Throughout the centuries, cities were located in the vicinity of rivers, in order to take advantage of the services that they provided. However, from the middle of the 20th century, cities began to grow dramatically, as they had not done in previous centuries and, in most cases, with their backs to the rivers. These stopped providing the services that they had provided continuously over the years, and became a nuisance, especially the smallest ones, for which many were piped or vaulted, while the rest were fitted between vertical walls of concrete, in order to make the land “available” for urban growth, becoming in all cases marginal and abandoned areas.
The state of many rivers in our country, such as the Genil as it passes through Granada, the Besòs in the Metropolitan Area of Barcelona, the Río del Oro in Melilla, the Vinalopó in Elche, the Isuela in Huesca, the Guadalmedina in Malaga and the Manzanares in Madrid before the renaturation, clearly portray this situation. Practically all of them were deeply affected and transformed by the urban growth of the 20th century and, associated with it, the discharge of wastewater and garbage. Their riverside vegetation was eliminated and they were channeled into rectilinear channels, and in some dams were built because the Mediterranean rivers were not aesthetically valued and everything had to be done to appear a large flow. Even if it meant his death, because it became a pool of stagnant water, dark and smelly in summer, unable to harbor hardly any life.
However, social perception in recent years has begun to change. From being ignored, they have come to be recognized as a value that must be taken care of. Citizens increasingly value the renaturation of river courses, as it is a way of bringing nature to the heart of cities, where concrete predominates. Having in the city a river whose banks are covered by trees and shrubs, observing and enjoying a diverse community of native fish and bird species, is considered an environmental and landscape element that must be present in large cities, since fact contributes to improve the quality of life of its inhabitants.
From a purely environmental point of view, recovering the environmental values of urban rivers allows them to return to being ecological corridors that connect well-preserved ecosystems before and after the city. In addition, the extension of flora and the movement of fauna along these corridors not only increases biodiversity, but also strengthens ecosystems in the face of increasing environmental degradation caused, among other processes, by climate change.
The renaturation of urban rivers has already started in different cities around the world. In the United States, at the beginning of the 21st century, the city of Los Angeles began the transformation of the river that bears the same name, Los Angeles. The wide concrete channel where the races and car chases of many movies were made, has been changing due to social pressure and the will of the public administrations, which created the “Los Angeles River Revitalization” Plan to clean the river’s garbage, avoid wastewater discharges, create flood zones for river flooding and create banks and areas with native vegetation, among other actions.
In Europe, at the end of the 20th century, the city of Munich, along with other German cities, began a process to re-naturalize its urban river, the Isar, which was completely canalized. It was possible to give more space to the river, islands with sediments were created, old concrete defenses were removed and a public beach was created, among other actions.
In Spain, the cleaning of rubbish in the riverbeds and the sanitation of wastewater have been one of the first generalized actions in cities, which have led to an improvement in the quality of the water of urban rivers. Undoubtedly, the extension of the sewerage and sanitation network, the construction of storm ponds, the increase in the number of treatment plants and the improvement of their operation, have been key to reducing pollution by wastewater discharges, these actions being essential so that urban sections of rivers can be re-naturalized.
Thus, in Spain we already have examples of urban river renaturation, such as the Arlanzón river, in Burgos, or the Bernesga river, in León. Both currently bring remarkable environmental and aesthetic values to their respective cities. It is also important to mention the recent case of the Manzanares river passing through the city of Madrid, whose renaturation began in 2016, at the initiative of Ecologists in Action, which developed the first project, and which has also monitored both the environmental improvement and maintenance actions, as well as the natural evolution of the river.
The so positive evaluation from the social and environmental point of view that has been made of the renaturation of the Manzanares, has pushed Ecologists in Action to extend the proposal to other rivers that have been cited previously as examples of the deterioration that the river courses have suffered. urban: the Besòs river in the Metropolitan Area of Barcelona, the Genil river in Granada, the rivers that cross Barakaldo, the Vinalopó river in Elche, the Río del Oro in Melilla, the Isuela river in Huesca, the Zapardiel river in Medina del Campo , the Piles river in Gijón, the Guadalmedina river in Malaga, the Tirteafuera river in Argamasilla de Calatrava, the Francolí river in Tarragona and the Lagares river in Vigo.
