2016
Salt intrusion threatening Dutch
drinking water
Picture: https://awd.waternet.nl/bezoekersinfo/
Fay Lexmond
Maarten van Pelt
[email protected] [email protected]
+31647487391
+31642022836
Bergstraat 8a, 6701 AC Wageningen
10/4/2016
Wageningen UR
1
Contents
Introduction .............................................................................................................................. 4
Position .................................................................................................................................... 4
Urbanization in the Netherlands ................................................................................................. 4
Climate change and sea level rise .............................................................................................. 5
Problem .................................................................................................................................... 6
Salt intrusion along the coast .................................................................................................... 6
Possibilities ............................................................................................................................... 8
Proposition .............................................................................................................................. 11
Transport ............................................................................................................................. 11
Treatment water ................................................................................................................... 11
Infiltration method ................................................................................................................ 11
Location ............................................................................................................................... 12
Costs and benefits ................................................................................................................. 12
References .............................................................................................................................. 13
2
3
Introduction
The Netherlands is for multiple reasons a beautiful place to live, but how will we keep the
Netherlands a liveable and safe place? Climate change is posing a clear threat to the inhabitants of
the Netherlands. Due to global warming, polar ice is melting and the sea level is rising. With the
increase in sea level, the storm intensity will increase (Carter, 1991), causing an increase in dune
erosion. Since 26% of the Netherlands is located beneath NAP (PBL) our dunes are of great
importance. The dunes that protect us are also a source of fresh water for the areas lying behind
these dunes. For this proposal we are looking at the cause of this threat and how can we fulfill the
water demand.
Position
The current trends of importance for this proposal are changing freshwater demand on location;
being influenced by the amount of inhabitants; and the possibility to win enough drinking water
from the “Amsterdamse Waterleidingduinen”.
Urbanization in the Netherlands
Expected for the Netherlands is a growth in the number of inhabitants for the upcoming years.
Since march 2016 17-million inhabitants are living in the Netherlands. In 2040 the amount of
inhabitants will be 18.1 million. Expected is that the growth will be strong/large in period 20152025, mainly international migration, after which the growth rate will decrease. This growth is not
equally distributed over the entire country. Just like previous years it is expected that the amount
of inhabitants will decrease in the rural areas, especially at the eastern border. In the Randstad
however the population density will increase strongly. In Figure 1 is the expected growth depicted
for COROP-areas, an area with core acting as a care taking centre, and for the municipality for the
period 2015-2030. In this figure it becomes clear that in the middle of the Netherlands and
especially in the Randstad the most and strongest growth is expected. Along the borders a
decrease or stable situation is visible (Kooiman et al, 2016).
The fresh water demand for the use of drink water in these red, growing areas will increase.
Because more people will have to drink, more water will be needed. With water savings can the
amount of water used for showering, washing be limited. How much water is going to be needed in
the future is hard to predict.
Figure 1: Relative growth of population per COROP-area (left map) and per municipality (right map) 2015-2030. (Kooiman et
al, 2016)
4
Climate change and sea level rise
Climate change has always been around but the problem now is that it is changing so fast that
balances cannot recover. This is not only threatening the environment but also us, humans and our
way of living.
Climate change has a lot of effects and consequences. One of these effects is sea level rise. This
rise is caused by expanding of seawater, change in salt content, melting of glaciers and ice caps,
break down of the bigger ice caps on Antarctica and Greenland (PBL & KNMI, 2015). Melting of
these big caps will result in a lower mass present. This decrease in mass will cause a decrease in
pull of water towards the mass. So a change in water distribution over the oceans will occur.
Because there are so many different aspects that have influence on sea level rise, a prediction is
very hard to make. There is a continuous debate and predictions might keep changing.
That sea level rise will occur is pretty sure but it will not be homogeneously over the planet.
Differences between shape of coasts, characteristics of sea floor and wind patterns are some of the
features determining possible sea level rise (PBL & KNMI, 2015).
Worldwide average sea level rise is expected to be between 26 and 82 cm. For the Dutch coast was
a rise of around 2 mm per year since 1900. There is no clear acceleration being noticed, which is
the case for the worldwide average. This difference is due to the big variations from year to year,
this is in consistency with wind(behaviour/patterns) (PBL & KNMI, 2015).
