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

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)

Bars Humps

3

Beachwidth (DF – LW) [m]

Du

ne

foo

t

m

igra

tio

n

rate

[m

/y]

All at once Gradual 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

Indirect vs direct

flats flats

channel

delta

flats flats

channel

delta

Direct Indirect

5Outline

1. Problem introduction

2. The idea

3. Aggregated modelling (ASMITA)

4. Process-based modelling (DELFT3D)

5. Discussion and conclusion

6

North Sea

-15 m

-10 m

-5 m

-5 m

0 5 10 km

NAP -5 m

Study area

Ameland

Pin

keg

at

Schiermonikoog

Lauwerszee

Zout

kam

perla

ag

Engelsmanplaat

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

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

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

Outside world

Ebb-tidal

delta

Channel

Flats

Aggregated modelling ASMITA

Purpose: find out time scales, volumes and behaviour

12

Amelander inlet (SLR = 20 cm/c)

13

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

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

Cases

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

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

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.)

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)