Frisian Coast Bartholomae

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Development of the East Frisian Islands over the last 1000 yearsDevelopment of the East Frisian Islands over the last 1000 years

Natural and anthropogenic impact at Natural and anthropogenic impact at the East Frisian coast the East Frisian coast -- last 1000 last 1000 years and future perspectivesyears and future perspectives

Alexander BartholomäSenckenberg Institute


PastPast, , PresentPresent and Futureand Future

PastPast::-- developmentdevelopment of of thethe barrierbarrier islandisland systemsystem-- land land relamationrelamation and and dikedike constructionconstruction

PresentPresent::-- DykeDyke maintainancemaintainance, , preservationpreservation of of thethe modern modern WaddenWadden SeaSea systemsystem

-- HazardHazard analysisanalysis and and riskrisk managemantmanagemant

Future:Future:-- IntergratedIntergrated CoastalCoastal Zone Zone ManagmentManagment

withwith alternative alternative conceptsconcepts in in coastalcoastal zonezoneprotectionprotection and and ecosystemecosystem conservationconservation

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PastPast: East : East FrisianFrisian coastcoast 800 AD800 AD

Without dike line (based on historical maps, by Homeier 1969)



with dikes without dikes

- land reclamation - southward migration by transgression- reduction of tidal prism - tidal flats with natural salt marshes- loss of accommodation space

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PresentPresent and Future: East and Future: East FrisianFrisian coastcoast



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PastPast to to presentpresent: : SeaSea--levellevel riserise

Discontinuous sea-level rise with transgressive and regressive phases


M

Pellworm

Langeoog

Rottumeroog

y = - 0.04x + 1.28r = 0.92

y = - 0.04x + 1.07r = 0.91

y = -0.08x + 1.24r = 0.75

y = -0.05x + 0.81

r = 0.90

R

V

V

P

Pellworm

Langeoog

Rottumeroog

y = - 0.04x + 1.28r = 0.92

y = - 0.04x + 1.07r = 0.91

y = -0.08x + 1.24r = 0.75

y = -0.05x + 0.81

r = 0.90

Examples of energy gradients

sample pointregression lineconfidence interval 95%

prediction interval 95%

sett

ling v

elo

city [cm

/s] at 5°C

and S

=3%

island dike

Mando

[km]

0.0

1.5

0.5

2.0

1.0

0.0

1.5

0.5

2.0

1.0

0.0

1.5

0.5

2.0

1.0

0.0

1.5

0.5

2.0

1.0

Denmark

Schleswig-Holstein

East Frisland

West Frisland

Energy Energy gradientsgradients in in thethe WaddenWadden SeaSea

other regionsof the Wadden Sea

Sea-level rise results in:- coarsening of sediments- sediment lag effectsclose to the dike line

- Elevation of tidal flats- Wadden Sea squeeze(all below breakpoint)

53°42' N

53°46' N

007°20' E 007°30' E 007°40' E

Langeoog

Baltrum

Spiekeroog

mainland

0 5 km

1.4

1.4

1.4

1.4

1.4

1.0 1.0

1.0

2.0

2.0 2.0

2.0

coarse

fine

Sediment Sediment beltsbelts alongalong thethe East East FrisianFrisian coastcoast

back-barrier tidal flatof Spiekeroog island

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Wadden Sea squeeze and sea level rise


ReconstructionReconstruction of of thethe fullyfully developeddeveloped tidaltidalsystem system withoutwithout dikedike constructionsconstructions

presentdike line

pleistocene sands

N

W E

S

53°36'N

53°34'N

007°25'E 007°30'E 0 km 5 km

0

10

25

50

75

100

Langeoog

mud flats

Spiekeroog

mudcontenttotalsediment(in %)

saltmarsh

sand flats

mixed flats

mean high water level (1.4 m abovechart datum)

- lost area: more than 50 % of the entire tidal system- mud flat and salt marsh deposits landward of the present day dike line

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SaltSalt--marshmarsh erosionerosion

Preditecd salt-marsherosion along thecoastal dike line

Wittig et al. (2004)

With summer dikes ordammed retention pits

Under certain wave &water-level conditions,broken-wall constructionpatters can preventsalt-marsh erosion

Mai & Zimmermann (2002)


Human Human responsesresponses to to thetheexpectedexpected seasea--levellevel riserise

Risk analysis:- storm-flood risks- hydraulic boundary conditions at coastal constructions- risk assessment for local environments

