Otto Intze and the construction of the dams

Andreas Schlenkhoff on a hydraulic engineer and construction designer whose achievements for the Bergisches Land region are still impressive today

Until the end of the 19th century, there was not a single dam in the Bergisches Land. Only mill ponds stored water at night, which could be used by industry during the day. A dam as we know it today was considered unbuildable under Prussian rule. An engineer with vision changed this view and is still regarded as a pioneer with his designs today: Otto Intze.

Prof Dr Andreas Schlenkhoff researches and teaches in the field of water management and hydraulic engineering at the University of Wuppertal. "Otto Intze was one of the best-known hydraulic engineers, an engineer who was not only able to find innovative solutions to technical issues, but also developed complete solutions for the urgently needed water supply in summer during an important industrial development phase and helped initiate the construction of dams throughout Prussia."

Professor in Aachen at the age of 26

After studying engineering in Hanover, Otto Intze became a founding professor of structural and hydraulic engineering at the newly established Royal Rhenish-Westphalian Polytechnic School in Aachen at the age of just 26, and later became its rector. "He was working for an English company in Russia and had built a railway line there," says Schlenkhoff. "These railways travelled with steam locomotives and they needed water. And this water was in the water towers. Intze developed a method of building water towers that was much cheaper than anything else before, and this has been called the Intze principle ever since. The principle refers to a method of building tanks for water reservoirs and steel construction. From 1870 onwards, he worked very intensively with building materials, making him a true master builder." However, he was not only a brilliant engineer and problem solver, he also had the gift of communicating his proposed solutions clearly, so that he was able to inspire those responsible in the industry and convince local authorities and the government of the viability of his ideas and designs.

First dams in Belgium and France

The construction methods of the first dams were known from Belgium, France and England. It is certain that Intze had gathered extensive information from his travels and improved existing ideas. In order to implement these ideas in the Prussia of the time, he gave many lectures that emphasised the feasibility of building a dam. "Today we might call that river basin management. At that time, there was a lack of basic hydrological and water management data as well as technical construction methods. The basic data on water management still had to be collected in the course of surveys and measurement campaigns," says Schlenkhoff. Dam walls had never been built in Germany before 1880 and Intze naturally needed allies. "One of these allies was the Lennep building contractor Albert Schmidt, who was then also involved in other construction companies, as Intze did a lot of planning but very little building."

Germany's first drinking water dam

Between 1889 and 1891, the Eschbach dam in Remscheid was built according to Intze's plans as Germany's first ever drinking water dam. It was followed by the Bever, Lingese, Ronsdorfer, Barmer, Solingen, Neye and Brucher dams from 1896 to 1914 in the same way.In gratitude for this continuous water supply, the people of Remscheid awarded Otto Intze honorary citizenship as early as 1893. It is also worth mentioning in this context that today's Wupper Association and the Ruhr Association were actually founded on his initiative and that of his fellow campaigners. "It wasn't just the water supply for the metalworking industry, but also for the cloth makers. Nobody remembers today, but in 1883 there were devastating floods, but there were also periods when there was no water at all. The dangers of typhoid and cholera and other diseases, which always occur "when the sewage disposal and drinking water supply does not work" are related to this, but were not yet known in this way, explains the expert. "The walls were built as so-called gravity walls, i.e. the water pressure could generally be maintained by the weight of the wall alone. The shape of the wall was slightly curved at the top and shaped over its height so that the water pressure could not cause the structure to topple. The pressure lines are always within the structure so that no tensile stress occurs. This is particularly important for preventing cracks from forming. In addition, the individual bricks were hewn by hand so that a good bond could be achieved and Intze had probably also used a special mortar that was almost waterproof. From today's perspective, however, it must be said that Otto Intze may have forgotten something at the time, and that is the pressure from buoyancy, known as the water pressure at the bottom of the dam, which then reduces the weight of the dam by the amount of buoyancy. This was probably not known, or Intze believed that the wall to the ground was actually tight." In the 1980s, Schlenkhoff reports, the dam standards were amended and it was realised that the safety requirements did not meet today's standards, as the bottom water pressure was not taken into account in the Intze dams. "By the end of the 1990s, all Intzetal dams had been extensively renovated as a result. The Eschbach dam was the first to be completely overhauled using a process from Italy, supervised by a hydraulic engineering professor from Aachen." Basically, dams are, on the one hand, safety-relevant structures with a high potential for damage in the event of failure, but on the other hand they are always well equipped, well maintained, controlled and monitored.

Intze's expertise was in demand throughout the country

"Intze's ideas and concepts were very far-reaching and not only concerned the Bergisch region, but also the Ruhr area and Upper Silesia, for example," reports Schlenkhoff. "He was a sought-after expert throughout Prussia and was also held in very high esteem in the Prussian parliament. If you didn't separate wastewater and water extraction, you had big problems. This was even more pronounced in the Ruhr region than in the Bergisches Land." If wells were used near polluted rivers, for example, they were often just as polluted and so reservoirs were relocated outside of settlements in order to improve the water quality. "Most of the drinking water reservoirs that are in operation today and where drinking water is used directly are also fenced in," says Schlenkhoff, citing the Sengbach reservoir and the Herbringhaus reservoir as examples. "This also applies to a limited extent to the Eschbach dam, where the associated waterworks are currently being reactivated after many dry years. The original water treatment plant was extensively renovated and will probably be back in operation next year. Back then, the water was pumped to Remscheid, and the principle is still the same today."

