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

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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

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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.

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