River Restoration of the Manzanares River in the surroundings of the Royal Site of El Pardo (Madrid)

Image author: Dirección General del Agua. Confederación del Tajo

The Manzanares River, as it passes through the historic Royal Site of El Pardo, has undergone various hydromorphological alterations over the years, which profoundly transformed both the riverbed and its banks. These transformations resulted in the significant loss of river space, habitat diversity, both longitudinal and transverse connectivity of the river, and public accessibility to its banks.

In response to these challenges and in compliance with the EU Water Framework Directive, an ambitious restoration project was initiated with the aim of improving the ecological status of the river. This project was aligned with the environmental objectives of the Hydrological Plan of the Tagus Hydrographic Demarcation and had the collaboration of Patrimonio Nacional, which manages Monte de El Pardo. The focus was on rehabilitating and enhancing this stretch of the river, which extends from the Pardo reservoir to the confluence with the Trofa stream, covering approximately six kilometres.

This segment of the Manzanares River was catalogued in the Hydrological Plan as a body of water of a "Very Modified" nature. The intervention sought not only to restore the river's natural conditions but also to better adapt it to the expected effects of climate change, such as reduced flows and an increase in the frequency and intensity of extreme weather events. In addition, it sought to restore an area of great environmental and cultural value, improving biodiversity, ecological functionality, and the public experience of the river.

The project directly addressed river restoration needs by implementing management practices that included reconfiguring the riverbed, restoring riparian vegetation, and improving the river's connectivity and accessibility for citizens and local wildlife. The techniques applied have sought to reverse the negative impacts of past human interventions and create a more resilient and dynamic river corridor that could withstand current and future pressures.

With a vision towards long-term sustainability, this project not only improved the ecological status of the Manzanares River, but also served as a model for future river restoration initiatives in other similar contexts, both nationally and internationally. The results of this project were expected to contribute significantly to the science of river restoration and integrated watershed management, providing valuable lessons on the interaction between human activities and river systems in urban and peri-urban settings.

Case Study Description

Challenges:

The River Manzanares in the area surrounding the Royal Site of El Pardo has been affected over the years by a series of alterations of a hydromorphological nature which have led to significant changes in the conditions of both the riverbed and its banks. The river appeared as a succession of backwaters because of the existence of a series of barriers of different types in the riverbed.

One of these barriers was a "pseudo-natural" weir formed at the confluence of the River Manzanares with the Arroyo de la Trofa because of the accumulation of sediments (mainly sand) from the intense erosion of the basin of this stream. But these were not the only alterations affecting the basin of both watercourses: the Manzanares river in the section under study presented a hydrological regime in which, on the one hand, the circulating flow was insufficient to mobilise the sediments at the confluence with the Trofa stream, and on the other, the lack of sediments in this flow was creating problems of incision along the whole stretch and, in general, the loss of river space; in addition, a high nutrient content had been detected in the Trofa stream.

The alterations would probably be aggravated in a scenario of climate change, where it was foreseeable that the usual flows would decrease, and the frequency and intensity of flood episodes would increase. If to this is added the increase in temperatures, the most immediate effects expected would be the reduction and homogenisation of the aquatic biotope, an increase in incision processes and greater eutrophication with the consequent development of helophytes and the decay of riverbank vegetation.

Therefore, this intervention was proposed to adapt these bodies of water and the associated ecosystems to the effects of climate change, which can be simplified into three main phenomena:

The increase in temperatures would lead to a greater deterioration of the riverbed, with the eutrophication of its waters, an increase in the existing reeds and an increase in the mortality of the riverside woodland.
Reduced rainfall would mean that the reservoir upstream of this reach would have greater flood protection capacity, making the river downstream increasingly resemble a wetland with a constant flow. The absence of floods would encourage the siltation of the riverbeds and the development of in-channel vegetation.
On the other hand, intense precipitation events would have the opposite effect on the Trofa stream basin, favouring greater erosion than currently exists.

Objectives:

Contribute to the improvement of the ecological status of the Manzanares River and the Trofa stream and to serve as a pilot example of a climate change adaptation measure in the field of river management.
Ensure compliance with environmental and hydrological objectives in accordance with current regulations (Hydrological Plan and Flood Risk Management Plan of the Tagus Hydrographic Demarcation)
Restore of the hydrological, morphological, and ecological naturalness of the river (permeabilization of artificial structures, recovery of riverside groves and altered areas)
Return the longitudinal and transverse connection of the channel.
Recovery of accessibility to the riverbed, promoting public use.
Bring the river closer to its users by adapting paths and optimizing the spaces for public facilities.
Reduce the risks of flooding in the area and downstream, in the city of Madrid.
Extend the environmental corridor of the Manzanares River (establish a meeting point between the city and the natural environment).

Adaptation measures implemented in the case study:

Structural/physical: Engineering alternatives and options for built environments

Structural/physical: Ecosystemic options

Social: Information options

Solutions:

IN THE MANZANARES RIVER

Actions for the recovery and improvement of river habitat

Prior to the works for the permeabilization of barriers in the Manzanares River, fish of native species were rescued (capture and transfer).
By placing rocks and/or logs in the river section, the number and diversity of refuge and reproductive microhabitats for aquatic organisms was increased.

