In the 21st century, coastal basins in southern Europe face unprecedented pressure: overexploitation of aquifers, accelerated seawater intrusion, and the loss of ecological functionality. In the Campo de Gibraltar, particularly in the Algeciras area, the inland advance of seawater threatens both freshwater supplies for human and industrial use and the resilience of high-value ecosystems. According to data from the Guadalete-Barbate River Basin Authority, piezometric levels in certain aquifers have dropped by more than 10 meters over the past two decades, while salinity in critical points exceeds 2 g/L, above the threshold that compromises potability and agricultural use.
This project proposes a regenerative, technically advanced intervention to reverse that trend: hydrological restoration through managed aquifer recharge, physical control of saline intrusion, and optimization of existing water resources. The combination of hydraulic barriers, green infrastructure, and continuous monitoring systems aims not only to stop the advance of the saline wedge but also to gradually restore the hydrogeological balance. The impact is tangible: every cubic hectometer of freshwater infiltrated and stored acts as a shield against the irreversible loss of the region’s productive and ecological capacity.
The Campo de Gibraltar is an international hub for logistics, industry, and port operations. Securing its water future is not only an environmental issue, it is a matter of competitiveness, investment attraction, and social stability. This project fully aligns with the principles of additionality, intentionality, and traceability established by VWBA 2.0, with physical traceability ensured through piezometers and hydrogeological modeling, and digital traceability through georeferenced systems and third-party audits. In a global context where coastal water stress is intensifying, Algeciras has the opportunity to lead a replicable model for coastal aquifer restoration.
The main challenge in Algeciras is saline intrusion, caused by decades of groundwater abstraction exceeding natural recharge, exacerbated by reduced surface water inflows and sea level rise. This has led to a progressive deterioration in groundwater quality, increasing dependence on external sources and raising treatment costs. The dual risk is clear: loss of availability for priority uses and irreversible degradation of strategic aquifers.
The technical opportunity lies in combining nature-based solutions with hydraulic engineering measures to restore aquifer functionality. The project includes the construction of freshwater injection barriers, controlled infiltration zones through artificial wetlands, and the use of high-quality reclaimed water for recharge, aligned with WQBA standards to ensure that no contaminants are introduced. The initial estimated recharge volume is 1.5 hm³/year, with a projected reduction of saline intrusion by more than 60% within the first decade.
In the short term, the benefit will be a measurable improvement in water quality at key abstraction points and a reduction in electrical conductivity at the interface zone. In the medium and long term, the project is expected to restore storage capacity and improve the basin’s resilience to prolonged droughts. The model is scalable to other coastal basins in Spain and across the Mediterranean facing similar challenges.
The project is led by the local water operator, supported by technical experts in coastal hydrogeology, technology providers for real-time monitoring, and the oversight of an independent verification entity. For companies with strong ESG commitments and Water Positive strategies, this is a high-impact opportunity: investing in water security, protecting coastal ecosystems, and safeguarding the viability of a critical economic hub.
The project operates on three coordinated fronts, articulating a technical-operational strategy to identify, intervene, and restore the affected aquifer:
Remote detection and technical validation: A systematic mapping effort is carried out using multispectral satellite imagery (Copernicus Sentinel-2), infrared thermal sensors, and LIDAR-equipped drones. These tools help identify thermal depressions, surface moisture variations, and linear features indicating the presence of active or abandoned wells. The resulting geospatial models are validated on-site through inspections, geolocation of water intakes, and initial physico-chemical sampling.
Physical intervention: Prioritized wells are sealed technically by injecting bentonite slurries or polymer resins into confined layers, depending on soil type and depth. This operation includes mechanical cleaning, borehole profiling, and staged sealing to ensure hydraulic separation between layers. All procedures follow environmental permitting and are carried out under the protocols of the Hydrographic Confederation or competent authority. Each intervention is documented for traceability and auditing purposes.
Managed recharge zones: In areas where natural infiltration historically occurred or in undeveloped lands, artificial recharge areas are designed using green infrastructure. These include biofilters composed of siliceous sand, gravel, and native coastal vegetation that act as living filters. Infiltration is regulated using surface distribution systems such as swales or infiltration trenches, designed to maximize slow recharge during rainfall events while offering temporary retention and runoff control.
The project is implemented in five successive technical stages, with continuous and integrated development of measurement, control, construction, and verification activities. These stages are designed to ensure both volumetric water benefits and water quality improvements in accordance with VWBA A-5 and WQBA standards.
