HS5.2.2

The transboundary aquifers are of utmost importance to sustain water supply in present days. The exploitation of these aquifers has to be only in a sustainable and rational way, in order to sustain the quantity and quality of the aquifers' groundwater. A transboundary aquifer is developed in karstified limestones between the lakes Great Prespa (shared between North Macedonia, Albania, and Greece ) and Ohrid (shared between North Macedonia and Albania). The karst mountainous area is characterized by the presence of numerous crevices, sinkholes, as surface forms, and caves, canals, etc., as underground forms. The elevation of Prespa Lake is about 153 m higher than that of Ohrid Lake, and the two lakes represent a common hydraulic system, protected by international conventions. Prespa Lake is characterized by a continuous decline in water level during the last decades. The transboundary karstic aquifer is a complex system, discharging through numerous karstic springs (e.g., Saint Naum, Tushemisht, etc.), and operating as a hydrocollector and hydroconductor between the lakes. The aquifer is vulnerable to external pollution, as well as to climate changes affecting the lakes’ ecosystems. Agriculture, livestock, and tourism are the main activities in the wider area.

The DPSIR (Driver-Pressure-State-Impact-Response) model, adopted by European Environmental Agency, was applied in GIS context, in order to study and analyze the main causes of pressures and to optimize the measures for integrated aquifer management. In addition, the aim of DPSIR technique is the correlation of the driving forces and pressures with the present status of the complex hydraulic system and finally to optimize the aquifer management. The major driving forces that affect the Prespa-Ohrid basin are the irrigated agriculture, the livestock, the tourism development, and population growth. The main pressures are the overexploitation of the aquifer, water pollution, and the decline of the water level of Lake Prespa.

Based on the results of DPSIR, a set of measures and appropriate policy responses are proposed. Finally, DPSIR is a valuable tool for local authorities and administrators in order to plan and implement strategies for integrated and sustainable management of the transboundary karst aquifer and its dependent ecosystems.

How to cite: Voudouris, K., Kiri, E., Reci, H., and Kolokytha, E.: Application of DPSIR method for integrated management of the transboundary aquifer in Prespa-Ohrid basin, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-419, https://doi.org/10.5194/egusphere-egu21-419, 2021.

Land subsidence produced from the exhaustive groundwater exploitation is a phenomenon that has critical effects in many areas around the world, especially in water-scarce areas. Among the objectives of the RESources managEment by integrating eaRth observation deriVed monitoring and flOw modelIng Results (RESERVOIR) project (GA nº 1924), one of them is the identification of the stakeholder requirements and groundwater conceptual model setup for several pilot sites. The present work is related with the Alto Guadalentín aquifer study case (SE Spain). To achieve the mentioned objective, a workshop was organized and a large number of potential stakeholders from local authorities, environmental agency, water supply companies, NGOs, insurance companies and regulatory institutions were summoned. During the workshop most important RESERVOIR activities were presented. Once the workshop was finished, a questionnaire that proposes the evaluation of the main problems in the area related to the groundwater management was sent to all participants. Results disclose that 55% of stakeholders consider that the principal problem in the Guadalentín aquifer is the overexploitation, and 50% of stakeholders regard that the lack of managerial, planning, and technical instruments are the most relevant issues to be addressed and solved. In more detail, the survey reveals that the monitoring coverage is inadequate in terms of: (a) groundwater levels monitoring (50%); (b) water quality measurement frequency (40%); and (c) water quality measurement points spatial distribution (55%) Even that area is reporting the highest subsidence rates in Europe, this problem is not considered as the most important, probably because affects agricultural areas and minimal damages were reported. Finally, 90% of the stakeholders have previous knowledge about groundwater modelling, but only 45% within them have information about the specific applications for which the model is employed in the Alto Guadalentín aquifer. Main conclusion leads to confirm that the measurements taken in the past have proved to be insufficient to reverse the state of the overexploitation of the aquifer. From this, some management measures must be strengthened, and several technical tools should be introduced to improve the groundwater management. On the other hand, improving the use of the numerical model of the Alto Guadalentín aquifer to support decision-making, as well as, updating the model by coupling it with the subsidence phenomenon through the definition of subsidence risk indexes would lead to a sustainable and holistic groundwater management.

