Watch the video in which Marinus van Dijk of Water Board Vallei and Veluwe explains why they choose Eijkelkamp Soil & Water and NIVUS equipment for their flow monitoring.
The Renkums Beekdal, located at the edge of the Veluwe, a region in the Province of Gelderland, the Netherlands, is a very interesting creek valley from an ecological and hydrological perspective. It is also a challenging area due to the highly complex soil structure with many different soil layers. To properly understand how the water system within this creek valley functions, the Vallei en Veluwe Water Board has asked Eijkelkamp Soil & Water to set up a permanent flow rate measuring point.
Marinus van Dijk, who works in the Water Board’s Planning Department, speaks with a great deal of passion about the Renkums Beekdal creek valley and the measures that are being taken to make the valley future-proof. ‘It is a beautiful creek valley with many differences in height. The water comes from the Veluwe and runs steeply down towards the Rhine, with much seepage, creeks and cultural history. In the past, water mills were driven by the creeks. These creeks were often raised and coated with loam to retain the water. Quite an amazing system that in the past produced a great deal of water. The groundwater levels generally were somewhat higher and there was virtually no groundwater extraction.’
‘The situation in the Veluwe has changed for a number of reasons, including land use. Due to past intensive grazing practices, it has, so to speak, turned into a bare hill covered with heath. When there is bare soil, any precipitation that falls directly soaks into the ground. Due to the wood production that was to follow later on, the area was extensively forested, particularly with pine wood. But a key characteristic of pine wood is that it evaporates a great deal of water. While this is not a reason for reduced groundwater levels as such, after over 100 years it became noticeable and the enormous aquifer on the Veluwe nevertheless started to subside. Not to forget drinking water extraction. There are several extraction points here in this area. While these are of course essential, they ultimately do affect the groundwater system.’
‘Nowadays this means that we are confronted with reduced and unpredictable water levels. In summer we are increasingly confronted with stagnant water, as well as dried-out areas. This is why we are currently undertaking repair work together with the Province of Gelderland and the Vitens drinking water company to make the water system more robust, make better use of the available water and to enable the ecology to flourish. However, the Renkums Beekdal is not making things easy for us. It is a difficult area to interpret from a hydrological perspective. The entire Veluwe region is a large push moraine with haphazardly positioned soil layers of clay, loam, sand and gravel. This is almost impossible to map and model. Of course you can conduct many deep drillings, but this comes with a significant price tag.’
‘Many years ago we set up a measuring network, also in collaboration with Eijkelkamp Soil & Water. But in hindsight it was not a good configuration. It was a rather technical solution, focused on high accuracy and also designed to measure very low rates of flow. The measuring equipment was excellent, and produced high-quality data, but when there are very few opportunities to measure anything, you ultimately still end up with nothing. At that point we said, let’s try something different.’
‘We disassembled the measuring sites and at the end of the creek valley, at its discharge point, we created a single measuring channel that is always operational and works well, with high as well as low flow rates, that does not push up the water too much and incorporates fish passages. It has become a robust and really good measuring point that will last us for years. It is not susceptible to blockage and overgrowth. The bottom of the measuring channel is concrete and two metres wide. The vertical walls of the measuring channel are made of wood and are 1 metre high. Four NIVUS Transit Time Sensors have been installed on the vertical walls. These sensors alternately transmit and receive high-frequency ultrasonic signals. The difference in time (Delta T), caused by measuring against the direction and then in the direction of flow, provides a correlation of the entire water volume’s rate of flow. In addition, an I-sensor has been installed to measure water height without making contact with it, so that the water’s surface area can be measured.’
‘Naturally we hope that over time this measuring point will provide some feedback about the measures we are currently implementing. Because the effect of the measures we are implementing is not going to be evident from one day to the next. It is not a measuring point that we are constantly checking and that we expect to provide us with data by the minute. Currently we are receiving data four times per day and that is perfect. The system has been performing well for several weeks. In December we measured the high flow rates caused by high levels of precipitation. The system is showing a consistent discharge rate without any interruptions. Perfect, in other words.’
The Vallei en Veluwe Water Board is responsible for providing safe dikes, clean and sufficient surface water and treated wastewater in the region bordered by the IJssel River, the Lower Rhine River, the Utrecht Hill Ridge and the Bordering Lakes. As such the Water Board oversees an area of 245,644 hectares and serves 1.1 million residents.