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The morphological target was to test the stability of the relocated material and if the transportation of the relocated material was towards the sandbar.
The ecological target was to test if the measure did not lead to significant negative effects.
Step 2: Degree of target achievement
On a morphological level, it can be concluded that the relocation test has been a success. The material seems to be stable despite the stability being slightly lower than the relocation test of 2004. This was, however, an expected effect given the different relocation technique that was used in 2006 and the more dynamic conditions in the deeper relocation location. The movement of the material is also mainly in the direction of the sandbar. The results of the feasibility study are therefore confirmed in this in situ trial. The sediment is placed into an area that has been eroding for several decades. The quantity of dredged material (1.4 million m³) is however low regarding the capacity of the eroded area and will therefore not significantly change the erosive hydrodynamic conditions.
On an ecological level it can be concluded that the relocation test did not lead to significant, detrimental consequences. Large-scale effects on the macrobenthos as a result of the relocation test in 2006 seem to have been avoided. This cannot, however, be stated with certainty in relation to the relocation location because no prior sampling was carried out in order to characterise the natural habitat and macrobenthos community.
Comparison with the relocation test of 2004: Both the morphological and ecological criteria were met in both tests, but from the results it was concluded that the traditional relocation technique (used in 2006) has a lower efficiency compared to the diffuser (used in 2004). This is confirmed by a comparison between the amount of dredged material (in hopper) and the amount of material (in situ) found based on volume calculations between topo-bathymetric surveys. It can be noted that the correction for density differences was not applied for this comparison. The diffuser technique has an efficiency of ca. 85%, while the traditional relocation technique has an efficiency of 75-80%. However, the criteria were met so both techniques are useful.
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Walsoorden pilot part B (2006): relocation of dredged sediment to a shallow water area at the edge of the Walsoorden sandbar
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 targetsThe morphological target was to test the stability of the relocated material and if the transportation of the relocated material was towards the sandbar.
The ecological target was to test if the measure did not lead to significant negative effects.
Step 2: Degree of target achievement
On a morphological level, it can be concluded that the relocation test has been a success. The material seems to be stable despite the stability being slightly lower than the relocation test of 2004. This was, however, an expected effect given the different relocation technique that was used in 2006 and the more dynamic conditions in the deeper relocation location. The movement of the material is also mainly in the direction of the sandbar. The results of the feasibility study are therefore confirmed in this in situ trial. The sediment is placed into an area that has been eroding for several decades. The quantity of dredged material (1.4 million m³) is however low regarding the capacity of the eroded area and will therefore not significantly change the erosive hydrodynamic conditions.
On an ecological level it can be concluded that the relocation test did not lead to significant, detrimental consequences. Large-scale effects on the macrobenthos as a result of the relocation test in 2006 seem to have been avoided. This cannot, however, be stated with certainty in relation to the relocation location because no prior sampling was carried out in order to characterise the natural habitat and macrobenthos community.
Comparison with the relocation test of 2004: Both the morphological and ecological criteria were met in both tests, but from the results it was concluded that the traditional relocation technique (used in 2006) has a lower efficiency compared to the diffuser (used in 2004). This is confirmed by a comparison between the amount of dredged material (in hopper) and the amount of material (in situ) found based on volume calculations between topo-bathymetric surveys. It can be noted that the correction for density differences was not applied for this comparison. The diffuser technique has an efficiency of ca. 85%, while the traditional relocation technique has an efficiency of 75-80%. However, the criteria were met so both techniques are useful.