodynamic forcing for the sediment transport model. The sedimenttransport model is run for 10 years (using hydrodynamic input in cyclicmode) until dynamic equilibrium is achieved. The sediment transportmodel has been calibrated against 9 observation stations. Comparisonwith detailed continues observations in the river mouth suggests thatthe model reproduces the intra-tidal and spring–neap variation in SSC(van Maren et al., 2015a). Six stations covering the estuary thalweg(see Fig. 1 for location) reveal that the along-estuary (monthly aver-aged) suspended sediment concentration is comparable with the snap-shot observations taken along the estuary (Fig. 8). The highest sedimentconcentration occurs on the extensive tidal flats in the head of the estu-ary and on the intertidal flats in theWadden Sea (Fig. 7), decreasing to-wards the tidal channels. This along-estuary SSC gradient is the result of



Fig. 8. Monthly averaged computed surface sediment concentration without extraction (black line), with extraction of 0.5 · 106 tons/year (port of Emden only, red line) and of1.8 · 106 tons/year (all ports, blue line) and observed surface sediment concentration (black dots, February through November) in 2012 at stations S1 to S6 (in kg/m3). See Fig. 1 forthe location of stations. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)


tidal asymmetries (in time or along-estuary) in the flow combinedwithfinite values for the critical shear stress and settling velocities (see e.g.van Maren and Winterwerp, 2013), and of gravitational circulation.Gravitational circulation generates an up-estuary flow near the bedand a down-estuary flow near the surface. Due to the typical increaseof SSC from the water surface towards the bed, gravitational circulationdrives an up-estuary sediment transport. Gravitational circulation in theEms Estuary may result from classical salinity driven estuarine circula-tion (as suggested by vanMaren et al., 2015a) or from tidal asymmetriesin vertical mixing (Pein et al., 2014).

Reproducing the up-estuary sediment transport processes is impor-tant for assessing the impact of extraction scenarios on SSC. From theavailable data-model comparison (the tidal dynamics (not shown here— see van Maren et al., 2015a), the along-estuary concentration gradi-ent, and the SSC dynamics in the mouth (see also van Maren et al.,2015a)) it is concluded that the up-estuary transport processes aresufficiently reproduced to quantify the effect of sediment extractionon averaged suspended sediment concentration levels.

In the baseline model, sediment depositing in the ports isdredged and disposed on the allocated dumping grounds. To assess

Fig. 9. Spatial distribution of the computed decrease in yearly averaged SSC when sediment


the effect of extraction, this sediment is not disposed in the estuary,but extracted. For this purpose we use two scenarios: extractingfrom the port of Emden only, and extracting from all ports. The ex-tracted volume from the port of Emden only is 0.5 million tons/year, which is an underestimation of the extraction rates (see vanMaren et al., 2015a for more details on this model shortcoming).Also extracting sediment from the ports of Delfzijl and Eemshaven bet-ter approximates the historic extraction rates (totalling 1.8million tons/year).

Extraction of 1.8 · 106 tons/yearmud (Figs. 8 and 9), leads to a reduc-tion in SSC of ~10mg/l in the outer estuary to ~100mg/l in the inner partsof the estuary (notably Dollard Bay). These numbers are comparablewiththe change in SSC computed with Eq. (5) (22.5 mg/l). Changes in SSC arerelatively small near the estuary boundaries but larger close to the sedi-ment sinks. The effect of extracting 0.5 million tons/year is about threetimes smaller compared to extracting 1.8 million tons/year (Fig. 8). Themodelled impact of extraction is therefore linear, in line with the massbalance approach (Eq. (5)). So despite their strongly contrastingmethod-ologies, both approaches provide similar changes in SSC as a result ofsediment extraction. This suggest that the large effects predicted for

accumulated in the ports and approach channels (total 1.8 · 106 tons/year) is extracted.




sediment extraction are realistic, and that the loss of sediment sinks haveled to a significant increase in SSC.

5. Discussion

The EmsEstuarymay beunique in the combined amount of availabledata, especially related to historical development, stratigraphic infor-mation, observational data covering 4 centuries, but especially in thelarge-scale sediment extraction. This allows the Ems Estuary to functionas an example for the effect of sediment sinks on estuarine SSC.

