Recursos hídricos subterrâneos num aquífero em delta de Llobregat (Barcelona)

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 30^km2 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.