How to cite: Navarro-Hernández, M. I., Guardiola-Albert, C., Valdes-Abellan, J., Ezquerro, P., Pla, C., Meisina, C., Bru, G., and Tomás, R.: Stakeholder perception for groundwater management from a subsidence point of view in the Guadalentín Valley (Spain), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9958, https://doi.org/10.5194/egusphere-egu21-9958, 2021.

    Groundwater is the largest freshwater resource available on Earth, and many coastal regions are depending on groundwater as a primary freshwater source. For example, in Busan and Incheon, two of the largest coastal cities in South Korea, 5.7% and 7.0% of freshwater uses are from groundwater while only 1.8% is from groundwater in Seoul, the capital of the country. Globally, groundwater availability is diminishing primarily by population increase, and especially in coastal regions, this problem is exacerbated by overexploitation and seawater intrusion, which causes groundwater contamination and further reduces its availability. Here, we view the groundwater system and its management for sustainability as a complex problem that is associated with various social, economic, and environmental factors. By adopting the City Blueprint Approach (CBA), which has been used extensively for assessing the sustainability of integrated water management of numerous cities on the globe, we identify water management factors that potentially have direct and indirect links and feedbacks with groundwater variables. We selected Busan and Incheon as case studies for coastal cities that are facing the risk of groundwater salinization by seawater intrusion. This study aims to 1) assess City Blueprint (CB) of selected coastal cities, 2) identify major factors for coastal groundwater management through correlation analysis, and 3) suggest management options regarding identified factors for sustainable groundwater management of the study areas. Our results on CB indicate that the groundwater quality and quantity of the selected cities are currently in ‘good’ status. Also, from the correlation analysis, we identified heat risk and freshwater scarcity as the major factors that potentially can affect groundwater quantity. For groundwater quality, the factors of voice and accountability, regulatory quality, and rule of law and control of corruption, most of which had not been explicitly considered for groundwater management, were identified as the major factors. Some of these factors were assessed from ‘little concern’ to ‘very concern’ for both cities. These results indicate that, regarding the linkages between groundwater variables and other factors in concern, more actions beyond environmental factors should be taken for sustainable groundwater management. This study helps to understand how non-conventional factors could contribute to coastal groundwater, and can provide extensive options for sustainable groundwater management.

Acknowledgement: This research was supported by the Development program of Minimizing of Climate Change Impact Technology through the National Research Foundation of Korea (NRF), funded by the Korean government (Ministry of Science and ICT) (NRF-2020M3H5A1080775).

How to cite: Lee, K., Chang, S. W., and Park, J.: Assessing groundwater management sustainability of coastal cities by utilizing the City Blueprint Approach, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13840, https://doi.org/10.5194/egusphere-egu21-13840, 2021.

Coastal agricultural watersheds face complex problems of water quantity and quality.  In many coastal agricultural watersheds, the problems arise from: i) the limited use of surface water, ii) the excessive groundwater abstractions for irrigation, and iii) the over-fertilization practices for crop yield magnification. These complex and interrelated problems may be studied by using an integrated modelling system of surface water and groundwater able to simulate the processes regarding the quantity and quality of water. In this study, water resources management and agronomic scenarios are developed for the evaluation of the quantity and quality of the groundwater system of the semi-arid coastal agricultural Almyros Basin, in Thessaly, Greece. The historical and current unsustainable irrigation and fertilization practices, the groundwater abstractions, and the limited use of surface water reservoirs have caused a large water deficit of the aquifer system, groundwater nitrate contamination and seawater intrusion, resulting in severe degradation of water resources. Land use change and agronomic scenarios, as well as, reservoir operation scenarios, are combined and simulated using an integrated modelling system.   The Integrated Modelling System consists of coupled models of: surface hydrology (UTHBAL), groundwater flow (MODFLOW), agronomic practices and nitrate leaching (REPIC, an R-ArcGIS based EPIC model), nitrate transport (MT3DMS), and seawater intrusion (SEAWAT). The models have been calibrated and validated against observations/measurements of various variables, e.g. groundwater table levels, crop yields, nitrate concentrations and chloride concentrations.  The feasibility of the simulation of the various scenarios have been, also, evaluated with indices of Crop Water Productivity (CWP), Nitrogen Use Efficiency (NUE) and Economic Water Productivity (EWP).

How to cite: Lyra, A., Loukas, A., Voudouris, K., and Mylopoulos, N.: Evaluation of water resources management and agronomic scenarios using an integrated modelling system for coastal agricultural watersheds: The case of Almyros Basin, Thessaly, Greece, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13137, https://doi.org/10.5194/egusphere-egu21-13137, 2021.

