How does water from the Belgian Ardennes find its way to the North Sea?

Seven weirs between Borgharen and the sea

 

River discharge is not easy, the innocent-looking River Meuse in the Netherlands proves it. Limestone prevents rainwater from sinking into the ground, which makes the way the river’s seven sluices and weirs in the Netherlands are managed rather special.

After nearly a century, the weir near the town of Grave is heading towards the end of its lifecycle. Yet, the barrage, one of the seven weirs and locks in the River Meuse, still functions properly. The weirs have been built after the supply of German coal stopped during World War I. Today, they play a crucial role in the transportation of goods by inland waterways. “If there weren’t any dams in the Meuse, like in the old days, the river would be nothing more than a pathetic little brook”, says engineer Herbert Michon (Dutch Directorate-General for public works and water management, Rijkswaterstaat).

The two of us are standing at the weir and lock complex near the town of Sambeek, where the River Meuse is absolutely not pathetic, but rather wide. Between the two riverbanks you will find, from West to East, three chambers, one fish ladder, two movable Stoney slides and an array of ‘locked’ Poirée gates between twelve yokes. Altogether this is a huge barrage in the river, preventing the river water from flowing freely towards the sea. This means that barges can continue to navigate, although sluices will cause some delay.

The river’s seven sluices and weirs, situated between Borgharen, North of the city of Maastricht, and Lith in the province of Brabant, provide Rijkswaterstaat’s lockkeepers with the means to check the water height in this rain river, varying from 44 metres above sea level near Maastricht to 1 metre near Lith.

110 barges per day

In the afternoon of August 17h, 2017, two lockkeepers are busy letting freight ships and private yachts pass the sluices. On average 110 barges are locked through the river each day. One man monitors ships that navigate upstream, his colleague the vessels heading downstream. Lockkeepers can limit the number of lock passages by allowing as many ships as possible in a chamber. This summer there was not enough rainfall to support sufficient water discharge, therefore no water was to be wasted. The discharge did not exceed 30 to 35 m3/s in July, according to Rijkswaterstaat’s Drought Monitor. The chambers of two weir and sluice complexes near Born and Maasbracht, where the river drops 11.5 metres, are connected. To waste less water during the locking process, the empty chamber was filled water from the full one, before the lock gates opened. The largest sluices in the River Meuse are equipped to allow for class V b push-towing vessels with a double load to pass through the locks.

‘Rain water does not sink into the ground, but ends up in the river, causing the water level to rise fast’

“We do have our own team of experts, who are constantly monitoring the weather forecasts for the River Meuse’s catchment area in France and Belgium. Our colleagues in Wallonia supply us with river discharge data and precipitation forecasts”, says Mr. Michon. “The Meuse River and its tributaries flow through rocky territory in the Belgian Ardennes. Rain water does not sink into the ground, but ends up in the river, causing the water level to rise fast.”

Precipitation

In order to operate the gates in the Poirée part of the weir (named after its designer), it takes more than just pushing the button. Weather warnings for extreme precipitation in the North of France and the Ardennes call for immediate action; the weirs have to be lowered. Near the river bank situated East of the town of Sambeek, a hoisting machine is parked in a large warehouse. The machine can be moved across the weir by rails, where it takes out the Poirée gates, gradually and horizontally to prevent too big flow openings. The crane transports the gates to the river bank and leaves them there. Finally the yokes are rearranged, after which the lowering of the dam is complete. The yokes hinge on their foundation and can be placed almost flat on the ground. This way, the water can flow almost freely to the sea, even when the river has reached peak levels. On average the dam is lowered 15 times a year.

The weirs in the River Meuse have been built after the supply of German coal via the River Rhine stopped during World War I. The coal mines in the Dutch province of Limburg had to fill the gap. To find an efficient and affordable way to transport the coal to the western parts of the Netherlands, the River Meuse had to be made navigable. “The weirs thank their existence to this need for transport”, explains Mr. Michon. “We also had to build two canals, the Juliana canal, and the Maas-Waal canal. Five weirs are identical to the one near Sambeek, with next to the sluices Stoney and Poirée gates. The weirs near Borgharen (the most southern one), and Lith (the most northern one), have been built later, and differ.”

The Borgharen complex was completed in 1929, the Lith weir in 1936. Both have a gate-valve system, which the other five weirs have not. Big gates are responsible for controlling the water flow. At lower discharge levels, under 300 m3/s, gates are at ground level. The operator controls the discharges with valves on top of the gates. Unlike the Sambeek weir, the weirs in Borgharen and Lith are operated by remote control. Grave is a Poirée weir as well, but is constructed differently than Sambeek. The yokes that form the framework for the panels/gates are not standing on a concrete floor, but are hanging on a traffic bridge, supported by blocks. When a large discharge forces the Grave weir to be lowered totally, the yokes are not put on the ground, but pulled up and folded under the bridge.

Twofold task

Weirs have a twofold task. Letting dosed amounts of water pass through, especially during periods of drought when the discharge varies between 25 to 30 m3/s, to ensure parts of the river are deep enough, and let the water flow as freely as possible to the North Sea. There aren’t that many barges left that carry coal, but still, 110 commercial inland navigation vessels prove every day that the importance of rivers as transport corridors has increased.

After nearly a century, most of the weirs are heading towards the end of their lifecycle. Rijkswaterstaat has maintained, and modernised the weir and lock complexes, replaced parts, and installed new machines, nevertheless complete replacement is now on the agenda. The Dutch Directorate-General for public works and water management organised brainstorm sessions in 2015 about the desired design of new weirs. What should these wet complexes look like for the next hundred years, and what can they do?

That question describes nothing less than “a big, and complex challenge which can’t be met by Rijkswaterstaat alone”. The Directorate-General wants to join forces with the business community, knowledge partners, and specialised managers in this field. Now, two years later, there are no concrete plans or designs yet. The Grave weir is scheduled to be replaced in 2028, so there is still some time left.

Source: Benno Boeters, Technisch Weekblad

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