Risk and Coastal Zone Management: e.g. by the „Coastal Protectionand Sea-level Group (CPSL) Policies, Strategies, Management

Projekts and Activities:COMRISK (Common Strategies to reduce the risk of storm

floods in coastal lowlands)DEKLIM (German Climate Change Research Program)KRIM (Climate change and preventive risk and coastal zone

management along the German North Coast)ICZM Integrated Coastal Zone ManagementENCORA (Initiative for Coordination Action within European

coastal research and practitioners communities)LOICZ (Land-Ocean Interactions in the Coastal Zone)

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BreakpointBreakpoint analysisanalysis (CPSL 2001/2005)(CPSL 2001/2005)

Moderate increase in sea level :

≤ 3mm/year for large basins≤ 6 mm/year for small basins

≤ 8.5 mm/year for salt marshes3 – 6 mm/ year pioneer zone

- present dynamic equillibrium still active

- Increase of duration of tidal inundationimplies stronger sediment accumulationon tidal flats and salt marshes (longersettling period)

- Elevation of tidal flats; and expansion ofsalt marshes

Major sea-level rise:

- massive erosion of salt marshes- in sandy areas, erosion rate increases between250% (6mm/yr) and 330% (8.5mm/yr)

- fore-shore erosion, retreat of barrier islands

Changes in wave and /or tide-domminated sections are not considered


Main Main topicstopics of of coastalcoastal protectionprotectionand and managementmanagement

Sea dikes

Salt-marsh management

Habitatmaintenance

Outbanking of summer polders

Dunemanagement

Sand nourishmentDike strenghening over the last centuries

time: height / lenght / volume

2000: 7.8 m / 105 m / 325 m³

1955: 5.9 m / 56 m / 149 m³

1200: 1.0 m / 5.5 m / 3 m³

1600: 3.0 m / 19 m / 32 m³

2100: 8.5 m / 150 m / 500 m³ ????

1900: 4.8 m / 33 m / 82 m³

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Reinundation of sommer dikes - Salt marshaccretion in protected areas (Langeoog island)

by courtesy of Freund (2006), ICBM Marine Lab.

accumulation rate 5 cm/month

Nordsee

Niederlande Deutschland

Helgoland

Däne mark


ConceptConcept of of creatingcreating artificialartificial tidaltidal basinsbasinsin in thethe sheltershelter of of thethe dikesdikes

Schematic drawing of an artificial tidal basin with multipleand sustainable usages, including tourism.

Dike

Sluice

mean high-tide level�

- controlled tidal range- slow infilling with clay

- new salt marsh formation- ideal breeding conditions

- new clay resource- ideal for aquaculture

- tourismus

lowdike

♣♣♣

��new

salt marshes

tidal flat

Sea Land ��

tidal channel

�mean low-tide level

tidal basin

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Subdivision of an Subdivision of an artificalartifical tidaltidal basinbasin in in thethesheltershelter of of thethe dikesdikes byby multiple multiple usageusage conceptsconcepts


Summary and Outlook

�� Land Land reclamationreclamation and and dikedike constructionsconstructions alreadyalready reclaimedreclaimed moremore thanthan50 % of 50 % of thethe formerformer fullyfully devolopeddevoloped tidaltidal systemsystem

�� In order to In order to thethe predictedpredicted seasea levellevel riserise, to , to preservepreserve thethe modern modern systemsystemand/orand/or preventprevent furtherfurther changeschanges in in thethe WaddenWadden SeaSea environmentenvironmentindividualindividual solutionssolutions forfor a a IntegratedIntegrated CoastalCoastal Zone Zone ManagmentManagment areareessential:essential:

�� -- IncreaseIncrease of of accommodationaccommodation spacespace�� -- saltsalt marshmarsh, dune and , dune and habitathabitat managementmanagement on on individualindividual scalesscales

�� -- dikedike strengheningstrenghening and and retreatretreat, , reinundationreinundation of of summersummer dikedike areasareas,,�� -- outbankingoutbanking summersummer polderspolders, , reactivationreactivation of of retentionretention pitspits

ThereforeTherefore wewe needneed::

�� -- IndividualIndividual casecase studiesstudies forfor individualindividual sitessites�� -- CollaborationCollaboration betweenbetween dikedike protectionprotection and and environmentalenvironmental protectionprotection

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Frisian Coast Bartholomae