Nature-Based Solutions for Water Management in the Peri-Urban

Photo Stories

The axis Besòs: The pathway of nature-based solutions for social cohesion, Barcelona, Spain

Authors: Montse Badia Puyol, Andrea Ramírez Agudelo, Elisabet Roca Bosch

This river restoration in Barcelona Metropolitan Area shows two NBS types, a riverside park and constructed wetlands. These nature-based solutions (NBS) were implemented at the beginning of this century to address water challenges related to quantity, with the goal of reversing the river Besós overall degradation of water quality due to industrial pollution and waste. Moreover, water quantity issues were related to freshwater withdrawals, water-stressed flows, and in contrast to flooding risks due to torrential rains. To address these concerns, a large-scale river restoration project began in 1996, primarily funded by European funds. The project aimed to improve the riverbed's environmental conditions, and in particular its water quality and hydraulic capacity, as well as to open up the river's banks for passive recreational use consistent with risk management. The restoration project included 2 NBS types: Constructed Wetlands, as a final purification step, integrated to the Montcada i Reixac wastewater treatment plant (2003). Aside from a 22-hectare, 9-kilometer-long riverside park that blends urban and natural landscapes as a mix of blue and green infrastructure.

The river Besòs intervention has an added value for this peri-urban area because of the high degree of multifunctionality of the space, which benefits nearly 1 million visitors each year and who benefits in aspects such as the availability of a space for gathering, physical health, relaxation and promoting community activities. Currently, the meeting of the Besòs River with the Mediterranean coastline is a landscape in transformation that shows the challenges of the contemporary metropolis, where the NBS approach to involve more ecological concerns could be an advantage for a socially sustainable dialogue, supported by the capacities built (social and technical) throughout its implementation.

This photo story aims to illustrate the Besòs river as a backbone green-blue infrastructure for this peri-urban area, thus, it is recognized as the Besòs axis (l’Eix Besòs), which has been transformed in three aspects:
1) Peri-urban landscape and restoration
2) NBS implementation: Services and benefits
3) The future: land uses changes and the urbanised waterfront

The first aspect of Peri-urban landscape and restoration will expose the environmental recovery and the re-naturalised landscape as a consequence of the industrial heritage (pollution and degradation) (Photos 1 to 4). The second aspect is related to the NBS implementation: Services and benefits show how the use of nature has transformed the area, not only through its waterfront, but also in the new activities for recreation, walking and contemplation (Photos 5 to 8). The third aspect is the future: land uses changes and the urbanised waterfront shows the ongoing process of urbanisation and exposes the pressures for a future connection between the river’s mouth and the Mediterranean Sea (Photos 9 to 12).

Lessons to take away from the Besòs case study, is how this long-term process has benefited from two features: the existence of an organisation coordinating daily actions for NBS maintenance (Consorci Besòs), and, second, the existence of a strategic policy instrument (Agenda Besòs) as a consensus for shared leadership and integration of municipalities.The title photo depicts River Besòs and its encounter with the Mediterranean Sea at Barcelona Metropolitan Area, 2019.


Montcada i Reixac Wetlands restoration. September 2020

The intervention developed in the Eix Besòs can be divided into three sections along the stretch of the river up to its mouth. The first sector, which corresponds to the one furthest away from the mouth of the river, is the construction of wetlands, which was carried out in 2003, as an example of an NBS water purification system, in the Montcada i Reixac wastewater treatment plant. The aim of this action is to achieve ecological restoration both at the level of the riverside ecosystem and at the level of water quality in order to conserve the natural river flow, reduce water pollution (related to industry) and the odours also from industrial discharges. Wetlands play a crucial role in climate change adaptation. It increases community’s resilience to the impacts of climate change such as natural disasters including floods, storm surges and drought.

La Conca del Besòs - The river´s basin

One of the environmental challenges of the project is to improve the environmental quality of the whole riverside area of the river. The peri-urban area furthest away from the city corresponds to a green belt that must contain the pressures to be built upon. Through the implementation of NBS, such as wetlands, it is possible to make the urban landscape compatible with the natural landscape through a good management of both. In this way, almost untouched natural areas can be preserved. A good and sustainable management of these natural areas promotes an increase of species richness, a decrease in the risk of flooding. It also helps to close water cycle gaps and rebalance their functioning.

Seasonal changes in the river's streamflow

Thanks to the restoration of the peri-urban area and the implementation of all the necessary infrastructure to build and restore the Besòs river park, which corresponds to the second section of the Eix Besòs intervention, the problems related to changes in the river flow associated with the different seasons of the year have been reduced. We see, then, that the risk of flooding has decreased not only due to the new infrastructures of the river park but also from its improved management. The management of the whole project has been carried out by the Consorci Besòs and the Agenda Besòs, the latter being a strategic policy instrument as a consensus for shared leadership and integration of municipalities.

Biodiversity and water in the Besòs

As a result of the reduction of water pollution and the improvement in water treatment, an increase in biodiversity, both animal and plant, has been observed along the banks of River Besòs. Since the beginning of the Eix Besòs restoration project (1996-2006), the riverside ecosystems of the area have been monitored in order to increase the resilience of the different species populations as much as possible. This has been achieved thanks to the implementation of the above-mentioned wetlands and the restoration of the Besòs river park.


