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Hydrologic connection and habitat improvement in the meanders of the lower course of the Arga River (Navarra)

Guillermo Cobos Campos/Fototeca CENEAM

Until the 1970s, the lower section of the Arga River, near its confluence with the Aragón, meandered through a wide floodplain, with intense fluvial dynamics. At the time, it was deemed necessary to carry out works to contain the river's floods, leading to its rectification and channelling in the section from the town of Falces to the mouth of the Aragón River.

By the mid-1980s, it was observed that the channelling was insufficient, and the river overflowed during some floods. Additionally, the shortening of the new route increased the flow velocity, causing serious imbalances and damage in this area of significant ecological interest.

These phenomena have worsened in recent years, due, among other factors, to the effects of climate change.

Case Study Description
Challenges: 

The project is being carried out within the framework of the National River Restoration Strategy, as part of the WATER line of the PIMA-Adapta Plan of the Ministry for Ecological Transition and the Demographic Challenge (MITECO). Its objective is the development of climate change adaptation projects in the public hydraulic domain, physically adapting bodies of water such as rivers, wadis, or wetlands.

The project, titled "Hydrological Connection and Habitat Improvement in the Meanders of the Lower Section of the Arga River (Navarra)," aims to restore the natural values of the lower course of the Arga River, which have suffered degradation over the last few decades as a result of its channelling through cuts and earthen mounds. These interventions led to the abandonment of old meanders and the partial disappearance of the riparian vegetation.

For this reason, the project seeks to continue the recovery of the Arga River's meanders, restoring their natural functionality and dynamics, reestablishing the longitudinal and transversal continuity of the river system, and reducing the risk of flooding. Additionally, the project aims to improve available habitats and facilitate the movement of associated fauna, such as the European mink (Mustela lutreola) and the otter (Lutra lutra), among other species. All of these actions are designed to be compatible with the human activities taking place in the area.

The project focuses particularly on the Soto Sardilla meander in the municipality of Funes, at the confluence of the Arga and Aragón rivers.

Objectives: 

The project "Hydrological Connection and Improvement of Habitats in the Meanders of the Lower Section of the Arga River (Navarra)" is being carried out in several phases. The first phase concluded in 2017 and involved actions in the old Soto Sardilla meander of the Arga River, near its confluence with the Aragón River, in the Municipality of Funes (Navarra), covering about 2 km in length. The objectives were:

  • Opening the channel at the exit of the meander
  • Improving water quality in the meander by removing the accumulated sludge from an old spill
  • Recovering the floodplain by removing breakwaters at the confluence of the Arga and Aragón rivers
  • Protecting slopes through specific actions
  • Naturalizing intervention areas and improving river habitats for the European mink, through reforestation compatible with agricultural crops and poplar cultivation
  • Creating wetlands and islands through irregular excavations in the ground

The second phase was included in the PIMA Adapta 2017 Plan, with work starting in November 2017 and extending until 2020. The main goal of this phase has been to continue the work initiated in phase 1 while incorporating new actions aimed at restoring the natural functionality and dynamics of the Arga River, in a way that remains compatible with human activities in the area. The scope of action for this phase coincides with that of phase 1, focusing on the confluence of the Arga and Aragón rivers and the Soto Sardillas meander.

The key works in phase 2 included:

  • Improvement of water quality in the meander by continuing the removal of accumulated sludge, completing the work started in phase 1
  • Floodplain recovery by removing the fill material deposited during the channelling works, continuing the phase 1 efforts
  • Restoring an old meander that had been converted to agricultural use, by removing the fill and constructing a channel that reconnects the old Arga riverbed with the Aragón River
  • Naturalizing the intervention areas by planting native riparian species
  • Constructing two wetlands adapted to the biological needs of the European mink, in addition to the three created during phase 1
  • Channelling the Arga River downstream of the Funes urban area and setting back defence dikes to protect at-risk elements, such as the industrial estate
  • Replacing affected services, such as ditches, roads, and the Las Mesicas weir and park
  • Complementary actions to enhance public engagement with the newly created spaces through the design of itineraries and the publication of informative materials about the actions

With phases 1 and 2 completed, the third phase will focus on the following objectives:

  • Reconnecting the entrance of the Soto Sardillas meander with the current course of the Arga River
  • Improving water quality in the Soto Sardillas meander
  • Restoring longitudinal continuity in the Soto Sardillas meander
  • Reconnecting the outlet of the Soto Sardillas meander with the current course of the Arga River

The planned actions are located in the Soto Sardillas meander and on the land between the start of this meander and the current Arga River course, covering approximately 2.5 km, entirely within the municipality of Funes (Navarra), just downstream of the urban area.

