The harbour Project finalised
Every year, the water authority and the council dredgethe harbour . The channel is dredged once every four to five years. Dredgingallows seawater to flow back and forth again, making the small harbor accessibleto ships. This dredging is costly, and the results are variable but always short-lived. After just one storm, the channel can become silted up again. The water authority and council whether a structural solution in the form of a flushing channel was possible. This has proven unfeasible. The water board and council work together to keep the harbour accessible. Dredging and plowing will continue.
What did we study?
Noorderzijlvest Water Authority the council were looking for a structural, cost-effective, and sustainable solution to the silting up of the channel leading to the harbour . A flushing bay, similar to the small harbors in the Wadden Sea along the German coast—such as the one at Nessmersiel—seemed like an ideal solution. In this video from HDidee Advies & Coaching, you can see how the tidal basin at Nessmersiel in Germany works.
This video from HDidee Advies & Coaching shows how the flood control reservoir near Nessmersiel in Germany works.
(Do you have any questions about the video of the tidal flat near Nessmersiel in Germany? If so, please send an email to info@noorderzijlvest.nl)
Extended Tide, tidal bore © near Nessmersiel (DL) from Skyfixion on Vimeo.
What is a flushing basin?
A tidal lake is a body of water that fills and empties with the tides. At high tide, the lake fills up; at low tide, it empties again. By carefully regulating the filling and emptying of the lake, we can prevent the channel from silting up repeatedly. This more or less natural solution requires little maintenance, can operate fully automatically, and eliminates or significantly reduces the need for dredging.
What causes the channel to silt up?
The cause of the silting up is a natural phenomenon. The annual silting up of the salt marshes (a natural process) causes the bottom of the channel and the small harbor to rise higher and higher. As a result, less and less water harbour into the channel and harbour at high tide, and consequently less and less harbour back out at low tide. Without a sufficiently strong (tidal) current, every spot in the Wadden Sea will silt up.
Before 1981, we were able to harbour the harbour from silting up further using the sluice gate. At high tide, we stored large volumes of water to flush out the channel at low tide. Due to the construction of the delta dike and our desire to better align water managementwith the needs and requirements of the inland areas, in 1981 pumping station Noordpolderzijl was built. This rendered the old sluice gate obsolete. For safety reasons, the gatewas bricked up.
How did we determine whether this would work for Noordpolderzijl as well?
In several locations in Germany, flushing channels have been constructed that have been functioning effectively for decades. The channel at Noordpolderzijl is comparable to the German sites in terms of length, location, and soil composition. So it could work. We investigated whether this solution is actually suitable for Noordpolderzijl and in what form it could comply with all laws and regulations. We also considered the views of the local community and the extent of support for this solution. The results of the studies conducted are available in a number of reports.
- Expert Consultation on Options for the Noordpolderzijl Flushing Channel, HDidee Advies & Coaching, September 2014 (PDF, 1 MB)
- Progress on the final solution for the Noordpolderzijl navigation channel, November 2016 (PDF, 2.4 MB)
- Progress on the final solution for the Noordpolderzijl navigation channel, November 2016 – appendices (PDF, 2.8 MB)
- Progress on the final solution for the Noordpolderzijl navigation channel, May 2017 (PDF, 13 MB)
What do we do now?
The floodplain will not be created. However, the water authority and the council will continue to work together to keep the small harbor accessible. Dredging and plowing will continue. water authority council first tested this alternative dredging method council 2018. A type of “rake” is used to loosen the hard layers of silt on the bottom. The seabed is closely monitored during the work. This allows us to determine exactly where the hard layers and thresholds are located. The method proved successful in 2018. This video shows how the new dredging method works. With this new approach, we are keeping the harbour accessible harbour possible for ships.
Schedule
finalised
See also
Subsidy project
The project was an Interreg North Sea Region project and was funded by the North Sea programme the European Union’s European Regional Development Fund.