The computed sediment sinks from 1550 to present provide a first-order estimate of the amount of sediment annually extracted from theEms Estuary. Uncertainties remain related to the three-dimensionalnature of the deposit, the bulk density of the material, and the ratio oforganic material, sand and mud. Nevertheless the work presentedhere demonstrates that typically around 3 · 106 tons of fine-grainedsediment annually deposited in or was extracted from the estuary upto 1994. About 0.5 · 106 tons/year deposits after 1994 within the EmsEstuary itself, although an additional 0.8 · 106 tons is annually extractedfrom the lower Ems River draining into the Ems Estuary. Such sedimentsinks are large compared to the instantaneous suspended sediment con-centration that is present in the water column: the numerical modelsimulates that typically only 0.2–0.4 · 106 tons is suspended in thewater column. An annual change in sediment sinks of 1 · 106 tons ormore therefore has a substantial impact on SSC, as has been demon-stratedwith 2 approaches. These reveal that an average annual decreaseup to 10 mg/l may be expected at the mouth of the estuary when1.8 · 106 tons/year of fines are annually extracted, but may be up toseveral 10s of mg/l at the head of the estuary.

Despite the shortcomings of both model approaches, they providesimilar ballpark numbers for the effect of sediment sinks on the SSC,strengthening confidence in the accuracy of the outcome of bothmodels. The qualitative agreement between observational data, themass balance, and the numerical model therefore suggest that SSC inthe Ems Estuary is rising, at least partly in response to loss of sedimentsinks. Observational data available after 1990 reveal that the sedimentconcentration is indeed increasing, in the order of 0.5 to 3% per year.The slow response of SSC in the data (with a gradual increase in thepast 20 years) suggests that the response time of SSC is (at least) severaldecades. The effect of net sediment deposition on tidal flats on SSC issimilar to sediment extraction through dredging activities. With even

Fig. 10. Overview of former channels and sub- to supratidal flats in theWadden Sea area of thesubtidal area; 2=present day intertidal area; 3= channels and incursions formed and filled upendiked; 6 = higher Pleistocene landscape and barrier islands.


more sediment historically depositing on the flats (3 · 106 tons/yearfrom the 16th to 20th century), the SSC in the Ems Estuarywas probablylower in the past.

An increase in SSC resulting from land reclamations is not unique tothe Ems Estuary. The intertidal areas of many estuaries and tidal basinsworldwide have been reclaimed. The Ems Estuary is part of theWaddenSea, which is composed of multiple tidal basins and estuaries. Theexposed (seaward-facing) tidal flats used to be much wider in thecross-shore direction. Many more sheltered tidal basins and estuaries(providing accommodation space for mud deposition) used to intersectthe hinterland (Fig. 10). In its pristine state (before human interven-tions) the Wadden Sea must have had a very high ability to trap fine-grained sediments. Most of thewide, gently sloping tidal flats borderingthe Wadden Sea have been reclaimed and basins and estuaries havebeen closed off. As a result only half of the original size of the WaddenSea still remains (Reise, 2005). In the 20th century, the Zuiderzee(3600 km2) and Lauwerszee (90 km2) and the German lower Elbe(150 km2), Meldorfer Bucht (48 km2), and Nordstrander Bucht(33 km2) were reclaimed or closed (Reise, 2005). This implies a massivereduction of the sediment accommodation space in the Wadden Sea,and therefore its ability to trap fine-grained sediments. The change inmud deposits resulting from this work is larger than earlier studies indi-cate. Dellwig et al. (2000) suggest that mud deposition decreased from2.3 · 106 tons/year in the Holocene to a present-day 1 · 106 tons/yearin the German part of the Wadden Sea, which is comparable to our esti-mates for the Ems Estuary alone.

It is known that the reclamations in the Dutch part of the WaddenSea have led to increasing sedimentation rates (Wang et al., 2012b;Elias et al., 2012), but do not result in re-establishment of mudflatsand salt marshes (Flemming and Bartholomä, 1997), and consequentlyled to a loss of important habitats (Reise, 2005; Lotze et al., 2005). Basedon the work presented here, land reclamations and closure of basinsmust have had an additional effect: they increased SSC levels in thebasins of the Wadden Sea and therefore the average suspended matterconcentrations in the Wadden Sea must have been substantially lower.The main source of historic observations approximating the suspendedsediment concentration is light attenuation. Giesen et al. (1990) com-piled visibility observations in the Wadden Sea collected between1920 and 1980 (Fig. 11), parameterised with a light attenuation coeffi-cient k. The light attenuation increases with increasing turbidity andin the Wadden Sea, the main factor influencing turbidity is SSC (van

Netherlands and Lower Saxony. Estuary in the centre is the Ems Estuary: 1= present-day; 4= existing tidal channels that were filled up; 5= lowerHolocene coastal zonewhich is



