Analysis of Water Level Data for the Eems-Dollard estuary

5/26/2018 Analysis of Water Level Data for the Eems-Dollard estuary

Memo

To

Deltaprogramma Wadden

Date

10 December 2013Number of pages

45

From

Zheng Bing Wang

Albert Oost

Direct l ine

+31 (0)88 33 58 202E-mail

[email protected]

Subject

Analysis of water level data for the Ems-Dollard Estuary

1 Introduction

In the last decades the human interferences have led to two changes in the Ems-Dollard

Estuary: increase of the turbidity and intensifying of the tidal intrusion. The two changes are

related to each other and they strengthen each other. However, it is still not clear which humaninterference (land reclamation, harbour development, deepening of the navigation channels,Sperrwerken, etc.) have had the most influence for the observed changes. Also the

morphological development in the estuary, natural or not, can have had influence on the

observed changes. Improved insight in which human interferences and morphological

development have led to the largest changes in the water movement is important for the long-

term safety strategy.

The objective of the present study is to find out which human induced changes have had most

effects on the changes of the hydrodynamics in the Ems-Dollard Estuary.

The changes of the hydrodynamics is evaluated by analysing the data collected at all the tidal

gauges in the system, from seawards side to landwards side: Huibertgat, Borkum, Emshaven,

Delfzijl, Knock, Nieuwe Statenzijl, Emden, Leerort, Papenburg, Herbrum. The time series ateach station is divided in periods of about a lunar day (two tidal cycles). For each period the

tidal characteristics are analysed in order to obtain detailed information concerning the

development in time of the tidal amplification, tidal asymmetry, etc.. Further a detailed

inventory of the human interferences is made. By comparing the development of the

interferences to that of the tidal characteristics we hope to obtain better insight into which

interference led to which changes in the hydrodynamics.


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2 Available data and methods of analyses

2.1 Study area and tidal dataThe Ems-Dollard Estuary under consideration includes the Outer-Ems, the Dollard and the

Ems River. A distinction between the inner and outer parts of the estuary will be made with as

boarder between the two the barrier Sperrwerk. Figure 1 shows the study area with the

positions of the tidal stations.

Figure 1. The Ems-Dollard Estuary and the tidal stations (mi snog Borkum and Herbrum).

On the Dutch side there are four stations, Huibertgat, Emshaven, Delfzijl and Nieuw Statenzijl.

At these stations the water levels have been measured with different starting dates. In the past

the measurements were recorded with a 1 hour time interval and the more recent data are with

a time interval of 10 minutes. In table 1 the periods in which data with the two time intervals are

available are given for each station.

Table 1. Tidal records at the Dutch stations

Station Period 1 hour interval data Period 10 minute interval data

Huibertgat 19-01-1973 - 02-09-1987 Since 03-09-1987

Emshaven 29-12-1978 07-01-1988 Since 07-01-1988

Delfzijl 01-01-1971 -31-12-1986 Since 01-01-1987

Nieuw Statenzijl 01-01-1979 - 07-01-1988 Since 07-01-1988

On the German side there are eleven stations, from seawards to landwards: Borkum-S,

Borkum-F, Knock, Emden, Pogum, Terborg, Leerort, Weener, Papenburg, Rheden and

Herbrum. At these stations The HW-LW data are available with different start-date are given in

Table 2.


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Table 2. HW LW records at the German stations

Station Start date HW-LW dataBorkum-S 31-10-1935

Borkum-F 1-10-1963

Knock 1-11-1977

Emden 1-10-1949

Pogum 1-10-1949

Terborg 1-11-1969

Leerort 1-10-1949

Weener 1-1-1970

Papenburg 1-10-1949

Rheden 1-11-1982

Herbrum 1-10-1949

Furthermore, for the most recent period, since end last century, water level records with a time

interval of 1 minute are available for a couple of stations. As the period of this dataset is

relatively short and the longer dataset of HW-LW already supply the characteristics of the

development of the tide in the estuary it is not used in this study.

2.2 Analysis methodsThe water level data at the four Dutch stations have been analysed by dividing the whole

period into intervals of 24 hours and 50 minutes. For each of the intervals, a Fourier series is

determined. This method is first applied to the Guadalquivir River for analysing the effects of

river flood events on the tidal amplification in the estuary (see Wang et al., 2013). For the

period in which only 1 hour interval data is available the data is first linearly interpolated to 10

minutes time interval in order to be able to make the same analysis for the whole period in

which water level records are available.

The analysis produces for each time interval of about a day (50 minutes more) the averaged

water level, amplitudes and phases of the diurnal, semi-diurnal and quarter-diurnal tidal

components. Note that e.g. the semi-diurnal component is the combined result of al semi-

diurnal tidal constituents (M2, S2, N2, ).

With respect to a standard harmonic analysis (see e.g. Pawlowicz et al., 2002) or the

admittance method (Munk and Cartright, 1966) this method is better suited for identifying

sudden changes as it provides day to day variations. A drawback of this method is that the

results show scatters due to short-term variations. However, this can be filtered out by t ime

averaging using a proper averaging period.

For the 11 German stations the HW-LW records are analysed. Each record contains the waterlevel (LW or HW) and the time in the format dd-mm-yyyy-hh-mm. The method of analysis is

depicted in Figure 2. Each time a time frame indicated by the box is considered. The first 4

records are used to determine (averaged) LW and HW. The last record is needed for

determining the (averaged) rising and falling periods. Each time the box is moved by one data

point, resulting in the same number of records in the output- file as in the input-file. The

averaged HW (/LW) is equal to the average of the first two HW (/LW) values. The tidal range is

equal to the difference between the averaged HW and the averaged LW. The mid-tide is

determined as the average of the averaged HW and the averaged LW. The daily difference is

determined by taking the averaged value of the difference between the two HW values and that


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between the two LW values. The rising (/falling) period is determined by taking the averaged

value of the two rising (/falling) periods.

Figure 2. Analysis of the HW-LW dataset.

The Dutch data and the German are different and they are analysed using different methods.

However, the results of the two analyses contain similar information for the same

characteristics of the tidal wave in the estuary. In Table 3 an overview of the characteristics ofthe tide and the corresponding parameters in the output of the two analyses is given. In the

present study emphasis is put on the tidal amplification and the tidal asymmetry in the estuary.

These two aspects are respectively discussed in the next two chapters.

Table 3. Corresponding parameters from the two analyses for the various characteristics of tide

Characteristic tide Fourier series HW-LW analysis

Mean water level Average water level a0 Mid-tide

Tidal amplification Amplitude semi-diurnal comp. a2 Tidal range

Tidal asymmetry Quarter- and semi-diurnal comp. a4/a2,

Difference falling and rising

per.

Diurnal tide Amplitude diurnal component a1 Daily inequality

2.3 Inventory of human interferenceAn inventory has led to a long list of events in the system including human interferences and

natural events like major flooding in the early history (see Appendix). Looking at the recent

history, two major types of human interferences can be identified: land reclamation and

deepening of the navigation channels. Figure 3 shows the historical development of the total

reclaimed area from the Ems-Dollard Estuary. Most reclamation took place before 1900 and in

the period in which the tidal data are analysed no more land reclamation took place.


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Figure 3. Historical development of land reclamation in the estuary

Figure 4 shows the historical development of the navigation depth in the various parts of the

estuary. Two deepening period of the navigation channel in the Ems River (inner estuary) can

be identified. Roughly from 1950s to 1960s the navigation channel between Leerort and

Papenburg were deepened to the same depth as the downstream part (from ~ 4m to ~5.5 m).

The from the mid 1980s to the mid 1990s the navigation channel in the whole Ems River (from

Emden to Papenburg) is deepened from 5.7 m to 7.3 m.

Figure 4. Historical development of the navigation depth in the various parts of the estuary

Other human interferences include many types of engineering works. Most of these

engineering works are not expected to have substantial influences on the changes of the tidal

intrusion in the system. Those expected to have more influence are listed in the following table.


