Dutch coasts in transition

8/11/2019 Dutch coasts in transition.

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Dutch coasts in transitionPavel Kabat, Louise O. Fresco, Marcel J. F. Stive, Cees P. Veerman, Jos S. L. J. van Alphen,

Bart W. A. H. Parmet, Wilco Hazeleger and Caroline A. Katsman

The Netherlands has a long and varied history of coastal and river flood management. The anticipation

of sea-level rise during the twenty-first century has renewed the push for sustainable solutions to

coastal vulnerability.

The Netherlands is a densely populatedcountry situated primarily in coastallowlands. Te Dutch coast, which

is entirely along the North Sea, is 350 kmlong. At present, nine million residents

of the Netherlands live in the coastalareas vast regions at an elevationbelow sea level. Roughly 65% of thecountrys gross national product about400 billion is generated in this region;the harbours and airports scatteredthroughout the lowlands are vital to thecountrys infrastructure and serve asimportant international transport routes forpeople and goods. Furthermore, the coastallowlands host a number of the countrysgoods and services industries. Althoughthis key region is protected by dykes anddunes along the coast, future sea-level rise

could put it at risk.

Flood protection standardsTe need for flood protection is etchedon Dutch collective thinking. In 1953,a storm surge broke through the dykesand inundated the southwest coast withmetres of water. Property destruction wasdevastating and over 1,800 people werekilled. Te Dutch central governmentimmediately set up a committee the(first) Delta Committee to charta course of action to prevent futuredisasters. Te committee recommended

a series of engineering works to protectlow-lying areas, including the closureof several sea inlets, and made plansto reinforce and expand many of thedykes. Te implementation of theserecommendations fully began duringthe second half of the twentieth century,resulting in the construction of largeand numerous levees and dykes thatradically altered the appearance of thesouthwestern Netherlands.

Tus the existing standards for coastalflood protection date back to the 1960s andare based on the statistical likelihood oflarge storm surges as assessed at that time.

However, as revealed in the 2006 auditconducted by the Ministry of ransport,Public Works and Water Management,between 24 and 56% of current coastaldefences do not even meet the old

standards (see Fig. 1). And of course, thenumber of people and the value of the

property that need to be protected fromflooding has grown steadily.

A changing climate and the anticipatedrise in sea level will only add to thechallenges faced by the aging flood defence

system. Te Dutch government not onlyrecognized the growing vulnerability of

North Sea

Belgium

The Netherlands

Safety standard per dyke-ring area

1 in 10,000 per year

1 in 4,000 per year

1 in 2,000 per year

1 in 1,250 per year

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(also outside

The Netherlands)

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outside The Netherlands

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Figure 1 |Flood safety standards of dykes in The Netherlands. The current level of protection ranges from

a flooding probability of 1 in 1,250 per year inland to 1 in 10,000 per year along the coast.

2009VERKEERENWATERSTAAT

2009 Macmillan Publishers Limited. All rights reserved


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the lowlands, but also the opportunity tocapitalize on re-shaping and updating thewater management system to climate-proof the Netherlands1. In 2007, the Dutchgovernment therefore established a newDelta Committee to develop strategies forthe sustainable development of the coast

throughout the twenty-first century2. Tecommittee was given a broad mandate toassess medium- and long-term scenariosinvolving the entire coastal and riversystem, and to develop region-specificrecommendations. Te committees ultimategoal was to determine what needed to bedone so that the Netherlands could continueto thrive well into the twenty-first andtwenty-second centuries.

Sea-level scenariosAlthough partly outdated, the originalDelta Committee recommendations had

strong and well-thought-out basic flood-protection standards based on economicoptimization. Te resulting engineeringworks protected coastal areas from floodswith an occurrence probability of 1 in10,000 for a given year, and riverine areasfrom floods with an occurrence probabilityof 1 in 1,250 per year (Fig. 1). Te newDelta Committee started from the samethresholds, also recommending raising theflood protection levels of all dyked areas bya factor of ten.

Over the past century, relative sealevel along the Dutch coast has risen by

about 20 cm, a value that is similar toestimates of g lobal sea-level rise3. TeIntergovernmental Panel on ClimateChange (IPCC) projects a further riseof between 0.18 and 0.59 m globally by2100. o ensure that the flood protectionmeasures can withstand high valuesof sea-level rise, a study based onthe IPCC high emissions scenario(SRES A1FI) was initiated to provide anup-to-date, plausible upper-limit scenarioof climate and sea-level projections for theNetherlands. High-end estimates of icedischarge and regional effects, such as local

thermal expansion and coastal subsidence,place the upper limits of relative sea-levelrise for the Netherlands at 0.65 to 1.3 min 2100, excluding gravitational effects. By2200, high-end estimates increase to 2.0 to4.0 m of sea-level rise4.

