Ground water resources in a Llobregat delta aquifer (Barcelona)
Ground water
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People in charge of the innovative practice :
Enric Queralt – equeralt@cuadll.org
The continuous exploitation of the hydrogeological resources of the aquifer of the Llobregat delta has reduced piezometric levels and caused saline intrusion. The Catalan Water Agency together with the community of Users of the Llobregat Delta have promoted and developed multiple actions to improve the quality and quantity of the resources of the delta aquifer.
The recharge rafts are a set of rafts that integrates the sedimentation raft and the infiltration raft, they are works similar to wetlands. In them it is possible to improve the quality of the water before being infiltrated. The water that passes through the rafts comes from a secondary channel diverted from the Llobregat River.
Overexploitation favored the entry of seawater into the aquifer. The proposed solution to address the problem was a hydraulic barrier. The project was divided into two phases, the first began by injecting 50% of reclaimed water and 50% water from the network in 4 injection wells, quickly went on to inject 100% of reclaimed water from the Baix Llobregat WWTP. The second phase has not yet been completed and an injection flow of 15,000 m3/day is expected after the expansion of the Baix Llobregat WWTP.
Both actions require specific geographical conditions. While sedimentation ponds can be a more accessible and reproducible action in various environments, the barrier against saline intrusion requires a very specific problem and a greater demand for investments. Both are replicable proposals in the SUDOE region, but it is important to evaluate their suitability of these actions in the face of the installation of other initiatives that address the problem of quality and quantity of water resources.
Responsible entity
The “Agència Catalana de l’Aigua” (ACA) collaborates with the Community of Users of the Llobregat Delta (CUADLL) in the management of groundwater flows in a strategic area for the supply of the metropolitan athea such as the fluvio-deltaic aquifer of the Llobregat delta.
ACA is the public company of the Generalitat of Catalonia that is responsible for the planning and management of water in accordance with the basic principles of the Water Framework Directive. It seeks to guarantee the supply, availability of water and its quality at source
This action plan also promotes the sanitation of wastewater through more than 500 sewage treatment plants in service and the protection and conservation of water bodies and associated ecosystems.
CUADLL is a public law corporation attached to the ACA, subject to the provisions of water regulations and its own regulatory instruments (statutes and regulations).
They are members of the CUADLL, and are part of this, all users with the right to the use of groundwater whose catchments are located within the delta area, andare represented, mainly, the uses of supply, industrial and agricultural.
The objectives of CUADLL are:
- Directly manage the common interests of water use and its police.
- Inform on its own initiative, at the request of the Basin Agency or other agencies and entities of the Administration in the files that affect the water concessions, in those of work and in those referring to the request for new concessions within its territorial scope.
- Propose to the Hydraulic Administration, at its request or on its own initiative, the measures it deems appropriate in relation to its field of competence.
Manage the services delegated to you by the ACA.
Detailed explanation
Recharging ponds
The recharge action in Sant Vicenç dels Horts is not the only one that takes place in the Llobregat valley. In the towns of Castellbisbal, Santa Coloma de Cervelló recharging rafts were also installed.
The water is derived from the Llobregat River by a secondary channel managed by a manual gate that directs the flow to the sedimentation pond where the materials are deposited. This raft has a wetland-like behavior reducing turbidity and sedimentable materials. A pipe connects the sedimentation pond to the raft where the infiltration takes place.
The first objective of the facilities was to increase the amount of groundwater. This objective evolved by observing that the improvement in the quality of infiltrated water varied depending on the conditions.
In this context, a reactive layer was built to evaluate the impact of the degradation reactions that occur naturally between the pollutant and the soil in the vadosa zone.
The facility does not operate continuously, due to the need to maintain water quality.
Pauses also contribute to lessening the clogging effect.
Barrier against saline intrusion
To stop the advance of marine intrusion into the aquifer, ACA built a positive hydraulic barrier through 14 wells into which treated reclaimed water is injected. The objective of the hydraulic barrier is to prevent the entry of water from the sea into the aquifer and the deterioration of its quality.
First phase:
The injection water for the hydraulic barrier initially consisted of 50% reclaimed water from the Baix Llobregat WWTP while the remaining 50% was mains water. This model was quickly switched to 100% reclaimed water use due to the environmental and economic impact of using mains water for recharging. (F. Ortuño et al. 2009).
Four injection wells were drilled and equipped, which are located about 1,500 m from the coast, arranged parallel to it and separated from each other about 300 m.
Figure 2: Location of wells and WWTP del Prat. Retrieved from
The injection is carried out in the wells 24 hours a day. Since its inception, about 1,100,000m3 of reclaimed water has been injected into the aquifer. The injected water comes from the Baix Llobregat WWTP where additional advanced treatments of ultrafiltration, reverse osmosis (50% of the water) and UV disinfection are carried out, producing a total of 2,500 m3 / day of reclaimed water.
