Reintroduction of hydropower in the mills district of the Town of Bamberg (Germany)

About Bamberg

Bamberg is located in southern Germany, in the north of the Free State of Bavaria and in the region of Upper Franconia with a population of around 80,000. It is a good example of a central European town with a basically early medieval planand many well preserved ecclesiastical and secular buildings dating from the Middle Ages. The Town of Bamberg was inscribed on the World Heritage List under criteria (ii) and (iv) in 1993.

"From the 10th century onwards, this town became an important link with the Slav peoples, especially those of Poland and Pomerania. During its period of greatest prosperity, from the 12th century onwards, the architecture of Bamberg strongly influenced northern Germany and Hungary. In the late 18th century it was the centre of the Enlightenment in southern Germany, with eminent philosophers and writers such as Hegel and Hoffmann living there. Of particular interest is the way in which the present town illustrates the link between agriculture (market gardens and vineyards) and the urban distribution centre."

Statement of Outstanding Universal Value

Climate-related impacts

By 2020, the temperature in Germany has risen by 1.7 degrees Celsius compared to the pre-industrial age (Foken, 2021). The mean temperature in Bamberg has increased by approximately two degrees in the past 40 years, while the trend for mean yearly precipitations has reduced by approximately 5% (Meteoblue). The city is also affected by the urban heat island effect, whose effects are worsened by climate change and urbanisation, as buildings block cooling winds coming from the Main and up towards the Regnitz valley (source).   

According to the site management, due to the drought, the foundations of some historic building have shifted, and cracks have appeared on the Baroque façades. The damages require continuous conservation efforts and substantial ancillary measures. Additionally, the market gardens of the World Heritage property are being negatively affected by dry summers and rising water costs. Extreme rainfall and storms simultaneously endanger crop yields.

Traditional knowledge and practices

The Lower Mills District along the Untere Mühlbrücke (Lower Mill Bridge) is located at the heart of the Town of Bamberg. The ensemble once consisted of five mills of Medieval origin. At the end of World War II, the three connected mills were almost completely destroyed. Only the ruins of the Sterzer Mill remained next to the still intact neighbouring mill buildings.

Since the remains of the Sterzer Mill were in danger of collapsing due to the heavy damage, they were demolished in 1950 except for the ground floor façade and provided with an emergency roof. On the site of the former mills, a new building was erected from 2016, incorporating the structural remains of the historic Sterzer Mill. The natural building materials of which Bamberg’s monuments are largely made are durable and reparable. The resources tied up in those buildings are climate-neutral and environmentally friendly as in use for centuries. 

On the “Gründtlicher Abriß” (detailed map) of 1602, several water mill wheels along the river Regnitz testify to the use of hydropower. This continuity also endures in the urban horticultural areas in the eastern part of the city dating back to the Middle Ages. (Source: Informationsdienste Städtebaulicher Denkmalschutz Nr. 44 – Klimagerechte Stadtentwicklung in historischen Quartieren. Kommunale Strategien und Maßnahmen (2020)). While the continuous presence of mills on the river in the city centre was not described in the criteria for which the Town of Bamberg was included on the World Heritage List, the mills are located within the site boundaries and the usage of waterpower in a small scale has historical roots in this area of the city.

Climate action solutions and strategies 

Policy context

As a member of the "Climate Alliance”, the city of Bamberg cooperates with the surrounding municipalities. The driving idea is that both the city and its region would benefit from the energy transition: the city has a reliable supply of renewable energy, and the surrounding rural areas are the energy producer, generating income, allowing the development of new business models, and well distributed profits among municipalities. In fact, the city of Bamberg would not have been able to achieve its renewable energy goal if it wasn’t for rural support, considering the limited urban space (source).

The city of Bamberg's strategy to produce renewable energies is embedded in its climate change strategy and is integrated into the sustainable development of Bamberg. In 2009, the Fraunhofer Institute analysed the resource potential of the city and different scenarios were investigated to find the best energy models for the area. The city government involved the industry and engineering sectors in the planning process, as well as the local community. In 2011, the Climate and Energy Agency Bamberg was established to serve as the office of the Climate Alliance Bamberg. In 2012, the city along with 31 municipalities formed the “Regionalwerke Bamberg GmbH’’ to combine strategic efforts.

In 2019, the City of Bamberg adopted a new Management Plan for its World Heritage property. It contains the main guidelines, instruments and organisational structures that are relevant for the conservation of the site and its Outstanding Universal Value. In context of climate change, growing scarcity of resources and social inequality, sustainable development takes on increasing importance especially for World Heritage sites. The Management plan sets out examples of innovative, sustainable projects, including 100% Eco-electricity generated by renewable energy, which has contributed to the urban sustainable development (source). 

