Foto: Wasserwirtschaftsamt München
Improving Flood Protection and Recreational Opportunities by Redesigning the Isar
In 1995 in the city of Munich, Germany, the “Isar-Plan” was initiated; a project group aimed at restoring the Isar river. The goal was to change the shape and function from an artificial canal bed into a more natural river state. The restoration of 8km of the river was a great achievement, improving flood control, attracting 30,000 people for recreation and improving biodiversity. Thanks to the excellent stakeholder cooperation carried out during the project, today the surrounding infrastructure, people and visitors benefit from the Isar-Plan, alongside the local economy.
The Adaptation Journey
The positive impact
The project successfully improved protection against flooding by developing a more natural river landscape, which gives space to the river. In 2005, this was confirmed by a flood which influenced the area and provided evidence for where restoration has reduced or avoided flood damage. When comparing the River Isar to other rivers in southern Germany, it has been demonstrated that the restoration has improved flood control and reduce the damage that could have been caused. The project has also significantly benefited biodiversity through the creation of new habitats for animals and plants, and by allowing fish to move through the river where earlier there had been barriers. Furthermore, the changes have improved the bathing water quality, which means Munich inhabitants and visitors can swim in the river and benefit from the attractive landscape for many recreational activities.
How does it work?
The ‘renaturalization’ of rivers involves implementing specific measures that return a river to a more natural state, often resulting in a greater diversity of animals and plants and increased water quality. In addition, it can help to reduce flooding, sometimes supported by engineered flood defences like dykes (walls that hold back river water). In the River Isar, a range of measures were chosen to restore it to a more natural state and ensure flood protection.
The choice of measures was influenced by the surrounding infrastructure. In built-up areas around the river, engineered ‘rear’ flood defences were required to comply with building safety standards. To give engineered flood-defences a more natural, it was found that reinforcement infrastructure can be built below ground and covered with vegetation. Some flood defence measures were chosen to maintain the existing natural undergrowth on the dykes to conserve the ecosystems and to maintain areas for recreation. The best protection from flooding was found where bank protection measures were supplemented by willows or turf. Thin willow rods, which develop after cutting the willow plant back every 2/3 years, provides a very good hold against erosion damage.
A sufficient water run-off capacity was generated by broadening the main channel bed – this simultaneously enables near natural and flat river bank stabilisation. Bank stabilisation is a method of protecting the river bank from soil erosion. This avoids sediment (or soil) build up in the river downstream, helps to maintain the water storage capacity of the river, and improves the flow of water for wildlife.
Rough ramps were designed to enhance the natural development of the river state. These can imitate natural river rapids or steep angles in the river bed. The resulting pools, stone rock steps, downstream gravel banks and gravel islands play an important role in the ecology of the river, helping the shape and function of the river to become more natural. An added benefit of these river features in that it makes the site attractive for recreation.
It was also found that earlier damages from floods, like pools, dips in land and gravel banks, are now connected to River and can provide a home for fish and insects. This can be enhanced by allowing deadwood to remain in these areas after flooding, and at the first stages of development these habitats were protected with turf and willow by the constructors. This has supported river wildlife.
The Isar was originally an artificial canal bed.
Stakeholder engagement was central to the success of the Isar Plan. To support engagement with local people and business, diverse mediums were used including: an internet platform, info brochures, excursions, workshops. TV and press, round table discussions, info-points and a service telephone. In addition, engagement with people was particularly important in the design of the adaptation measures. A landscape design competition was held for a 1.6 km urban stretch along the river. This gave a voice to the local population for the design of the area, as well as raising awareness of the importance of the measures for flood protection.
A supporting study was conducted by the interdisciplinary working group of “Isar Plan”, which supported the redesign of the landscape through an examination of the flooding situation, the need for recreational area at the riverside, and an evaluation of the area’s biodiversity. The result was a conflict and value analysis which allowed the trade-offs between the different aspects to be understood and on which the development goals were defined.
Operation and maintenance
It was an 11-year project with 5 years of preliminary work. Adaptive management was used to create the successful solution, and a big flood in 2005 negatively impacted the developments.
Obstacles and challenges
Whilst public engagement with those impacted by the project (otherwise called stakeholders) was carried out successfully, it was not without its pitfalls. Stakeholder dialogue was challenging, and at times and involved controversial discussions, public arguments and strong campaigns. Good mediation and cooperation were necessary to resolve conflict and find a balance between two proposed schemes, which promoted different amounts of re-naturalisation of the river.
How much did it cost?
Total cost: 35 million euros.
Revitalization of water elements Agriculture landscape Water purification and recycling Flood control measures Povodně a přívalové srážky Eroze půdy