Dams in the past and today

"The actual tasks of a dam have essentially remained the same. It is about storing the water that flows away 'unused' in winter and is then stored for the dry periods in summer." Compared to the much smaller mill ponds, it was now also possible to plan with the dams. In the 1920s and 1930s, there was a shift towards dams. The Möhne dam (1908-1913) and the Eder dam (1908-1914) were very large structures (based on the Intze principle) and required huge amounts of quarry stone, which meant more labour and costs. Materials and equipment had changed since the turn of the century. Schlenkhoff explains: "Concrete was available in better quality than in Intze's time, and large-scale equipment and, above all, mechanical construction methods had been developed that could loosen, transport and properly reinstall large quantities of rock and soil. That made embankment dams more attractive." Modern dams are operated as so-called 'multifunctional dams'. "In addition to the drinking water supply, flood protection and ensuring an ecologically necessary minimum water flow in the water bodies are the top priorities. Later, recreational use was added, which is very important today, but must always remain a secondary priority from a water management perspective." The high level of recreational use is also due to the fact that the Bergisches Land only has a few lakes, but life on the water is very attractive and appealing to many people. For the future, Schlenkhoff adds: "In my view, it would also be appropriate if our society not only thought about adapting utilisation and operation, but also about other options to improve security of supply for the next hundred years, just as Intze did."

Dam masters check that everything is in order every day

Dams are complex structures that require constant inspection and maintenance. This is why practically everything is checked. "Dams are perhaps among the best maintained, inspected and monitored structures in Germany. The requirements for the stability of the system, or the safety against failure of the barrier structure, have always been very high," says Schlenkhoff. In addition to the DIN standards, which are regularly adapted to the generally recognised state of the art, the national and international professional associations are also continuously working on guidelines, bulletins and other regulations relating to structural safety and operation. In addition, the supervisory authorities of the district governments ensure that the dam operators comply with these rules. "A dam inspection is carried out once a year. An in-depth safety inspection is carried out every five and every ten years. These inspections concern all operational facilities, such as the functionality of the bottom outlets, the condition of the measuring equipment and also anomalies such as cracking, which is regularly checked by means of an inspection tour inside the dam wall, seepage water or displacements and deformations." Dam masters carry out daily inspections and record their findings in a dam book.

Dam construction is viewed critically today

Water is a valuable commodity, but dam construction is also viewed critically. They are associated with considerable ecological changes and damage to nature and the landscape. The long-term consequences of large dams cannot be predicted. The researcher comments: "No man-made measure is without impact on the environment. In Germany, I would say provocatively, there is almost no natural landscape, it is all cultivated landscape, it is all designed. If man creates a rape field or a spruce forest five kilometres long and one kilometre wide, is that nature? Certainly, large structures also result in major interventions. But if I look at the reservoirs as a whole in terms of area and then list all the existing sports grounds or airports next to them, if I take roads, settlements or our agriculture, where is the greater impact? It all has an impact on the environment. Or our lakes and rivers: in 2002, the EU passed a Water Framework Directive with huge targets for good ecological status, which expires in 2027 and has yet to be achieved." No matter what you build, you have to comply with the existing environmental guidelines, which is very important. First of all, interventions should be avoided if they are not absolutely necessary. "But if I realise that I have to build another dam, for example in the Ahr valley, then I have to consider whether there are alternatives. If there aren't, then I have to make this intervention, otherwise I can't protect the people. The alternative would be to relocate everyone there. But you have to explain that to the people."
The scientist explains that it is a major problem to convince society that an intervention of particular intensity nevertheless leads to very high benefits overall. In the case of flooding, the benefits are often not recognised, because if damage is avoided, it is impossible to see that the damage would have occurred. "We should ask the question about possible solutions. Flooding or water scarcity in Germany is not a 'God-given punishment' and we are not helplessly at the mercy of climate change," says Schlenkhoff, "so we have to think about adaptation measures." That's why we have to keep demonstrating the benefits. "I have helped plan several flood retention basins as an engineer and I believe that we have a good planning approval procedure. This is a public procedure that may not reach everyone, but those interested and affected have the opportunity to participate. However, I fear that society's trust in institutions will continue to dwindle. And that expert knowledge, which Intze used to convince his fellow human beings, will lose its value in today's jungle of information and disinformation. Unfortunately, this also applies to the importance of engineers within the university if the university does not succeed in linking engineers closely with practical problems and solutions."

Planning times are 10 to 20 years

"We are happy with our democracy, but that also means that we can't please everyone," says Schlenkhoff, "if you want to please everyone, then you don't do anything. We have set ourselves rules that are very restrictive. We have built up very high barriers to prevention. We have planning periods of 10 to 20 years for hydraulic engineering projects. You always have to weigh things up carefully and then a decision has to be made (on a discretionary basis). And then it has to be communicated that this is not arbitrary, but that it is inevitable for society as a whole that this or that will be done. I've been doing flood protection for 40 years now and there are always people who supposedly know better, but ultimately delay the processes and the necessary flood protection."

Otto Intze has undoubtedly made a significant contribution to dam construction. "If a critic were to suggest a better solution than dams, then dams would of course be superfluous," concludes Schlenkhoff, "but I don't see that happening for the next hundred years!"

Uwe Blass

Prof Dr Andreas Schlenkhoff is head of the Water Management and Hydraulic Engineering teaching and research area in the Faculty of Architecture and Civil Engineering at the University of Wuppertal.