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At the same time, they want to retain the water and delay its discharge to prevent flooding downstream. Royal Eijkelkamp was engaged to develop a flow measurement system in the Ruiten Aa, near the villages of Vlagtwedde and Smeerling in eastern Groningen.
In the past, the Ruiten Aa was canalized. In the process, bends were removed from the stream and the stream was enlarged. "More than ten years ago we started to restore the Ruiten Aa to its former state," says Ronald Leeraar district hydrologist at Waterschap Hunze en Aa's. "Meanwhile, the area has been designated as Natuur Netwerk Nederland, the former Ecological Main Structure and labeled an ecological connecting zone. This means that certain nature and vegetation must be encouraged in the stream valleys. This is subject to a number of conditions, such as restoring the natural dynamics of the stream, but also retaining water in the stream valleys for longer. Real-time steering is then essential."
"To achieve the set goals, it is important to restore the flow in the stream," Leeraar continued. "The Ruiten Aa has been narrowed and deepened so that the water is led through a funnel, so to speak. All the weirs have also been removed. On one of those former weirs there was already a flow measurement system in combination with an inlet system to direct the water dosed via a bypass through Smeerling and drain the vast majority via Vlagtwedde to the Ruiten Aa canal. So a new flow measurement system had to be realized that also talks real-time again with a new weir/fish passage for the bypass. This is not only to limit the amount of water to a certain maximum (too much water means flooding in Smeerling), but also to maintain the natural dynamics of the stream using formulas. So with more discharge, more water also goes to Smeerling." Tom Basten, Project Manager at Royal Eijkelkamp: "That sounds logical on paper, but still brings the necessary practical challenges."
In the preliminary phase, in consultation with the water board, it was decided to shift the course of the Ruiten Aa a few meters to the west. "This has made the course for the measurement trajectory somewhat smoother, making the flow in the profile more laminar and increasing the reliability of the measurement," Basten explains. "It is also expected that, by moving the Ruiten Aa, there is less risk of embankment subsidence. It also allowed us to install the flow measurement system in the dry. The flow measurement system uses four measurement paths set up at different heights and crosswise. Based on data from these ultrasonic sensors (matched to the width of the waterway and current water level) combined with the current water temperature, the flow and flow rate can be calculated. All this data is sent to Hunze and Aa's main station, so that based on this the weir can be controlled further on in real time."
After the flow measurement system was installed, the new run was made aquifer and the old run was filled in. During the Site Acceptance Test of the flow measurement system earlier this year, checks were made regarding the water levels and actual flow rates of the measurement paths relative to each other. Also, upon completion, the linking of the data to the water board's main station was also checked. "The initial results are good," Leeraar says. "We expect to put the new setup into service in the spring."