Fig. 11. Light attenuation coefficient k in the Western Wadden Sea, using data of Giesenet al. (1990), suggesting a decreasing visibility from 1920 to 1990. The R2 correlationcoefficient is only 0.18 because of the large scatter in the k-values. See Giesen et al.(1990) for references to the original data.


der Heide et al., 2007; Philippart et al., 2013). The light attenuation ob-servations reveal an increase in k, and therefore probably an increase inSSC. This increase was caused by changed hydrology (following the clo-sure of the Zuiderzee in 1932), and loss of sea grass beds (trapping sed-iment), according to Giesen et al. (1990). In contrast, Philippart et al.(2013) conclude that the turbidity in the Western Wadden Sea hasnot changed in the past 4 decades. However, they analyse a single sta-tion which is close to open sea, and changes resulting from land recla-mations will be larger close to the coastline (where most of themeasurements in Fig. 11 are concentrated). Even more, the most dra-matic changes in turbidity probably occurred in the period before1970 (the starting period in the data analysed by Philippart et al.,2013). We therefore conclude that the SSC in parts of the Wadden Seahave increased (as in Fig. 11), at least partly because of land reclama-tions and/or closures of tidal basins (Fig. 10).

The remaining estuaries in the Wadden Sea (the Elbe, Weser, andEms) have become very turbid (see Winterwerp et al., 2013) and theports established in these estuaries require large amounts of mainte-nance dredging. We have argued that the loss of accommodationspace is at least partly responsible for this increase in SSC. However,channel deepening also leads to higher SSC levels, as demonstrated byWinterwerp et al. (2013) for a.o. the Elbe and Ems estuaries. There aretwo explanations for this apparent contradiction. First, the increase inSSC as a result of deepening is often in the upstream areas of the estuar-ies whereas loss of accommodation space mostly impacts the outer es-tuary. Deepening of the tidal Ems River (draining into the Ems Estuarynear the port of Emden, see Fig. 1) has locally lead to hyperconcentratedconditions (van Maren et al., 2015b), whereas the impact on the outerestuary may have been limited (especially with the Ems River actingas a net sediment sink). Secondly, deepening will only lead to highSSC if the amount of available sediment is sufficiently large. This supplyof sediment has increased because of loss of sediment sinks. Landreclamations therefore contribute to the high turbidity in the upper es-tuaries, even though deepening triggered the transition to highly con-centrated systems. The Wadden Sea estuaries are not unique, andsimilar fine-grained heavily impacted coastal systems are found allover the world, such as along the heavily populated Chinese (Wanget al., 2012a) and Korean (Williams et al., 2013; Williams et al., 2014)coastlines. Based on the work presented here, we expect that also in


these areas the suspended sediment concentrations of near-shorewater bodies has increased, or may increase in the near future.

Supplementary data to this article can be found online at http://dx.doi.org/10.1016/j.margeo.2016.03.007.

Acknowledgements

Part of this work has been carried out for the project ‘MudDynamicsin the Ems–Dollard’, funded by the Dutch Ministry of Public Works infulfilment of the requirements for the Water Framework Directivesand the MIRT project ‘Ecological Perspectives for the Ems–Dollard2050’, funded by theDutchMinistry of PublicWorks and theDutchMin-istry of Foreign Affairs. We thank Marcel Taal for reviewing an earlierversion of thismanuscript, and two anonymous reviewers for their con-structive comments.

References

Beets, D.J., van der Spek, A.F., 2000. The Holocene evolution of the barrier and back barrierbasins of Belgium and the Netherlands as a function of relative sea level rise, lateWeichselian morphology and sediment supply. Neth. J. Geosci. 79, 3–16.

Chernetsky, A.S., Schuttelaars, H.M., Talke, S.A., 2010. The effect of tidal asymmetry andtemporal settling lag on sediment trapping in tidal estuaries. Ocean Dyn. 60,1219–1241.

de Jonge, V.N., 1983. Relations between annual dredging activities, suspended matterconcentrations and the development of the tidal regime in the Ems estuary. Can.J. Fish. Aquat. Sci. 40 (Suppl. 1), 289–300.

de Jonge, V.N., Schuttelaars, H.M., van Beusekom, J.E.E., Talke, S.A., de Swart, H.E., 2014.The influence of channel deepening on estuarine turbidity levels and dynamics, as ex-emplified by the Ems estuary. Estuar. Coast. Shelf Sci. http://dx.doi.org/10.1016/j.ecss.2013.12.030 (01/2014).