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Table 4. Other relevant human interferences

Year Interference1984-1990 Streamlining of the river curve radius at the Bight of Weekeborg and the Bight of

Stapelmoor by about 400 m each

1998-2002 Construction Emssperrwerk at Gandersum


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3 Ampli fication of the tide in the estuary

3.1 IntroductionFor the amplification of the tide we look at the semi-diurnal component, the major tidal

component in the area. For the Dutch stations we use the amplitude of the semi-diurnal

component and for the German stations we use the averaged tidal range to determine the

amplification factor between two stations.

2_ upstream station

2_downstream station

Amplification factor =a

a

(1)

For the German stations a2in this equation is replaced by the averaged tidal range.

The original results from the analyses contain a lot of scatters. Most of the scatters are

caused by the spring-neap variation (Wang et al., 2013). Therefore the results are presentedtogether with a line with smoothed results by moving averaging over 57 data points.

3.2 Outer part of the estuary

For the outer part of the estuary we mainly look at the four Dutch stations. The amplification

factors between the other three stations and the most seawards station Huibergat are

respectively shown in Fig.5a, Fig.5b and Fig.5c. The amplification in the part betweenEmshaven and Huibergat (Fig.5a) shows little trend. Only a very small increase between the

end and the begin of the data record can be observed.

Figure 5a. Development of amplification factor between Emshaven and Huiberhat.


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Figure 5b. Development of amplification factor between Delfzijl and Huiberhat.

The amplification factor between Delfzijl and Huibergat (Fig.5b) shows more increase in t ime,

but it is still l imited. The increase mainly happened in two periods, between 1975 and 1987 and

after 2000.

The amplification factor between Nieuwe Statenzijl and Huibergat (Fig.5c) shows no long-term

increase. It is further noted that the tidal amplitude at Nieuwe Statenzijl apparently containmore/stronger fluctuations others than the spring-neap variation. At the other two stations

(Fig.5a and Fig.5b) the smoothed signal using moving averaging contains much weaker

fluctuation which is mainly due to seasonal variation. A possible cause for this aberrant

behaviour is that the effective drag in the Dollard is influenced by stochastic factors e.g. storms

via their influence the sediment concentration.


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Figure 5c. Development of amplification factor between Nieuwe Statenzijl and Huiberhat.

Another way to examine the behaviour of a certain part of the estuary is by looking at the

relation between the amplification factor and the amplitude of the tide. Figure 6 shows thisrelation for the part between Delfzijl and Huibergat. The pattern shown in this figure is typical

for a low turbid system. By low turbid we mean that the suspended sediment concentration is

not high enough to influence the apparent roughness (see Winterwerp and Wang, 2013,

Winterwerp et al., 2013, Wang et al., 2013). With constant roughness the dissipation due to the

bottom friction is much stronger during spring tide than during neap tide, as the friction term in

the momentum equation is proportional to the square of the flow velocity. This explains the

decreasing amplification with increasing amplitude. The figure shows the relation for two

different periods in two separate panels. By comparing the two panels with each other it can

also be seen that the tidal amplification becomes slightly stronger in time.

Figure 6. Relation between amplification factor and the tidal amplitude (Delfzijl/Huibergat)


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Figure 7. Relation between amplification factor and the tidal amplitude (NW Statenzijl/Delfzijl),

Left: recent period, Right: whole dataset.

Figure 7 shows the same relation for the part between Delfzijl and Nieuwe Statenzijl. Theamplification of the tide between these two stations behaves quite different. The decrease of

the amplification factor with increasing amplitude is no more as clear as in Fig.6, especially for

the more recent period (left panel Fig.7). This can indicate that in this part of the estuary the

turbidity is higher and it causes a lowering of the apparent roughness. The behaviour can then

be explained by the fact that at spring tide the stronger flow causes higher suspended

sediment concentration which in turn causes more lowering of the apparent roughness.

However, two other observations make it less certain. First, as observed in Fig.5c, the tidal

amplitude at Nieuwe Statenzijl contains other (unexplained) fluctuations. Second, the

amplification factor as shown in Fig.7 is not very high which seems to be contradictory with the

low roughness due to high turbidity reasoning. Therefore the nearby two German stations areused to examine this aspect. Figure 8 shows the development of the amplification factor

between Emden and Knock (based on tidal range) and Fig.9 shows how it depends on the tidal

range. Note that these two stations enclose about the same area as the two Dutch stations, butthey are located along the other bank of the estuary and there is a dam at the mouth of the

Ems River. The development of the amplification factor (Fig.9) shows two remarkable

differences compared to along the Dutch side. First, the amplification factor is larger and

second, it shows more increase in time. Similar to the observation on the Dutch side, the

amplification factor does not show clear decrease with increasing tidal range (Fig.9), indicating

that this part of the estuary is indeed turbid enough that the apparent roughness is influenced

by the suspended sediment concentration. Apparently the location of the station Niuewe

Statenzijl is such that the water level there is also influenced by other factors. The most likely

explanation is that the tide at this station is influenced by the discharge of fresh water at the

Sluices near the tidal gauge station.


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Figure 8. Development of amplification factor between Emden and Knock

Figure 9. Relation between amplification factor and the tidal range (Emden/Knock), Left: whole

dataset, Right: recent period.

3.3 Inner part of the estuary

Along the inner part of the estuary, between Emden and Herbrum, only German stations are

present. At the five stations Emden, Pogum, Leerort, Papenburg and Herbrum the data series

are the longest. Therefore the analysis of the tidal amplification will focus on these five stations.

Figures 10 through 13 show the characteristics of the tidal amplification in the four sections

between the five stations. In each figure the development of the amplification factor in time is

shown together with its dependence with the tidal range (at the downstream station) for the

whole dataset, the recent period and the early period.


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Figure 10. Characteristics of the tidal amplification between Emden and Pogum. Upper left:development of the amplification factor in time. Upper right: dependence on tidal range, wholedataset. Lower left: recent period. Lower right: early period.

Between Emden and Pogum (Fig.10) the amplification factor shows a clear increase in the

period 1975 1985. Before this period a slight decreasing trend is observed and after this

period no clear trend is observed. Another remarkable feature is that since the mid 1980s the

time variation of the amplification factor shows much less scatter than before. The decrease of

the amplification factor with increasing tidal range is not clear, indicating that this is a high

turbid area, at present as well as in the early period (before 1961).

The tidal amplification between Pogum and Leerort (Fig.11) shows two increasing period, inthe 1960s and between the mid 1980s and the mid 1990s. A remarkable feature is that theamplification factor shows some extreme lows in a number of periods. It seems that theseextreme lows occur more often in the most recent period. The dependence of the amplificationfactor to the tidal range shows more a decreasing trend compared to that between Emden andPogum (Fig.10), but it is still not the same typical variation as shown in Fig.6 for a low turbidarea. Moreover, this trend does not show a significant difference between the early period andthe most recent period.

The amplification factor between Leerort and Papenburg shows increasing trend until the mid1970s. This is followed by a decreasing period of about 7 year and then an increasing perioduntil around 1990. Since around 1990 the amplification factor remains more or less constant.The amplification factor does certainly not show a decreasing trend with increasing tidal range.In the most recent period it does not show much change with changing tidal range and in theearlier period it even shows a slight increasing trend.

The amplification factor between Papenburg and Herbrum shows similar development as thatbetween Leerort and Papenburg. The only difference is that in the period since around 1990 itshows a decreasing trend rather than constant. The amplification factor shows an increasingtrend with increasing tidal range, especially in the early period.


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Figure 11. Characteristics of the tidal amplification between Pogum and Leerort. Upper left:development of the amplification factor in time. Upper right: dependence on tidal range, wholedataset. Lower left: recent period. Lower right: early period.

Figure 12. Characteristics of the tidal amplification between Papenburg and Leerort. Upper left:development of the amplification factor in time. Upper right: dependence on tidal range, wholedataset. Lower left: recent period. Lower right: early period.


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Figure 13. Characteristics of the tidal amplification between Herbrum and Papenburg. Upperleft: development of the amplification factor in time. Upper right: dependence on tidal range,whole dataset. Lower left: recent period. Lower right: early period.

