Departement Mobiliteit en Openbare WerkenMaritieme Toegang

A synthesis onthe assessment of an alternative disposal strategy to

serve sustainability in the Scheldt estuary ir. Frederik Roose

Flemish Government, Mobility and Public Works Department, Maritime Access Division, Belgium

ir. Yves Plancke, ir. Stefaan Ides Flemish Government, Mobility and Public Works Department, Flanders Hydraulics Research, Belgium


Table of contents1. Long Term Vision (2001)2. Alternative disposal strategy (2001)3. Feasibility study (2002-2003)4. First pilot study (2004-2006)5. Second pilot study (2006-2008)6. Large-scale application7. Conclusion


1. Long Term Vision (2001)

= a framework for sustainability

Focusses on 3 utility functions:- Safety against flooding- Navigable access to harbours Morphology- Naturalness

Conservation of multiple channel system Contribution by well-considered dredging/disposal strategy

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2. Alternative disposal strategy (2001)- Morphological dredging (PAET): dredging as a tool to preserve morphological diversity

- Pilot project: reshaping Walsoorden sandbar


3. Feasibility study (2002 – 2003)

- Field measurements (dGPS-floats, sediment transport)- Physical scale model (hydrodynamics and sediment transport):

- most suitable location for disposal test- a large amount of sediment can be stored

- Numerical model (hydrodynamics):- Increase of flow velocity in channels with reshaped sandbar

=> Promising results



4 First pilot study (2004 – 2006)


4.1 Setup of the 1st pilot study

- 500.000 m³

- Diffuser

- Evaluation criteria

- Monitoring program of 1 year


4.2 Morphological monitoring program

- Rapid detection of possible negative evolutions, by

- Repeated multibeam echo sounding surveys

- Occasional LiDAR-flights

- Volume calculations in control zone









=> 1 year after disposal test: more than 80% of disposed sediment remains within control zone


4.3 Ecological monitoring program

- Detect changes in macrobenthos community

- essential role in estuarine ecology

- sensitive to environmental changes

- Subtidal: BACI-design (Before – After – Control – Impact)

-Intertidal: changes in particle size distribution, silt content and macrobenthos community

=> None of the observed effects are significant or can be distinguished from long term trends


4.4 Conclusions from 1st pilot study

- A well-considered disposal management may contribute to a sustainable morphological management

- The disposed sediment is stable enough to allow the usual disposal technique


5 Second pilot study (2006 – 2008)


5.1 Setup of the 2nd pilot study

- phase 1: 500.000 m³

- phase 2: 770.000 m³

- Direct release from dredger

- Long-term monitoring program

- Succes when disposed sediment remains or moves towards sandbar












- Repeatedly multibeam echo sounding surveys




=> Sediment transport towards Walsoorden sandbar


5.3 Ecological monitoring program

=> After 2.5 years no significant negative effects have been related to the pilot projects


6 Large scale application- Current disposal strategy handles maintenance dredging material

- Application of alternative disposal strategy is necessary for handling sediment from enlargement

=> 3 additional disposal locations near sandbars


7 Conclusion- Long Term Vision: acknowledges human impact, further interventions should not endanger preservation of estuary

- Morphological diversity can be attained by a well-considered morphological management

- Combination of study tools is necessary for a decent assessment: a feasibility study and two pilot projects confirm alternative disposal strategy

- Large-scale application

- Other tools towards morphological diversity in the Scheldt estuary ??

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