Presentation in Nagoya 11-2019(1)
I feel very honoured to be invited to tell you about our experiences withwater management in the delta area of the South West of the Netherlands.
In my introduction I will show you what the ecological drawbacks are ofbuilding dams in an estuary and how we try to solve these problems.
My name is Tjeerd Blauw. Till 2014 I worked for the Government of theProvince of Zeeland, part of this Delta area, and as such I was involved inthe policy planning for this area.
That is why I like to share our experiences with you.
First I like to show you where I come from.
(2), (3), (4)I am happy to be here, because we have something in common, or better
said: we have someone in common: (5) Johannis de Rijke. He was born
1842 in Colijnsplaat, (6) a village not far from my home in Middelburg.
Almost 150 years ago he came to Japan to work as an engineer to prevent
rivers from flooding. He worked also in this area. On the Nagara River, theIbi River and the Kiso River.
There is a certain similarity between this area and the area where I comefrom: three rivers come together and flow into the see. (7) In the area
where I come from these are the River Rhine, the River Meuse and the River
Scheldt. Together they formed the Delta Area of South West Netherlands,
between Rotterdam and Antwerp in Belgium.
(8) This is a closer look at the area. In de north Rotterdam, in the south
Antwerp.
This area not always looked like this. (9) From the last ice age /glacial
period till 1000 years ago this area was covered with mainly peat and salt
marshes. People had to adapt themselves to the natural forces.
From about 1000 years ago people started to build dikes to protect
themselves and to conduct agriculture. The landscape changed
considerably. (10) As you can see here, the whole region now consists of anetwork of dikes.
Dikes can protect but can also collapse. Especially in the past whenengineering techniques were weakly developed. Therefore it is not
surprising that many flood disasters occured. (11) Here you see the main
floodings since 838
1(12) In 1953 a large and till now the last flood disaster happened in theSouthwest of the Netherlands. More than 1800 people died.
The National Government decided to execute the Delta Plan.(13) One of thegoals of this plan was to shorten the coastline with more than 700 km bybuilding dams. Only in the North and in the South no dams were built,
because these are the waterways to the harbours of Antwerp andRotterdam.
Haringvliet was not closed by a dam, (14) but with sluices, that are open
during low tide to let the water of the rivers Rhine and Meuse flow into theNorth Sea. During high tide the sluices are closed to prevent seawater fromflowing into the Haringvliet. In this way the Haringvliet was made afreshwater reservoir.
Before we built the dams there was a transition zone between the rivers
and the sea. It is called an estuary, a dynamic and productive environment
with tides, changing river flows and salinity gradients.
The Delta works transformed the estuary into separated water basins. The
dynamics of the estuary almost completely disappeared fromthe area.
(15) The original plan was to build solid dams between the islands and tocreate a large freshwater lake behind these dams. This freshwater should
be used for agriculture.
During the execution the plan has been changed several time and theconcept of a large freshwater lake slowly disappeared.
In the sixties of the last century environmental awareness arose. There wasa lot of protest against building a dam in the Oosterschelde. A coalition offishermen and environmentalists feared the disappearance of the valuablesaltwater ecosystem of the Oosterschelde, famous for its Oysters andMussels. (16 ) In the seventies the government decided not to build a dam,
but a storm surge barrier, that only closes when very high water levels areexpected at the North Sea.
The result of this: the Oosterschelde stayed a tidal saltwater system.
(17) North of the Oosterschelde a dam was built separating Grevelingenfrom the Northsea(18). In the eighties it was decided to keep theGrevelingen Lake salt because of its valuable saltwater ecosystem and therecreational value of the lake.

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1997 the Delta project was finished. (19) Here you see the final result. Only
the VZM and the HV are freshwater systems.
As time passed, it became increasingly evident that elimination of the
dynamic processes of an estuary has ecological drawbacks. Lack of exercise
and motion is unhealthy for people. Similarly, eliminating or reducing the
dynamic interplay of an estuary also causes all kinds of unhealthy situations.
Each of the Delta water basins suffers from problems that can be traced
down to the disappearance of the dynamic processes of the estuary.
Basically the focus of the Deltaplan was on water safety. That isunderstandable considering the catastrophe of 1953. But in retrospect itshould have been better if also other aspects of water were taken into
account. With other words integrated water management should have been
better than sector-focused water management.
(20) Water is not only an enemy, but also a friend. We have to protect
ourselves against the water, but we also have to realize, that we need thewater. For nature, for economy, for every aspect of our live.
The only thing we can do now is to repair the drawbacks. I will give you ashort overview of these problems and the way we try to solve them.
As I told already each of the Delta water basins suffers from problems thatcan be traced down to the disappearance of the dynamic processes of theestuary.
The dynamics of estuaries can be characterized by several aspects. Someare shown here (21). (Involving nutrients, river and tidal flows, salinity
gradients, morphology etc.)
For (almost) every aspect of the estuarine dynamics we can find a waterbasin in the South West Delta area where the loss of that aspect causes anecological problem. For most of the problems the solution is to partly bringback the dynamics of the estuary.
Bringing back the tides implies, that the salt concentration of the water willincrease. This is a problem when the freshwater in the lake is used for
agriculture. If this is the case, we have to create an alternative way tosupply freshwater. We do this by replacing the inlet to a place more
upstream, where the river water is and will stay fresh.

