The Eastern Scheldt storm surge barrier, completed in 1986, is the largest of a series of construction projects (“Delta Works”) in the southwest of the Netherlands to protect a large area of land around the Rhine-Meuse-Scheldt delta from the sea. The Easter Scheldt storm surge barrier is 9 km long and consists of 65 pillars of 30-40 m high and 62 sliding doors of 42 m wide x 6-12 m high. There are three channels (Hammen, Schaar and Roompot) with 39.5 m wide gates running from north to south, separated by two artificial islands.
Tocardo began developing the Oosterschelde Tidal Power (OTP) project in 2008. In November 2015, five T2 turbines were installed onto a 50 meter long structure at gate Roompot 8, on the Eastern Scheldt side of the barrier. The 50m long support structure, with turbines attached, was transported and installed using a special barge and Mammoet’s self-propelled modular transporter.
Each T2 turbine has two rotor blades of 5.5 m diameter which face the North Sea. The distance between the blade plane and protective stones on the bottom is around 5.5 m, and the distance between the rotor planes of neighbouring turbines is 1.2 m. Together the turbines produce 1.25 MW of power, which is enough to supply around 1000 local households.
Eastern Scheldt storm surge barrier, between islands of Schouwen-Duiveland and Noord-Beveland.
In 2010, a permit for the installation of the OTP project was granted under the Nature Conservancy Act 1998 by the Ministry of Economic Affairs (reference DRZZZ /2010-4034). The permit remains valid from 16 December 2010 to 16 December 2030 and can be accessed from here: https://puc.overheid.nl/natuurvergunningen/doc/PUC_1096_17/1/
Condition 7 of the permit requires that monitoring should be undertaken surrounding the occurrence effects on seals and ‘sand hunger’ as a result of altered tidal range due to placement and use of the tidal turbines in the Eastern Scheldt.
Following acquisition of the OTP project in 2020, work has progressed the commissioning and testing phase of the project. On 9 February 2021 it was announced that the OTP project had resumed full continuous operations.
The Dutch government has granted Tocardo permission to install one more array of turbines in gate Roompot 10. This installation will be evaluated by the management of the storm surge barrier (with consideration for structural safety) the Dutch government (with a focus on environmental effects), and Tocardo (in terms of costs and energy production).
Tocardo intends to install turbines in up to 17 gates in the future.
Key Environmental Issues
The construction of the Eastern Scheldt storm surge barrier caused tidal flow velocities to fall to a level on which they are no longer able to transport a significant amount of sediment through gullies and onto tidal areas. As a result intertidal areas slowly erode to a level below mean sea level and therefore the area is experiencing “sand demand”.
However, the main environmental issues related to the installed T2 turbines are:
- Potential impacts around the restricted movements of harbour porpoise through the storm surge barrier; and
- Potential impacts around the restricted movements of harbour seals through the storm surge barrier.
Papers, Reports, Research Studies
- Monitoring getijdenturbines Oosterscheldekering (Oosterscheldekering Tidal Turbines Monitoring Annual Report 2018)
- Effects of the Eastern Scheldt Storm Surge Barrier and tidal energy turbines on harbor porpoise (Phocoena phocoena) and harbor seal (Phoca vitulina) movements
Verbeek, M.C., Labeur, R.J., Uijttewaal, W.S.J., (2020). Estimating the stability of a bed protection of a weir-mounted tidal turbine. International Marine Energy Journal. Available from: https://marineenergyjournal.org/imej/article/view/45
Post-Installation Monitoring: Oosterschelde Tidal Power project
|Stressor||Receptor||Study Description||Design and Methods||Results||Status|
|Displacement||Marine Mammals, Cetaceans, Pinnipeds||Annual counts of harbour porpoises (Phocoena phocoena) and harbour seals ( Phoca vitulina) since 2009 (Leopold and Scholl, 2019)||Monitoring of harbour seals and harbour porpoises performed in sub-work package 1.6: Trend analysis of seals and porpoises present in Voordelta and Oosterschelde.||The storm surge barrier is likely to restrict the movement of harbour porpoises, because eddies and turbulence within and around each gate form an acoustic barrier during flood and ebb tides, and because each open gate forms a relatively narrow physical passage. |
The existing array of five turbines in gate Roompot 8 makes the passage through the open gate smaller, though ~5.5 m of water remains between the blade planes and the stony bottom protection below. Due to the presence of the turbines, porpoises are expected to be less likely to cross the barrier through gate Roompot 8. This effect of the existing turbines applies to only one of the 62 gates.
Harbour seals are considered likely to cross the storm surge barrier with ease and minimal effects, regardless of the existing turbine array.