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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)

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

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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) Slide 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 Slide 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 Slide 4 4 Indirect vs direct flats channel delta flats channel delta Direct Indirect Slide 5 5 Outline 1. Problem introduction 2. The idea 3. Aggregated modelling (ASMITA) 4. Process-based modelling (DELFT3D) 5. Discussion and conclusion Slide 6 6 North Sea -15 m -10 m -5 m 0 510 km NAP -5 m Study area Ameland Pinkegat Schiermonikoog Lauwerszee Zoutkamperlaag Engelsmanplaat Slide 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). Slide 8 8 Slide 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. Slide 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. Slide 11 11 Outside world Ebb-tidal delta Channel Flats Aggregated modelling ASMITA Purpose: find out time scales, volumes and behaviour Slide 12 12 Amelander inlet (SLR = 20 cm/c) Slide 13 13 Amelander inlet (SLR = 20 cm/c & 0.5 Mm 3 /y) Slide 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. Slide 15 15 Cases Based on physical expertise and practical considerations (e.g. minimum required depth for dumping) we have selected 7 possible nourishment locations. Slide 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 Slide 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.) Slide 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)