Table of contents
- Executive summary
- 1. Introduction
- 2. Fall and rise of urban rivers and lakes
- 3. Coping with key challenges for urban rivers and lakes
- 3.1 Water availability and supply
- 3.2 Water quality
- 3.3 Structural changes
- 3.3.2 Hydromorphological restoration of urban rivers and lakes
- 3.3.3 Uncovering Europe’s hidden rivers
- 3.3.4 Restoration to cope with urban flood risks
- 4 Lessons learned and way forward
- Acknowledgements
3.3.2 Hydromorphological restoration of urban rivers and lakes
3.3.2 Hydromorphological restoration of urban rivers and lakes
Since the 1980s, in several parts of mainly western and northern Europe, an increasing number of river restoration projects has been developed and realised in urban areas. Many of these have been based on the insight that attention to ecological aspects of river maintenance can enhance the creation of attractive open spaces and the establishment of a more natural landscape. A multitude of benefits related to urban river restoration has been recognised especially:
- Leisure and recreation for residents, nature experience for individuals, enhancement of city aesthetics;
- Flood control and protection;
- Climate change adaptation, e.g. related to retention areas which give room to the river and measures addressing impacts such as urban heat islands or stormwater; and
- Freshwater ecology and cross-linking of habitats, creation of retreat areas for endangered species, enhancement of biodiversity.
Since the adoption of the WFD in 2000, urban river restoration is partly driven by the goal to reach good ecological status or potential also for physically modified stretches of rivers in urban areas.
Especially in densely populated and industrialised areas, restoration of urban rivers contributes to a high quality of the environment as well as to a high quality of life. Urban rivers are often the only functioning or potential reservoirs of biodiversity and open spaces in cities. Thus, the active protection and restoration of such areas is part of the repertoire of fundamental practices for shaping cities’ spatial order and sustainable development (Bender et al., 2012).
Much of urban river restoration concentrates on small rivers and streams, which are often developed in the context of broader city strategies on restoration. The small River Mayesbrook in London, for instance, has become a flagship urban restoration project as part of the London Rivers Action Plan. After restoration (of riverside wetlands, woodland planting, the creation of new meandering channels and the improvements of the river banks), the River Mayesbrook reached good ecological status according to the WFD. The restoration of the stream Igelbäcken in Stockholm has greatly improved habitat characteristics for the rare fish species stone loach, which also plays a strong communicative role for stimulating restoration actions in the Swedish context.
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Mayesbrook, London: Enhancement of community space and natural landscape through stream restoration The restoration of the Mayesbrook Park in east London is a flagship project for the London Rivers Action Plan published in 2009, the first ever plan for restoring all of London’s rivers (see section 3.3). Before its restoration, run down sports facilities, two polluted artificial lakes and a straightened, realigned and fenced river sunk into a deep concrete channel made up the landscape at the Mayesbrook Park (Natural England, 2013). The Mayes Brook was characterised in the Thames River Basin Management Plan 2009-2015 as one of the worst water bodies in the area, failing to achieve Good Ecological Potential due to hydromorphological modifications, poor water quality and low ecology (Thames River Trust, 2015). The main driver for the restoration project on the River Mayesbrook in London was the identified need for revitalisation of the park where the river is located, as well as water quality improvements. The restoration of the Mayes Brook and Mayesbrook Park lakes in London was also identified as a measure to improve hydromorphology and water quality in the first River Basin Management Plan for the Thames River Basin District. The main aim of the restoration measures implemented was to enhance the community space and achieve a more natural landscape that, at the same time, could become a model for climate change adaptation in a city environment (Greater London Authority, n.d.). The river restoration measures implemented included the creation of a new floodplain (1.5 ha), riverside wetlands, woodland planting, the creation of new sinuous water channels and the re-grading of river banks. After restoration, the river is showing rapid morphological recovery and improved ecological resilience, helping the water body progress towards Good Ecological Potential. In addition to the ecological benefits, the restoration of the River Mayesbrook in London has provided many additional benefits such as health benefits, and improvement in the quality of life and wellbeing of the local inhabitants, improved safety through greater park usage, socio-economic benefits to local sports clubs as well as an educational resource for the local schools. An assessment of the ecosystem services provided by the restored Mayesbrook published estimated a substantial lifetime benefit-to-cost ratio of £7 of benefits for every £1 of investment (Everard et al., 2011). The study highlighted the social and health aspects improving the quality of life and wellbeing of local communities as the more important benefits of the intervention. Photo: @xxx |
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The Igelbäcken stream in Stockholm: Important for ecology and recreation The Igelbäcken is, in a city context, a relatively undisturbed stream. It is considered one of Stockholm’s most ecologically valuable rivers and provides access to nature and recreation for a huge number of inhabitants in the northwestern parts of Stockholm. The stream has a unique population of the (for Sweden) rare fish species stone loach, which has become an iconic indicator species of the stream and is widely used communicatively for stimulating restoration and other environmental measures. Previously implanted signal crayfish is believed to impair the preconditions for stone loach. Fishing is prohibited in the stream. Restoration efforts in River Igelbäcken have included re-meandering parts of its stretches and adding bottom substrates such as gravel and stone. The purpose of these measures was to increase the turbulence in the water and achieve better oxygenation. Trees and shrubs has been planted along the river to increase shadowing and lower water temperature during hot summer periods In 2006, the City of Stockholm established the Igelbäcken Nature Reserve. The nearby municipalities of Solna and Sundbyberg have formed reserves for their parts of Igelbäcken valley. Within the inter-municipal Igelbäck Group collaboration between municipalities, the County Administrative Board and several NGOs has been conducted over 15 years. Stone loach. Photo:@xxx |
Some urban restoration projects target the recovery of floodplain ecosystems from historical river regulation and drainage. Such an example comes from the city of Leipzig in Germany where ongoing restoration efforts on the urban River Luppe aim to improve the floodplain dynamics, increase the quality of habitats for plants and animals and to maintain and increase ecosystem functions and services for people.