Dellwig, O., Hinrichs, J., Hild, A., Brumsack, H.-J., 2000. Changing sedimentation in tidal flatsediments of the southern North Sea from the Holocene to the present: a geochem-ical approach. J. Sea Res. 44 (2000), 195–208.

Efron, B., Tibshirani, R., 1993. An Introduction to the Bootstrap. Chapman & Hall, London.Elias, E.P.L., Van der Spek, A.J.F., Wang, Z.B., de Ronde, J.G., 2012. Morphodynamic devel-

opment and sediment budget of the Dutch Wadden Sea over the last century. Neth.J. Geosci. 91–3 (293–310), 2012.

Esselink, P., Bos, D., Oost, A.P., Dijkema, K.S., Bakker, R., de Jong, R., 2011. Exploration oferosion of the marshes in the Ems–Dollard. PUCCIMAR Rapport 02, A&W Rapport1574 (in Dutch).

Ey, J., 2010. Initiation of dike-construction in the German clay district. Wadden Sea Eco-system 26, 179–183.

Fabricius, K.E., De’ath, G., Humphrey, C., Zagorskis, I., Schaffelke, B., 2013. Intra-annual var-iation in turbidity in response to terrestrial runoff on near-shore coral reefs of theGreat Barrier Reef. Estuar. Coast. Shelf Sci. 116, 57–65.

Flemming, B.W., Bartholomä, A., 1997. Response of theWadden Sea to a rising sea level: apredictive empirical model. Dtsch. Hydrogr. Z. 49 (2–3), 343–353.

Flemming, B.W., Nyandwi, N., 1994. Land reclamation as a cause of fine-grained sedimentdepletion in backbarrier tidal flats (southern North Sea). Neth. J. Aquat. Ecol. 28,299–307.

Friedrichs, C.T., Aubrey, D.G., 1988. Non-linear tidal distortion in shallow well-mixed es-tuaries: a synthesis. Estuar. Coast. Shelf Sci. 27, 521–545.

Gerritsen, F., 1952. Historical and hydrographical investigations in the Ems estuary. Min-istry of Public Works, Hoorn, Report D41 (17 pp. (in Dutch), http://publicaties.minienm.nl/documenten/historisch-hydrografisch-onderzoek-eems).

Giesen, W.B.J.T., van Katwijk, M.M., den Hartog, C., 1990. Eelgrass condition and turbidityin the Dutch Wadden Sea. Aquat. Bot. 37, 71–85.

Herrling, G., Niemeyer, H.D., 2007. Long-term spatial development of habitats in the Ems–Dollard estuary. Harbasins Report.

Herrling, G., Elsebach, J., Ritzmann, A., 2014. Evaluation of changes in the tidal regime ofthe Ems–Dollard and Lower Weser Estuaries by mathematical modelling. Die Küste81, 353–368.

Jensen, J., Mügge, H.-E., Schönfeld, W., 1990. Development of water level changes in theGerman Bight — an analysis based on single value time series. Proc. 22nd ICCEDelft, Netherlands.

Köthe, H., Thies, C., Plaswig, U.N., 2003. Umweltaspekte zur Planung und Bewirtschaftungvon Baggergutablagerungsflächen der Wasser- und Schifffahrtsverwaltung desBundes (WSV) BfG -Jahresarbeitsprogramm-Nr.: 2678, 1 (Fassung BfG – 1376, 48pp. & Anhang).

Krebs, M., 2006. Water quality aspects for optimisation of maintenance dredging in theEms Estuary. Presentation 2006 at WSA Emden (in German).

Krebs, M., Weilbeer, H., 2008. The Ems–Dollart Estuary. Die Küste 74, 252–262.Lotze, H.K., Reise, K., Worm, B., van Beusekom, J., Busch, M., Ehlers, A., Heinrich, D.,

Hoffmann, R.C., Holm, P., Jensen, C., Knottnerus, O.S., Langhanki, N., Prummel, W.,Vollmer, M., Wolff, W.J., 2005. Human transformations of theWadden Sea ecosystemthrough time: a synthesis. Helgol. Mar. Res. 59 (1), 84–95.