The works in this third phase include:

  • Hydraulic connection between the Arga River and the Soto Sardillas meander
  • Restoring longitudinal continuity of the meander by improving the permeability of existing obstacles
  • Complementary actions to enhance and integrate the works
Adaptation measures implemented in the case study: 
Structural/physical: Engineering alternatives and options for built environments
Structural/physical: Ecosystemic options
Solutions: 

The planned actions are located at the confluence of the Arga and Aragón rivers and in the old Soto Sardilla meander, part of the Arga River, covering approximately 2 km. This section runs through the municipality of Funes, immediately downstream from the urban centre, situated in the southeast of the province of Navarra. The project is divided into three phases: the first has been completed, the second is currently in execution, and the third is in the drafting stage.

1- Actions carried out in phase 1:

  • Opening of the channel at the outlet of the Soto Sardilla meander
  • Recovery of the floodplain in the areas surrounding the channel opening and at the Arga-Aragón confluence
  • Improvement of water quality in the meander by removing part of the sludge from old discharges
  • Naturalization of intervention areas and improvement of habitats for the European mink
  • Replacement of affected roads

2.- Actions in execution in phase 2:

  • Improvement of water quality in the meander
  • Floodplain recovery
  • Naturalization of intervention areas and habitat improvement for the European mink
  • Complementary actions to replace affected services

3.- Actions being drafted in phase 3:

  • Hydraulic connection of the Arga River at the entrance to the Soto Sardilla meander
  • Restoration of longitudinal continuity of the meander by improving the permeability of current obstacles
  • Complementary actions for the enhancement and integration of the works
Importance and relevance of the adaptation: 

The measures implemented in the project aim to provide the river ecosystem with greater long-term resilience to cope with disturbances that are intensifying and worsening as a result of climate change, and consequently to maintain its capacity to provide ecosystem services.

Given the challenges outlined, the various measures implemented are essential to achieving these objectives.

The improvement of the channel morphology (opening the Soto Sardilla meander, removal or setback of protection and defence structures) and the floodplain (removal of poplar groves and lowering the land level), aimed at increasing drainage capacity and flood mitigation, contribute to reducing the damage caused by floods, both now and in the future, especially considering the forecast that these events will occur with greater frequency and intensity.

The improvement of the riparian structure (naturalization and revegetation of the intervention areas), water quality (removal of mud, reforestation), and morphology helps to maintain suitable habitats for fauna of conservation interest. This is further complemented by the creation of specific habitats, such as wetlands for the European mink (Mustela lutreola).

Additional Details
Stakeholder engagement: 

The execution of the project is an example of administrative coordination, as although it is financed by MITECO (funds from the PIMA Adapta plan (OECC) and the General Directorate of Water (DGA)), the collaboration of the Government of Navarra and the City Council of Funes is essential for its execution. Without their involvement, this project could not have been developed.

The project is also supported by an important process of public participation involving all social agents and stakeholders in the area, through various dissemination actions and guided tours. All dissemination efforts are being developed in collaboration with the Government of Navarra, through the public company Gestión Ambiental de Navarra, and the City Council of Funes.

Among the dissemination actions are:

  • Planting days carried out with primary school students from public schools in Funes and Villafranca (Navarra), aimed at raising awareness and involving the local community in the river restoration and meander reconnection project being developed in the lower section of the Arga.
  • Guided tours of the works under the title "Looking at the river with different eyes."
  • Informative exhibition at the Casa de la Cultura de Funes.
  • A video edition by the Ebro Hydrographic Confederation and MITECO titled "Arga, the canal that became a river again" to publicize the project. It premiered at the summer cinema in Funes and has since been shown on various occasions during conferences and dissemination activities. The video is currently available on the websites of the aforementioned bodies.

All the works are subject to exhaustive environmental control and monitoring, carried out by the environmental body of the Autonomous Community of Navarra. The results are presented to the Environmental Monitoring Commission, created in compliance with the Resolution on the environmental assessment of the project. This commission meets periodically and includes representatives from the Autonomous Community of Navarra and the General Administration of the State, through the Ebro Hydrographic Confederation and the General Directorate of Water of MITECO.

Project interest: 

The actions described represent a novel approach to flood risk management, compared to traditional methods, by expanding the river space and restoring it through measures that also contribute to improving existing riparian habitats and creating new ones. These measures are serving as a test bed and demonstration case, with the aim of replicating them in other areas of the basin.