Subsidence, because of shrinking of peat, is not being taken into account in these predictions for
the Netherlands. Because this is very variable across the Dutch coast. Also there are no clear
predictions for the future of these processes available (PBL & KNMI, 2015).
The sea level rise along the Dutch coast is depending on the global temperature development. The
G’s and W- scenarios are predictions of (G) a temperature rise of 1 degree in 2050 and 1.5 degree
in 2085 and (W) a rise of 2 degree in 2050 and 3.5 in 2085. In Figure 2 is the prediction of sea
level rise in cm compared to NAP shown for these two scenarios. This has been researched by the
IPCC but no difference between L- & H-scenarios, change in wind patterns, has been made.
Because the change of the important airflow patterns above Europe has no dominant effect on the
sea-level rise on long term. In every scenario is the expected sea level rise between 2050-2085
higher than the since 1900 observed pace. Around 2085, depending on the global warming, a rise
of 25-80 centimetre is expected (PBL & KNMI, 2015).
Figure 2 Sea level rise along the Dutch coast for the period 1900-2100; as being observed (black) and according to the
KNMI’14-scenario’s (green for G-scenario; purple of W-scenario). (PBL & KNMI, 2015)
5
Problem
Salt intrusion along the coast
One of the biggest sources of water for Amsterdam is the Amsterdamse Waterleidingduinen (2/3 of
the demand). However, sea level is rising and an increase in salt intrusion is expected. The
freshwater bulb will decrease in size where an increase is needed. Therefore a new freshwater
source is needed. In Figure 3 is shown how salt intrusion occurs.
Figure 3: The initial sea level is indicated by SLi. After a rise of sea level of SLR the final sea level is SLf. The position of the
water table is assumed to be fixed at a certain point inland. The elevation of the water table is initially high above SLi and
changes to hf above SLf where hf=hi−SLR. The initial depth of the saltwater–freshwater interface is di=40hi below SLi. At the
final position of the sea the depth of the saltwater–freshwater interface is df below SLf. At this location the saltwater–
freshwater interface has risen an amount Δd=di+SLR−df or 40hi+SLR−40hf=−40hi+SLR−40(hi−SLR)=41×SLR. (Carretero et
al, 2013)
Seawater intrusion into aquifers is considered by the International Panel on Climate Change (IPCC)
to be an important impact of sea-level rise. A research was done on the impact to groundwater in
case of 1-m rise in sea level for the low lying coast of Partido de La Costa, Argentina. Two
scenarios were being modelled. The first scenario assumed a constant lateral flux of freshwater.
The vertical upward flow of inland water-table is that case allowed to keep pace with sea-level rise.
For the second scenario a constant water-table elevation was assumed. For this one no vertical
migration of fresh groundwater was possible. An increase in sea level rise will directly translate to a
lowering of the hydraulic gradient across the shoreline and inward flow of salt water will be
enhanced (Carretero et al, 2013).
Both cases resulted in landward movement of saltwater as shown in Figure 3. A big difference in
distance of migration was being modelled (25-40 vs 200m). Hydrogeological parameters, hydraulic
conductivity and aquifer thickness are of influence on saltwater intrusion (Carretero et al, 2013).
In case of freshwater extraction in the Amsterdamse Waterleidingduinen, water is being
transported from the river Rhine into the dunes to prevent the nature from drought stress and to
prevent the groundwater level from dropping. This Rhine-water is being pretreated before being
injected. So comparing the Amsterdamse Waterleidingduinen to the research done in Argentina, it
would match the fluxed fixed scenario(Carretero et al, 2013).
The problem of salt intrusion is being evaluated on local scale. But it can become a problem for
other areas in the same kind of situation. Water saving is going to be an important concept, saving
on usage as well as trying to collect water.