Morton, R.A., Ward, G.H.,White,W.A., 2000. Rates of sediment supply and sea-level rise ina large coastal lagoon. Mar. Geol. 167, 261–284.


doi:10.1016/j.margeo.2016.03.007

doi:10.1016/j.margeo.2016.03.007

http://refhub.elsevier.com/S0025-3227(16)30025-1/rf0005









http://dx.doi.org/10.1016/j.ecss.2013.12.030

http://dx.doi.org/10.1016/j.ecss.2013.12.030























http://publicaties.minienm.nl/documenten/historisch-hydrografisch-onderzoek-eems

http://publicaties.minienm.nl/documenten/historisch-hydrografisch-onderzoek-eems
























Mulder, H.P.J., 2013. Dredging Volumes in the Ems–Dollard Estuary for the Period 1960–2011. Unpublished report, Dutch Ministry of Public Works (in Dutch).

Nichols, M.M., 1989. Sediment accumulation rates and relative sealevel rise in lagoons.Mar. Geol. 88, 201–209.

Oost, A.P., 1995. Dynamics and sedimentary development of the DutchWadden Sea withemphasis on the Frisian Inlet: a study of the barrier islands, ebb-tidal deltas, inletsand drainage basins. Geol. Ultraiect. 126 (PhD Thesis Utrecht, 518 pp.).

Pedersen, J.B.T., Bartholdy, J., 2006. Budgets for fine-grained sediment in the DanishWadden Sea. Mar. Geol. 235 (1–4), 101–117. http://dx.doi.org/10.1016/j.margeo.2006.10.008 (20 December, ISSN 0025-3227).

Pein, J.U., Stanev, E.V., Zhang, Y.S., 2014. The tidal asymmetries and residual flows in EmsEstuary. Ocean Dyn. 64 (12), 1719–1741.

Philippart, C.J.M., Salama, M.S., Kromkamp, J.C., van derWoerd, H.J., Zuur, A.F., Cadée, G.C.,2013. Four decades of variability in turbidity in the western Wadden Sea as derivedfrom corrected Secchi disk readings. J. Sea Res. 82, 67–79.

Postma, H., 1961. Transport and accumulation of suspendedmatter in the DutchWaddenSea. Neth. J. Sea Res. 1, 148–190.

Postma, H., 1967. Sediment transport and sedimentation in the marine environment.Estuaries, Special Publication 83, pp. 158–179.

Puls, W., Heinrichs, H., Mayer, B., 1997. Suspended particulate matter budget for theGerman Bight. Mar. Pollut. Bull. 34, 398–409.

Reise, K., 2005. Coast of change: habitat loss and transformations in the Wadden Sea.Helgol. Mar. Res. 59 (1), 9–21.

Sha, L.P., 1990. Geological research in the ebb-tidal delta of “Het Friesche Zeegat”.Wadden Sea, The Netherlands, Report R.G.D. Project 40010 (20 pp.).

Töppe, A., 1993. Zur Analyse des Meeresspiegelanstieges aus langjährigenWasserstandsaufzeichnungen an der Deutschen Nordseeküste. Mitt. des Leichtweiß-Instituts der TU Braunschweig, H. 20 (132 pp.).

van den Boogaard, H.F.P., Uittenbogaard, R.E., Mynett, A.E., 2006. Generalised cross-covariance analysis for uncertainty estimation of shifts in time series. Proc.Hydroinformatics 2006 Vol. II. Research Publishing, Chennai, pp. 1543–1550.

van der Heide, T., van Nes, E.H., Geerling, G.W., Smolders, A.J., Bouma, T.J., van Katwijk,M.M., 2007. Positive feedbacks in seagrass ecosystems: implications for success inconservation and restoration. Ecosystems 10 (8), 1311–1322.

van Kessel, T., Vanlede, J., de Kok, J.M., 2011b. Development of a mud transport model forthe Scheldt estuary. Cont. Shelf Res. 31, S165–S181. http://dx.doi.org/10.1016/j.csr.2010.12.006.

van Kessel, T., Winterwerp, J.C., van Prooijen, B., van Ledden, M., Borst, W., 2011a. Model-ling the seasonal dynamics of SPM with a simple algorithm for the buffering of finesin a sandy seabed. Cont. Shelf Res. 31, S124–S134. http://dx.doi.org/10.1016/j.csr.2010.04.008.

van Maren, D.S., Winterwerp, J.C., 2013. The role of flow asymmetry and mud propertieson tidal flat sedimentation. Cont. Shelf Res. 60S, S71–S84.

van Maren, D.S., Liew, S.C., Hasan, G.M., 2014. The role of terrestrial sediment on turbiditynear Singapore's coral reefs. Cont. Shelf Res. 75–88 http://dx.doi.org/10.1016/j.csr.2013.12.001.


