Bart Schultz
In the collection system of Rijnland, the water level is maintained as much as possible at 0.61 metres below NAP (Normal Amsterdam Ordnance Datum) in summer and 0.64 metres below NAP in winter. Most of the excess water in the collection system is pumped out by pumping stations at Katwijk, Spaarndam, Halfweg, and Gouda, with capacities of 5,640, 1,890, 1,980, and 2,400 cubic metres per minute, respectively. In total, this means that a water layer of 15 millimetres can be pumped out daily from the entire area of Rijnland. This is a considerable capacity for such a large area in the Netherlands, and is only needed in extreme cases. In this way, the water level in the collection system is well under control.
The largest pumping station, named after King Willem-Alexander in 2013, is located at Katwijk. This pumping station discharges the excess water into the North Sea through a short canal. The pumping station is a Protected National Monument. Although most of the water discharged here was first pumped out from the polders, it still contains a significant amount of contaminants. These primarily consist of plastic waste, which is then discharged into the North Sea via this pumping station.
As a result of a citizen's initiative, a bubble screen called the Limes Bubble Barrier was installed in 2022 in the canal in front of the pumping station at Katwijk. This screen diverts contaminants, primarily plastic, present in the water to the bank, where they are collected in a collection box and then removed. The name Limes is derived from the former northern border of the Roman Empire, which at the time formed a large part of the Netherlands by the course of the Rhine River, which flowed into the North Sea, primarily at Katwijk. It was considered appropriate to use it to mark the boundary for plastic waste.
Bubble screens themselves are not new. They have been used in the Netherlands for years to minimize salt intrusion, particularly at shiplocks along the North Sea coast. As far as I know, an application designed to minimize the discharge of pollutants from canals into the North Sea is new and therefore an interesting step in the water management of the Netherlands.
I recently attended a conference about the Bubble Barrier. They explained how the barrier came about, how it works, and which other citizen initiatives exist to remove pollutants from the banks of rivers, lakes, and canals. We also visited the Bubble Barrier. All in all, it was an interesting conference. It is important, of course, that we prevent pollutants from entering the water as much as possible. However, it is also crucial that if they do get in, they are removed as much as possible before the water is discharged into the North Sea.
The Bubble Barrier only works when there is a current in the canal. This is the case when the pumping station is operating. Operation of the Bubble Barrier has been taken over by the Water Authority of Rijnland. The Water Authority is working to connect the Bubble Barrier to the pumping station so that they switch on and off simultaneously. This is a new development that is certainly worth emulating.
