Developing the transboundary Long Term Vision of the Scheldt Estuary – an untold story

Figures & data

Figure 1. Map of the Scheldt Estuary with the lower reaches (Bath to Vlissingen) located in the Netherlands and the middle to upper reaches (Antwerp harbour to Gent) located in Flanders, a province of Belgium. The characteristics of the Long Term Vision agreed bilaterally in 2001 are listed.

Source: Map adapted from VNSC (2019).

Figure 2. The process followed in developing the Long Term Vision for the Scheldt Estuary, specifying each of the four steps of the process. The Long Term Vision is characterized in terms of accessibility, flood safety, nature and the morphology of the estuary.

Figure 3. The integrated three-level hybrid modelling system that translates hydro-morphological simulations via ecologically relevant indicators to characteristic abiotic zones and physiotopes, which are linked through the conceptual ecosystem model at its heart to the ecosystem goals (Slinger, 2000).

Table 1. Combinations of management interventions and exogenous developments (cases) considered relevant in assessing the response of the natural environment of the Scheldt Estuary.

Case number	Case description	Details
1	Depoldering (Sea Scheldt only)	Permanently increasing the storage capacity in the freshwater reaches
2	Depoldering (Sea Scheldt and Western Scheldt)	Permanently increasing the storage capacity in the freshwater, brackish and estuarine reaches of the Scheldt Estuary
3	Conservative Dredging, Disposal and Sand Mining	An extrapolation of the existing policy into the future with no new disposal or sand-mining sites
4	Channel Deepening to 14 m	Dredging the channel to a depth of 14 m also involves disposing of the dredged sediment
5	Channel Deepening and Depoldering (Sea Scheldt only)	A combination of the interventions from cases 1 and 4
6	Improved Freshwater Quality	Improving the quality of the freshwater flowing into the upper reaches of the Scheldt Estuary, particularly reducing carbon and nutrient loads
7	Nature compensation	Artificially creating intertidal physiotopes in the brackish and freshwater reaches
8	River Flood	An exogenous event associated with a temporary increase in freshwater, raised water levels and stronger currents
9	Moderate Sea Level Rise	An ongoing exogenous influence associated with the average predicted range of sea level rise
10	Channel Deepening to 14 m under Moderate Sea Level Rise	A combination of the interventions from case 4 and the exogenous influence of case 9
11	Channel Deepening and Depoldering (Sea Scheldt only) under Moderate Sea Level Rise	A combination of the interventions from cases 1 and 4 and the exogenous influence of case 9

Table 2. Aggregated range within which the criteria vary until the seventh iteration (no further changes occur thereafter) for 11 cases. .

Criteria	Case 1	Case 2	Case 3	Case 4	Case 5	Case 6	Case 7	Case 8	Case 9	Case 10	Case 11
Morphological diversity – mouth				Strong negative–moderate positive	Strong negative–moderate positive					Strong negative–moderate positive	Strong negative–moderate positive
Morphological diversity – Western Scheldt-west			Moderate negative	Strong negative–moderate positive	Strong negative–moderate positive					Strong negative–moderate positive	Strong negative–moderate positive
Morphological diversity – Western Scheldt-east			Weak negative	Moderate negative–moderate positive	Moderate negative–moderate positive			Weak negative–weak positive		Moderate negative–moderate positive	Moderate negative–moderate positive
Morphological diversity – Zeescheldt	Weak negative–weak positive	Weak negative–weak positive		Weak negative–moderate positive	Weak negative–moderate positive			Moderate negative–moderate positive		Weak negative–moderate positive	Weak negative–moderate positive
Freshwater water quality	Moderate negative–Moderate positive	Moderate negative–Moderate positive		Weak negative–weak positive	Moderate negative–moderate positive	Weak to strong positive	Weak positive	Moderate negative–moderate positive		Weak negative–weak positive	Moderate negative–moderate positive
Brackish water quality	Moderate negative–moderate positive	Moderate negative–moderate positive		Weak negative–weak positive	Moderate negative–moderate positive	Weak to strong positive	Weak positive	Moderate negative–moderate positive	Weak positive	Weak negative–weak positive	Moderate negative–moderate positive
Brackish turbidity				Zero–moderate positive	Zero–moderate positive	Moderate negative		Weak negative to weak positive		Zero–moderate positive	Zero–moderate positive
Estuarine turbidity				Zero–moderate positive	Zero–moderate positive					Zero–moderate positive	Zero–moderate positive
Silicon limitation	Weak negative–weak positive	Weak negative–weak positive			Weak negative–weak positive	Moderate negative–zero		Weak negative–weak positive			Weak negative–weak positive
Freshwater–marine gradient	Weak positive	Weak positive		Zero–weak positive	Zero–weak positive			Weak negative–moderate positive		Zero–weak positive	Zero–weak positive
Full range of physiotopes	Moderate negative–moderate positive	Moderate negative–moderate positive	Weak negative	Moderate negative–weak positive	Moderate negative–moderate positive		Weak positive	Moderate negative–moderate positive	Weak positive	Moderate negative–weak positive	Moderate negative–moderate positive
Freshwater marsh vegetation	Strong negative–strong positive	Strong negative–strong positive		Moderate negative–moderate positive	Moderate negative–moderate positive		Moderate positive	Strong negative–strong positive	Weak negative–weak positive	Moderate negative–moderate positive	Strong negative–strong positive
Brackish marsh vegetation	Moderate negative–zero	Moderate negative–moderate positive		Weak negative–moderate positive	Moderate negative–moderate positive		Weak–moderate positive	Moderate negative–moderate positive	Weak–moderate positive	Weak negative–moderate positive	Moderate negative–moderate positive
Estuarine marsh vegetation	Weak negative	Weak negative–weak positive	Moderate negative	Strong negative–moderate positive	Strong negative–moderate positive			Weak negative–weak positive	Weak–moderate positive	Strong negative–moderate positive	Strong negative–moderate positive
Diadromous fish	Moderate negative–moderate positive	Moderate negative–moderate positive	Moderate negative	Strong negative–moderate positive	Strong negative–moderate positive	Weak negative–strong positive	Weak positive	Moderate negative–strong positive	Weak positive	Strong negative–moderate positive	Strong negative–moderate positive
Complete food web	Moderate negative–moderate positive	Moderate negative–moderate positive	Moderate negative–zero	Moderate negative–weak positive	Moderate negative–moderate positive	Weak negative–moderate positive	Zero–weak positive	Moderate negative–moderate positive	Zero–weak positive	Moderate negative–weak positive	Moderate negative–moderate positive

Note: Text in italics indicates where the response to case 2 differs from that of case 1, where case 5 differs from that of case 4, and where case 11 differs from that of case 10.

VNSC. (2019, April). Systeemanalyse natuur Schelde-estuarium. Gezamenlijk feitenonderzoek van stakeholders, deskundigen en de Vlaams-Nederlandse Scheldecommissie (in Dutch). Implementing Measures for Sustainable Estuaries (IMMERSE), Interreg North Sea region. https://northsearegion.eu/media/14997/ltp-n-systeemanalyse-natuur-schelde-estuarium.pdf

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Slinger, J. H. (2000). The link between morphology and ecology in the Long Term Vision for the Schelde Estuary. A conceptual framework and preliminary results (Resource Analysis Report RA/00-430).

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Data availability statement

Supplementary data on the meetings of the NWG are available from the author upon substantiated and reasonable request as they contain personal information and would have to be individually redacted.