3.3 Discussions and conclusions

In the outer part of the estuary the tidal amplification has become stronger. Question arises if

this is sufficient for explaining the increased extreme high water in the area. The increase ofthe amplification factor is about 5% (see e.g. Fig.5b for Delfzijl), corresponding to an increasein HW during spring tide of about 7 cm in the whole period of 50 years (1973-2013), or a long-term trend of about 1.8 mm/y, similar to the effect of sea-level rise. Due to the stronger tidalamplification the HW trend thus can have a double value as the trend of the mean sea-level.The trend of the yearly maximum water level at Delfzijl is estimated to be about 4.5 mm/y. Thisis more than the combined effect of sea-level rise and the stronger tidal amplification. Theremaining part can be explained for a large extent by the increase of the tidal amplitude at themouth of the estuary (see Fig.14).


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Figure 14. Development of the amplitude of the semi-diurnal tide at the mouth of the estuary,Huibergat station.

For the outer part of the estuary it is hard to identify which particular human interference hascaused / triggered the observed development of the tidal amplification. As the increasing trendin the tidal amplification (see e.g. Fig.5b) is still continuing it is important to take this intoaccount in future strategy for the safety against flooding. It is also worth to notice that in themost recent period tide with largest amplitude tend to be relatively more amplified (see rightpanel of Fig.6: the cluster of dots on the right are all above the solid line).

The way in which the tidal amplification depends on the amplitude of tide indicates that the

major part of the outer estuary is low turbid in the sense that the sediment concentration doesnot influence the apparent roughness. Only in the most landwards part of the Dollard thebehaviour of the tidal amplification indicates that the system is turbid.

The change of the tidal amplification in the inner part of the estuary, the Ems River, is muchstronger than in the outer part. Upstream of Pogum the amplification becomes much stronger.The amplification factor between Leerort and Pogum increased by more than 20% sincearound 1950, between Leerort and Papenburg by more than 30%, and from Herbrum andPapenburg by more than 10%. The tidal range in the most upstream part of the estuaryincreased enormously as reported by others (see e.g. Winterwerp et al., 2013).

The much stronger changes of the amplification in the inner part of the estuary can better berelated to the reported human interferences (see Chapter 2), especially to the deepening of the

navigation channel. There are two major deepening periods for the navigation channel in theinner part of the estuary. The first one is from end 1940s and 1960 in which the navigationchannel between Leerort and Papenburg has been deepened to about the same depth as thedownstream part between Emden and Leerort. The second one is from end 1980s to mid1990s in which the navigation channel through the whole length from Emden to Papenburg isdeepened by about 1.5 m. These periods corresponds well with the development of the tidalamplification in the Ems River. It is e.g. very plausible to argue that the two increasing periodsof the amplification factor between Papenburg and Leerort are triggered by the two majordeepening activities of the navigation channel.

The relation between the amplification factor and the tidal range in the inner part of the estuaryconfirms that the Ems River is a high turbid system. The data seem to indicate that the system


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was already high turbid in the past. However, observations by others indicate that the turbidity

at present is much higher than in the past (see Vroom et al., 2012). This contradiction may beexplained by the following hypothesis: The river was very shallow in the past, so the tidalamplification is very sensitive to the change of bedding forms which adjust to the flow conditionrapidly.

Concerning spatial distribution the present analysis indicates that the region between Pogumand Leerort can be a relatively low turbid region, in the past as well as at present.


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4 Tidal asymmetry

4.1 Relevance of tidal asymmetry and the indi cators

Tidal asymmetry is an important mechanism causing residual sediment transport in estuaries

and tidal lagoons. For an estuary like the Ems Estuary with fine sediment there are two kinds of

asymmetries which are important: asymmetry in falling- and rising-tide periods and asymmetry

in HW and LW slacks.

If falling-tide is longer than rising tide it means that the flow velocity during flood is stronger

than during ebb, as the discharge and flow velocity is proportional to the time derivative (falling

or rising rate) of the water level. Stronger flood-velocity than ebb-velocity causes a landwards

residual sediment transport as sediment transport rate is more than linearly proportional to the

flow velocity. Therefore the tide is called flood-dominant when falling-tide period is longer thanrising-tide period. For the German stations the periods of falling- and rising-tide are

determined. So the straightforward indicator for this type of tidal asymmetry is the difference

between the falling-tide period and the rising-tide period. For the Dutch stations the indicators

are the amplitude ratio and the relative phase-lag between the quarter-diurnal component and

the semi-diurnal component determined from the Fourier series analysis. The relative phase-

lag (phase of quarter diurnal component minus two times the phase of semi-diurnal

component) indicates the nature (flood- or ebb-dominant) of the tidal asymmetry and the

amplitude ratio indicates the strength of the asymmetry. The tide is flood-dominant if the

phase-lag is between 0 and -180 degree. The flood dominance is the strongest if the phase-lag

is equal to -90 degree.

If HW-slack is longer than LW-slack suspended sediment will have more time to settle down

during HW-slack favouring import of fine sediment into the estuary. For the German stations noindicator is available for this type of asymmetry. For the Dutch stations again the amplitude

ratio and the relative phase-lag between the quarter-diurnal component and the semi-diurnal

component determined from the Fourier series analysis are used as indicators. The difference

between the HW-slack and the LW-slack is the longest if the phase-lag is equal to -180 degree.

4.2 4.2 Outer estuary

For the outer estuary the relation between the quarter diurnal and the semi-diurnal components

at the four Dutch stations are used for investigating the development of the tidal asymmetry.These two parameters at the four stations are shown in Figures 15 through 18 respectively.

At Huibergat (Fig.15) the relative phase lag does not show any long-term increasing or

decreasing trend. It varies around a value not much larger than -180 degree. Note that -180

degree forms the distinction between flood-dominant (larger values) and ebb-dominant (smallervalues). The tidal wave at the mouth of the estuary is thus slightly flood-dominant. It is alsoobserved that the relative phase-lag shows a large scatter mainly due to the spring-neap

variation. The amplitude ratio shows a slight increasing trend until around 1990. This means

that the flood-dominance at the mouth of the estuary became slightly stronger in that period. As

the relative phase-lag is around -180 degree the tide asymmetry between the HW- and LW-

slacks is important for residual sediment transport in this estuary.

At Emshaven (Fig.16) the amplitude ratio shows a continuous increasing trend in time while the

relative phase-lag shows a decreasing trend. Based on the development of the phase-lag the

tide is becoming less flood-dominant (concerning falling-tide and rising tide) in time, but the


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development of the amplitude ratio indicates that the tidal asymmetry becomes stronger. For

this station the development of the tidal asymmetry (falling- and rising-tide periods) is thus notclear based on the developments of these two parameters. Concerning the asymmetry in the

HW- and LW-slacks the development is towards the situation favouring import of fine sediment.

Figure 15. Relative phase-lag (upper panel) and amplitude ratio (lower panel) between the

quart-diurnal component and the semi-diurnal component at Huibergat.


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Figure 16. Relative phase-lag (lower panel) and amplitude ratio (upper panel) between the

quart-diurnal component and the semi-diurnal component at Emshaven.


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quart-diurnal component and the semi-diurnal component at Delfzijl.

At Delfzijl (Fig.17) the same opposite trends of the two parameters can be observed and it is

even more pronounced. Concerning the asymmetry in the HW- and LW-slacks thedevelopment is towards the situation favouring import of fine sediment.

At Nieuwe Statenzijl (Fig.18) the amplitude ratio shows an increasing trend in the period until

around 1990, and since then the long-term trend is not clear. The relative phase-lag does not

show any clear long-term trend. It is further observed that a strong seasonal variation is

present at this station, as also is observed in the tidal amplification.


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quart-diurnal component and the semi-diurnal component at Nieuwe Statenzijl.