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Leipzig: Revitalization of an urban floodplain forest The city of Leipzig is situated between the floodplains of the rivers White Elster, Pleiße and Parthe, which form a green belt classified as a significant Central European floodplain ecosystem resulting from widespread floodplain forests. Interventions such as river regulation measures, extensive diking and the drainage of agricultural and pasture fields have had significant impacts on the floodplain. Furthermore, the creation of the river section Neue Luppe (New Luppe) to serve flood protection in the 1930s also resulted in several impacts. Former river sections were cut off and could not provide the floodplain forest with water anymore. As a result, the formerly water-rich floodplain landscape now suffers from massive drop of the groundwater table and is drying out. Today the area consists of many dry river beds without connectivity and a decrease of dynamic floodplain ponds and oxbow lakes. This is a threat among others also to the biodiversity of the floodplain forest and related ecosystem services. At the same time, the floodplain of Leipzig has an important function as recreational area and significantly contributes to quality of life of the city residents. The restoration project “Lebendige Luppe” (Living Luppe) is one of the largest projects on floodplain and river restoration in Central Germany and it started in 2012. The objective is the revitalization of more than 16 km of a former river course in the floodplain ecosystems. Dried-up river arms of the former water-rich floodplain, especially of the river Luppe, are to be filled and reconnected again with water and create a continuous water landscape. The aim is for significant floods to reach large areas of the floodplain via the new river course. It is planned to achieve inundation of at least 30% of the floodplain area via the new river. The groundwater table should be stabilised and raised by about 1 meter in most parts of the project area. The project is considered part of a mosaic of different measures needed to achieve more extended revitalisation of the floodplain in the future and is planned as a no-regret measure. Major flood events in January 2011 and in June 2013 inundated most of the project area and showed that, as a result of the project Lebendige Luppe, the floodplain is fulfilling its function of protecting the city against inundation. The idea for the restoration of the River Luppe and the revitalisation of the floodplain was based on preparatory work of the Green Ring Leipzig, an initiative of Leipzig and the neighbouring municipalities for a number of projects to enhance the environmental character of the city. Lebendige Luppe – Heuwegluppe at inundated state. Photo: @Maria Vitzthum |
Despite the potential benefits of hydromorphological restoration both in ecological and recreational terms, restoration of urban rivers and streams is not always feasible or desirable to the extent of similar restoration activities in rural areas. Flood risk protection of densely populated areas in downtown parts of cities remains a priority and is, in the same time, a barrier to extensive restoration projects. Due to such limitations, the administration of the city of Vienna follows a stepping stone approach to improve the hydromorphology of rivers. According to this approach, restoration has started from the outskirts of the city and moves into the city step by step, as the urban sections of the rivers are more difficult to restore.
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Vienna: A stepping stone approach to river restoration Vienna, Austria, is crossed by three main rivers (Danube, Wien and Liesing) which were heavily modified in the 19th century to protect the city against floods. As a result of the changes in hydromorphology, problems with eutrophication arose. Most of the water bodies in Vienna are heavily modified water bodies, so the environmental objective according to the WFD is to achieve good ecological potential in most cases. In recent years the Vienna city administration has started to execute a series of projects on all three rivers, with the goal to achieve good “ecological potential” of urban water bodies, to reduce eutrophication and to enable migration for fish and benthic invertebrates, by removing migration barriers where possible. Measures executed were targeted at restoring the riverbed and semi-natural riverbanks, re-introducing meanders, replacing bed drops with bed sills so as to remove migration barriers and enhancing wastewater treatment. In improving the hydromorphology of rivers, the administration has started activities from the outskirts of the city and moves into the city step by step, bearing in mind that the urban sections of the rivers are more difficult to restore partly due to the lack of space in the urban area. For the urban stretches, master plans are developed in each case for the entire stretch, starting the implementation with the River Liesing (2015-2021) and continuing with the River Wien in the next WFD period (2021-2027). The restoration is foreseen to continue until 2027. River Liesing before (left) and after (right) restoration. Photo:@MA45 Webel. |
Photo: @MA45 Webel
Photos: (c) MA 45 / Webel (left), (c) MA 45 / Wiener Wildnis