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Figure 3: Schematic diagram of cross-sections of 3 situations a) no sea-level rise, b) flux controlled with ΔxT 38 m for a 1 m
rise, c) head-controlled scenario with ΔxT 211 m. W is recharge, q0 is fresh groundwater flow under shoreline per unit length of
shoreline, xi is the distance inland from shore, hi is water table at inland position xi, z0 is the depth of the base of the aquifer
below the instantaneous sea level, xT is the location of the toe of the saltwater wedge and ΔxT is the variation in the position of
the toe of the saltwater wedge due to changes in sea level in b) and c).(Carretero et al, 2013)
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Possibilities
Fulfilling the water demand from a different source could be a solution. In 2000 1187 Mm3 drinking
water was produced of which 79% (940 Mm3) was covered by public supply wells, the other 21%
was extracted from surface waters. Figure 4 is a map of the Netherlands which shows the Public
Supply Well Fields (PSWF) and the landscape in which they are situated. From the 940 Mm3 (in
2000) 46% was pumped from (semi)confined aquifers. Semi-confined aquifers are most protected
against anthropogenic pollution from the surface, because they are situated underneath an
aquitard. Pollution cannot reach this layer easily. The artificial recharge systems (eg. Amsterdamse
Waterleidingduinen) have the largest capacity (19% of total production with only 9 PSWF’s) and
they have the lowest closing rate. Phreatic PSWF’s are highly vulnerable to pollution as are
limestone PSWF’s because they are exposed to the atmosphere and pollutants can easily infiltrate.
As can be seen in Figure 4, 8 out of 9 wells are situated in the coastal dunes and one is located in
the sandy uplands in Limburg. The Veluwe is also situated in sandy upland (Mendizabal et al,
2009).
The Veluwe could be a solution, the area is well-known for the good quality of the water that is
being extracted. A similar approach like in the Amsterdamse Waterleidingduinen could be
implemented. Water from the river Rhine could be transported to an elevated location in the
Veluwe and then flow through a similar system.
At the moment no artificial recharge is present in this area. In the coastal wells the water from the
Rhine is used. First, it is being treated and after injection the water interacts with effusive rock of
marine origin. In Table 1 and Table 2 are the characteristics of the different aquifer types visible. At
the Veluwe, most public supply wells (the water winning wells) are from phreatic and
(semi)confined sources. As can be seen in the two tables, water from the Veluwe will be
characterized by sand/sandstone (eolian for phreatic and glacial for semi-confined). The aquifers
for both types on the Veluwe are lying deeper than the other artificial recharge wells (Mendizabal
et al, 2009). Way of injecting the water is important aspect to consider.
Figure 4: Spatial distribution of the national network of PSWF’s projected on top of a landscape map of The Netherlands.
Classification according to source water and aquifer type in: phreatic, (semi)confined, AR, RBF (river bank filtrate) and
limestone. The Dutch national groundwater quality monitoring network (LMG) is also shown (Mendizabal et al, 2009).
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Table 1: Main factors determining the water quality abstracted by public supply well fields with G) fresh, autochthonous, actual
groundwater P) fresh, autochthonous paleo groundwater AR) artificially recharged water, RBF) river bank filtrate, S)
saline/brackish groundwater (Mendizabal et al, 2009).
Table 2: General characteristics of the 5 types of water resources for public drinking water supply in The Netherlands, ~2008,
a water production in year 2000 ASL= above sea level; BLS below land surface (Mendizabal et al, 2009).
In case of the Amsterdamse Waterleidingduinen the water for infiltration comes from the Lekkanaal
in Nieuwegein and is transported via three pipelines of 1,200/1,500 mm diameter of total 210 km
length. The Lekkanaal is a manmade side-branch of the river Rhine (Tielemans, 2007).
This water is being pretreated in Nieuwegein (at intake site) before being transported and
infiltrated. This pretreatment exists in this case of coagulation, flocculation with FE3+ ions,
sedimentation and rapid sand filtration. In other cases also micro-sieving is being used. The first
three treatments are applied to remove suspended particles, phosphates, heavy metals,
microorganisms and organic matter. Rapid sand filtration then removes the last suspended
particles and reduces organic matter, iron, manganese, ammonium and algae concentrations. Also
an pH correction with caustic soda is being applied. The quality of the raw surface water is variable
over the year. Especially temperature and turbidity can vary a lot, this influences the flocculation,
settling behaviour, filtration and biological processes (Tielemans, 2007).
The source of the water could still be the Rhine. Only a different intake location and infiltration
location should be used. Important for the intake location is likelihood for algae growth; high DOC
concentrations and high turbidity. This is the case at the intake at Andijk, IJsselmeer (Tielemans,
2007). These cases need more or different pretreatments or pretreatment might take longer.
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Next step is the infiltration, there are two possible ways of infiltration: open and deep well
infiltration. In the Amsterdamse Waterleidingduinen they use open infiltration with ditches. The
water infiltrates into the phreatic groundwater and is mixed with infiltrated rain water forming a
large storage of fresh water. The Waternet system consists of 40 ditches with a total length of 24.6
km and average width of 35m. Transport between the ditches is possible through canals
(Tielemans, 2007).
