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The main target was to restore processes that lead to the development of a tidal wetland. Therefore the Ketenisse area was levelled in 2002 with a weak slope below mean high water level, creating the optimal starting conditions for the development of intertidal mudflats and marshes. After restoration (since the end of 2002) the area is again an intertidal flat habitat in the brackish part of the Scheldt that is flooded twice a day. And monitoring results of the first year suggest that Ketenisse polder has the potential to develop towards a varied and normal functional intertidal area (Van den Bergh 2005).
Step 2: Degree of target achievement
However, based on wider monitoring results (Gyselings et al. 2004, Van den Bergh 2005, Gyselings et al. 2006, Van den Neucker et al. 2007, Speybroeck et al. 2011) we conclude that the degree of target achievement is rather medium. The slopes at the extreme ends of the site are too steep and net erosion takes place. In the central part two aspects of the final design differed significantly from the original plan. Some areas, where the topsoil was not useful as construction material for dikes, were not excavated below mean high water level and remained almost supratidal. The old dike was not removed according to plan and as a result almost flat plateaus, with a steep slope towards the river were constructed instead of a gentle overall slope from the dike to the river. This had consequences for the habitat functions of the site. At T0 higher vegetation was already in place, supratidal as well as tidal marsh vegetation. Some of it died off; in other places it remained and served as source for typical fauna and flora. The plateaus now provide low dynamic habitat. They silted up and a relatively rich macro-benthic invertebrate community was built up, providing extra foraging and roosting time and space for birds.
The differences in the starting conditions were reflected in the differences in evolution across the site (Van den Bergh 2005). On the sheltered and wider Kpd and Kpe sections in general net sedimentation was observed with sediments of low MGS, high OM content and chlorophyll a concentrations (Van den Bergh 2005). These areas also contain relative high macrobenthos densities and are selected by typical species such as Common Shelduck and Pied Avocet for foraging. The other, more dynamic sections also show erosion in some parts, generally have higher MGS, lower OM content, Chlorophyll a concentrations and macrobenthos densities (Van den Bergh 2005). They attract other bird species. Succession stages of tidal marsh vegetation were observed and most apparent on the sections with a weak slope.
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Ketenisse wetland - small scale tidal wetland restoration in the brackish part of the estuary
Table of content
- 1. Description of measure
- 1a. Measure description
- 1b. Monitoring
- 1c. Monitoring results
- 2. Execution of main effectiveness criteria
- 2a. Effectiveness according to development targets of measure
- 2b. Impact on ecosystem services
- 2c. Degree of synergistic effects and conflicts according to uses
- 3. Additional evaluation criteria in view of EU environmental law
- 3a. Degree of synergistic effects and conflicts according to WFD aims
- 3b. Degree of synergistic effects and conflicts according to Natura 2000 aims
- 4. Crux of the matter
- 5. References
Additional information
for this measure:
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for this measure:
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Effectiveness according to development targets of measure
Step 1: Definition of development targetThe main target was to restore processes that lead to the development of a tidal wetland. Therefore the Ketenisse area was levelled in 2002 with a weak slope below mean high water level, creating the optimal starting conditions for the development of intertidal mudflats and marshes. After restoration (since the end of 2002) the area is again an intertidal flat habitat in the brackish part of the Scheldt that is flooded twice a day. And monitoring results of the first year suggest that Ketenisse polder has the potential to develop towards a varied and normal functional intertidal area (Van den Bergh 2005).
Step 2: Degree of target achievement
However, based on wider monitoring results (Gyselings et al. 2004, Van den Bergh 2005, Gyselings et al. 2006, Van den Neucker et al. 2007, Speybroeck et al. 2011) we conclude that the degree of target achievement is rather medium. The slopes at the extreme ends of the site are too steep and net erosion takes place. In the central part two aspects of the final design differed significantly from the original plan. Some areas, where the topsoil was not useful as construction material for dikes, were not excavated below mean high water level and remained almost supratidal. The old dike was not removed according to plan and as a result almost flat plateaus, with a steep slope towards the river were constructed instead of a gentle overall slope from the dike to the river. This had consequences for the habitat functions of the site. At T0 higher vegetation was already in place, supratidal as well as tidal marsh vegetation. Some of it died off; in other places it remained and served as source for typical fauna and flora. The plateaus now provide low dynamic habitat. They silted up and a relatively rich macro-benthic invertebrate community was built up, providing extra foraging and roosting time and space for birds.
The differences in the starting conditions were reflected in the differences in evolution across the site (Van den Bergh 2005). On the sheltered and wider Kpd and Kpe sections in general net sedimentation was observed with sediments of low MGS, high OM content and chlorophyll a concentrations (Van den Bergh 2005). These areas also contain relative high macrobenthos densities and are selected by typical species such as Common Shelduck and Pied Avocet for foraging. The other, more dynamic sections also show erosion in some parts, generally have higher MGS, lower OM content, Chlorophyll a concentrations and macrobenthos densities (Van den Bergh 2005). They attract other bird species. Succession stages of tidal marsh vegetation were observed and most apparent on the sections with a weak slope.