As the trends of the developments of the two parameters of the quarter-diurnal tide do not give

exclusive and clear indication about the consequence for the tidal asymmetry, we also look atthe German stations in the outer part of the estuary. For these stations we only have the

difference between the falling-tide period and the rising-tide period. A positive value of this

difference indicates flood-dominance and a negative value indicates ebb-dominance. In Fig.19

the development of this difference at the stations (from seawards to landwards) Borkum-S,

Knock, Emden and Pogum is shown. Note that in this figure only the filtered (smoothing out the

spring-neap variation) data are shown. The figure confirms that the tide at the mouth of the

estuary is slightly flood-dominant and this has not been changing much in the time. Landwards

in the outer estuary the tide used to be more flood-dominant than at the mouth in the past.

However, the development in time has reversed this spatial variation at present. The tide at the

landwards end of Dollard is now less flood-dominant than at the mouth of the estuary, and it is


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now even slightly ebb-dominant. Figure 18 further shows that there are two periods in which

the flood-dominance at the stations Emden and Pogum decreased: a short period since around1965 and the period after 1995.

Figure 19. Tidal asymmetry, indicated by the difference between the falling-tide period and the

rising-tide period at the German stations in the outer estuary.

4.3 Inner estuary

For the inner estuary, the Ems River we only have the German stations at which the difference

between the falling-tide period and the rising tide period is available as indicator for the tidalasymmetry. Figure 20 shows this parameter as function of time for the stations (from

downstream to upstream) Emden, Leerort, Papenburg and Herbrum, together with the station

Borkum-S at the mouth of the estuary.


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rising-tide period at the German stations in the inner estuary + Borkum-S at the mouth of theestuary. The spring-neap variation is already filtered out by averaging over 57 periods.

Figure 20 shows that at Leerort the tidal asymmetry remains more or less unchanged through

the whole period. At the two more upstream stations, Papenburg and Herbrum, the flood

dominance has increased since about 1990 and since 2010 this change seems to slow down

again. At the downstream station Emden the development is in the opposite direction, turned

from slight flood-dominant to slight ebb-dominant. Figure 21 shows the development at Leerort

together with the two surrounding stations Weener (upstream) and Terborg (downstream). This

figure makes it clear that Leerort forms a turning point in the river concerning the development

of the tidal asymmetry indicated by the difference between the fall ing period and the rising

period. Upstream of this station the tide becomes more flood-dominant in time and downstream

of it the tide becomes less flood-dominant. It is further observed that the seasonal variation of

the tidal asymmetry increases in the upstream direction, indicating the seasonal variationmainly corresponds to the variation of the river discharge.


rising-tide period at the stations around Leerort. The spring-neap variation is already filtered

out by averaging over 57 periods.

4.4 Summary

In summary the following conclusions are drawn from the analysis: Change in tidal asymmetry is accelerated in the period 1990. Since around 2010 the

change is slowed down again.

Leerort seems to form a turning point in the development of the difference between the

falling period and the rising period in time. Upstream of this station the change is in the

more flood-dominant direction and downstream of this station the change is in the

opposite direction.

There is a clear seasonal variation indicating the influence of river discharge (see

Chapter 5).


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Concerning present spatial variation there is a difference between the Dollard and the

Ems River. In the Dollard (estuary) the t ide becomes less flood-dominant in theupstream (landwards) direction, whereas in the Ems River the tide becomes more

flood-dominant in the upstream direction.

Concerning slack water asymmetry the development in the outer part of the estuary

(Dollard) has been in the direction of favoring import of fine sediment.


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5 Mean water level and mid-tide

5.1 Development of the mean water level / mid-tideThe development of the averaged water level gives an indication of the sea-level rise and the

development of the hydraulic drag in the system. For the four Dutch stations the a0component

from the Fourier series analysis is used (Fig.22). In the outer part of the estuary the averaged

water level is little influenced by the river discharge. At the stations Huibergat, Emshaven and

Delzijl the slight increasing trend corresponds to the sea-level rise. However, it seems that the

increasing trend becomes less in the landwards direction, indicating a decreasing trend of the

hydraulic drag (for the small effect of the river discharge). It is noted that the hydraulic drag is

influenced by the apparent roughness as well as the water depth. Moreover, the longitudinal

water level gradient is also influenced by the tidal flow. At the station Nieuwe Statenzijl the

averaged water level is on average higher than at the other three stations and no increasing(long-term) trend can be observed, which is again an indication for the decreased hydraulic

drag.

Figure 22. Averaged water level determined from the Fourier series analysis for the four Dutch

stations. The dots are the original data for the analysed periods of 24 h and 50 min. The solid

line is the moving average over 57 periods.

For the German stations the mid-tide is presented in Figures 23 through 28. The slightincreasing trend at the most seawards station Borkum-S represents the sea-level rise (Fig.23).

At Emden the increasing trend can hardly be observed (Fig.24). This agrees with the

observation that the increasing trend becomes less in the landwards direction. At Pogum

(Fig.25) the long-term trend becomes a decreasing one, which can only be explained by the

decreased hydraulic drag. This decreasing trend becomes stronger in the more landwards

station Leerort (Fig.26). At Papenburg the decrease of the mid-tide in time is most clear and it

is more concentrated in the periods 1965-1975 and from1980s to mid 1990s (Fig.27). At the

most upstream station Herbrum (Fig.28) the development of the mid-tide follows the same

trends as at Papenburg but the change is less than at Papenburg.


Date


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The drop of the averaged water level at Papenburg and Herbrum starting in the mid 1980s is

possibly effected by the bend cuttings at the Bight of Weekeborg and at the Bight ofStapelmoor, carried out in the period 1984-1990 (see Table 4 in Chapter 2). However, the

effects seem to be very big for these relatively minor interferences. Therefore, the main cause

of this drop is probably the deepening of the navigation channel (Fig.4).

Figure 23. Mid-tide at Borkum-S. The dots are the original data for the analysed periods of 24 h

and 50 min. The solid line is the moving average over 57 periods.

Figure 24. Mid-tide at Emden. The dots are the original data for the analysed periods of 24 h

and 50 min. The solid line is the moving average over 57 periods.


Date


27/45

Figure 25. Mid-tide at Pogum. The dots are the original data for the analysed periods of 24 hand 50 min. The solid line is the moving average over 57 periods.

Figure 26. Mid-tide at Leerort. The dots are the original data for the analysed periods of 24 hand 50 min. The solid line is the moving average over 57 periods.


Date


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Figure 27. Mid-tide at Papenburg. The dots are the original data for the analysed periods of 24h and 50 min. The solid line is the moving average over 57 periods.

Figure 28. Mid-tide at Herbrum. The dots are the original data for the analysed periods of 24 hand 50 min. The solid line is the moving average over 57 periods.

5.2 Influence of river discharge

Figure 29 shows that variation in time of the tidal range at the four stations Emden, Leerort,

Papenburg and Herbrum, after that the spring-neap variation is fil tered by averaging over 57

lunar days. Even after the filtering of the spring-neap variation the tidal range still shows

fluctuation in time above the long-term trend, especially at the upstream stations Paperburg

and Herbrum. A more detailed investigation learned that this concerns a seasonal variation, as

the fluctuation has a period of one year (see Fig.30).


Date


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Fig.29 Tidal range after that the spring-neap variation is filtered by averaging over 57 lunar

days.

Fig.30. Tidal range after that the spring-neap variation is fil tered by averaging over 57 lunar

days.

The seasonal variation of the three upstream stations Herbrum, Papenburg and Leerort are in

phase, low in the winter and high in the summer. The amplitude of the variation decreases from

upstream to downstream. These characteristics indicate that the variation is due to the effect of

varying river discharge. The lower tidal range is caused by higher discharge. At the most

downstream station of the Ems River, Emden, the seasonal variation is no more in phase with

the three upstream stations. This indicates that the variation has a different cause, probably

Tidal range

0

0.5

1

1.5

2

2.5

3

3.5

4

1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015

year

tidalrange(m)

Emden

Leerort

Papenburg

Herbrum

Seasonal variation of ti dal range

1

1.5

2

2.5

3

3.5

4

2000 2001 2002 2003 2004 2005

year

tidalrange(m)

Emden

Leerort

Papenburg

Herbrum

Borkum-S


Date


30/45

due to the variation outside. To show this the tidal range at Borkum-S, a station at the open

sea, is also plotted in Fig.30. It can indeed be seen that the variation at Emden is more inphase with this station.