The purpose of renaturation of an urban river is to recover in it a certain naturalness, within the possibilities that currently exist in cities. However, for the renaturation of an urban stretch of a river to be environmentally effective, the elimination or opening of the dams that impound the water is essential, since it must flow freely; the cleaning of waste from the riverbed, including of course the elimination of the concrete surface when there is one; and the creation of margins and banks, which must be revegetated with native tree and shrub species. To these actions can and should be added the elimination of exotic species, silvicultural treatments to promote habitat diversity and, therefore, existing biodiversity, and the installation of nest boxes for insectivorous birds, small raptors and bats throughout the channel, among many others. All are feasible actions, with little or no inconvenience to the public, since they are all carried out on the course, feasible and sustainable over time with little budget. In return, the city gains a lot in quality of life and environmental improvement.
Recovering riverbank vegetation on the banks and islands of urban rivers means improving the functioning of the river ecosystem, favoring the formation of shelters and shading the water, forming an ideal habitat for a large number of animal and plant species. In addition, the tree-lined banks enhance the urban landscape and increase the interest and socio-cultural potential of the section.
The actions to be carried out must have the objective of increasing the function of an environmental corridor for the mobility of the flora and fauna communities. The presence of banks, and even islands, with vegetation, will allow the different animal species to use the river axis, recovering the connectivity between the natural areas located upstream and downstream of the urban section. As well as for migrant fauna at higher scales, for example, contingents of small birds that would find in the river trees a place of refuge for temporary rest on their migratory route, and also for some species as a wintering place.
On the other hand, from the hydrological point of view, a flow regime closer to the natural one is an important improvement compared to dammed rivers. Damming supposes a loss of water quality due to the phenomena associated with stagnant waters – eutrophication, anoxia, turbidity, floating debris, siltation of the bed – while the natural flow of the river ends these problems. In addition, the vegetation that grows on islands and banks naturally purifies the continuous flow of water much more than expected, as shown by the results of the water analyzes that are periodically carried out upstream and downstream of the renatured urban stretch of the river. Manzanares. All this always without posing a risk to avenues, although the truth is that, if an adequate free section is maintained, these actions in general are positive in order to alleviate the effects of avenues, by reducing the speed of the water and its pernicious effects.
From the social point of view, the effects of the proposed actions are also a great improvement, let us not forget that these are stretches of rivers along which thousands of people pass almost daily for a good part of their lives. Citizens will find in the river itself, in its sheet of water and its immediate banks, a space of interest for contemplation and for a true approach to the natural values of the river. You will appreciate the dynamics of nature changing in shapes and colors according to the seasons of the year, which contributes significantly to education and environmental awareness. The renaturation of urban sections of rivers directly affects an improvement in the quality of life of the people who live in these cities.
These actions have been well accepted by some administrations. In this way, in the General State Budgets for this year 2021, an important economic item was included for the municipalities to carry out these actions in the urban sections of their rivers. However, the response from city councils is being uneven. While some city councils have already publicly expressed their desire to re-naturalize the urban sections of their rivers, and are going to request the funds that the state budgets enable for this, others have no intention of doing so, as they still consider the artificialized channels as a signal. of progress, and even some still struggle to fill the river and be able to establish buildings and infrastructures on it.
What is certain is that when a project to re-naturalize an urban stretch of a river begins, nature usually reacts quickly and even spectacularly, and comes to count almost immediately, with the acceptance by the vast majority. of citizenship, as it happened in the city of Madrid, where for the first time in many years, the majority of the Madrid population feels proud of its river.
Let’s hope that the competent administrations, both those that have shown interest and willingness, and those that have not yet done so, will have the necessary environmental and social sensitivity to carry out the renaturation of the urban stretches of their rivers, as this would always imply a important environmental improvement in cities, as well as in the quality of life of the population living in them.