Actions to improve the vegetation cover.

Silvicultural works and elimination of exotic vegetation. These included cleaning up the vegetation by pruning and clearing and, in some cases, the removal of specimens in poor phytosanitary condition.
Restoration of riparian vegetation. Irregular corpses of native species were planted in bands parallel to the riverbed and singular trees were protected.

Recovery and improvement of hydrological continuity

Trofa sediment removal. The homogenization of the flow regime in the Manzanares River and the increase in erosion and discharges from several wastewater treatment plants in the basin of the stream generated an island of sediments, which was partially removed, seeking a suitable slope for the bed to recover the original width of the river.
Lowering slab station gauging. The foundation slab of the Mingorrubio gauging station was removed to lower the current bed level and eliminate the backwater produced upstream.
Installation of a fish ramp at the El Pardo weir to facilitate the migration of native fish species.

Morphological recovery of the riverbank space.

Removal of fill and smoothing of slopes, improving accessibility to the river.
Restoration of the “Las Madroñeras - Freijo” ravine. The Madroñeras ravine, a complex of gullies, had been used for aggregate extraction at the time of the construction of the El Pardo dam.
Sustainable public use and interpretation of nature
Installation of a pedestrian walkway to recover the communication between both banks, eliminated with the demolition of the old gauging station of Mingorrubio.
Adequacy of roads and trails of different typologies. The paths affected by the earthworks were adapted to guarantee the safety of users.
Interpretative material. Posters and signage. Information panels showing the main natural and/or cultural features of the river were installed. In addition, the network of trails and paths was signposted.

ACTIONS IN THE TROFA RIVER

Zone closed to wildlife.

Hunting closure. To minimize the causes of erosion, the area from where the stream crosses the railroad line to where it flows into the Manzanares River was enclosed.
Troughs - ponds. Since the enclosure restricts the use of part of the stream basin, it was considered necessary to install troughs outside the enclosure.
Enclosure at the confluence with the Manzanares River. At the confluence point, the fence that delimits “Monte El Pardo” suffered periodic breakage due to the flooding of the stream. A permanent structure was built to withstand the floods and allow the evacuation of large volumes of water and sand.

Raising of the bed and lateral reconnection

Installation of hydrotechnics. This facilitated land mobilization and slope smoothing, raising the bed, and enhancing the functionality of the floodplain, favouring the connection of vegetation with the water table. These techniques also contributed to sediment retention, vegetation recovery and the natural purification of water coming from the municipalities in the upper part of the basin.
Sediment traps. To contribute to the stability of the materials contributed to the earthworks, “fixed points” were established in the riverbed that, as sediment traps, produce a backwater upstream.

Restoration of riparian vegetation and undergrowth.

In the strip closest to the stream, deep-rooted ash trees were planted, and willows were staked, while in the areas farther from the stream, bushes, shrubs, and trees of species native to the area were planted.

Phytodepuration

High nutrient levels were detected due to the effluents reaching the stream. Macrophytes with high phytodepuration potential were planted, creating a biotope of interest for avifauna and amphibians.

GENERAL ACTIONS

Maintenance and conservation

Replacement of “marras”
Maintenance irrigation
Maintenance of paths
Sanitation of riparian vegetation
Ecological and environmental monitoring

During the following three years, the effect of the measures on the ecological state of the water body, the hydromorphological state, the state of the vegetation, etc., will be evaluated. The work already conducted in this regard has made it possible to design part of the actions to be conducted in phase 2 of the project.

Importance and relevance of the adaptation:

Enhancing Ecological Resilience:

Habitat Adaptation: The project directly addressed the adaptation of critical riverine habitats for local biodiversity. In the face of climate change challenges, such as extreme temperatures and altered rainfall patterns, the restoration of these habitats ensured the survival and prosperity of native species, both flora and fauna.
Water Resource Management: Adapting river management to expected changes in the flow regime due to climate change was critical to maintaining the ecological health of the river, preventing eutrophication and better managing water resources in the region.

Flood Risk Reduction:

Flood Control: The project increased the river's capacity to handle more intense and frequent flood events, an anticipated effect of climate change. This reduced the risk of flooding, which could have devastating consequences for both ecosystems and nearby human communities.

Water and Biodiversity Conservation:

Recovery of Natural Spaces: by restoring the river's natural continuity and morphology, the project facilitated the creation and conservation of wetlands that function as important reservoirs of biodiversity and as natural water retention systems. These spaces were essential to adapt to water scarcity and to maintain the necessary ecological cycles in a changing climate.

Additional Details

Stakeholder engagement:

Promoter administration: Directorate General for Water. Tagus Hydrographic Confederation (Ministry for Ecological Transition - MITECO).
Collaborating administrations: Directorate General of the Spanish Office for Climate Change (OECC), National Heritage, Madrid City Council, Autonomous Community of Madrid.
University: Escuela Técnica Superior de Ingeniería de Montes, Forestal y del Medio Natural (Universidad Politécnica de Madrid).
Research Centres: Centro de Estudios y Experimentación de Obras Públicas (CEDEX).
Other entities envolved: "Asociación Vecinal de El Pardo" and "Asociación Vecinal de El Pardo en Común".