Fig.31. Tidal range and water surface slope, both after fil tering of spring-neap variation by

averaging over 57 lunar days.

Fig.32. River discharge, daily value and smoothed over 57 lunar days.

At this moment no river discharge data is available for the whole period. However, a

reasonable indicator for the river discharge is the averaged water level, or the mid-tide, at the

most upstream station (Herbrum). An even better indicator is the difference between the mid-

tides at the two upstream stations (Herbrum and Papenburg), which is a direct indicator of the

tide-averaged water surface slope. Figure 31 shows this parameter together with the tidal

range at Herbrum. The figure shows a clear correlation between the two. It can thus be

Mid-tide difference Herbrum-Papenburg and tidal range at Herbrum

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

2000 2001 2002 2003 2004 2005

year

Mid-tidedifferenceHerbrum-

Papenburg(m)

1.5

1.7

1.9

2.1

2.3

2.5

2.7

2.9

3.1

3.3

3.5

TidalrangeatHerbrum

(m)

Mid-tide difference tidal range


Date


31/45

concluded that the river discharge has a substantial influence on the tidal amplification in the

upstream part of the tidal river. Figure 32 shows the river discharge (only available since 1998)in the same period. It indeed shows a very good correlation with the difference between the

mid-tides at the two most upstream stations.


Date


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6 Concluding discussions

The analysis of the water level data collected in the Ems-Dollard Estuary helps us to obtain

better insight into three aspects of the development of the estuary: tidal amplification, tidal

asymmetry in relation to sediment transport, and hydraulic drag. In the following the findings

from the analysis concerning these aspects are summarised before discussing about how the

developments are related to the various human interferences.

Tidal amplification and safety issues

Amplification of the tide has been strengthened considerably in the estuary, especially in the

inner part, the Ems River. Fortunately this has no consequence for safety against flooding in

the inner part of the estuary as the Ems River is protected by the Emsspaerrwerk. Even for the

outer part of the estuary, the Dollard, where the increase of the tidal amplification factor hasbeen limited, the strengthened tidal amplification is still an important factor for the increase of

(extreme) high water level in the estuary. Basically there are three factors influencing the

development of (averaged) HW in the estuary, the sea-level rise, the increase of tidal range at

the open sea and the tidal amplification. For the extreme high water, relevant for the safety

issue, the development of the wind climate and the response of the estuary to storms are

important as well. From the results of the analysis we learn that the developments of the three

factors influencing the (averaged) HW can explain the observed trend in the extreme HW

(yearly maximum). Between the three factors, the contributions of sea-level rise and

strengthened tidal amplification are similar, both much larger than that of the increase of the

tidal range at the open sea. It is noted, that contradictory to the other two factors, tidal

amplification is directly related to the morphological development in the estuary under influence

of the human interferences. The development of the tidal amplification in the estuary needs to

be taken into account for determining the future safety strategy.

Tidal asymmetry and sediment transport

Tidal asymmetry is an important mechanism influencing residual sediment transport. For fine

sediment two types of tidal asymmetry are relevant. The first type concerns the unequal

periods of rising water level and fall ing water level, corresponding to unequal maximum velocity

during flood and during ebb. The second type concerns the asymmetry of the durations of HW-

and LW-slacks. From the analysis it is concluded that for the Ems-Dollard Estuary the second

type tidal asymmetry is important for causing landwards residual sediment transport. In the

outer part of the estuary this type of asymmetry has been developing in the direction of

favouring more sediment import. Although the limited data do not provide information

concerning the development of this type tidal asymmetry in the inner part of the estuary, we

expect that the development has been in the same direction. For the development of the first

type tidal asymmetry the station Leerort seems to form a turning point in the system. Upstreamof this station the development has been in the direction of more flood-dominant, whereas

downstream of this station the development is in the direction of less-flood dominant (/ebb-

dominant). The changes have been accelerated in the recent period since around 1995. It is

noted that the development of the horizontal tide at a certain location is related to the

development of the vertical tide in the whole upstream area. It is then not evident that the

development of the first type tidal asymmetry has caused more sediment import into the

estuary at present than in the past. Analyses of turbidity data (see e.g. Vroom et al., 2012)

have shown that the sediment concentration in the estuary has been increased in the last

decades. This implies that the sediment import has been increased in order to balance the

increased export due to dispersion. The causes of the increased import should thus be found


Date


33/45

from the developments of the second type tidal asymmetry and of other processes /

mechanisms including estuarine circulation and sources & sinks (e.g. dredging and dumping).Earlier analysis concluded that the change of dredging and disposal of the dredged material in

the estuary is important for the increase of turbidity in the estuary (Wang, 2013).

Hydraulic drag

Hydraulic drag is related to both aspects discussed above. It has direct influence on the tidalamplification as energy dissipation due to hydraulic drag is an important factor influencing the

tidal amplitude in the estuary. In a turbid area the apparent roughness is influenced by the

sediment concentration as the density gradient over the water depth caused by suspended

sediment has a damping effect on turbulence (Winterwerp et al., 2009). The positive feedback

between the strengthening of tidal amplification and sediment import has been considered as

the mechanism that has caused the observed development in the Ems River (Winterwerp and

Wang, 2013; Winterwerp et al, 2013).

In the present analysis the apparent hydraulic roughness has been investigated by looking at

the dependence of the tidal amplification on the tidal amplitude (/range). The results of the

analysis indicate that the whole Ems River and the most inner part of the Dollard behave as

turbid area in the sense that the sediment concentration is high enough to influence the

apparent roughness.

Relation to human interferences

An inventory learned that many human interferences have taken place in the estuary since as

early as the Middle Ages (see Appendix). These interferences may be divided into three types:

land reclamation, improving and maintaining navigation channel, and engineering works

especially for flood defence. Land reclamation works are all carried out before the period in

which water level data are available and analysed. Therefore the influence of this typeinterference cannot be identified in the present analysis. The influence of the deepening of the

navigation channel on the tidal amplification has been clearly identified for the inner part of the

estuary, the Ems River. The deepening has also caused a drop of the mid-tide at the upstream

part of the river, although the bend cuttings in the river can also have contributed to the drop.

For the outer part of the estuary, the Dollard, it has not been possible to relate the development

of the tidal amplification and of the tidal asymmetry directly to particular human interference.

Apparently, for this relative larger area the gradual morphological development has been as

important as the direct effect of the human interferences.


Date


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7 References

Munk, W.H., Cartwright, D.E., 1966. Tidal spectroscopy and predication. PhilosophicalTransactions of the Royal Society of London, Series A 259, 533581.

Pawlowicz, R., Beardsleyb, B. and S. Lentzb, 2002, Classical tidal harmonic analysis including

error estimates in MATLAB using T_TIDE, Computers & Geosciences 28 (2002) 929937.Vroom, J., Van den Boogaard, H.F.P. en D.S. Van Maren, 2012, Mud dynamics in the Ems-Dollard,

Research phase 2, Analysis existing data, Deltares report, 1205711-001.

Wang, Z.B., Winterwerp, J.C., and Qing He, 2013, Interaction between suspended sediment and

tidal amplification in the Guadalquivir Estuary, submitted to Ocean Dynamics.Wang, Z.B., 2013, Kansrijke lange termijn veiligheidstrategien Ems-Dollard, Notitie voor Delta

Programma Wadden.

Winterwerp, J.C., Lely M. and Qing He, 2009. Sediment-induced buoyancy destruction and dragreduction in estuaries. Ocean Dynamics, 59 (5) 781-791

Winterwerp, J.C. and Z.B. Wang, 2013, Man-induced regime shifts in small estuaries I: theory,

submitted to Ocean Dynamics.Winterwerp, J.C., Wang, Z.B., Van Brackel, A., Van Holland, G. and F. Ksters, 2013, Man-

induced regime shifts in small estuaries II: a comparison of rivers, submitted to OceanDynamics.


