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Iconic watermill at the Arenberg Castle restored to place of honour
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Iconic watermill at the Arenberg Castle restored to place of honour

The watermill at the castle of Arenberg got a thorough overhaul resulting from a successful fundraising campaign.

6 minutes
10 September 2020

The watermill at the castle of Arenberg can once again be admired in all its glory. At the beginning of this summer, the reconstructed mill wheels made their return to Arenberg Park. This put the finishing touch on a thorough overhaul resulting from a successful fundraising campaign.

The watermill at Arenberg Castle is one of the oldest mills in Flanders. The first historical mention dates from 1286. In the sixteenth century, the mill consisted of two buildings situated on the right and left banks of the Dyle and connected by a bridge. The mill on the right bank probably disappeared during the seventeenth century. Archival sources show that the function of the watermill changed over time. The mill was used for the production of grain, buckwheat and oil, or saw use as a sawmill.

After the First World War, the Arenberg family donated the castle and the surrounding park to KU Leuven. In 1954, the mill building underwent a thorough renovation to accommodate classrooms. Presumably that was when the mill mechanism was removed from the interior. The wheels and lock system – which date back to the early twentieth century – have been preserved but have deteriorated considerably, prompting a thorough overhaul. Because of its historical and industrial value, the watermill was listed as a monument at the end of the twentieth century.

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Green energy

Initially, the Faculty of Applied Science and Engineering, together with KU Leuven Technical Services, came up with a plan to get the watermill running at full speed again and thus generate green energy. The calculations showed that the mill wheels could produce an annual yield of no less than 216,000 kilowatt hours. ‘That’s about twice the current green energy yield of the university,’ says Joris Snaet of the Monuments and Architectural Maintenance Division at KU Leuven. The proceeds from that energy generation would even recoup the costs of the restoration in fifteen to twenty years.

Yet the promising plan to generate energy via this historic monument was premature. It soon became apparent that a permanent activation of the mill would have dire ecological consequences. ‘The wheels don’t turn on running water, but on the power of raised water’, Joris Snaet. To raise the water level, the lock system’s bulkheads have to be lowered. ‘This would actually create two separate ecosystems in the Dijle, which is unacceptable in the context of contemporary nature and biodiversity management.’

A fish ladder or a partial diversion of the river is a possible solution, but any such a diversion would make the mill building and its surroundings an island. This in turn would have consequences for the people flow and accessibility around Arenberg Castle. Even more alarming is that a backwater of the Dijle upstream would, among other issues, cause the Doode Bemd nature reserve, downstream areas and even Leuven's city centre to once again be susceptible to flooding.

Historical eye-catcher

With this knowledge in hand, it was recommended to opt for a purely aesthetic restoration of the watermill. In addition, the water is no longer raised, as the wheels ‘freewheel’ on the power of the flowing water without generating any energy. The mill is thus mainly preserved as a historical monument.

More than a year ago, the iron wheels were dismounted for renovation. ‘The environment was demanding,’ says Joris Snaet. The mill wheels had to be lifted – with the help of a seventy-tonne crane – over the roof of Arenberg Campus. In January, heavy rain also caused severe flooding. ‘The site area, as demarcated by sheet piling, was transformed into what we called “the swimming pool”,’ says Joris Snaet. Afterwards, the consequences of the corona crisis were also felt at the site; only after the lockdown ended could work carefully restart.

Despite all the obstacles, the wheels made their return to the castle of Arenberg at the beginning of this summer. Due to the formation of considerable amounts of rust, recuperation of the original mill wheels turned out not to be feasible. The new wheels are, however, a precise reconstruction of the original ones. In addition to the wheels, the outer walls on the Dijle and the stone dams on which the wheels rest were also restored. The duckweed screen was renewed and the old lock system was treated and painted to protect against rust.

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Save the mill

The restoration works have cost about 400,000 euros. The restoration was able to begin thanks to the financial support of the KU Leuven Sustainability Office. The university committed itself to providing half of the total amount. The dean's office of the Faculty of Engineering Science then took the initiative to crowdfund the remaining 200,000 euros.

For this purpose, a fundraising campaign called ‘Save the mill’ was launched. The KU Leuven Heritage Fund of the Fundraising and Alumni Relations Office contributed to the project. ‘Save the Mill’ started in 2017 and was successfully completed after a year and a half. The success of the campaign has also contributed to the creation of a crowdfunding platform to increase the involvement of alumni in restoration and other KU Leuven projects in the future.

The campaign was mainly aimed at (former) KU Leuven engineering students. This is not entirely coincidental: Arenberg Park – where the watermill is located – is part of the Faculty of Engineering Science’s Arenberg Campus. In the 1950s, the park was designed in the style of an American university campus, a lively place where students could eat, exercise, study together and take classes.

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Many engineering alumni have warm feelings from the dynamics of this ‘living campus’. The watermill in particular evokes these memories, as engineering students pass by the mill almost every day. Local residents and anyone who used Arenberg Park as a backdrop for communion or wedding photos could also identify with the mill. This is evident from the impressive engagement and nostalgic testimonials given by numerous donors.

Moreover, the age-old technology appeals to the imagination. Watermills date from ancient times and at the same time represent the future: a watermill produces energy without any CO emissions. ‘The wheels spinning in the water are a magnificent sight,’ says Joris Snaet. ‘A working watermill is a perfect symbiosis of nature and technology.’

Thanks to donors’ efforts, the restoration took on a broader meaning that goes deeper than the purely architectural aspect. The ‘Save the mill’ fundraising campaign responded to this sentiment by offering gifts so that donors who gave at certain donation levels received a bolt or blade from the mill. Those tangible memories were handed over in mid-July at the official inauguration of the restored watermill.

A working watermill is a perfect symbiosis of nature and technology.

Future energy generation?

Amazingly, the mill wheels turned during the inauguration. Together with colleague Gert Maessen and professor Yvan Verbakel (Faculty of Engineering Science), who were able to help bring the project to fruition, inserted preliminary, shallow bulkheads for two of the six water courses. This raised the water level locally – around the stone dams – by about ten centimetres, whilst the entire water level of the Dyle remained unchanged. ‘To our great delight, the wheels began to turn effectively. Not at full speed, but they did turn!’

Although it was primarily an aesthetic restoration, the mill now offers new opportunities for research projects on energy generation. In collaboration with professors and students from the university, research will continue as to whether a minimal backwater can generate green energy without ecological consequences.

Yet one question continues to arouse curiosity and fascination among donors: ‘Could it still work?’ ‘In the end, this turned a weakness of the project into a strength,’ concludes Joris Snaet. Who knows, maybe the watermill at Arenberg Castle will generate more than just memories in the future.

Support the Save the Mill heritage project