Ad van der Spek

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Ad van der Spek Jan Mulder

• Large-scale future maintenance of the Dutch
  coast
• Learning from nature

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Introduction

• Goal
• putting coastal maintenance into the right
  perspective
• connecting daily practice to long-term coastal
  evolution, anticipating future accelerated
  sea-level rise

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Long-term coastal evolution

• supply gt demand
• regression
• supply demand
• stabile
• supply lt demand
• transgression

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Accommodation space ( demand ! )

• basal topography relative sea level

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Long-term coastal evolution

• 1. basal topography relative sea level
• accommodation space
• demand
• 2. accommodation space sediment supply
• coastal evolution !!

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Future changes in balance

• topography is fixed
• RSLR accelerates (predictions)
• sediment supply ???

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Large-scale coastal evolutionexamples from The
NetherlandsRelative sea-level rise

• trendcurve
• absolute sea-level rise
• land subsidence

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Paleo-geographyc. 5000 BP

• demand gt supply

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Paleo-geographyc. 2600 BP

• demand lt supply

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Holocene sediment budget

• Define sources and sinks
• Calculate the volume of coastal deposits
• Construct a time frame
• curve relative sea-level rise
• growth of volume with time
• Sediment Accumulation during Holocene

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Holocene sediment budget1. Sources sinks

• sinks
• coastal plain deposits
• tidal basins
• barriers
• sources
• North Sea floor
• Pleistocene headlands
• rivers
• older coastal deposits

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Sink the coastalplain

• tidal basins
• estuaries
• beach barriers

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Cross-section

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Total volume Holocene coastal deposits

• ( in billion m3 )
• lithology volume percentage
• --------------------------------------------------
  --------------------------------
• sand 151 - 157 67 -70
• mud 59 - 65 26 - 29
• peat 11 5
• --------------------------------------------------
  --------------------------------
• Total 226 100

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Holocene sediment budgetInfilling with time

• period percentage volume volume / yr
• (billion m3) (million m3)
• --------------------------------------------------
  --------------------------------------
• Atlantic 60 136 41
• (8000-5000 BP)
• Subboreal 30 67 27
• (5000-2900 BP)
• Subatlantic 10 23 7
• (since 2900 BP)
• --------------------------------------------------
  --------------------------------------

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Conclusion

• No longer natural
• large-scale
• sediment accumulation
• !!!

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The Hague, we have got a problem !

• Solution
• Do it yourself !
• Nourish the beach and shoreface (1990)
• Nourish the coastal foundation (2001)
• Nourish the coastal plain? (20..?)

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Keeping up by nourishing sand
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Keeping up with sea-level rise

• Sea-level rise 18 60 85 cm/century
• Coastal foundation 7 23 33
• Wadden Sea 4,5 15 21
• Westerschelde 0,5 1,7 2,4
• ______________________________________
• Total volume
• nourishments 12 40 57 Mm3/year

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how about the coastal plain ?
coastal foundation
coastal plain
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Interested?

• Regional Sediment Deficits in the Dutch
  Lowlands Implications for Long-Term Land-Use
  Options
• Van der Meulen et al. (2007), J. Soils Sediments
  7 (1) 9-16
• http//www.tno.nl/content.cfm?contextmarktencont
  entcaselaag1188item_id406

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Concluding remarks

• help mother nature !
• it works !
• plenty of sand in the North Sea
• raising the coastal plain?
• we have got time, but dont wait too long!

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Thank you for your attention !
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Holocene sediment budget3. Constructing a time
frame

• curve relative sea-level rise
• assumptions
• basin fills up to MSL
• growth of volume with time
• corrections
• infilling tidal basins lagging behind RSLR
• reworking of older coastal deposits

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Flow deposits sand on edge of tidal flats