Date


35/45

Appendix Inventory of human in terferences

Per event 2

types are

possible

Year Event Region Land Type Type Remarks Surface

area (ha)

1277 Dyke collapse, fol lowed by steplike

increase tidal area

Dollard GE,

NL

Flooding

1287 Dyke collapse, fol lowed by steplike

increase tidal area

Dollard GE,

NL

Flooding

1362 Second Marcellusflood: a larger ingression

into the Dollard area

Dollard GE,

NL

Flooding

14th/15t

h

century

Wirdum/Canhusen, W Marienhafe,

Schwee, E Norden and near Greetsiel

Leybucht GE land

reclamation

2960

1454 Fail ed attempt to dyke par t of Doll ard ar ea Dol lard GE,

NL

Flooding

1509 Largest Dollard flooding Dollard GE,

NL

Flooding Vloed was op 26 september

1509

1509-

1511

Second Cosmas- & Damianflood,

Allerheiligenflood of 1510 & Antoniflood of

1511: lagest extension of the Dollard area

formed

Dollard GE,

NL

Flooding

ca. 1520 Total area Dollard Dollard GE,

NL

Flooding Data Source perhaps not reliable -40000

Before

1550

First dyking Dollard gebied ten zuiden en

oosten van Winschoten en Beerta timing

uncertain

Dollard NL land

reclamation

Before

1545

Dollard NL land

reclamation

Total polder areas before 1550

westside Dollard Source

perhaps not reliable

6800

Modderland, Vledder, Finsterwolder-

Hamrik, etc

Dollard NL land

reclamation

Total polder area eastside

Dollard Source perhaps not

reliable

1550 Beerster Hamrik or the so-called Inner

lands of Nieuw-Beerta.

Dollard NL land

reclamation

Total polder areas before 1550

eastside Dollard Source perhaps

not reliable

7050

1551 Westermarscher Altes Neuland, Norden Leybucht GE land

reclamation

578

1556 Sderneuland, Norden Leybucht GE land

reclamation

633

1583 Westermarscher Neuland, Norden Leybucht GE land

reclamation

585

1585 Osteeler Neuland, Osteel Leybucht GE land

reclamation

228

1581-

1631

Measures to redirect the flow of the Ems in

a northern meander of the Nesserland to


Date


36/45

maintain the access to the harbour of

Emden. 4.5 km long dam of oak poles was

constructed, the Nesserlander Hoofd, in an

attempt to block the new channel W of

Emden. The attempts were finished in

1631.

1589 to

1593

Addinggaster Neuland, Norden Leybucht GE land

reclamation

229

1597 Scheemder en Eexter Hamrikken (polder

Scheemderzwaag)

Dollard NL land

reclamation

1100

eind 16e

eeuw

Reclaimed land at E Frisian Dollard Dollard GE land

reclamation

1500

eind 16e

eeuw

Total area Dollard Dollard GE,

NL

land

reclamation

Data Source perhaps not reliable -35000

1600 Uncertain dyking Dollard Dollard NL land

reclamation

1603 Schoonorth, Krummhrn Leybucht GE land

reclamation

418

1605 Alt-Bunderneuland Dollard GE land

reclamation

ohan Seems was one of the

owners and became Dyke-

warden

936

1622

(kadijk)

1626

accretions of Midwolda and Scheemda Dollard NL land

reclamation

1150

1636 Polder? Dollard NL land

reclamation

1657 below Beerta, Blijham and Bellingwolde,

from Drieborg to Nieuwe Schans.

Dollard NL land

reclamation

???? 2575

1665 aanwassen van Midwolda en Scheemda Dollard NL land

reclamation

1675/76 1st Midwolderpolder or Oud Nieuwland Dol lard GE,

NL

land

reclamation

1850

1678 Charlotten-Polder, Norden Leybucht GE land

reclamation

602

1682 Charlottenpolder, Dollard GE land

reclamation

Regent: Herzogin Christine

Charlotte; 60 ha op NL gebied =

Lintelopolder

255

1695-

1696

Kroonpolder (1701??) Dollard NL land

reclamation

480

1701 2e Midwolderpolder or: Nieuwland Dollard NL land

reclamation

650

1707 Bunder Interessentenpolder with Norder-

und Sder-Christian-Eberhards-Polder

Dollard GE land

reclamation

1391

1715 Kleiner Addinggaster Polder, Norden Leybucht GE land

reclamation

76

1740 Stadpolder Dollard NL land

reclamation

397

1752 Landschaftspolder (originally Neue Bunder

Polder)

Dollard GE land

reclamation

1225


Date


37/45

1768 Magotspolder, Krummhrn Leybucht GE land

reclamation

85

1769 Oostwolderpolder Dollard NL land

reclamation

1200

1769 Leysandpolder, Norden Leybucht GE land

reclamation

145

1770 Hagenpolder, Krummhrn Leybucht GE land

reclamation

133

1773 Heinitzpolders (first attempt) Dollard GE land

reclamation

1780 zogen sich die

Interessenten`zurck und der

Anwachs wurde neu vom

Landeherrn verpachtet.

1774 Zuckerpolder, Norden Leybucht GE land

reclamation

15

1775 Buscherpolder, Norden Leybucht GE land

reclamation

48

1775-

1776

1st destruction of dykes Heinitzpolder Dollard GE Flooding

1781 Schulenburger Polder, Norden Leybucht GE land

reclamation

241

1789 Lorenz- & Friederikenpolder, Norden Leybucht GE land

reclamation

60

1796 Heinitzpolders (second attempt) Dollard GE land

reclamation

1794 tat sich zum zweiten

Mal eine Unternehmergruppe als

Pchter zusammen, darunter der

landschaftliche

Administrator J. H. von Halem,

Wasserbauinspektor Franzius

oder Amtsverwalter D. Kempe

zusammen, um die F lche von 1

104 Diemat (davon 170 Diemat

Privateigentum) bis 1796 ein

zweites Mal einzudeichen.

626

1804 Wynhamster Kolk at Ditzumerverlaat Dollard GE land

reclamation

of a lake?

http://de.wikipedia.org/wiki/Bund

e

160

1804 Angernpolder, Krummhrn Leybucht GE land

reclamation

49

1804 Teltingspolder, Norden Leybucht GE land

reclamation

28

1819 Finsterwolderpolder Dollard NL Land

reclamation

1178

1825 2nd destruction of dykes Heinitzpolder

1826 Heinitzpolders (third attempt) (now

sleeper-dyke)

1833 Breaching and restoration of dyke

Oosterwolderpolder

Dollard NL Flooding

1842 First potato flour factory Dollard NL Land

reclamation


Date


38/45

1845-

1848

Stad polder & Knigspolder (water

defence Emden)

Emden GE Land

reclamation

1845-

1848

lift-lock Nesserland Lift lock

1845-

1848

Construction of Emder Fahrwasser Emden GE Channel

deepening

1846 Ernst-August-Polder, Norden Leybucht GE land

reclamation

218

1854 Emden, Duitsland Emden GE land

reclamation

1860 Start canalisation Lower Ems Tidal River

Ems

GE Canalisatio

n

Weir

1862-

1864

Reiderwolderpolder (1e afdeling = w side) Dollard NL Land

reclamation

1170

1870/71 Construction of 13 rubble mounted groins

on the Geise sand bank

Emden GE Training

walls

1872-

1900

Groins on Geise shoal Emden GE Training

walls

1872-

ca. 1890

Construction of (old) training walls and

groins at N-side o f Geisercken

Emden GE Training

walls

1874 Kaiser-Wilhelm-Polder Emden GE Land

reclamation

Dyke

constructio

n

1874 Kanalpolder GE land

reclamation

doublure met vorigen?

1872-

1874

Reiderwolderpolder 2e afdeling Dollard GE Land

reclamation

390

1875-

1878

Construction scouring sluice Nieuwe

Statenzijl (drainage and dyke shortening)

Dollard NL Scouring

sluice

Dyke

constructio

n

1875-

1876

Johannes Kerkhovenpolder (1st attempt)

1876 Sluice Nieuwe-Statenzijl Dollard NL Scouring

sluice

W eir Tekst " weir" wel lich t incorrec t.

