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DSD-INT 2019 Morphodynamic effects of peat compaction in a fluvial-tidal basin - Roelofs

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Presentation by Lonneke Roelofs, University of Utrecht, The Netherlands, at the Delft3D and XBeach User Day: Coastal morphodynamics, during Delft Software Days - Edition 2019. Wednesday, 13 November 2019, Delft.

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DSD-INT 2019 Morphodynamic effects of peat compaction in a fluvial-tidal basin - Roelofs

  1. 1. Faculty of Geosciences River and delta morphodynamics Morphodynamic effects of peat compaction in a fluvial-tidal basin A case of sinking natural levees Lonneke Roelofs MSc Marcio Boechat-Albernaz MSc, dr. Harm Jan Pierik, prof. dr. Maarten Kleinhans dr. Sanneke van Asselen, dr. Helena van der Vegt, dr. ir. Bert Jagers, Aulia Valencia MSc
  2. 2. Combination of two projects Levee morphology and evolution in the fluvial- tidal realm MSc thesis – Numerical modelling & fieldwork Peat compaction and delta evolution, a case study on natural levees & crevasses Internship Deltares – Numerical modelling
  3. 3. Levees
  4. 4. Peat compaction Berendsen, 2005 Van Asselen, 2010
  5. 5. Case study: Oude Rijn From tidal to fluvial Levees played a role in closing Well preserved due to peat >0 m <-2 m Height w.r.t. NAP
  6. 6. Numerical modelling Delft3D Water depth (m) • 4 sand fractions • 1 silt fraction • 1 clay fraction
  7. 7. Numerical modelling Peat compaction Model by Van Asselen (2010) Peat thickness and organic content (LOI) Peat thickness Natural strain Primary compaction (stress) Secondary compaction (time)
  8. 8. Numerical modelling Water depth (m)
  9. 9. Results without compaction
  10. 10. Results without compaction 2 0 -2 -4 -6 -8 -10 Elevation(m) SandSiltClay Tidal amp 0.25 m River Q 700 m³/s
  11. 11. SandSiltClay Tidal amp 0.25 m River Q 700 m³/s
  12. 12. General development Q constant No tide Q variable No tide Q constant Small tide Q constant Large tide 10 5 0 Distance(km) 10 5 0 Distance(km) 0 5 10 15 20 Distance (km) 0 5 10 15 20 Distance (km)
  13. 13. Peat Overbank Point bar Channel belt Older dep. Grain size C14
  14. 14. Results with compaction
  15. 15. Increasingpeatthickness Elevation (m) Deposition (m)
  16. 16. Increasingpeatthickness
  17. 17. Discussion Tides largely influence levee morphology, and evolution Increase width & height -> effective distribution Crevasses Peat compaction increases levee thickness and crevasse length Balance between compaction & sedimentation important for development
  18. 18. Discussion Adding compaction to Delft3D gives insight in Evolution of levee morphology in compaction prone environments Influence of compaction on formation and evolution of crevasse channels in peat rich environments Further developments needed Peat growth ■ The entrainment of sediments in peat deposits ■ The suffocation of peat vegetation Dynamic system -> avulsions

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