1. Nutrients.
In the original estuarine situation, nutrients – as they flow from the3river to the sea – are gradually converted into algae, zooplankton,
bottom-dwelling invertebrates, and shellfish, which in turn served asfood for populations of fish and birds and us. However, in a stagnant
lake situation, excess nutrients lead to excessive (blue-green) algal
blooms.
a. (22)Lake Veere. After building the Zandkreekdam and theVeerse Dam this newly created lake turned out to be a brackishlake with high nutrient loads from the surrounding agriculturalland and a long retention time of the water because of thedisappearance of the tides. The results: algal blooms and anoxic
bottomlayers. (23) The solution: in 2004 a new connection
between the lake and the tidal Oosterschelde was built. (24)
Lake Veere changed from a brackish lake into a saltwater lakewith (small) tides and short retention time. (25) Nutrient
concentrations decreased and transparency increased. We see
no algal blooms anymore and restoration of the saltwater
ecosystem.
b. (26) Another example of this nutrient problem is Lake
Volkerak-Zoom: a non-tidal stagnant freshwater lake withheavy nutrient loads and a high water retention time. The
result: (27) heavy blue-green algal blooms making the lake
unfit for recreation. We found out that the only way to solve
this problem is to make this lake a salt and tidal lake again.
Salt: to prevent the growth of blue greens; tidal: to prevent
stratification. The freshwater of the lake is used for agriculture.
So we first have to create an alternative freshwater supply.
(28) At this moment parts of the alternatives are being built.
The inlet of fresh water will be dislocated to a place upstream.
At the same time we see a light improvement of the blue green
algal situation and the development of valuable freshwaternature. So at this moment there is a discussion: Why should we
make the lake salt? A lot of fierce discussions at this moment.
Till now the future of this lake is unclear. We expect someclarity from the national government at the end of this year.
2. (29) Hydro-morphology
Oosterschelde: Since we built the Storm Surge Barrier smaller
quantities of water are flowing in and out.
The tidal channels are too large for these smaller quantities of water.
Natural processes to reach a new dynamic equilibrium are therefore
reshaping the morphology of the basin. (30) In this process, valuableareas of mud flats, salt marshes and shoals are disappearing and4

eroding as bottom sediments are redistributed to fill in the deeperchannels.
These tidal areas are very important for birds and seals. We foundout, that the only solution for this problem is sand replenishment. Thefirst pilot’s show that this solution works. At this moment we executea program for sand replenishment of the Roggeplaat, a shoal justbehind the storm surge barrier. 1,3 million cubic meter sand will beput on the shoal. This started the first of October and will be finishedat the end of December.
3. (31) Vertical mixing of the water. The tidal energy in a natural
estuary prevents stratification. But in Lake Grevelingen: despite of
the existing small connection between the lake and the North Sea
there are problems. The tidal energy is too small to prevent
stratification of the lake, resulting in anaerobic bottom layers (32)These layers are growing every year. (33) Under water it looks like
this: above 4 m water depth it is OK, but below 4m it looks terrible.
Neither fish nor shellfish can live here. The recreational value and thevalue for fishery is endangered. The only solution is a bigger
connection with the North Sea. ((34) A computer model predicts thatthe problem of oxygen depletion is almost completely solved then.
The national government promised 75 million euro extra to build thisconnection. (35)Probably before the end of this year a decision will
be taken about the plan to realize the connection and eventual thetidal energy plant. The connection should be ready in 2026
4. (36) Salinity gradients.
In natural estuaries there is a salinity gradient from freshwater in therivers to a salinity that equals the salinity of seawater. This gradientmakes it possible for fish to migrate from the sea into the rivers andfrom the rivers into the sea. If this gradient is changed into a sharptransition between seawater and river water migration is impossible,
because fish die from the osmotic shock.
(37) Haringvliet sluices worked in one direction. River water could
flow out into the North Sea, but seawater could not flow into theHaringvliet. There is a sharp transition from seawater to river water,which makes fish migration almost impossible.
It took more than 18 years to decide to open the sluices a little bit inorder to create a salinity gradient in the Haringvliet allowing fish tomigrate from the North Sea into the rivers and vice versa. It took solong to convince farmers and industries that the salinity gradient canbe managed and to realize the alternative freshwater supply(38)Saltwater is not allowed to come to the freshwater canal to theharbour of Rotterdam. Freshwater inlets in the zone between the5sluices and the canal are removerd to a place upstream.
Finally with some pressure from the European government level thegovernment decided to open the sluices a little bit. At 15-th ofNovember last year the minister decided that the sluices can be putajar. But because of the low river water flow it took till 16-th ofJanuary, before one sluice really was left ajar.
(39)Since then an implementation period started. This period can becharacterized as a step by step careful testing of the salt distribution
in relation to the management of the sluices. “Step by step and careful”
because it is very , very important that the freshwater supply foragriculture and industries is not disturbed.
In periods of low river water flow the sluices have to be closed.
Before that closure the system has to be flushed with freshwater toremove all the saltwater from the system. This will be tested in aseries of flushing scenario’s. The first test learned that flushing iseffective at riverwater discharges above 3500 m3/s. Next test will be
flushing at lower discharges. In this way knowledge will be collected
about management risks in order to fine tune the management of thesluices.
At the same time a program started monitoring migrating fish species.
Also other ecological aspects will be monitored.
(40)In this way we slowly and careful will open the front door of theRiver Rhine and the River Meuse for migrating fish.
Summarizing:
The lessons we learned from the drawbacks of the Delta works are (41)that almost all ecological drawbacks of the Delta works can be solved
by bringing back the estuarine dynamics.
that it is better not to approach an issue only in terms of safety oragriculture or water quality. A shift is needed from this sector –focused water-management to integrated water management that
integrates all relevant aspects, including ecology and economy. Withan integrated, comprehensive approach drawbacks of the Delta
works could have been avoided.
that ecosystems are complex. The consequences of interfering into
these complex systems are not always known beforehand. That is
why Henk Saeijs, founder of the concept of integrated watermanagement, said once:(42)Nature is the best engineer. Think twice before you interfere.

6(43) Thank you for your attention

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