Integrated hydrogeological models
for sustainable aquifer exploitation and management in a climate change scenario.
GIRBESÒS project
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People in charge of the innovative practice :
Carme Barba – carme.barba@upc.edu
In this sense, it is necessary to develop tools that allow evaluating different management strategies and that in turn minimize the impact on the river, water ecosystems and the effects on third parties. These tools must integrate all the conditions to which the aquifer is subjected, including climate change. Thus, GHS has developed an integrated management model of the water resources of the Besòs which reproduces the different hydrogeological units.
On the other hand, the 3D model developed takes into account the different contouring conditions that include flows, natural recharge extractions etc. It is remarkable how the model makes explicit the river as an active part in the model and not as a contour parameter.
Responsible entity
El Underground Hydrology Group (GHS) of the Universitat Politècnica de Catalunya (UPC) is a research group consolidated by the Generalitat de Catalunya. It is one of the world’s leading research groups in the field of hydrogeology, working on the characterization and modelling of aquifers for more than 30 years. Its mission is to promote research, teach and transfer knowledge to society.
The GHS is made up of 8 senior professors/researchers, 3 post-doctoral researchers and around 25 PhD and Master’s students. The main lines of research addressed by the GHS are:
- Hydrogeological modelling
- Hydrogeochemical modelling
- Transport processes in the porous medium
- Co2 storage
- Artificial recharge of aquifers
- Coastal aquifers and groundwater discharge into the sea
It is worth emphasizing the role of the GHS in the knowledge, monitoring and modelling of local hydrogeological resources, in particular, of the aquifers of the Llobregat and Besòs delta. The models developed by the GHS in these basins integrate in great detail the geological structures of the environment and are able to faithfully reproduce the interactions of groundwater with the different elements that condition its flow (e.g. underground infrastructures, river courses, rainfall dynamics, aquifer exploitations, etc.).
The GHS collaborates with different organizations, both in the public sector (administrations, universities) and private, carrying out research and development projects.
Detailed explanation
Although the aquifers associated with the Besòs River were intensively exploited during the first half of the nineteenth century and part of the second, their use was never planned or carried out in a sustainable manner. The poor quality of the water bodies due to indiscriminate exploitation and a lack of control, forced the abandonment of a large part of the uses subterráneos en la cuenca.
With the creation of the ACA and its plans of actions and measures, the recovery of the quality and quantity of groundwater resources has been progressively recovering. The improvement of water quality in the Besòs basin and the restoration of piezometric levels compared to the 1970s is a fact that has once again put the Besòs as a reference point in the future planning of the ACA.
In order to guarantee the supply of the population, the ACA plans to increase extractions in the Besòs aquifer in order to produce drinking water to supply Barcelona and its metropolitan area.
In this sense, it is necessary to develop tools that allow evaluating different management strategies and that in turn minimize the impact on the river, water ecosystems and the effects on third parties. These tools must integrate the effects on the hydrological cycle that climate change is already evidencing, and that will worsen in the future (increase in evapotranspiration and decrease in effective recharge, greater occurrence of extreme climatic phenomena, reduction of flows in rivers and consequent increase in the concentration of pollutants, sea level rise and advancing marine intrusion). Knowing these effects and finding tools to alleviate or adapt to them is fundamental for the survival of natural and human systems.
In this sense, the GHS has developed a model of integrated management of the water resources of the Besòs. Integrated hydrogeological models are those that reproduce the behavior of underground flow and solute transport taking into account the interaction of the river with the aquifer and the presence of underground infrastructures that may cause an impact on the aquifer.
This integrated model is based on a 3D geological model, which reproduces the different hydrogeological units in the field of study, thanks to the review and interpretation of approximately 800 soundings. The 3D geological model includes the different underground infrastructures that intercept the aquifer, such as the different metro tunnels and the tunnel of the high-speed line as it passes through Montcada i Reixac.
The hydrogeological model has been developed with the free code MODFLOW 6 that solves the flow equation by the method of integrated finite differences. This approach is ideal to be able to generate unstructured meshes, which allow a better adaptation to the contours, a greater discretization before singular objects in the terrain and the definition of different layers with different hydrogeological properties.
The different layers of the model are zoned based on different transmissivity values, according to the bibliographic values and according to the established geological model.
On the other hand, the model takes into account the different boundary conditions (lateral flows, pumped extractions, drainage in tunnels, natural recharge) and makes explicit the river as an active part in the model and not as a mere contour condition.
The model settings across the scope are considered very good, since the average square error at most control points is between 0.2 and 2 meters. This fact becomes even more relevant if one takes into account that the hydrogeological system of the Besòs delta has a very large sedimentological complexity.
The good adjustments of the model make it a very powerful tool to be able to simulate future scenarios and plan the different management strategies under a context of climate change. The simulations may include predictions made by the Intergovernmental Panel on Climate Change (IPCC), i.e. sea level rise, reduced flows in surface courses or rising temperatures, which has a direct effect on evapotranspiration and natural recharge of the aquifer.
