North Polderzijl Port Project completed
Every year, the Noorderzijlvest water board and the municipality of Eemsmond dredgethe Noordpolderzijl harbor. The channel is dredged once every four to five years. Dredgingallows seawater to flow back and forth again, making the harbor accessibleto ships. This dredging is expensive and the results are variable, but always short-lived. After just one storm, the channel can become silted up again. The water board and municipality investigated whether a structural solution in the form of a flushing lake was possible. This proved not to be feasible. The water board and municipality will continue to work together to keep the port of Noordpolderzijl accessible. Dredging and plowing will continue.
What did we investigate?
The Noorderzijlvest Water Authority and the municipality of Eemsmond were looking for a structural, cost-effective, and sustainable solution to the silting up of the channel to the port of Noordpolderzijl. A flushing basin, similar to the Wadden Sea harbors on the German coast, such as Nessmersiel, seemed 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 tidal bore near Nessmersiel in Germany works.
(Do you have any questions about the video of the tidal pool at Nessmersiel in Germany? Please send an email to info@noorderzijlvest.nl)
Extended tide, tidal bore © near Nessmersiel (DL) from Skyfixion on Vimeo.
What is a flushing sea?
A tidal lake is a lake that fills and empties under the influence of the tides. At high tide, the lake fills up, and at low tide, it empties again. By carefully regulating the filling and emptying of the lake, we can prevent the channel from silting up again and again. This more or less natural solution requires little maintenance, can be fully automated, and requires little or no dredging.
What causes the channel to silt up?
The cause of the silting up is natural. The annual silting up of the salt marshes (a natural process) causes the bottom of the channel and the harbor to rise higher and higher. As a result, at high tide, less and less water flows into the channel and harbor, and at low tide, less and less flows back out. Without a sufficiently strong (tidal) current, every spot on the Wadden Sea silted up.
Before 1981, we were able to prevent further silting up of the harbor with the sluice gate. At high tide, we stored large quantities of water, which we used to flush the channel at low tide. Due to the construction of the delta dike and because we wanted to better align water managementwith the wishes and needs of the inland areas, theNoordpolderzijl pumping stationwas built in 1981. This made the old sluice gate redundant. For safety reasons, the sluice gatewas bricked up.
How did we investigate whether this also works for Noordpolderzijl?
A flushing lake has been constructed in a number of places in Germany and has been working well for decades. The Noordpolderzijl channel is comparable to the locations in Germany in terms of length, location, and bottom 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 importance of the opinion of the local community and the extent to which there was 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 lake, HDidee Advies & coaching, September 2014 (PDF, 1 MB)
- Progress on definitive solution for Noordpolderzijl shipping channel, November 2016 (PDF, 2.4 MB)
- Progress on definitive solution for Noordpolderzijl shipping channel, November 2016—attachments (PDF, 2.8 MB)
- Progress on definitive solution for Noordpolderzijl shipping channel, May 2017 (PDF, 13 MB)
What shall we do now?
The flushing sea will not be created. However, the Noorderzijlvest water board and the municipality of Eemsmond will continue to work together to keep the harbor accessible. Dredging and plowing will continue. The water board and municipality first tried this different method of dredging in 2018. A type of "rake" is used to loosen the hard layers of silt on the bottom. The waterbed 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 the new method, we are keeping the harbor as accessible as possible for ships.
Planning
Completed project
See also
Grant project
The project was an Interreg North Sea Region project and was subsidized by the North Sea Program of the European Regional Development Fund of the European Union.