KEYWORDS: Saltwater intrusion, Geochemistry, Groundwater extraction  

ABSTRACT: With an average annual rainfall of 800-1150 mm/year, the Binh Thuan province is one of the driest places in Vietnam. The quantity and quality of groundwater play a significant role in the agriculture, aquaculture development and daily life of the local communities. In 2012, the national center for water resources (Nawapi, 2012) delineated the seawater intrusion extent in Binh Thuan based on the total dissolved solids (TDS) content of water samples taken from shallow boreholes. The threshold of 3g/L and 1.5g/L were exceeded in the estuaries of the Luy, Long Song and Ca Ty rivers. In recent years, the prolonged droughts combined with the sea level rise and the over-extraction of groundwater during the dry season increased dramatically the seawater intrusion process especially in the estuaries of the province.

The geochemistry of groundwater in the Luy River catchment was studied to investigate the contamination of the aquifers and identify the processes taking place. From 1991 to 2015, 98 water samples had been taken from the wells in the area in both dry and rainy seasons. 71% of the water samples were fresh while 21% and 5% were lightly saline and moderately saline respectively. In summer 2020, 110 new water samples from both shallow and deep wells were collected in the Luy river catchment in wells from 3m to 40m. The TDS values are ranging from 105 to 23080 mg/L and can be classified into 4 groups: freshwater (48%), slightly saline (40%), moderately saline (8%) and very saline (4%). The samples show that the seawater intrusion expands not only horizontally at shallow depth along the river but also deeper down the aquifer in most of the study area, what is also confirmed by geophysical data. Freshwater samples were mostly collected at a depth lower than 10m. The chemical composition of water samples were analyzed showing evidence of seawater intrusion, but also the occurrence of freshening processes within the study area. Together with the presence of saltwater at larger depths, this points towards a situation more complex than previously thought. Saltwater intrusions are likely not only related to interaction with the river estuary, but also to the presence of fossil saltwater in the aquifer, and to groundwater pumping and irrigation practices.

REFERENCES

NAWAPI. 2012. Hydrogeological mapping at scale 1:50000 in Ninh Thuan and Binh Thuan provinces. In Vietnamese. 

*Corresponding Author. Email: Linh.PhamDieu@UGent.be

How to cite: PHAM Dieu, L., Cong Thi, D., Thibaut, R., Paepen, M., Segers, T., Dang Thi, H., Ho Huu, H., Nguyen, F., and Hermans, T.: Geochemical characterization of groundwater and saltwater intrusion processes along the Luy River, Binh Thuan, Vietnam, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-906, https://doi.org/10.5194/egusphere-egu21-906, 2021.

The progressive population growth in coastal areas constitutes a huge worldwide problem, particularly relevant for coastal aquifers of the Mediterranean basin.

The increasing use of groundwater and the effect of seawater intrusion makes the study of coastal aquifers extremely relevant.

There are various measures, practices, and actions throughout the world for managing groundwater when this natural resource is subject to salinization risk.

This research focused on the seawater intrusion, classifies the different practical solutions protecting the groundwater through salinization mitigation and/or groundwater salinity improvements along the Mediterranean Area.

The literature review was based on 300 papers, which are mainly international journal articles (76%). The rest includes conference papers (11.8%), reports and theses (7%), and books or chapters of a book (25%).

Three main schematic groundwater management approaches can be distinguished for the use of groundwater resources at risk of salinization.

The engineering approaches pursue locally the discharge increase avoiding or controlling the salinity increase.

The most recent experiences of tapping submarine springs were realized using underground concrete dams, tools shaped like a parachute or tulip, or a fiberglass telescopic tube-bell, especially in the case of karstic aquifers.

The current widespread form of the engineering approach is to address the issue of groundwater exploitation by wells.

More complex solutions use subhorizontal designs. Subhorizontal tapping schemes were realized using tunneling and/or boring in combination with wide-diameter wells or shafts.

These works include horizontal drains or radial tunnels bored inside the saturated aquifer, shafts excavated down to the sea level with radial galleries or drains realized together with weirs to improve the regulation of the discharge rate and of salinization. Application of these solutions in areas where a thin fresh groundwater lens floats on the saline groundwater, as in the case of narrow and highly permeable islands, can yield high discharges, thus causing a very low drawdown over very wide areas. These solutions were successfully applied in Malta Islands.