Deep well infiltration makes use of deeper lying confined/semi-confined aquifers. No interaction
with the phreatic water, so less influence of possible pollution from the surface. Also the
environmental and ecological impact of these wells is minimal. But with this technique clogging of
the pipes can be a serious problem (Tielemans, 2007).
A possibly better solution is to collect rainwater in the Amsterdam urban area. In the city a lot of
hard surface (roads/buildings/etc) prevents rainwater from infiltrating. This water will runoff as
surface water into sewage towards rivers eg. This water could be collected and used for this area.
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Proposition
Transport
The water which is going to be infiltrated needs to be transported towards the location on the
Veluwe. Water can be transported through natural waterways or through pipelines. Natural
waterways would be cheaper but the Veluwe is higher situated than the river Rhine. So transport
through pipelines is necessary. A pipe would be needed from the river towards the infiltration
location and from the outlet of the area towards a distribution point. The transport towards the
location needs to be done in present of pumping because of the higher elevation of the Veluwe.
Transport towards the distribution point has the benefit of downhill direction.
The easiest and cheapest solution would be to use existing pipelines. In the Veluwe, Liander is
managing
the
network
of
gas
and
electricity.
(https://www.energieleveranciers.nl/netbeheerders/gas) A collaboration or arrangement with them
might make the transport part easier and less expensive. For Liander it might also be positive
because of the possible change in the role of gas in the Netherlands.
“The gas demand in the Netherlands is decreasing and will decrease for the next decades. Though
it will keep an important role as a flexible source of electricity and material for industries.” (Jeroen
de Joode, ECN, in an interview with ENSOC). Also the national gas extraction has declined over the
last 10 years. Because of the extraction but also the major E&P companies have reduced their
exploration efforts and the number of wells drilled as well as the size and total volume of
discovered gas reserves has declined because of small sizes and other geologically unfavourable
aspects (Herber et al, 2014)
Because of a decrease in gas demand for households, parts of the gas transport network might not
be needed for gas transport anymore. ENEXIS is looking for possibilities for this trend, but does not
operate in our area of interest. (http://sustainablebusinesschallenge.nl/Uitdagingen/)
Treatment water
The way to pretreat the water is at the place of intake. This way no extra transport paths are
needed and maintained. The Rhine splits into the IJssel and the Neder-Rhine near Arnhem. In the
south of Arnhem there is a sewage treatment plant, RWZI Arnhem-Zuid, of the type Bio P +
voordenit (Stichting Nederlandse watersector). Bio-P is the biological removal of phosphate. With
this treatment there is also the possibility to combine the removal of P with the removal of different
types of nitrogen. (Koninklijk Nederlands Waternetwerk). Also Vitens has multiple water winning
plants in this area. Treating the raw water at an existing plant would reduce the costs and efforts
to realise the idea. More research needs to be done on the exact quality of the raw water to
determine all the necessary treatments.
Infiltration method
The options for infiltration were: open infiltration and deep well infiltration. For open infiltration a
lot of ground is needed for the ponds or ditches. It is also more vulnerable to pollution at the
surface because the water will flow through the phreatic layer. On the Veluwe there is a lot of
nature, here the pollution would be minimal. On the other hand the nature reserves are protected
areas and we do not want to decrease the size of the area with a water infiltration station.
Deep well infiltration will save space and is less vulnerable to pollution from the surface. A problem
with deep well method is clogging. clogging occurs due to deposition of suspended matter and
bacterial growth. So the pretreatment is an important feature to minimize the clogging potential.
Since unclogging is economically unfavourable it needs to be prevented. Determining the clogging
potential will give information about the state of the pipes. Research is already been done on
predicting the clogging potential and experiments are being done in Limburg with an artificial
recharge deep well infiltration.
The Modified Fouling Index (MFI), and assimilable organic carbon content (AOC) show to be
valuable parameters but cannot predict the clogging rate by themselves. The Parallel Filtration
Device (PFD) can give a more accurate clogging potential in combination with MFI and AOC then
using only the PFD.
Deep well infiltration is chosen for injection of the water. Important is the quality of the infiltrate,
to get a minimal clogging potential. Also measurements should be done to determine when
clogging is likely to occur. For the costs should be kept in mind that once every so many years the
pipes might need to be unclogged.