The urbanisation process along the riverside park

The urban history of the context of Eix Besòs, shows a process of urbanisation characterised by low urban densities with high building heights, the absence of block centres that contrast with large extensions dedicated to industrial estates. Over time, the change of economic activities has questioned the coexistence with the industrial complexes, revealing the environmental weaknesses of activities which leave environmental impact, such as odoriferous quality, degraded quality of the river water and beaches, etc.

Overview of the riverside park

To deal with flooding, firstly, an alarm system was installed in the Besòs river park itself, which warns when the river level rises above normal. Secondly, as mentioned above, the care of the riverside green zone is another of the mechanisms for preventing the risk of flooding. In order to keep this riverside ecosystem stable, a timetable has been established for access to the park so that users can make regulated use of it. The conservation of river banks is an adaptation mechanism against climate change and its possible consequences.

The infrastructure shadows and the thermal comfort

The transformation and improvement of the services of the Besòs river park have made it possible to offer the neighbourhood a place where they can enjoy outdoor activities such as walking, taking the dog for a walk, playing sports, or simply enjoying an open and spacious area where the user can relax and reduce stress. All this has been possible thanks to the restoration of the pedestrian paths and cycle lanes. In addition, being a protected green space, one can find shaded areas where the thermal sensation, especially in hot weather, decreases.

A place to meet, ride a bike and enjoy nature

Since the park has a better equipped space where outdoor activities such as those discussed above can take place, the area has become a meeting place where users can come with their families, friends or themselves. This allows the community to create social bonds different from those that may flourish in their homes or in their routine activities associated with more urbanised areas. In short, the river park aims to encourage the neighbourhood to be more in contact with nature as it is one of the key elements to increase social well-being and improve the health of the population.


Vegetables for sale

NBS inherently offer primary benefits and additional secondary co-benefits. Transforming the landscape provides the primary benefit of an improvement in water quality, while at the same time providing the co-benefit of mitigating flooding through the creation of alternative water ways. Reducing particle spreading also supports improved water quality and concurrently provides the potential co-benefit of improved ecological status and biodiversity in the area. Remediating contaminated water will remove pollutants from water in the Kjørbekk stream, but can also provide additional social, economic and environmental co-benefits. Social co-benefit is felt via an improvement in the aesthetics of the area, economic co-benefits are felt through an enhanced flood protection and environmental co-benefits are achieved via an improvement in the state of the native ecosystem. From a city development perspective, opening the river can potentially increase property value.

Innovation and green walls

The Consorci del Besòs together with the Agència Catalana de l’Aigua which are two of the actors involved in the restoration of the Besòs river axis, are carrying out projects and activities related to the ecological restoration and environmental quality of the Besòs river park. One example is the so-called "green wall pilot" which is a light metallic structure that has been built on top of the retaining wall that separates the city limit from the river level to avoid possible flooding. Different plant species have been planted on this structure to regulate the thermal sensation of the environment. It is a pilot test that is being considered to be built along the promenade of the park as a possible mechanism to regulate the thermal sensation of the area. Such actions encourage innovation projects and enhance community culture.

Other risks: Gentrification and injustice

The creation of the Besòs river park and the restoration of the entire river axis also aims to regulate urban growth and reduce the risk of mass gentrification. In other words, to control the implementation of large infrastructures and industrial activities that could be detrimental to the health of the river ecosystem and the neighbourhood itself. The aim is therefore to achieve coexistence between the changing built environment and the increasingly lively natural landscape. All these changes must be carried out with the participation of the citizens in order to make them more fundamental and successful.

The encounter with the Mediterranean

The implementation of the NBS in the Besòs has shown the relationship between a multi-functional landscape, as an example of re-naturalization, for a more socially cohesive area. Nowadays, the challenge is to intervene in the river’s encounter with the Mediterranean Sea, which corresponds to the third section of the Eix Besòs. In this intervention, it will be relevant to incorporate the learnings of this process not only for the purpose of promoting re-naturalized Mediterranean waterfront through active participation and collective decision making, but also to better manage the risks related to climate changes and to promote a more just urban process of change.

Finally, this NBS implementation demonstrates how river restoration can become a continuous process. The success of the intervention is multidimensional with aspects such as the recovery of the water quality, the management of the fluctuating river’s stream flows, as well as the multifunctional landscape, the risk management strategy, and the promotion of a green, public, free and open space which actively supports social cohesion dynamics. Nowadays, recapitulatuion on all these achievements is required for a broader adoption of a process of constant action to include the challenges posed by climate extreme events, particularly to protect against heat waves and flooding under a coordinated multi-sectoral strategy. Lessons from the Besòs case study include how this long-term process has benefited from two features: the existence of an organisation coordinating daily actions for NBS maintenance (Consorci Besòs), and the existence of a strategic policy instrument (Agenda Besòs) as a consensus for shared leadership and municipal integration. Furthermore, in order to address the peri-urban water challenges holistically, citizens could be part of the leading group making decisions on how to better maintain this biotic infrastructure because they benefit directly from the intervention and have first-hand experience with this goal of making a compatible use of mobility, passive recreation, and re-naturalization.