The discharge management approach encompasses at least an entire coastal aquifer and defines rules concerning groundwater utilization and well discharge.

A multi-methodological approach based on monitoring networks, spatiotemporal analysis of groundwater quality changes, and multiparameter well logging is described in Apulian karstic coastal aquifers (Italy). The core is the definition of the salinity threshold value between pure fresh groundwater and saline groundwater mixture. The basic tools were defined to be simple and cost-effective to be applicable to the widest range of situations.

The water and land management approach should be applied on a regional scale. The main choice for this approach is pursuing water-saving measures and water demand adaptation. A multiple-users and multiple-resources-water supply system model was implemented to evaluate the effectiveness of the increasing maximum capacity of the surface reservoir and managed aquifer recharge in Apulia, a semi-arid region of Southern Italy.

How to cite: De Giorgio, G., Zuffianò, L. E., and Polemio, M.: Groundwater and salinization risk: tapping works and management experience in the Mediterranean Area, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9991, https://doi.org/10.5194/egusphere-egu21-9991, 2021.

The Belgian coastal phreatic aquifer is mostly characterized by salty/brackish pore water at shallow depth. The eolian dunes delimiting the sandy beach are one of the few locations where fresh potable water can be found. The drinking water demand of the coastal region is putting high pressure on these water resources, especially during the touristic summer season. Also, the dryer summers that were faced over the last years increase the need for solutions.

At Oostduinkerke, the Intercommunale Waterleidingsmaatschappij van Veurne-Ambacht (IWVA) combines the pumping of groundwater in the dunes with artificial surface (since 2002) and underground recharge (since 2014) for more sustainable exploitation. The infiltrating water is treated effluent from a nearby sewage treatment plant (Aquafin, Wulpen). The recharge in the dunes reduces the risk of attracting salty/brackish water from the North Sea and the lower lying polder area in the South and allows for more stable groundwater levels, especially around the infiltration lake.

To assess the efficiency of the managed aquifer recharge project, we collected electrical resistivity tomography (ERT) data offshore, on the beach, and part of the dunes. Marine continuous resistivity profiling (CRP) were performed during both low and high tide. The latter provide a good overlap with the land ERT. The profiles were collected in front of the IWVA site, as well as, to the west and east, to assess the lateral variation of the salt-freshwater distribution in the aquifer. Based on the electrical resistivity distribution, we are able to identify the patterns of submarine groundwater discharge (SGD) and saltwater intrusion in the study area.

The infiltration of treated wastewater directly affects the piezometric levels of the surrounding area. Before the exploitation started in the dunes (1947), the natural freshwater heads were higher west of the infiltration area, due to the presence of a shallow clay layer (Vandenbohede et al., 2008). The higher hydraulic heads are also seen on recent groundwater models (Lebbe, 2017), but despite the larger hydraulic gradient in the West, the pore water resistivity seems to be higher in front of the IWVA site based on our data. Also, the zone of discharge is found below the low water line in front of the infiltration site, while it is seen on the beach to the west and east. We can assume that the SGD flux is largest in front of the recharge site (Paepen et al., 2020). Therefore, SGD seems to be enhanced by artificial recharge in this area. Further research is needed to validate this.

Lebbe, L. (2017). Grondwatermodel van de geplande wijzigingen in waterwinning Sint-André. Opdrachtgever: Intercommunale Waterleidingsmaatschappij van Veurne Ambacht (IWVA).

Paepen, M., Hanssens, D., Smedt, P. D., Walraevens, K., & Hermans, T. (2020). Combining resistivity and frequency domain electromagnetic methods to investigate submarine groundwater discharge in the littoral zone. Hydrology and Earth System Sciences, 24(7), 3539-3555.

Vandenbohede, A., Van Houtte, E., & Lebbe, L. (2009). Sustainable groundwater extraction in coastal areas: a Belgian example. Environmental Geology, 57(4): 735-747.

How to cite: Paepen, M., Walraevens, K., and Hermans, T.: Effect of artificial recharge on submarine groundwater discharge: a Belgian case study, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7495, https://doi.org/10.5194/egusphere-egu21-7495, 2021.