van Maren, D.S., van Kessel, T., Cronin, K., Sittoni, L., 2015a. The impact of channel deep-ening and dredging on estuarine sediment concentration. Cont. Shelf Res. 95, 1–14.http://dx.doi.org/10.1016/j.csr.2014.12.010.

van Maren, D.S., Winterwerp, J.C., Vroom, J., 2015b. Fine sediment transport into thehyperturbid lower Ems River: the role of channel deepening and sediment-induceddrag reduction. Ocean Dyn. http://dx.doi.org/10.1007/s10236-015-0821-2.

van Straaten, L.M.J.U., 1960. Transport and composition of sediments. Verh. Kon. Ned.Geol. Mijnb. K. Gen./Geol/ Serie DI. XIX 279.

van Straaten, L.M.J.U., Kuenen, Ph.H., 1957. Accumulation of fine grained sediments in theDutch Wadden Sea. Geol. Mijnb. 19, 329–354.

van Veen, J., 1950. Ebb and flood channel systems in the Netherlands tidal waters. J. R.Dutch Geogr. Soc. 67, 303–325 (in Dutch).

Vos, P.C., 2015. Origin of the Dutch Coastal Landscape. Long-term Landscape Evolution ofthe Netherlands During the Holocene, Described and Visualized in National, Regionaland Local Palaeogeographical Map Series (PhD thesis, Utrecht University, Barkhuis,Groningen, 359 pp.).

Vos, P.C., Gerrets, D.A., 2004. Archaeology, a major tool in the reconstruction of the coastalevolution of Westergo (The Northern Netherlands). Quat. Int. 133–134, 61–75.

Vos, P.C., Knol, E., 2015. Holocene landscape reconstruction of the Wadden Sea area be-tween Marsdiep and Weser. Explanation of the coastal evolution and visualizationof landscape development of the northern Netherlands and Niedersachsen in fivepalaeogeographical maps from 500 BC to present. Neth. J. Geosci. 94-2, 157–183.

Vroom, J., van den Boogaard, H.F.P., van Maren, D.S., 2012. Mud dynamics in theEms–Dollard, research phase 2: analysis existing data. Deltares Report1205711.001 (97 pp.).

Wang, Y.P., Gao, S., Jia, J., Thompson, C.E.L., Gao, J., Yang, Y., 2012a. Sediment transportover an accretional intertidal flat with influences of reclamation, Jiangsu coast,China. Mar. Geol. 291–294, 147–161. http://dx.doi.org/10.1016/j.margeo.2011.01.004 (1 January, ISSN 0025-3227).

Wang, Z.B., Hoekstra, P., Burchard, H., Ridderinkhof, H., De Swart, H.E., Stive, M.J.F., 2012b.Morphodynamics of the Wadden Sea and its barrier island system. Ocean Coast.Manag. 68, 39–57. http://dx.doi.org/10.1016/j.ocecoaman.2011.12.022.

Weilbeer, H., Uliczka, I., 2012. Model studies for sediment management in the Outer Ems.BAW Report Nr. A3955 03 10144 (61 pp. (in German)).

Williams, J., Dellapenna, T., Lee, G.-H., 2013. Shifts in depositional environments as anatural response to anthropogenic alterations: Nakdong Estuary, South Korea. Mar.Geol. 343, 47–61. http://dx.doi.org/10.1016/j.margeo.2013.05.010 (ISSN 0025-3227).

Williams, J., Dellapenna, T., Lee, G.-H., Louchouarn, P., 2014. Sedimentary impacts of an-thropogenic alterations on the Yeongsan Estuary, South Korea. Mar. Geol. 357,256–271. http://dx.doi.org/10.1016/j.margeo.2014.08.004 (1 November, ISSN 0025-3227).

Winterwerp, J.C., Wang, Z.B., van Braeckel, A., van Holland, G., Kösters, F., 2013. Man-induced regime shifts in small estuaries — I: a comparison of rivers. Ocean Dyn. 63(11–12), 1293–1306.

Wurpts, R., Torn, P., 2005. 15 years of experiencewith fluidmud: definition of the nauticalbottom with rheological parameters. Terra Aqua 99, 22–32.































http://dx.doi.org/10.1016/j.csr.2010.12.006









http://dx.doi.org/10.1007/s10236-015-0821-2






















http://dx.doi.org/10.1016/j.ocecoaman.2011.12.022











Documents

The effect of land reclamations and sediment extraction on ...The effect of land reclamations and sediment extraction on the suspended sediment concentration in the Ems Estuary D.S