After the drafting of the project, coordinated by the Directorate General for Water and the Tagus Hydrographic Confederation of the Ministry for Ecological Transition (MITECO), with the collaboration of the Spanish Office for Climate Change of the MITECO, work began on the fluvial restoration of this section of the Manzanares River to achieve its environmental recovery and adaptation to climate change.

About the surrounding population, several meetings were held with neighbourhood associations to explain the planned actions and resolve doubts about the implementation. During the months of March and April 2017, a study was conducted to ascertain the assessment of the Manzanares River restoration project, the perception of the environment, characterise the visitors, and find out the influx and habits of the visitors.

A project website was created as one of the initiatives that favoured the dissemination of the project, allowing the progress of the works and the results obtained to be known.

A project information stand was set up next to the Somontes car park, where at weekends the public was informed about the river restoration work to be conducted.

Project interest:

The aim was for this project to serve as a pilot example of a measure for adapting to climate change by promoting the management of the river environment.

The river restoration project for the Manzanares River in El Pardo (Madrid) included a series of actions and some guidelines for the development and management of the area, with the aim of improving the state of the river and its immediate surroundings and guaranteeing its conservation and enhancement.

Given the great potential of the Manzanares river for public use and environmental education, due to its proximity to the city of Madrid, it was considered of great interest to carry out the restoration of the river in the surroundings of the Real Sitio de El Pardo, thus contributing to the improvement of the ecological state of the river and the recovery of this space of great environmental value.

In addition, in this first phase of the project, pilot actions were incorporated, which were subsequently monitored, allowing an initial evaluation and redefinition of the actions for subsequent phases. Phase 2 is expected to begin in the coming months, and in this phase these pilot actions have already been included in a more generalised manner, once their effectiveness has been verified, which could also be exported to other scenarios with similar problems.

Success and limiting factors:

One of the key aspects of the project was to improve the public's perception of the problems that threaten the river ecosystem and that result in these visible symptoms: dry vegetation, deepening and narrowing of the riverbed, areas of dammed water... The project area is one of the areas most used by the people of Madrid for leisure activities, and from the outset it was considered that informing the population was a priority to ensure the acceptance and success of the project. To this end, several information days were held during the drafting phase, and during the execution phase explanatory posters were installed, continuing with these information tasks as the project progressed.

Another of the fundamental issues was the coordination and collaboration between administrations. This was an area where the competencies of several administrations converged, and achieving good coordination was a determining factor in achieving the project's objectives. Thanks to the involvement of all of them, the project was executed according to plan, and it is foreseen that in the coming months, once the environmental processing is completed, phase 2 of the project will begin, which extends from the confluence with the Trofa stream to the San Fernando Bridge (Madrid).

Budget, funding and additional benefits:

This project was financed by the PIMA ADAPTA Plan (Environmental Action Plan for Adaptation to Climate Change in Spain), with an investment of €2,151,798.62.

The costs of this action consisted of the cost of project implementation. As for the benefits, these were those derived from the improvement achieved in the functioning of the rivers, serving the objective of compliance with the requirements of the Water Framework Directive, and guaranteeing the provision of goods and services to society. This included a reduction in expected flood damage and a significant reduction in the costs incurred annually for the conservation of the public water domain.

Legal aspects:

The project was framed within the Hydrological Plan of the Spanish part of the Tagus Hydrographic Demarcation, complying, among the proposed hydromorphological measures, with those relating to the reduction of the pressures of regulation elements thanks to the improvements in river continuity and restoration it included.

On the other hand, this section of the Manzanares River was identified as one of the areas of significant potential flood risk, and the project complied with the measures contemplated in the Flood Risk Management Plan for the Spanish part of the Tagus Hydrographic Demarcation.

The river restoration came into compliance with the objectives of the Water Framework Directive and the Floods Directive.

In addition, this section was within the Special Area of Conservation of the "Manzanares River Basin" and, in turn, was a Special Protection Area for Birds "Monte de El Pardo", with a Management Plan that included among its Guidelines on the conservation of Natural Resources several measures aimed at the fluvial restoration of its water bodies and the improvement of the riverside vegetation.

The project was submitted for environmental assessment and was the subject of a Resolution of the Secretary of State for the Environment, by which the Environmental Impact Report of the project was formulated, which included all the environmental requirements of the project (Resolution of 10 October 2016, of the Secretary of State for the Environment, which formulated the environmental impact report of the project River restoration of the Manzanares River in the surroundings of the Real Sitio de El Pardo (Madrid), BOE no. 259 of 26 October 2016).

Implementation time:

November 2016 – November 2019

Reference Information

Contact:

General Directorate of Water. Sub-Directorate General for Integrated Management of the Public Hydraulic Domain.