Groundwater development in coastal aquifers of southwest Bangladesh is challenged by both natural and anthropogenic activities resulting in a landward migration of marine waters and increase in the risk of seawater intrusion. In some cases, infiltration of dissolved evaporite salts in the shallow aquifer and presence of connate water in the deep aquifer (DA) are the sources of groundwater salinity other than modern seawater intrusion. A detail investigation of these sources is imperative for a sustainable development and management of coastal aquifers. This work investigates the hydrogeochemical processes affecting groundwater chemistry by interpreting conventional plots, ionic delta, HFE-diagram, stable isotopes, and geochemical modelling. There are three hydrogeological units delineated in this area: upper shallow aquifer (USA) (<100 m bgl), lower shallow aquifer (LSA) (100-200 m bgl) and DA (below 200 m bgl). The hydrochemistry data reveal that the median values of total dissolved solids of the aquifers have a decreasing trend from top to bottom: USA with 7012 mg/l, LSA with 2622 mg/l and DA with 787 mg/l. Sodium is the dominant cation in all waters. The dominant anion in DA is HCO₃^-, but in shallow aquifers Cl^-. The main water type based on the classification of Stuyfzand (1989) is the brackish to saline NaCl type in the shallow aquifers. The Br^-/Cl^- ratio and relatively enriched δ¹⁸O values in these NaCl waters suggest an origin derived from evaporate dissolution. Reverse cation exchange during intrusion, replacing Na⁺ with Ca²⁺, results in CaCl and CaMix water types. These waters infiltrate into the LSA. The water in the DA is mainly fresh NaHCO₃+ type which originated by cation exchange from infiltrating fresh water. Ca²⁺ was replaced by Na⁺ due to the cation exchange, the water became undersaturated with respect to calcite and secondary calcite dissolution caused elevated bicarbonate concentrations. Near the present-day shoreline and at larger depths, the NaHCO₃+ type water mixes with connate water, increasing salinity. The enriched δ¹⁸O values in the DA suggest an origin in a warmer climate, implying that this water has infiltrated a long time ago, much farther inland, probably during the Holocene climatic optimum. It can be expected that the salinization of the shallow aquifers will continue to increase if evaporite deposition and seasonal flooding occur. For a sustainable use of the groundwater resource in this coastal region and to prevent from even further worsening of water quality in its shallow aquifers, it is advised to develop future exploitations in the DA.

Key words: Groundwater chemistry; Stable isotope; Evaporite; Cation exchange; Calcite dissolution.

How to cite: Sarker, Md. M. R., Camp, M. V., Hossain, D., Islam, M., Bhuiyan, Md. A. Q., Ahsan, Md. A., Bennett, G., and Walraevens, K.: Understanding the Hydrogeochemical Evolution of Groundwater in Coastal Aquifers of Southwest Bangladesh, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9767, https://doi.org/10.5194/egusphere-egu21-9767, 2021.

Saltwater intrusion in coastal aquifers is one of the most challenging and worldwide environmental problems, severely affected by human activities and climate change. It represents a threat to the quality and sustainability of fresh groundwater resources in coastal aquifers. Saline water is the most common pollutant in fresh groundwater which can also compromise the agriculture and the economy of the affected regions. Therefore, it is necessary to develop engineering solutions to restore groundwater quality or at least to prevent further degradation of its quality.

For this purpose, the goal of the Interreg Italy – Croatia MoST (MOnitoring Sea-water intrusion in coastal aquifers and Testing pilot projects for its mitigation) project is to test possible solutions (such as underground barriers, cut-off walls, recharge wells and recharge drains) against saltwater intrusion properly supported by field characterization, laboratory experiments, monitoring of hydrological parameters, and numerical models.

This works shows the preliminary results of an ongoing modelling study carried out for a coastal farmland at Ca’ Pasqua, in the southern part of the Venice lagoon, in Italy. A three-dimensional finite-element density-dependent groundwater flow and transport model is developed to simulate the dynamics of saltwater intrusion in this lowlying area. The model is used to assess the potential effects of a recharge drain recently established at 1.5 m depth along a sandy paleochannel crossing the organic-silty area. The goal of the intervention is to mitigate the soil and groundwater salinization by spreading freshwater supplied by a nearby canal. The beneficial consequences of the recharge drain should be enhanced by the higher permeability of the paleochannel.

How to cite: Travaglino, M. E. and Teatini, P.: Density-dependent 3D FE modelling of a recharge drain to mitigate saltwater contamination at the Venice farmland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2897, https://doi.org/10.5194/egusphere-egu21-2897, 2021.