1877-

1878

Kanalpolder ? Land

reclamation

Scouring

sluice

626

1880-

1888

Construction Ems-Jade-Kanal.

1883 Johannes Kerkhovenpolder (2nd attempt) Dollard NL Land

reclamation

Waterway depth: 4.8-5m below

MHW3 between Emden and

Leerort; 4.0-4.5m below MHW

between Leerort and Papenburg

397

waarvan

22

buitendijks

1892-

1899

Construction Dortmund-Ems-Kanal, with

the extension of the Ems-

Seitenkanal from Oldersum to Emden.

1892-

1899

Breakthrough of meandering river arms at

Rhede and Tuxdorf (upstream of

Papenburg)

Tidal River

Ems


Date


39/45

1895 Construction parallel dam on Geise and W

of Pogum (training walls S side of Emder

Fahrwasser)

Emden GE Training

walls

1896-

1900

Construction of a rubble mounted

connection between the existing groins on

the Geise sand bank

1898 Start dredging Oost-Friesche Gaatje Middle

reaches

Ems

GE Channel

deepening

Vermoedelijk doorgraving van

keileem

1897-

1899

Construction of f irst weir at Herbrum Tidal River

Ems

GE Weir Jaartal wellicht afgerond

1900 Water quality in Groningen called

disasterous

Groningen NL Data

begin

20e

eeuw

Main shipping lane changed from Bocht

van Watum to Oost Friesche Gaatje (due

to filling of Bocht van Watum)

Middle

reaches

Ems

GE Trac

change

1901 Present-day Emden sea port is opened as

the terminal point of the Dortmund Ems

Canal. Start maintaining Emden

Fahrwasser at 7m SKN (see remark),

dredging of Oost Friesche Gaatje en

Gaatjebocht.

Emden GE Harbor

constructio

n

Channel

deepening

SKN used to be defined as the

average of spring low water

levels. Since 2005 it is set equal

to LAT (Lowest Astronomical

Tide)

1907 Construction new lock sluice Nieuwe-

Statenzijl (beroepsvaart)

Dollard NL Lift lock

1907-

1913

Harborpolder Emden and construction of

the big sea sluice (harbor enlargement)

Emden GE Harbor

constructio

n

Lift lock

1910-

1922

Larrelt-Wybelsumpolder Emden GE Land

reclamation

Dumping

location

improvement N side of Emder

Fahrwasser

1750

1911 Breakthrough of meandering river arms at

Mark

1911-

1929

Waterway depth: 4.8-5m below MHW3

between Emden and Leerort; 4.0-4.5m

below MHW between Leerort and

Papenburg

Tidal River

Ems

GE Channel

deepening

1912-

1924

reclamation mud flats between Knock and

Emden

Emden Land

reclamation

1913 Schoonorther Polder, Krummhrn Leybucht GE land

reclamation

377

1914-

1922

Sea dyke construction Emden-Knock ( see

also 1922 for fin ish)

Emden GE Dyke

constructio

n

1922 Larrelter & Wybelsumer Bucht Emden GE Land

reclamation

1924 Carel Coenraadpolder Dollard NL Land

reclamation

1500

tot 1924 Last reclamation Dollard.total tidal area

given

Dollard GE,

NL

Land

reclamation

Sou rce p erh aps not rel iab le -10 000


Date


40/45

1925 Breakthrough of meandering river arm at

Pottdeich (close to Weener)

Tidal River

Ems

GE Trac

change

1928 Breakthrough of meandering river arm at

Coldam (close to Leerort)

Tidal River

Ems

GE Trac

change

1928 Cirksenapolder, Krummhrn Leybucht GE land

reclamation

41

1929 Neuwesteel, Norden Leybucht GE land

reclamation

646

1930 Fixation western point of Geise Emden GE Training

walls

1930-

1935

Extension of the Geise training wall

towards its western end (Geiseweststeert),

construction of three groins on the

opposite side of the channel

Emden GE Training

walls

1930-

1933

Construction training wall Rysumer

Nacken

Emden GE Training

walls

1930-

1932/9

Stabilization of the waterway by a bended

training wall at Knock (leitwerk Knock)

Knock GE Training

walls

Stabilization of the waterway by

construction of a training wall

near Knock

1932-

1939

Waterway depth: 5.5m below MHW

between Pogum and Leerort; 4.1m below

MHW between Leerort and Papenburg

Channel

deepening

1932 training wall Knock finished Knock GE Training

walls

1932-

1933

Lengthening Geiseleitwerk with 2 km to

the W (formation of Geisesteert)

Emden GE Training

walls

1932-

1933

Construction 4260m long ne w

Geiseleitwerk N of the old one, with 9 short

groins (fixation Geise-terminus)

Emden GE Training

walls

1933 Construction 9 groins in front of sea dyke

Emden-Knock

Emden GE Training

walls

1938 Borssum-Jarssumerpolder ? GE land

reclamation

Dumping

location

(shortening dyke and deposition

of dredging sludge)

1948 Deepening Emder Fahrwasser to -8.5 m

SKN

GE Channel

deepening

1950 Leybuchtpolder, Norden Leybucht GE land

reclamation

1005

1954 Sedimentation field Rysumer Nacken into

use (dam between the heightened and

strengthened training wall and main land

at Rysum) (untill 1995)

? GE land

reclamation

Dumping

location

1954 Land disposal site for dredging sludge

"landstort Emden-Riepe" for dr edging

sludge from the Emden harbor (untill 1992)

Emden GE Land-based

dumping

Dumping

location

1954 Leda weir Leda GE Weir

1955 Start of in tense dredging between

Papenburg and Leerort

Tidal River

Ems

GE Channel

deepening


Date


41/45

1958-

1961

Construction of 2.2 km long training dam

Seedeich and 12 km Geise training wall

(Geiseleitdamm) from Pogum to

Geisesteerwert and 17 new groins,

deepening of Emder Fahrwasser to -9m

SKN

1959 Construction harbor Leer Tidal River

Ems

GE Harbor

constructio

n

1959 Start gas mining Groningen Field Groningen NL Data

1960 Start Dutch dyke strengthening (Deltawet)

with sediment dredged from the estuary

(untill 1991)

Groningen NL Dyke

constructio

n

Sand

mining

1960- Summer dykes Tidal River Ems are

replaced by winter dykes

Tidal River

Ems

GE Training

walls

ca. 1961 Deepening Emder Fahrwasser (SKN -8,5

m)

Tidal River

Ems

GE Channel

deepening

1961 Geiseleitdam Emden GE Training

walls

1961 Deepening Emder Fahrwasser (SKN? -9

m). Suction dredging becomes normal.

Tidal River

Ems

GE Channel

deepening

Dredging

method

1961-

1962

Narrowing of river between Hebrum and

Papenburg by extension of groins or to the

width of the old groins (Niemeijer cs).

Deepening of Leerort-Papenburg to -5 m

below MHW.

1961-

1968

Extension of Geisedam (12 km s tarting at

Pogum) and construction of dams at the

sea dyke at the N side of Emder

Fahrwasser of 2250 m length and 5 short

groins (training works Emder Fahrwasser)

Emden GE Training

walls

1962 Construction of harbor channel Delfzijl,

1962 Stop dredg ing Boch t van Watum

1963 Start German dyke heightening with sand

from the estuary (untill 1992)

Lower

Saxony

GE Dyke

constructio

n

1963 W ofPogum Tidal River

Ems

GE Land

reclamation

Dyke

constructio

n

coastal protection 43

1963 Start gas mining Groningen Fie ld and

related subsidence

Groningen NL Subsidence VOLUME?

