Departement Mobiliteit en Openbare Werken

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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
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Table of contents

1. 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 application
7. Conclusion

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• 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

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• 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
• gt Promising results

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• 4 First pilot study (2004 2006)

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• 4.1 Setup of the 1st pilot study

• 500.000 m³
• Diffuser
• Evaluation criteria
• Monitoring program of 1 year

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• 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

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• 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

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gt 1 year after disposal test more than 80 of
disposed sediment remains within control zone
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• 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
• gt None of the observed effects are significant
  or can be distinguished from long term trends

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• 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

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• 5 Second pilot study (2006 2008)

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• 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

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• 5.2 Morphological monitoring program

• Rapid detection of possible negative evolutions,
  by
• Repeated multibeam echo sounding surveys
• Occasional LiDAR-flights
• Volume calculations in control zone

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• 5.2 Morphological monitoring program

• Rapid detection of possible negative evolutions,
  by
• Repeatedly multibeam echo sounding surveys
• Occasional LiDAR-flights
• Volume calculations in control zone

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gt Sediment transport towards Walsoorden sandbar
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• 5.3 Ecological monitoring program

gt After 2.5 years no significant negative
effects have been related to the pilot projects
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• 6 Large scale application

• Current disposal strategy handles maintenance
  dredging material
• Application of alternative disposal strategy is
  necessary for handling sediment from enlargement
• gt 3 additional disposal locations near sandbars

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• 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 ??