In 2020, the Climate Alliance of the city and district of Bamberg commissioned an analysis of climate change-related risks and opportunities. In workshops and meetings, the project team developed local strategies together with representatives of the city and the district office, civil society actors, associations and the mayors of the municipalities. The climate adaptation concept for the city and district of Bamberg was presented to the Regional Climate Council in May 2021. 

Project: re-introduction of hydropower

In 2015, the Munich company Kraus Real Estate and Hydropower, together with the Bamberg-based architectural firm Rosenberg, submitted a design that proposed resuming hydroelectric power generation at the site of the former water mills, combined with a building to house a World Heritage visitor centre, including catering facilities. After an intensive planning and approval phase, the two-year construction period followed, and the turbine was launched into operation in 2018. A three-bladed, low-vibration Kaplan turbine with a runner diameter of 2.4 metres was installed horizontally. This was made possible by merging the water rights of the three former mills. Due to the small size of the construction site and the narrow road conditions in the old town all deliveries were carefully coordinated: the individual parts of the turbine were lowered into the turbine shaft from a distance using a heavy-duty crane and then assembled, as the load-bearing capacity of the Lower Mill Bridge is limited to 30t. A traditional builder of water mills was hired to provide an appropriate approach for historic environment and adapt new technologies.

The new building by architect Heinz Rosenberg is characterised by clear lines and a simple sandstone façade. The construction work was preceded by archaeological excavations, which revealed some 900 oak piles. The dendrochronological examination of a part of the foundation piles revealed dates from the 11th to the 18th century, which corresponds to the numerous fires and the respective reconstruction of the mills. At the beginning of the construction work, all the still usable sandstone blocks of the Sterzer Mill were numbered, removed and temporarily stored before they were finally integrated into the new façade as a reference to the past. Other elements such as door grilles and ceramic insulators were also preserved as part of this façade. The building is now leased by the Municipality and used as the Bamberg World Heritage Centre. 

The 15t turbine is not visible, fish friendly, adapted to the shallow river and thoroughly insulated with rubber matting to protect the terrace above and the building from noise and vibrations. Since its installation, the hydroelectric power plant has been supplying 100% green electricity directly into the municipal power grid. The turbine is generating energy for around 300 households, corresponding to an annual output of approx. 750,000 kWh, which is considerable in view of the low height of the waterfall

While generating renewable energies is not always compatible with World Heritage status, the use of the most modern technology made it possible to continue the long-standing exploitation of hydroelectric power at this site without posing a negative impact on the OUV and attributes of the Town of Bamberg World Heritage property.

Since 2019 the Bamberg World Heritage Centre has opened to public visitors, and the entire structure has been in use. It is situated on the top floor of the new building, with an exhibition area and library.  There is a restaurant on the ground floor with a large terrace above the turbine. 

The ongoing efforts by local communities and the Bamberg World Heritage Office have created an opportunity for the residents of Bamberg to strengthen the connection with their cultural heritage and promote sustainable energy consumption. In line with this vision, as of 2022, the guided tours organised by the World Heritage Office include a visit to the turbines in order to raise awareness about renewable energies.

The project shows the potential for Public-Private-Partnerships to contribute to sustainable urban development and enhanced environmental sustainability, as well as the contribution of historic practices for renewable energy production and finding solutions for energy production in cities.

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Sources: Ms Patricia Alberth, Site Manager, City of Bamberg, 2022; “Reintroduction of hydropower in the mills district of the World Heritage city of Bamberg” by Patricia Alberth, originally published in ISG-Magazin 2022/4 “Ressource Denkmal” 

Sustainable development

The initiative aims to contribute towards sustainable development by addressing the following Sustainable Development Goals:

To learn more

• Read about the project in the e-publication "Bamberg World Heritage Centre" [in German].
• Visit the website of the Bamberg World Heritage Office. 
• Browse through the Climate Adaptation Plan for Bamberg (in German).

Contact

Bamberg World Heritage Office

• Website: welterbe.bamberg.de/en
• Address: Untere Mühlbrücke 5, 96047 Bamberg, Germany
• Email: info@welterbe.bamberg.de

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Credits

© UNESCO, 2023. Project team: Jyoti Hosagrahar, Alba Zamarbide, Carlota Marijuan Rodriguez, Altynay Dyussekova. 
Cover image: © Limes.Media/Tim Schnarr

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