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. 2 Humps vs bars 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) BarsHumps

3. 3 Beachwidth (DF – LW) [m]Dunefoot migration rate [m/y] All at onceGradual dune strengthening (50 years) Gradual vs all at once 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. 4 Indirect vs direct flats channel delta flats channel delta Direct Indirect

5. 5 Outline 1. Problem introduction 2. The idea 3. Aggregated modelling (ASMITA) 4. Process-based modelling (DELFT3D) 5. Discussion and conclusion

6. 6 North Sea -15 m -10 m -5 m 0 510 km NAP -5 m Study area Ameland Pinkegat Schiermonikoog Lauwerszee Zoutkamperlaag Engelsmanplaat

7. 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. 8

9. 9 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.

10. 10 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.

11. 11 Outside world Ebb-tidal delta Channel Flats Aggregated modelling ASMITA  Purpose: find out time scales, volumes and behaviour

12. 12 Amelander inlet (SLR = 20 cm/c)

13. 13 Amelander inlet (SLR = 20 cm/c & 0.5 Mm 3 /y)

14. 14 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.

15. 15 Cases  Based on physical expertise and practical considerations (e.g. minimum required depth for dumping) we have selected 7 possible nourishment locations.

16. 16 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

17. 17 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.)

18. 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)