The planned tidal reservoir in Vellage is fundamentally different from the polders that will potentially be installed to improve the estuary habitats along the river: it is a "pilot reservoir", meaning that it will be used to test whether and how tidal reservoirs influence the desired improvement of water quality – and it is not installed permanently.
The testing phase has been given a temporary term of about two years before the tidal reservoir in Vellage will be relinquished, as per the current planning, and left to natural succession. During the flow tide a part of the incoming tide will be provisionally stored in the reservoir in order to support the outflowing water during the ebb. This, along with any potential measures with the Ems Barrier, aims to counteract any further silt contamination of the river. The Vellage tidal reservoir shall test the mathematical models underlying this hypothesis under real conditions.
Two types of location were initially investigated for the construction of the tidal reservoir in the vicinity of the Vellage oxbow lake. The planning both within the levees on the former peninsula and the offshore land surface (a larger basin with afflux and influx of parts of the oxbow lake) was discarded in the meantime. After the results of the soil samples taken in September during the Ems damming for the assessment of the "Genting Dream", the planning is now concentrated on the oxbow lake, as this location requires less soil transportation and it is expected that the sediment stored in the oxbow lake can be accommodated more easily. The soil samples had revealed that the soil in the oxbow lake of the Ems in Vellage consists of material similar to the silt commonly found in the Ems. This preferred location could be realised within a territory of ten hectares in the existing oxbow lake. This minimises encroachment in the surrounding environment. The initial estimation amounted to 20 hectares.
The soil samples in the oxbow lake required for further planning were examined for a third time in September. Because of these delays, it currently appears that construction will not commence by the end of the 2017 bird breeding season (mid-/late July). The Master Plan schedule for the Vellage tidal reservoir is thus delayed by one year. The feasibility study of silt reduction by the tidal reservoir would then be complete by late 2019.
By validating the hydromorphological modelling results the pilot polder should provide realistic information about the challenges of such construction measures, e.g. how to handle the soil excavated during construction of the polder – and how quickly such polders will be re-contaminated with silt. This information will be incorporated into the feasibility investigation for "tidal reservoirs".