An integrated visionStarting from the projections forclimate change and sea-level rise, andin combination with its own vision ofsustainable future development, the DeltaCommittee has presented an integralstrategy for the long-term protectionof the Dutch Rhine/Meuse delta and

North Sea coast. Tey have also maderecommendations for the development ofthe coast and the Dutch hinterland5. Testrategy moves beyond basic water safety:the integrated approach also includesprovisions for freshwater supplies, thepreservation of natural and recreationalareas, and sustainable energy.

Te committee has incorporated twocornerstones of flood protection: buildingwith nature and room for the river. Tebuilding with nature approach movesaway from engineered coastal protectionstructures such as levees and surge barriers,relying instead on beach nourishment andgrowth (Fig. 2). Indeed, whenever possible,they call for removing existing structuresto restore natural estuary and tidal regimeswhile still protecting against flooding.

Tey also recommend that additionalland be preserved from developmentalong the Rhine and Meuse rivers, to

accommodate increased river inundation.o ensure a continuous supply of freshwater, they suggest raising the level ofLake IJsselmeer by up to 1.5 m by 2100,to create a freshwater reservoir for theNetherlands and for possible freshwaterexport to southern Europe, which may beat increased risk of drought at the end ofthe century.

Tis advice was adopted in its entiretyby the Dutch Cabinet, and a new Delta Actand Delta Programme are being prepared.Tis legislation will provide a legal,administrative and financial frameworkto begin full implementation of these

recommendations. Yet although theimportance of such measures to perceptionsof flood safety is indisputable, thesemeasures are not without cost. Projectionsof future climate change, and the attendantsea-level rise, are not absolute; the Dutchpublic, and their elected policymakers,tend to see climate change as a threat to

prosperity, rather than to personal andsocietal safety. Te Delta Committee hastackled this public perception by presentingthe key challenges as opportunities for asustainable and innovative economy.

Financing coastal protectionTe proposed modifications will come ata price. Te Delta Programme will cost upto 1.6 billion per year until 2050 when thecost is anticipated to drop to a minimumof 900 million per year, not includingmaintenance and management costs,which could add an additional 1.2 billion

per year. But there are rewards for theseexpenses. Although not in the initialbudget, the Delta Programme includes anoptional 100 to 300 million per year foradditional beach nourishment. As well asflood protection, the committee predictsthat under the nourishment regime, thenorthern coast would expand seawardby about a kilometre, creating land forbeach reserves, nature and recreation.Such additional activities could bringthe total cost of the project, includingmaintenance, up to 3.1 billion per year upto 2050 about 0.5% of the current Dutchgross national product.

Figure 2 |Building with nature. Beach nourishment is one alternative approach to engineering in flood

management along the Dutch coast.

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In comparison, the potential cost ofdoing nothing could reach 3.7 trillionacross the entire country5, and even the costof a single dyke failure could range from10 to 50 billion. It is unlikely that the entirelow-lying coastal area would be flooded,but a dyke break in a densely populated

area would cause massive property loss anddamage. Te recommendations have anadded financial flexibility: the infrastructuremodifications and growth can be made in astepwise fashion, and are designed so thatthey can be readily upgraded if scenarios forfuture sea-level rise change.

An unexpected opportunityUnsurprisingly, these relatively costlysuggestions have become a source ofoccasionally heated public, political andacademic debate. Yet even with existinguncertainties about future climate,

economically viable and responsibleinvestments into adaptation measuresin the water safety sector and beyond

can be made in the Netherlands. Tesemeasures call for innovative solutionsand technologies in our struggle againstthe rising waters. We thus propose thatrather than being a financial burden,coastal protection can be seen as a pushto boost technological innovation, and to

invest in the development of long-lastingand sustainable infrastructure. We, andthe Delta Committee, suggest that for theNetherlands, climate change can be anopportunity for societal and economicgrowth and evolution, moving the countryinto a sustainable future.

