Modelos hidrogeológicos integrados

The GIRBESÒS project was born from the water need of the metropolitan area of Barcelona (AMB) and the possibility of exploiting the Besòs aquifer in order to supply the AMB. The project developed by the Underground Hydrology Group of the Universitat Politècnica de Catalunya GiRBESÒS addresses the problem of quantity and quality of the aquifer.

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.

1. Hydrogeological modelling
2. Hydrogeochemical modelling
3. Transport processes in the porous medium
4. Co2 storage
5. Artificial recharge of aquifers
6. 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.