One small sensor helps

ABOVE Both the high-water safety and nature development projects would be paid for with the proceeds from sand and gravel extraction along the Meuse BELOW A Keller 26X high-precision, media-isolated, piezo-resistive pressure A single Keller digital sensor sensor encased in a robust stainless-steel housing with high-quality cable gland. Typical applications are hydrostatic pressure is used as part of a flood safety programme measurement, level measurement for groundwater and surface water, and fill level measurement in the Limburg province in the Netherlands. of water – and fuel tanks

During 1993 and 1995, the province of Limburg was confronted with two floods on the river Meuse, which caused €200 million (R3.5 billion) in damage. Society demanded more flood safety, but the cost of some €700 million (R1.23 billion) was a stumbling block for years.

Eventually, an agreement was forged with Consortium Grensmaas – a partnership of contractors, gravel producers – and Natuurmonumenten, the Dutch organisation for the conservation and development of nature. It was agreed that both the high-water safety and nature development project would be paid for with the proceeds from sand and gravel extraction along the Meuse.

Gravel extraction Consortium Grensmaas extracts about 100 000 t of gravel every week – a quantity that requires an enormous logistical operation. “To give you an idea, 1 t equals 11 wheelbarrows. On an annual basis, we extract 4 500 000 t of gravel. And this gravel extraction is an important part of the Grensmaas project because it is the financial engine. Thanks to this gravel extraction, there are no costs for the taxpayer,” explains Hans van der Meer, head: Production and Technical Services at the Grensmaas gravel extraction site.

All gravel is transported by barge, with ships leaving and arriving continuously. A mix of sand and extracted gravel creates a mixture called tout venant. The gravel is rinsed and sorted using an ingenious system of conveyor belts, sieving machines, washers and screw conveyors.

Each dimension of gravel has its own final destination – from asphalt to decorative gravel. There is limited space on the site due to the widening of the river and sometimes a pile of gravel may be covered in water.

Water level Due to the nature of the production process, progress is largely dependent on the water level (which fluctuates hugely) in the Meuse. Van der Meer wanted to be able to monitor and record the water level properly. A Keller level sensor was mounted on a mooring post that communicates the water levels with the cloud via a LoRa network.

“This system gives me up-to-date information about the water level on a dashboard in my office. Thanks to the sensor’s communication with Keller's own Kolibri cloud, we now have all the information we need from that sensor. Since we have the ability to monitor it ourselves, we can also sound the alarm in good time,” explains Van der Meer.

The digital level sensor – Series 26 X – not only measures the water level, but also the temperature of both the water and the air. “We cannot produce if there is ice formation, so we also want to be aware of that risk as early as possible. Under normal circumstances, production here goes on for six days a week, 07:00 to 19:00. If we know that this is going to change, we need to be able to respond as quickly as possible,” concludes Van der Meer.