1963-

1966

Construction harbor dam Delfzijl to the SE Middle

reaches

Ems

NL Harbor

constructio

n

1967 Construction trans-shipment area Oude

WesterEms

Middle

reaches

Ems

GE Rede

1968 Finish of the ca. 12 km long Emden GE Training


Date


42/45

Geiseleitdamm and ca. 2 km long

Leidamm Seedeich

walls

1969 Enlarging of Huibertgat (draught 14 m) to

reach the trans-shipment area Oude

WesterEms

outer

reaches

Ems

GE Channel

deepening

1969-

1970

Broadening the outer harbor canal of

Delfzijl

Middle

reaches

Ems

NL Harbor

constructio

n

1969-

1972

Shift water way to Delfzijl in a W ward

direction (Oversteek Paapsand-Sd)

Middle

reaches

Ems

NL Harbor

constructio

n

1970 Construction trans-shipment station on the

Landemole Knock for transport dredging

sludge towards Rysumer Nacken

Knock GE Land-based

dumping

Dumping

location

1970- Decay Geiseleitdam Emden GE Training

walls

1971 From this year onwards annual dredging at

the sluice of Herbrum

Tidal River

Ems

GE Channel

deepening

1971-

1972

Enl argement of the Del fzij l Harbor Middle

reaches

Ems

NL Harbor

constructio

n

??

1971-

1972

Deepening of offshore approach to Emden

to -12.5m CD.

1972 Doekegat deepened and became part of

main shipping lane

? GE Channel

deepening

Trac

change

1972 End dredging Bocht van Watum Middle

reaches

Ems

NL Channel

deepening

1972 Oversteek Paapsand-Sd connects new

harbor entrance Delfzijl (at Oterdum) with

Gaatje Bocht

Middle

reaches

Ems

NL Channel

deepening

Harbor

constructio

n

1972 Construction Zeehavenkanaal Delfz ijl Middle

reaches

Ems

NL Harbor

constructio

n

1972-

1974

Construction new harbor entrance Delfzijl Middle

reaches

Ems

NL Harbor

constructio

n

1973 New harbor mouth Delfzijl at Oterdum

finished

Middle

reaches

Ems

NL Harbor

constructio

n

1973 Open ing deep sea por t Emshaven (ready) ou ter

reaches

Ems

NL Harbor

constructio

n

1976 After lowering ridge between Randselgat

and Doekegat the fairway moved from Old

Westerems to Randzelgat

? GE Channel

deepening

Trac

change

1976 From Randselgat to transshipment area

Oude WesterEms an entrance of 200m

broad and 15m depth has been dredged at

? GE Channel

deepening

Rede


Date


43/45

the SE Meeuwenstaart (see 1994)

1976-

1978

Closure old (W) harbor entrance of Delfzijl:

partially in 1976, totally in 1978

Middle

reaches

Ems

NL Harbor

constructio

n

1978 Start use of dredging sludge dump area at

the Mond van de Dollard for sludge from

Delfzijl (untill 1987)

Dollard NL Dumping

location

1979 Construct ion dyke S of Punt van Reide

(dyke shortening)

Dollard NL Dyke

constructio

n

1979 Breebaartpolder Dollard NL Land

reclamation

55.62

1981 Oversteek Paapsand-Sd gets depth of

SKN-7,5 m (See Karten Null, ong. GLW-

Spring)

? GE Channel

deepening

1982 At max 1/3rd of dredging sludge of Delfzijl

dumped in Mond van de Dollard

Dollard GE Dumping

location

1982 1st strong reduction of sewage water

disposal

Ems GE Data

1983/86 Deepening Lower Ems on trajectory

Emden-Papenburg to 5.7 m below MHW

(Homeric-deepening)

1983 Decis ion deepen ing Unte rems to 5,70m Tidal River

Ems

GE Channel

deepening

1984-

1986

Deepening Unterems to 5,70m Tidal River

Ems

GE Channel

deepening

1984-

1990

Streamlining of the river curve radius at

the Bight of Weekeborg and the Bight of

Stapelmoor by about 400 m each

Tidal River

Ems

1987 New dump location at Termunten instead

of Mond van de Dollard for sludge from

Delfzijl (untill 1990)

Dollard GE Dumping

location

1988/89 Shipping lane moved from Huibertgat to

West Ems (after deepening West Ems)

Trac

change

Channel

deepening

1989 New dump site Oude WesterEms for

sludge from Emshaven (before that

dumped at NW Borkum)

outer

reaches

Ems

GE Dumping

location

1990 Removal of 2 sills between transhipment

area and Gaatje Bocht

GE Channel

deepening

1990 About half of dredging sludge of Delfzij l

dumped in location Groote Gat (Mond van

de Dollard no l onger used)

GE Dumping

location

1990 Construction of new scouring sluice and

lift-lock Nieuwe Statenzijl

Dollard GE Lift lock Scouring

sluice

1991 New lock at Nieuw-Statenzijl ready Dollard

1991 Alternative dredging method in Emden

harbor (suspending and sailing through

Emden GE Dredging

method

Dumping

location

Jaartal mede op basis van

baggercijfers


Date


44/45

mud) which reduces dumping.

1991 Decision deepening Unterems for draught

6.30m

Tidal River

Ems

GE Channel

deepening

1991-

1992

Deepening Lower Ems on trajectory

Emden-Papenburg to 6.3m below MHW

(Zenith-deepening)

Tidal River

Ems

1992 End use of land dump Emden-Riepe for

dredging sludge from the Emden harbor

(since 1954)

Tidal River

Ems

GE Land-based

dumping

Dumping

location

1992 End German dyke heightening since 1963

with the finish of Kanalpolderdeich

Tidal River

Ems

GE Dyke

constructio

n

1992 Start use dredging sludge dumping field in

Wybelsumer Polder

Tidal River

Ems

GE Land-based

dumping

Dumping

location

1992 Second strong reduction in discharging

waste water

Tidal River

Ems

GE Data


6.80m

Tidal River

Ems

GE Channel

deepening

1993 Deepening Lower Ems on trajectory

Emden-Papenburg to 6.8m below MTHW

Tidal River

Ems

1994 Finishing use of trans-shipment station

Oude WesterEms

GE Rede


7.3m (Bemessungsschiff c.q. Werftschiff)

Tidal River

Ems

GE Channel

deepening

1994 Deepening Lower Ems on trajectory

Emden-Papenburg to 7.3m below MTHW

(Oriana-deepening)

Tidal River

Ems

1995 End sludge dumping on Rysumer Nacken

(since 1954)

GE Land-based

dumping

1996 Ems Energiecentrale fully oper ational outer

reaches

Ems

GE Data

1997 Official opening Emscentrale in Emshaven

(8th of april 1997)

outer

reaches

Ems

GE Data

?? Dumping dredg ing sludge from EPON-

harbor in N Bocht van Watum (small

amounts of sand en mud)

GE Dumping

location

?? Height en ing sea dyke Emden-Kno ck

(between 1963 and 1993 ???)

GE Dyke

constructio

n

1998-

2002

Construction Emssperrwerk at Gandersum GE Weir

2000 Opening Polder Breebaart via pipe GE Scouring

sluice

63

2001 Start of use Airset in Delfzijl harbor (air

and water inj ection)

GE Dredging

method

Naast sleephopperzuiger


Date


45/45

2001-

2002

Construction of Emssperwerk

2002 Finish of Sperrwerk Ditzum (ships with

draughts of 8,50m can pass to Unterems):

Emssperrwerk

GE Weir

2004 Dumping locat ion Bocht van Watum no

longer used

GE Dumping

location

2009 Dumping locat ion K2 in Mond van de

Dollard is used as a test (1 Mm3/jr) by

WSA-Emden

GE Dumping

location

2009 Start construction energie plants RWE and

NUON at Emshaven

outer

reaches

Ems

GE Data

2009-

2013

Deepening of Emshaven outer

reaches

Ems

GE Harbor

constructio

n

2010 Increase in length of Beatrixhaven in

Emshaven

outer

reaches

Ems

GE Harbor

constructio

n

2011 Increase in length of Wihelminahaven in

Emshaven

outer

reaches

Ems

GE Harbor

constructio

n

Analysis of Water Level Data for the Eems-Dollard estuary

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Transcript of Analysis of Water Level Data for the Eems-Dollard estuary