Second phase:
The second phase of the hydraulic barrier aims to inject into the aquifer 15,000 m3 / day, which is the minimum flow that is estimated necessary according to numerical models to completely stop marine intrusion. This phase foresees the expansion of the advanced tertiary effluent water treatment plant of the WWTP, the drilling and equipment of 11 new injection wells and 16 new piezometers, and the execution of all the necessary pipes.
The expansion of the water treatment plant is already in the testing phase, which will allow the obtaining of 15,000 m3/day of reclaimed water from the tertiary for injection in the second phase. The 11 new injection wells have already been drilled and equipped with cleaning pumps.
The 16 new control piezometers are already perforated and have also been equipped with automatic systems.
Institutional setting
ACA, attached to the Department of Climate Action, Food and Rural Agenda of the Generalitat of Catalonia, emerged from the merger of the Sanitation Board, the Water Board and the General Directorate of Hydraulic Works.
To alleviate the water deficit and recover the good status of the body of groundwater, and in accordance with the mandates derived from the Water Framework Directive, ACA carries out a series of actions agreed with the Community of Users of the Llobregat Delta, the Metropolitan Entity and the General Water Society of Barcelona (F. Ortuño et al. 2009).
Geographical setting
The lower valley of the Llobregat River and the delta are located southwest of the Metropolitan Area of Barcelona (AMB). The alluvial valley extends over an area of 30km2 and the delta at 80 km2. The system is composed of aquifers of high transmissivity, the aquifers are fed by the infiltration of rain, although they mainly feed on the infiltration of the river and agricultural infiltration.
The lower valley of the Llobregat is a free alluvial aquifer formed by several fluvial terraces that, when reaching the delta, in Cornellà, is divided into two, separated by a wedge of silt, one of shallow depth that covers a large part of the delta, and another deep, under the wedge of silt, which is therefore confined, and which is the important aquifer of the delta. (Custodio, 2007)
The system is of great importance due to its strategic nature for the population of the AMB (4 million inhabitants) (Fouillac, 2009).
The main aquifer of the Llobregat Delta has a generalized piezometric decline below sea level since the early 70s, as a result of overexploitation. This has led to the emergence and advance of marine intrusion into the aquifer, also facilitated by the excavations of the impermeable layer of contact between the aquifer and the sea in the port, which has led to a progressive worsening of the quality of groundwater. (Custodio, 1987; Custodio et al. 1976; Custodio et al. 1989; Iríbar, 1992; Iribar, 1997)
Historical overview
The first antecedents of aquifer recharge may have to be traced back to the Arab era, such as the Alpujarran lighthouses (Fernández Escalante et al, 2005) or the system of dikes and boqueras (Díaz Marta, 1989). The first modern managed recharge facilities date back to 1969 in the alluvial areas of Besós and Llobregat (Valdés, 1992). Another remarkable experience was carried out in the Llano de la Palma (Mallorca), using a mixed system based on irrigation with wastewater and injection of surpluses, when they exist, in wells drilled in very permeable calcarenites.
The Geological and Mining Institute of Spain (IGME) in collaboration with other organizations has been carrying out pilot experiments of artificial recharge since 1984, among which the following should be highlighted: three infiltration ponds in the Oja River (La Rioja); five infiltration ponds in the plain of Guadix (Granada); and a pit-type raft in Carmona (Seville).
In Barcelona, artificial recharge experiments have been carried out for many years to combat saline intrusion, a consequence of the massive extractions of the twentieth century. The first recharging facilities were built in the early 50s in the alluvial of the Besòs River and in the 60s in the alluvial aquifer of the Llobregat River (Custodio & Llamas, 1983; Valdés, 1992; Martín-Alonso, 2003). This last action, managed by the General Water Society of Barcelona, has recharged in some periods up to a maximum of 20 hm3 / year in wells located in the Delta with surplus water from the Water Treatment Plant of Sant Joan Despí. The recharge has been complemented by the scarification of the Llobregat riverbed, crossing the riverbed to favor the infiltration of water (Pérez-Paricio, 1999).
Evidence of benefits from implementation
Recharge ponds have a positive impact on improving the water quality of the aquifer while increasing the amount of resource available. However, these actions require large permeable areas to develop and a precise control of the quality of the water applied.
The low cost of the raft infrastructure and maintenance make the construction a sustainable element. Efficiency is variable, depending on floods throughout the year.
The hydraulic barrier against saline intrusion shows at the observation points of the aquifer a decrease in electrical conductivity (decrease in the concentration of chloride, sodium, potassium, calcium …) demonstrating that it prevents saline intrusion. The barrier is oxidizing in a reducing medium, the consequences it can have on the aquifer are being analyzed. The injection of water from tertiary treatment has generated an increase in the concentration of nitrates (5.8 mg/l).
Replication potential in SUDOE region
The replicability of both activities will require geographical conditions similar to the delta area and the Llobregat River.
Sedimentation and infiltration ponds are applicable without great difficulties or investments in areas that have large permeable extensions.