Additionally, the project is studying the effects of climate change in the Arga basin, particularly focusing on premature snowmelt and its relationship with the extraordinary flood episodes that have occurred in this basin over the past decade.

Regarding habitat improvement and creation, in addition to the actions aimed at creating wetlands and refuges for the European mink, it is worth highlighting the prospection of freshwater naiads typical of the Ebro basin, both in the Arga and Aragón rivers and in the Soto Sardillas meander, in order to study and inventory these populations.

Success and limiting factors: 

The floods of recent years, particularly in winter 2017 and spring 2018, have demonstrated the improvement in the flood situation in the municipality of Funes. The affected areas and the damage caused have been significantly reduced thanks to the expansion of the river space achieved through the works.

A key factor in achieving this objective has been the derigidization of the confluence of the Arga and Aragón rivers, facilitated by the removal of the breakwater protection. Additionally, the lowering of the land adjacent to the channel, after the removal of existing poplar plantations, has allowed for better flow lamination during flood situations.

At the same time, in this confluence area, a comprehensive improvement of the river ecosystem has been achieved, leading to the recovery of the habitat for the European mink, along with a reduction in its primary threats and an increase in the recurrence of floods.

Budget, funding and additional benefits: 

The project as a whole has an approximate budget of more than €9,000,000, to be applied in its three phases, with funds from the PIMA Adapta plan (OECC) and with funds from the General Directorate of Water (DGA) of the Ministry for Ecological Transition (MITECO).

The first phase, already executed, has had a budget of € 2,172,583.11, broken down into the following items:

Floodplain Recovery

€603,016.27
Improving habitats for the European mink

€283,960.12
Naturalization of the areas of intervention:  
  • Sludge extraction

€731,484.32
  • Environmental regeneration with plantations

€265,073.92
Corrective and preventive measures of environmental impact (includes hydromorphological monitoring and flood risk) €181,215.88
Slope protection

€3,050.08
Photographic and audiovisual tracking €65,000.00
Waste management €417.65
Health and Safety €39,364.87
 
The second phase, currently in execution, has a budget of € 6,139,662.03, distributed according to the following items:
 
Extraction of nitrate-contaminated sludge from the meander

€938,945.01
Realization of the weir for the outlet connection with the meander €45,686.79
Increase of the drainage section and river territory, revegetation in recovered areas

€1.565.060,40 
Execution of new setback motes, stabilization with bioengineering and revegetation

€564,913.64
Complementary actions:  
  • Restoration of affected services, restoration of recreational areas and Itinerary mink

€912,491.73
  • Recovery of specific habitats of the European mink

€907,858.55
  • Restoration of river habitats of conservation interest through revegetation

€470,387.04
Update of the SNCZI (National Flood Zone Mapping System)

€21,000.00
Hydromorphological monitoring

€140,000.03
Corrective measures for environmental impact €343,426.20
Waste management

€15,812.03
Health and Safety

€57,080.61

Finally, the third phase is currently being drafted, contemplating the connection of the Soto Sardilla meander with the main channel of the Arga, with the remaining budget available for its execution.

Legal aspects: 

This action has been declared of general interest and is part of the Plan to Promote the Environment for Adaptation to Climate Change in Spain (PIMA-Adapta), the National River Restoration Strategy and the Flood Risk Management Plan of the Ebro River Basin District approved by the Government by Royal Decree 18/2016.  of January 15.

Implementation time: 

The first phase had an execution period of 16 months, from November 2016 to March 2018. The second phase proposes an execution period of 36 months, from November 2017 to November 2020.

The third phase, which is being drafted, does not yet have a pre-set horizon of temporality.

Reference Information
Contact: 
  • Mónica Aparicio Martín, Head of MITECO Area
  • Sub-Directorate General for Integrated Management of the Public Hydraulic Domain
  • Email: maparicio@miteco.es
  • Phone: 915975541
Websites: 
Sources: 
  • Project for the hydrological connection and improvement of habitats in the meanders of the lower section of the Arga River (Navarre). Phase 1.- Annex No. 3: characteristics of the actions. 19 pp.
  • Project for the hydrological connection and improvement of habitats in the meanders of the lower section of the Arga River (Navarre). Phase 2.- Annex No. 3: characteristics of the actions.  30 pp.
  • LIFE Nature Project. - Ecosystem management of rivers with European mink. 16 pp.
  • Life-Gerve Newsletter 01 November 2006. Information on the ecosystem management of rivers with European mink. 12 pp.