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Smart nourishment of ebb-tidal deltas

Smart nourishment of ebb-tidal deltas. M. Kluyver (WL/TUD), Z.B. Wang (WL/TUD), M.J.F. Stive (TUD), M. van Koningsveld (WL/TUD). Acknowledgements: Delft Cluster Northsea and Coast (DC 05.20) Water Innovation Programme (WINN). Humps vs bars. Bars. Humps.

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Smart nourishment of ebb-tidal deltas

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  1. Smart nourishment of ebb-tidal deltas M. Kluyver (WL/TUD), Z.B. Wang (WL/TUD), M.J.F. Stive (TUD), M. van Koningsveld (WL/TUD) Acknowledgements: Delft Cluster Northsea and Coast (DC 05.20) Water Innovation Programme (WINN)

  2. Humps vs bars Bars Humps Roelvink, J.A., Reniers, A.J.H.M., Walstra, D.J.R. and van Ormondt, M, 2005. Shoreface nourishments: humps or bars? 5th International Conference on Coastal Dynamics 2005, Barcelona. Koster, L., J.A. Roelvink, D.J.R. Walstra, M. van Koningsveld, M.J.F. Stive, 2006. "Humps or Bars: Alongshore Nourishment Length as an Important Design Parameter." Journal of coastal engineering (Submitted)

  3. Gradual vs all at once All at once Gradual dune strengthening (50 years) Dunefoot migration rate [m/y] Beachwidth (DF – LW) [m] M.van Koningsveld, 2005. Meer zand met minder moeite.Smart nourishments: innovatieve zandige maatregelen voor het kustbeheer van de toekomst. WL|Delft Hydraulics report Z3912.00

  4. Indirect vs direct Direct Indirect delta delta channel channel flats flats flats flats

  5. Outline • Problem introduction • The idea • Aggregated modelling (ASMITA) • Process-based modelling (DELFT3D) • Discussion and conclusion

  6. -15 m -5 m -10 m Schiermonikoog -5 m Ameland Pinkegat Zoutkamperlaag Engelsmanplaat North Sea Lauwerszee 0 km 5 10 NAP -5 m Study area

  7. Problem introduction (1) • Increasing rates of sea-level rise will result in an increase of tidal basin volumes and a decrease of intertidal areas (Van Goor et al., 2003). • Additionally, adjacent coasts will suffer increased erosion rates (Stive, 2004).

  8. Problem description (3) • The ecologically most sensitive areas are the intertidal flats, a prime habitat for marine live and many north-south and vice versa migrating birds. • Socio-political as well as administrative (nat. & EU) pressures for mitigating action • Compensation of the effect of sea-level rise and/or subsidence by nourishment of the flats is a virtually impossible measure. • Not only would it destruct marine live, but also the subtle variation of sediment composition on these flats cannot easily be realised.

  9. The idea (an innovative solution) • In 2004 Stive and Wang came up with the concept of ‘overnourishing’ the ecologically less rich ebb-tidal deltas or channels with a wide composition of sediments. • After some preliminary calculations they found that this should be investigated in more detail for the Wadden Sea area.

  10. Outside world Ebb-tidal delta Channel Flats Aggregated modelling ASMITA • Purpose: find out time scales, volumes and behaviour

  11. Amelander inlet (SLR = 20 cm/c)

  12. Amelander inlet (SLR = 20 cm/c & 0.5 Mm3/y)

  13. Process-based modelling • Although the foregoing confirms that the idea is feasible physically from an aggregated scale perspective, the question arises how to actually execute the idea of ‘overnourishment’ in practice. • Issues here are: • (1) what locations of an ebb-tidal delta need to be considered? • (2) what volumes are needed as a function of time? • (3) what sediment composition is necessary? • To resolve these issues we have been undertaking preliminary process-based model studies.

  14. Cases • Based on physical expertise and practical considerations (e.g. minimum required depth for dumping) we have selected 7 possible nourishment locations.

  15. Preliminary findings from Delft3D • Behaviour of sand in 7 scenarios • a fixed bathymetry tide only (9.5 years – reduction of alternatives) • morphodynamic computations tide only (9.5 years) • morphodynamic computations tide and waves (1 year) • General findings: • Nourishment of ebb channels and ebb-tidal delta leads (initially) to redistribution of sands over the ebb-delta (waves important) • This sand may later be picked up again and brought into the inward directed sediment transport paths • Most direct effect was seen from feeding in or near channels

  16. Discussion en conclusions • Discussion • practical considerations limit the prediction horizon of processed based modelling (esp. given the relevant timescales here: several decades) • we only looked at the behaviour of one nourishment – not the effects of continuous overnourishment • However • Some locations are more effective than others (especially in the vicinity of channels) • In conclusion • The concept seems to work based on an aggregated analysis • Further detailed process analysis needed to resolve design issues on an operational level (location, sediment composition, volumes, etc.)

  17. Smart nourishment of ebb-tidal deltas M. Kluyver (WL/TUD), Z.B. Wang (WL/TUD), M.J.F. Stive (TUD), M. van Koningsveld (WL/TUD) Acknowledgements: Delft Cluster Northsea and Coast (DC 05.20) Water Innovation Programme (WINN)

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