During the remote diagnosis phase (0–2 months), the target area is characterized using multispectral satellite imagery (Sentinel-2) and high-resolution aerial thermography. This stage allows the detection of thermal anomalies, surface moisture changes, and linear features on the terrain that may indicate the presence of active, semi-abandoned, or illegal wells. The data are processed using geostatistical analysis tools and overlaid onto GIS layers covering land use, hydrogeology, and existing infrastructure. Variables such as NDVI, SWIR reflectance, and surface temperature are measured, enabling the generation of a georeferenced inventory of hydrological risk points and the establishment of a spatial baseline.
In the field campaign and sampling phase (2–4 months), the information generated in the remote diagnosis is validated on-site. Multiparametric probes are used to measure electrical conductivity (EC), temperature, salinity, and groundwater level in situ. A representative set of groundwater samples is collected for laboratory analysis focusing on chlorides, nitrates, sulfates, turbidity, and heavy metals. Active and abandoned wells are documented with precise coordinates, and a hydrogeological risk index is created based on depth, vertical connectivity, vulnerability to saline intrusion, and proximity to water bodies or urban areas.
The intervention design phase (3–5 months) includes a tailored technical formulation for each well to be sealed: depth, sealing method (bentonite, cement grout, or resins), access logistics, regulatory requirements, and work schedule. Simultaneously, managed recharge zones are designed using hydraulic modeling of the terrain, native vegetation selection, soil conductivity analysis, and rainfall event simulations to estimate potential infiltration rates. Key performance indicators (KPIs) are established, and a governance model for the construction phase is formalized.
During the technical sealing and construction phase (6–10 months), the selected wells are hydraulically sealed to eliminate uncontrolled vertical flows between aquifer layers. Each intervention is documented with technical sheets, georeferenced photos, and traceability of materials used. At the same time, recharge zones are implemented using siliceous sand biofilters and native coastal vegetation, designed as artificial wetlands or infiltration trenches with runoff control. Infiltrated flows begin to be measured using pressure sensors in monitoring chambers, and piezometric dataloggers are installed.
The continuous monitoring phase (10–24 months) includes the operation of an IoT sensor network that records variables such as groundwater level, EC, aquifer temperature, rainfall, and infiltrated flow. This network connects to a digital platform for data visualization and analysis, enabling real-time validation of project objectives. Monthly sampling is conducted to assess the evolution of groundwater quality, compared against the established baseline.
In parallel, the WQBA approach quantifies water quality improvements as the percentage reduction of contaminants compared to their baseline concentrations. A valid improvement is one that is consistent, verified by external laboratory testing, and maintained over at least three consecutive quarters.
Both the VWBA and WQBA methodologies are verified through external audits by accredited entities. Results are reported on the Aqua Positive platform using unique Water Benefit IDs (VWB IDs), ensuring transparency, comparability, and reputational value for stakeholders.
This project was conceived as a technical, environmental, and strategic response to the increasing degradation of coastal aquifers in the Campo de Gibraltar. It addresses the legacy of historical overextraction, unsealed and uncontrolled wells, and the saline intrusion associated with declining water tables. Against the backdrop of industrial pressure, coastal urbanization, and climate vulnerability, this initiative seeks to restore the hydrogeological balance of the subsurface by detecting, intervening in, and repurposing critical points of water loss and contamination.
The central objective is to identify, characterize, and technically seal abandoned, illegal, or disused wells that serve as vertical conduits for saline water intrusion, while simultaneously establishing new managed recharge zones to enhance natural rainwater infiltration. These actions are developed through an integrated water benefit accounting approach, combining VWBA to quantify effective recharge and WQBA to assess groundwater quality improvements.
Implementation begins with remote diagnosis using multispectral imaging (Sentinel-2), thermal analysis, and GIS modeling to map surface anomalies and generate a georeferenced inventory of potential risk points. Field campaigns with multiparametric probes and water sampling are then conducted to validate and prioritize wells based on their impact on aquifer quality. A piezometric and physico-chemical baseline is also established.
Following this characterization, a technical intervention plan is developed, including individual hydraulic sealing of each well using materials such as bentonite grout or expandable resins, depending on depth and geology. Recharge zones are created using vegetated biofilters, infiltration trenches, and runoff management systems. These zones function as green infrastructure to restore the aquifer’s hydrological balance, with real-time monitoring of infiltration flows and groundwater levels.
The final phase includes continuous monitoring for at least 24 months, utilizing IoT sensors, external audits, and reporting on platforms like Aqua Positive. Each benefit is assigned a traceable VWB ID and independently validated for additionality and permanence. In doing so, the project not only restores an essential ecological function but also enables the generation of Positive Water Credits (CAPs), which can be integrated into corporate water offset schemes.
In essence, is a model for advanced hydrological restoration in coastal water-stressed areas, with potential for national and international replication, and strong added value in terms of water sustainability, climate resilience, and collaborative groundwater governance.