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Location
For the location is looked at the usage of the land. Chosen is the Hoge Veluwe because it is mostly
nature. So expected is a minimal amount of pollution. The red circle in Figure 5 is the chosen
location, it is near national park the Hoge Veluwe but not in it.
After that the water is being infiltrated and the upwelled water is being collected, the water needs
to go through a last treatment to make it suitable for drinking. This could be done at the location,
but that would need an installation. It could also be transported towards an existing station nearby.
An extension of RWZI Arnhem-Zuid
Figure 5: Overview of Sewage purification plants and pumping station of the Waterschap Vallei en Veluwe (www.valleiveluwe.nl)
Costs and benefits
The benefits of this plan is that Amsterdam would not be depending so much on the winning of
water from the dunes anymore. This method does not need a lot of space and the water will be
under minor influence of the surface and phreatic layer. A good quality of the water is thus
expected. In cooperation with network managements, like Liander and existing water purification
plants like RWZI Arnhem-Zuid it might be possible to keep the costs down.
Costs would be made by installing the deep wells and connecting the wells to the transport system.
The latter might be the biggest costs, even if usage of existing pipelines is possible. The sewage
purification plant in Arnhem needs to be extended to be able to perform all the treatments.
A test well could be drilled in the area to check on the flow patterns and Rhine samples should be
tested on clogging potential.
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References
1)
Carter, R. W. G. "Near-future sea level impacts on coastal dune landscapes." Landscape Ecology 6.1-2
(1991): 29-39.
2)
Planbureau voor de Leefomgeving (2016). (http://www.pbl.nl/nieuws/nieuwsberichten/2013/hoebeschermen-we-ons-land-tegen-het-water). Bezocht op: 31-07-2016
3)
Kooiman, N. ; De Jong, A. ; Huisman, C. ; Van Duin, C. ; Stoeldraijer, L. “PBL/CBS Regionaal
Bevolkings- en huishoudensprognose 2016-2040: sterke regionale verschillen” 2016-08
4)
Planbureau voor Leefomgeving | Koninklijk Nederlands Meteorologisch Instituut (maart 2015)
Klimaatverandering Samenvatting van het vijfd IPCC-assessment en een vertaling naar Nederland
5)
Carretero, S. ; Rapaglia, J. ; Bokuniewicz, H ; Kruse, E. “Impact of sea-level rise on saltwater intrusion
length into coastal aquifer, Partido de La Costa, Argentina” Elsevier Continental Shelf Research Vol 61-62 (July
2013): 62-70
6)
Mendizabal, I ; Stuyfzand, P. J. “Guidelines for interpreting hydrochemical patterns in data from
public supply well fields and their value for natural background groundwater quality determination” Journal of
Hydrology Vol 379, Issues 1-2 (15 december 2009): 151-163
7)
Tielemans, M.W.M. “Artificial recharge of groundwater in the Netherlands” Water Practice & Technology
Vol 2 No3 (2007)
8)
Jeroen de Joode, ECN, in an interview with ENSOC https://www.ensoc.nl/nieuws/gas-blijft-belangrijkerol-spelen-in-toekomst
Bezocht op: 22-09-2016
9)
Herber, R. and de Jager, J. (2014) ‘Geoperspective Oil and Gas in the Netherlands – Is there a
future?’, Netherlands Journal of Geosciences - Geologie en Mijnbouw, 89(2), pp. 91–107. doi:
10.1017/S001677460000072X.
10)
ENEXIS http://sustainablebusinesschallenge.nl/Uitdagingen/
Bezocht op:15-09-2016
10)
Stichting Nederlandse watersector https://www.watersector.nl/rwzi/237/rwzi
Bezocht op 26-09-2016
11)
Koninklijk Nederlands Waternetwerk http://www.neerslag-magazine.nl/magazine/artikel/119/
Bezocht op 26-09-2016
10) Interactive map of sewage purification plants and pumping station within the Waterschap Vallei en Velluwe.
https://www.vallei-veluwe.nl/publish/pages/7366/gebiedskaart_2013-07-31.jpg
Bezocht op 29-09-2016
11) Hijnen, W. A. M., et al. "Determining the clogging potential of water used for artificial recharge in deep
sandy aquifers." Third Int Symp on Artificial Recharge of Groundwater (TISAR). 1998.
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