Project part-financed by the European Union (European Regional Development Fund)

The Interreg IVB North Sea Region Programme

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TIDE pilot 1: large scale execution “plaatrandstortingen” (2010), relocation of dredged sediment to shallow water areas near sandbars


The monitoring of this measure is still in progress. To evaluate the possible effects of the deepening of the navigation channel, including the new relocation strategy, an extensive monitoring programme was set up (Plancke et al. 2010). A special protocol, composed of several morphological (stability of disposed material) and ecological (evolution of ecotopes) criteria, is appended to the relocation license to, quasi continuously, evaluate the monitoring data. An independent group of experts (“Commission Monitoring Western Scheldt”) will supervise the evaluation of the monitoring and give at least every 2 years an advise on the relocation strategy.
The monitoring program aimes to control the maintenance of the multiple channel system, to control the stability of the disposed sediment to guarantee the development of new valuable habitats, and to make sure that the relocation activities do not harm any other part of the Western Scheldt (Table 2).
During execution (started in February 2010) an intensive monitoring programme will analyse the morphological and ecological effects of the relocated sediments, allowing adjusting the strategy if necessary. Important data that was collected were dredging and relocation volumes at the different locations (continuous follow-up), multibeam surveys and difference maps, current velocity measurements on and along the sandbars, Real Time Kinematic (RTK) elevation measurements and sediment composition on the sandbars.

Table 2. Development criteria
Criterion Explanation of the development targets
Conservation multiple-channel system - The water volume in the secondary channel is monitored and a maximum allowed deviation is defined.
Ecological benefits from the relocation activities - The stability of the relocated sediment is monitored to analyse the volume changes at the sandbars. The monitored volume changes are a consequence of the executed relocations and the natural sedimentation and erosion processes. The criterion for sediment stability after two years is 70%.
Development low dynamic habitat - The total surface of low dynamic habitat near the sandbars is determined based on the ecotopes maps (Fout! Verwijzingsbron niet gevonden.). The development target is a gradually increase in the surface of low dynamic habitat with 114 hectares within 5 years after starting the relocation activities. The interim target after two years is no deterioration.
Conservation of the surface ecological valuable habitat - Elevation of flat habitat and sandbars, also at the edges of the Western Scheldt and hence not only at the sandbars. In general, a decrease in the total surface of low dynamic habitat is not allowed. In addition, an elevation change of 5 cm or more per year is undesirable. The maximum allowed sedimentation and erosion rates depend however of the elevation of the location. The allowed erosion is absolute minimal at the lowest locations and the allowed sedimentation is absolute minimal at the highest locations. Four elevation classes are defined based on the duration of flood exposure.
- Current velocity at sandbar edges: as much as possible low dynamic habitat is the development target, i.e. current velocity of maximum 0.8 m/s.

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