Pavel Kabat1*, Louise O. Fresco2, Marcel J. F. Stive3,

Cees P. Veerman4, Jos S. L. J. van Alphen5,

Bart W. A. H. Parmet6, Wilco Hazeleger7

and Caroline A. Katsman7 are at the1Wageningen University and Research Centre,

PO Box 47, 6700 AA Wageningen, Te Netherlands,2

University o Amsterdam, PO Box 19268,1000 GG Amsterdam, Te Netherlands 3Delf

echnical University, PO Box 5048, 2600 GA Delf,

Te Netherlands, 4Bracamonte BV, Postweg 11,

6561 KJ Groesbeek, Te Netherlands, 5Ministry o

ransport, Public Works and Water Management,

PO Box 17, 8200 AA Lelystad, Te Netherlands,6Ministry o ransport, Public Works and Water

Management, PO Box 20904, 2500 EX Den Haag,

Te Netherlands and 7Royal Netherlands

Meteorological Institute (KNMI), PO Box 201,3730 AE De Bilt, Te Netherlands.

*e-mail: [email protected]

References1. Kabat, P., Van Vierssen, W., Veraart, J., Vellinga, P. & Aerts, J.

Nature438,283284 (2005).

2. http://www.deltacommissie.com/

3. Church, J. A. & White, N. J. Geophys. Res. Lett.

33,L01602 (2006).

4. http://www.deltacommissie.com/doc/deltareport_full.pdf

5. Aerts, J., Sprong, . & Bannink, B. (eds)Attention to Saety

(Aandacht voor veiligheid in Dutch) (Klimaat voor Ruimte, 2008);

available at .

Additional informationTis article is based on the deliberations and final advice

of the Delta Committee (see http://www.deltacommissie.

com/en/advies).

Land waters and sea levelDennis P. Lettenmaier and P. C. D. Milly

Changes in continental water stores, largely human-induced, affect sea level. Better hydrological models

and observations could clarify the lands role in sea-level variations.

Understanding the causes ofcontemporary sea-level rise isa prerequisite for projecting

future changes in sea level. Te maincontributions to the current rise in globalmean sea level of about 2 to 3 mm yr 1arethought to come from the loss of land-based ice masses such as ice sheets, icecaps and mountain glaciers, and from thethermal expansion of the oceans1. Tese

contributions are sufficient to explainthe observed rate of sea-level rise withinthe uncertainties of the constituentestimates2. However, the uncertainties inboth contributions are large enough toleave room for a significant additionalsource of sea-level rise (or, less likely,a sink) that could account for severaltenths of a millimetre per year. A numberof proposed mechanisms3could reducecontinental water mass and thereby explainany relatively small missing source ofsea-level rise2. Tese mechanisms couldalso markedly affect any acceleration ordeceleration of sea-level rise.

Land loses waterAs a simple consequence of massconservation, the ocean surface rises whenthe continents lose water. For example,wetland drainage entails deliberatereductions of water storage4, urbanizationcan suppress groundwater rechargeand thereby lower the water table5, andextraction of groundwater by pumping(sustainable or not) reduces aquifer

storage. Increasingly deeper seasonal thawof soil above permafrost might promotedrainage of the newly activated part ofthe soil profile6, which can contain largedeposits of ground ice. DisappearingArctic lakes7 though contributing littlemass on their own provide evidence thatthawing activates drainage pathways at thelandscape scale. On the other hand, reducedseasonal freezing of the soil surface couldalso enhance infiltration of water into soiland increase soil-water storage, particularlywhere permafrost is absent.

Each of the aforementioned effects couldreasonably generate a sea-level change

on the order of 0.1 mm yr1. However,quantitative estimates of the contributionsof these mechanisms to rising sea levels arebased on speculative global extrapolations ofuncertain local observations and data.

Land gains waterOne well-defined negative contributor tosea-level rise results from the sequestrationof water in man-made surface-water

reservoirs (Fig. 1). Near the middle ofthe twentieth century, the sequestrationof water in reservoirs depressed rates ofsea-level rise by more than 0.5 mm yr1on a decadal timescale. More recently,the rate of impoundment of water inreservoirs has slowed (and perhaps,we speculate, has even changed sign).Te implied rapid change in the role ofreservoirs is a result of two processes: aslow-down in the construction of dams anda gradual infilling of existing reservoirs bysediments, such that their water volumeslowly declines. (Reservoir sedimentationaffects sea level by the infilling process


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Dutch coasts in transition