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CEDA 20081 Prof. Em. Eng. J.J. Peters | Consultant Engineer Morphological Dredging a tool to improve nature values in rivers and estuaries?

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Presentation on theme: "CEDA 20081 Prof. Em. Eng. J.J. Peters | Consultant Engineer Morphological Dredging a tool to improve nature values in rivers and estuaries?"— Presentation transcript:

1 CEDA Prof. Em. Eng. J.J. Peters | Consultant Engineer Morphological Dredging a tool to improve nature values in rivers and estuaries?

2 CEDA Prof. Em. Eng. J.J. Peters | Consultant Engineer Link morphology – ecology? Perception is different among various partners / stakeholders Nature and ecology entered quite recently in management plans for rivers/estuaries Prediction of effects on nature values is really not easy as we miss usually knowledge about morphological and ecological functioning of rivers/estuaries

3 CEDA Prof. Em. Eng. J.J. Peters | Consultant Engineer What is morphological dredging? We refer to dredging in a system which morphology is dynamical, e.g., in large alluvial rivers or estuaries All dredging affects morphology, but Not all dredging is morphological Morphological dredging requires an understanding of the behaviour of the river, its channels and sandbars

4 CEDA Prof. Em. Eng. J.J. Peters | Consultant Engineer The Congo case Project to improve navigation conditions in Congo River’s maritime reach: –Started in 1968 at Hydraulic Laboratory Antwerp, based on scale model tests –Field data collected, showed the need for on-line method to steer dredging on the basis of morphological assessment and predictions –Based on long experience of hydrographers and dredging specialists (EXPERTISE)

5 CEDA Prof. Em. Eng. J.J. Peters | Consultant Engineer Some facts Goal: 30 feet in the wandering area Dredging effort between 2 and 10 Mio m 3 In average on 5 riffles Medium sand

6 CEDA Prof. Em. Eng. J.J. Peters | Consultant Engineer

7 CEDA Prof. Em. Eng. J.J. Peters | Consultant Engineer

8 CEDA Prof. Em. Eng. J.J. Peters | Consultant Engineer

9 CEDA Prof. Em. Eng. J.J. Peters | Consultant Engineer

10 CEDA Prof. Em. Eng. J.J. Peters | Consultant Engineer Predicting morphological changes

11 CEDA Prof. Em. Eng. J.J. Peters | Consultant Engineer Possible with simple means …

12 CEDA Prof. Em. Eng. J.J. Peters | Consultant Engineer Relationship dredging - depths Based on almost 90 years of records: –No unique relationship –Is governed by the river’s morphology –Obvious effect of (good or bad) management Consequently: –Use dredging as a tool to steer morphology –Work with nature when possible –Against it when needed

13 CEDA Prof. Em. Eng. J.J. Peters | Consultant Engineer Relationship dredging - depths

14 CEDA Prof. Em. Eng. J.J. Peters | Consultant Engineer The CSD Kallo experiment Critical situation in : –Complex river’s morphology (tortuous) –Inefficient dredging operations, because of –Deficient field data aquisition (priorities!) Consequently, in : –Use dredging as a tool to steer morphology and to prevent unwanted navigation channel –Hoppers were not suited, so CSD contracted and barges to dispose in secondary channels

15 CEDA Prof. Em. Eng. J.J. Peters | Consultant Engineer Morphological evolution

16 CEDA Prof. Em. Eng. J.J. Peters | Consultant Engineer Collapse of navigation route in 1987

17 CEDA Prof. Em. Eng. J.J. Peters | Consultant Engineer

18 CEDA Prof. Em. Eng. J.J. Peters | Consultant Engineer Shaving off a sandbar Hard river shores prevent development of a navigation channel and sandbar edge had to be dredged with the SCD (field draft drawing)

19 CEDA Prof. Em. Eng. J.J. Peters | Consultant Engineer The Western Scheldt case Deepening and widening the fairway with due attention for nature and safety –During activities of a reviewteam for a new management plans for the Scheldt estuary, Congo strategy was suggested but not retained because considered as inappropriate –In 2001, Port of Antwerp Expert Team proposed disposal of dredged material along edges of sandbars (see next presentation by F. Roose)

20 CEDA Prof. Em. Eng. J.J. Peters | Consultant Engineer The Walsoorden case study Proposal was based on desk study, mainly visual analysis of historical charts and expertise (a morphological diagnoses) ; a comprehensive study was then conducted in 2002 and 2003 with: –Analysis of historical data (desk study) –Field investigations (flow and sediment transport) –Scale model tests (fixed bed, flow and sediment paths) –Numerical simulations (Delft 2D and 3D codes)

21 CEDA Prof. Em. Eng. J.J. Peters | Consultant Engineer

22 CEDA Prof. Em. Eng. J.J. Peters | Consultant Engineer The Walsoorden proposal and result Survey alignments proposed before Flanders Hydraulics studies (M for middle, L for left, R for right, E for exterior) Multibeam survey at the end of the test disposal in December 2004 (disposal site suggested in 2002 confirmed during the Flanders Hydraulics comprehensive study)

23 CEDA Prof. Em. Eng. J.J. Peters | Consultant Engineer New disposal strategy After the success of the Walsoorden experiment, the strategy was taken up in the plans for the enlargement of the Western Scheldt navigation route (see presentation by M. Sas et al. On Ocober 2 nd ) However, more is needed for curbing the past morphological evolution which was responsible for a deterioration of the nature values (not everyone agrees with this statement …)

24 CEDA Prof. Em. Eng. J.J. Peters | Consultant Engineer Can we (or may we) develop a new morphology that can be good for navigation, nature & safety? Present fairway Future fairway?

25 CEDA Prof. Em. Eng. J.J. Peters | Consultant Engineer The questions are: Who trusts a strategy based on expertise rather than on modelling? How can we prove the ecological benefits of morphological management of this estuary? Can we trust morphological dredging (some ecologists call it “gardening”) What do we do if things go wrong?

26 CEDA Prof. Em. Eng. J.J. Peters | Consultant Engineer Thank you for your attention Questions?

27 CEDA Prof. Em. Eng. J.J. Peters | Consultant Engineer


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