In the case of the hydraulic barrier, the problem must be very concrete and severe to make a technological and operational investment of this caliber. Other options may need to be considered before opting for this type of prevention given the costs mentioned.
Both actions constitute important alternatives to the management of water resources among the various existing options, for example, using reclaimed water to meet uses that do not require quality water, but exploit water from the aquifer. Another alternative, also applied in Barcelona, is the use of desalinated water that generates enough water volume to satisfy the uses, reducing extractions and allowing the recovery of the piezometric level that would simultaneously lead to an improvement in the quality and quantity of groundwater, given, among others, by the reduction of marine intrusion.
Future outlook
Although recharge ponds (MAR) are a viable option in many exploited aquifers, whether in coastal or inland areas, involving an effective reuse of reclaimed water, hydraulic barriers are technological developments that require a very well defined problem and whose resolution satisfies the investments made. Demand reduction, reuse or desalination options may be more viable options than a hydraulic barrier in the future management of groundwater resources.
Key points of the innovative method
- Meet the challenge of water management in an overexploited area with limited resources.
- The availability of water allows to satisfy local activities avoiding conflicts between users.
- ACA and CUADLL lead multiple actions to address the problem of availability and quality, efficiency and innovation must be valued with historical perspective.
Acknowledgements
This innovative practice was suggested by João Simão Pires of Portuguese Water Partnership (PWP).
References
- Agència Catalana de l’Aigua (s/f) Sobre la ACA Consultado 15 de abril del 2022 https://aca.gencat.cat/es/laca/sobre-laca/
- Agència Catalana de l’Aigua (s/f) Comunidades de regantes o usuarios de agua Consultado 15 de abril del 2022 https://aca.gencat.cat/es/laigua/usos-de-laigua/comunitat-dusuaris-daigua/
- CUADLL (S/f). ¿Qué es la CUADLL?. Consultado el 15 de abril del 2022 https://www.cuadll.org/pages/cuadll
- F. Ortuño Gobern, J.M. Niñerola Pla, J.L Armenter Ferrando, & J. Molinero Huguet. (2009). La barrera hidráulica contra la intrusión marina y la recarga artificial en el acuifero del Llobregat (Barcelona, España). 235–250.
- Fouillac, A. M., Grath, J., & Ward, R. (2009). Groundwater Monitoring (P. Quevauviller, Ed.). John Wiley & Sons. https://books.google.at/books?id=R0a706yOnfEC
- Custodio, E. (2007). Fundación Centro Internacional de Hidrología Subterránea. In Real Acad. Ciencias Exac. Fis. Nat (Vol. 15, Issue 3).
- Custodio, E. 1987. Sea-water intrusion in the Llobregat delta, near Barcelona (Catalonia, Spain). Groundwater Problems in Coastals Areas, UNESCO. Studies and Reports in Hydrology nº 45. UNESCO, París: 436-463.
- Custodio, E., Cacho, F., Peláez, M.D., García, J.L. 1976. Problemática de la intrusión marina en los acuíferos del delta del Llobregat. II Asamblea Nacional de Geodesia y Geofísica. Seción de Ciencias Hidrológicas. Barcelona.
- Custodio, E., Manzano, M. Y Jones, B. (1989). Saline wáter in Llobregat delta aquifers, Barcelona, Spain. 28th International Geological Congress. Washington D.C. Abstracts: 3.288-3.289.A
- FERNÁNDEZ ESCALANTE, A. E., GARCÍA, M. y VILLARROYA, F. (2005): The careos from Alpujarra (Granada, Spain) an historical example of previous to XIII century artificial recharge system applicable to the XXI century. Characterisation and inventory ISMAR 5 proceedings 5th International Symposium on Management of Aquifer Recharge. Berlin 2005.
- DIAZ MARTA, M. (1989): Esquema histórico de la ingeniería y la gestión del agua en España. Revista de OP nº 13 España y el Agua, tomo 1 otoño 1989 pp 8-23.
- VALDES, J. L. (1992): Experiencias De recarga artificial en los acuíferos del río Llobregat y rio Besós Aguas de Barcelona (AGBAR) Barcelona.
- Custodio E. y M. R. Llamas (1983). Hidrología Subterránea. Omega. Barcelona (2 Vol.) 2359 pp.
- Valdés, J.L. (1992). Experiencias de recarga artificial en los acuíferos del Río Llobregat y Río Besòs. Aguas de Barcelona (AGBAR), Barcelona.
- Martín-Alonso, J. (2003). Combined Use of Surface Water and Groundwater for Drinking Water Production in the Barcelona Metropolitan Area. Riverbank filtration: the future is now!. Proceedings of the Second International Riverbank Filtration Conference. Melin, G. (Ed.). September 16-19, Cincinnati, Ohio. National Water Research Institute. Fountain Valley, California
- Pérez-Paricio, A. (1999b). “Site description Cornellà, Spain.” Proyecto Europeo de Recarga Artificial de Acuíferos. Universidad Politécnica de Cataluña (UPC), Barcelona.
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