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Effectiveness according to development targets of measure

Step 1: Definition of development target
The creation of a Flood Control Area with Controlled Reduced Tide (FCA-CRT) aims to develop an intertidal area that is qualitatively and quantitatively similar to outer-dike intertidal habitat. For Lippenbroek the objective was more specifically to restore tidal freshwater marsh habitat in an agricultural site where elevation relative to the estuarine marshes has lowered. Different processes (eg. tidal cycling; nutrient processing Si, N, P, O; and Sedimentation) and structures (eg. tidal marsh topography; tidal marsh vegetation; tidal marsh fauna) are monitored and studied since the opening of the CRT to analyse the functionality of the FCA-CRT. In fact, Lippenbroek is a pilot project for all other planned FCA-CRT such as Kruibeke-Bazel-Rupelmonde.

Step 2: Degree of target achievement
Overall, Lippenbroek started functioning as freshwater intertidal habitat since the introduction in March 2006 and hence was successful. The pilot test proved that also an embanked area that is not suitable for basic managed realignment (because it is situated too low in reference to the water levels in the estuary) can be restored by a FCA with CRT. Therefore this technique increases the number of suitable sites and avoids problems with suboptimal tidal regimes and artificial elevation increase with dredged material.

• The CRT construction (high inlet and low outlet) results in a normal tidal dynamism, however high tides are flattened (stagnant phase). Monitoring now shows that the development of an estuarine ecosystem is not hampered by prolonged inundation times when inundation height is limited (Maris et al.).
• A high sedimentation rate was monitored in Lippenbroek as well as erosion and the formation of a channel and creek network. This is positive for the creation of typical tidal marsh topography but can form a risk for the safety aspect of the FCA (storage capacity of the area). It is however too early to conclude about the effect on the safety aspect. Also at Lippenbroek, creek density and drainage capacity are not yet in equilibrium as indicated by the on-going structural evolution. Further development will most likely result in a flat marsh platform (merlons), incised by creeks (krenels, Figure 18).
• An important advantage of the high inlet sluice is that is aerates the incoming and often oxygen poor Scheldt water so that the pilot CRT never faced problems with anoxia. If hypoxia ever prevails in the estuary, which is not unlikely to occur in the Scheldt, a CRT will act as an oxygen rich refugia (Maris et al.). Also, the shallow water depth and low dynamics create a more favourable light climate in the CRT than within the estuary, so primary production is assumed to be much higher (Maris et al.).
• Nutrient processing (nitrogen, phosphorus and silica) was shown to be comparable in the CRT as in river marshes. CRTs act, just like estuarine marshes, as a sink for nitrogen. Lippenbroek shows a nitrogen removal of 1.0 kg/ha/tide with a sedimentation rate of approximately 30 mm/year on average (Maris et al.).
• The effect of Lippenbroek on the water quality of the Scheldt estuary is however not measurable since the pilot project is too small. Model measurements and the results of the pilot study however indicates that larger CRT areas (like Kruibeke-Bazel-Rupelmonde) could significantly improve the Scheldt ecosystem (Maris et al. 2008a).
• Shortly after the construction, an intertidal plant community established with fast eradication of terrestrial species and colonisation by tidal freshwater marsh species (Jacobs et al. 2009). Also the presence of bird and fish species indicates the installation of a fully developed intertidal ecosystem. This proofs that the prolonged inundation times when inundation height is limited (stagnant phase) does not hamper the colonisation by fauna and flora (Maris et al. 2008a). Furthermore, in the CRT sites which are currently being built (eg. Kruibeke-Bazel-Rupelmonde), biota is expected to develop even better as the habitat will be larger, less disturbed and more variable [3].

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