Future outlook
In recent years, administrations and local entities are making great efforts to achieve the ecological restoration of the Besòs River. More recently, the ACA has specified, in its recent Action Plan for the period 2022-2027, its intention to make a more intensive use of the water resources of the Besòs. The integrated management model developed by the GHS is presented as a planning tool capable of providing administrations with objective arguments for decision-making, guaranteeing the good management of water resources, adapting it to the challenges posed by climate change.
Institutional setting
The Catalan Water Agency (ACA), a public company of the Generalitat de Catalunya, is the entity that plans and manages the integral water cycle in Catalonia, always under the basic principles of the Water Framework Directive. The ACA, through its action plans and measures that are renewed every six years, sets the guidelines to guarantee the current and future supply and the quality of the resource at source. In addition, the ACA, through these action plans, ensures wastewater sanitation and the protection of water bodies and dependent ecosystems.
The current hydrological planning and its program of measures for the period 2022-2026 are especially focused on favoring mitigation and adaptation to climate change, ensuring the guarantee of supply while favoring the good state of water ecosystems.
Part of the measures of this planning cycle aim to finance projects in the Besòs river basin, especially focused on managing its underground water resources.
Although the ACA has the ultimate responsibility in the fulfillment of the measures, various organizations participate locally or transversally so that they develop optimally. In the case of the Besòs basin, bodies such as the Consorci del Besòs, the Consorci Besòs-Tordera, the water supply concessionaires, Barcelona Cicle de l’Aigua SA, the Diputació de Barcelona, the Metropolitan Area of Barcelona, etc. are involved in different parts of the management of the water cycle and in the preservation of the basin.
Geographical setting
The basin of the river Besòs has an area of just over 1000 km2. It extends from the northern slope of the Cordillera Litoral to the southern limit of the Plana de Vic, occupying part of the Vallès-Penedès tectonic trench, to the Mediterranean Sea, where it forms a small delta at the end of the alluvial plain.
The Besòs basin is formed mostly by alluvial and fluviodeltaic sediments of the ancient Quaternary and recent river terraces of the Holocene period. These quaternary materials are deposited on top of a plinth formed slates or Paleozoic granites in the river section, while in the deltaic zone they rest on a substrate of marls and pliocene clays.
The study area, in a regional context, is framed in the lower section of the alluvial basin of the Besòs River, from its confluence with the Ripoll River, through the Montcada Strait, to the delta and the mouth of the river (Figure 1).
Figure 1. Geographical location of the area under study, limits of the hydrogeological model and main interaction infrastructures. Source: GHS
The different sedimentary assemblages in the basin can be grouped into four hydrogeological units. From the Ripoll River to Sant Adrià de Besòs, there is a free aquifer, directly connected to the river with a mostly influential character. The materials are made up of clean gravels, sands and small silt-clay intercalations
In the delta area you can distinguish two more permeable levels, formed by sands and gravels, separated by a confining layer of lower permeability of prodelta deposits.
The transmissivities in the basin reach maximum values in the opening zone of the Strait of Montcada, with values close to 14000 m2/d.
The minimum values of this parameter would correspond to the sediments of the prodelta, being of the order of 10-2-10-3 m2/d.
Historical overview
The use of water from the Besòs basin does not in itself imply a novel strategy, since the exploitation of this aquifer has been carried out since the early twentieth century. In fact, thanks to the extraction of groundwater from both the Llobregat and the Besòs and Llano de Barcelona, the industry of the city experienced a great development throughout the last century. It is estimated that extractions for industrial uses and to supply the population reached their maximum value in the 1960s, with values close to 60 hm3 / year. However, with the migration of industry and due to the poor quality of groundwater due to pollution phenomena, underground resources in the Bajo Besòs and Llano area of Barcelona were no longer exploited so intensely. The levels of the aquifer were recovering with the cessation of overexploitation, so that, for years, they have been close to their natural level.
However, changes in land uses, and very specifically the phenomenon of urbanization in the second half of the twentieth century, have caused the progressive increase in levels to cause recurrent problems of filtration in underground infrastructures (garages, basements of buildings, tunnels, etc.). These drains reached maximum values during the nineties, with annual volumes of up to 10 hm3. Currently the case of Besòs is paradoxical: while on the one hand it is necessary to carry out pumping, drainage and exhaustion permanently to avoid affectations, on the other, this water is generally not used and ends up pouring into sewerage.
Evidence of benefits from implementation
Knowing the impact that climate change will have on the availability of water resources is essential to anticipate its effects and to be able to make a coherent planning to this framework. In turn, the model allows simulating scenarios in which mitigating measures are included to a possible increase in extractions or a possible decrease in the availability of water resources due to climate change. These mitigating measures have to do with the artificial recharge of aquifers, which allows recharging water from different sources (for example, river water or reclaimed water) thus increasing the available reserves.
Key points of the innovative method
- Modelo elaborado con código libre y de referencia a nivel mundial, que permite la implementación de malla no estructurada
- Herramienta muy útil para hacer planificación hidrológica y para la toma de decisiones
- Herramienta de adaptación al cambio climático
Acknowledgements
The innovative practice was suggested by Carme Barba (UPC). The development of this tool has been possible thanks to the participation and financing of the Barcelona City Council through the GiR-Besòs Project. The collaboration of Barcelona Cicle de l’Aigua, SA is also appreciated.
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