Morphological Dredging a tool to improve nature values

Morphological Dredging a tool to improve nature values in rivers and estuaries? CEDA 2008 1 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 CEDA 2008 2 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 CEDA 2008 3 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 online method to steer dredging on the basis of morphological assessment and predictions – Based on long experience of hydrographers and dredging specialists (EXPERTISE) CEDA 2008 4 Prof. Em. Eng. J. J. Peters | Consultant Engineer

Some facts • • CEDA 2008 Goal: 30 feet in the wandering area Dredging effort between 2 and 10 Mio m 3 In average on 5 riffles Medium sand 5 Prof. Em. Eng. J. J. Peters | Consultant Engineer

CEDA 2008 6 Prof. Em. Eng. J. J. Peters | Consultant Engineer

CEDA 2008 7 Prof. Em. Eng. J. J. Peters | Consultant Engineer

CEDA 2008 8 Prof. Em. Eng. J. J. Peters | Consultant Engineer

CEDA 2008 9 Prof. Em. Eng. J. J. Peters | Consultant Engineer

Predicting morphological changes CEDA 2008 10 Prof. Em. Eng. J. J. Peters | Consultant Engineer

Possible with simple means … CEDA 2008 11 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 CEDA 2008 12 Prof. Em. Eng. J. J. Peters | Consultant Engineer

Relationship dredging - depths CEDA 2008 13 Prof. Em. Eng. J. J. Peters | Consultant Engineer

The CSD Kallo experiment • Critical situation in 1987 -88: – Complex river’s morphology (tortuous) – Inefficient dredging operations, because of – Deficient field data aquisition (priorities!) • Consequently, in 1988 -89: – 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 CEDA 2008 14 Prof. Em. Eng. J. J. Peters | Consultant Engineer

Morphological evolution 1968 -1986 CEDA 2008 15 Prof. Em. Eng. J. J. Peters | Consultant Engineer

Collapse of navigation route in 1987 CEDA 2008 16 Prof. Em. Eng. J. J. Peters | Consultant Engineer

CEDA 2008 17 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) CEDA 2008 18 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 1992 -94 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) CEDA 2008 19 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: – – CEDA 2008 Analysis of historical data (desk study) Field investigations (flow and sediment transport) Scale model tests (fixed bed, flow and sediment paths) Numerical simulations (Delft 2 D and 3 D codes) 20 Prof. Em. Eng. J. J. Peters | Consultant Engineer

CEDA 2008 21 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) CEDA 2008 22 Multibeam survey at the end of the test disposal in December 2004 (disposal site suggested in 2002 confirmed during the Flanders Hydraulics comprehensive study) 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 …) CEDA 2008 23 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? CEDA 2008 24 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? CEDA 2008 25 Prof. Em. Eng. J. J. Peters | Consultant Engineer

Thank you for your attention Questions? CEDA 2008 26 Prof. Em. Eng. J. J. Peters | Consultant Engineer

CEDA 2008 27 Prof. Em. Eng. J. J. Peters | Consultant Engineer