Hydrostratigraphic setting and groundwater dynamics in high salinized low-lying farmlands at the southern margin of the Venice Lagoon

¹ Institute of Geosciences and Earth Resources, National Research Council, Padova, Italy

² Institute of Marine Sciences, National Research Council, Venice, Italy

³ Department of Geosciences, University of Padova, Padova, Italy

⁴ Regione Veneto - Soil Defence Regional Directorate, Venice, Italy

⁵ Land Reclamation Authority Adige Euganeo, Este-Padova, Italy

* Corresponding author: chiara.cavallina@igg.cnr.it

Key words: salt-water intrusion, groundwater dynamics, coastal plain, Venice

The coastal plain at the southern margin of the Venice lagoon is a low-lying territory, which is the result of river diversions, channeling, and hydraulic reclamation that took place over the last centuries. The mechanisms controlling the exchanges between surface water and groundwater progressively shifted from natural to artificial ones. Presently, most of this territory lays at ground elevation up to 3 m below the mean sea level and a complex network of drainage channels and pumping stations regulates the depth of the water table both to prevent flooding-waterlogging and to allow irrigation. Being at the lagoon margin and next to the sea, the aquifers of this area are heavily affected by salt-water intrusion that jeopardizes the farmlands productivity and specifically damages the crop yield. Focusing on the geology and stratigraphic architecture of the first 25-meters of the subsoil, in which the shallow aquifers are included, the sedimentary record consists in Pleistocene alluvial deposits and Holocene deposits. The latter show the typical transgressive wedge including prodelta, littoral and back barrier depositional environments. Specifically, the Holocene littoral sands contain the unconfined aquifer, which is almost continuous along the whole coastal strip.  Sedimentary bodies as paleo-channels and remnants of littoral ridges, commonly hosting unconfined aquifers, are present all over coastal plain. Pleistocene alluvial deposits contain the first locally confined aquifer.

Several past studies have revealed the complexity of freshwater-saltwater exchanges imposed by the concomitance of various forcing factors. However, a specific study on the dynamic of saline contamination of the groundwater is still missing. We present here the preliminary results of an ongoing research aimed to characterize the groundwater dynamics and disentangle mechanisms that control groundwater salinity in the shallow aquifer system of the low-lying farmlands adjacent to the southern Venice lagoon margin and the Brenta-Bacchiglione river mouth. The results of detailed analyses from various perspectives (based on sedimentary cores, continuous hydrological and hydrogeological data, geophysical surveys) are properly integrated to describe the dynamics in the shallow aquifer system. Particular attention is payed to the hydro-morpho-stratigraphic system in relation to the mechanisms driving the freshwater-saltwater exchanges. This research is developed in the frame of the Interreg Italy-Croatia project MoST (Monitoring Sea-water intrusion in coastal aquifers and Testing pilot projects for its mitigation), which addresses to improve the quality and sustainability of the human management of water resources in coastal areas.

How to cite: Cavallina, C., Bergamasco, A., Boaga, J., Donnici, S., Surian, B., Tosi, L., Zaggia, L., Bassan, V., Gabrielli, G., Socin, R., Artuso, A., Frison, L., and Gasparetto-Stori, G.: Hydrostratigraphic setting and groundwater dynamics in high salinized low-lying farmlands at the southern margin of the Venice Lagoon, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13280, https://doi.org/10.5194/egusphere-egu21-13280, 2021.

Sustainability Indices can be useful to quantify objective groundwater management strategy outcomes, particularly across regional scales and when local groundwater budget data is not readily available. Previous studies have used performance indicators to evaluate surface water systems, and their application to groundwater is expanding to address water availability concerns. Here, a groundwater sustainability index (GSI) is computed across coastal aquifer systems in Portugal and California using reliability (REL), resilience (RES), and vulnerability (VUL) performance indicators. Aquifers in these Mediterranean climate zones are susceptible to inter-annual and seasonal water storage fluctuations linked to climate forcings and drought. Piezometric levels in the selected aquifers in Portugal (Leirosa-Monte Real and Campina de Faro) and California (Napa and Santa Barbara), spanning a period from 1989 to 2019, are analyzed using a point-wise approach to provide an index-per-piezometer. The computation exposes that the resilience indicator is heavily influential in setting an aquifer system's overall sustainability classification. However, the most significant output from the GSI is a clear indication of how well (or poor) a specific aquifer can withstand drought conditions that occur in both California and Portugal throughout the 30-year span of this study. Lastly, comparing indices with different priorities (performance indicators), such as sustainability and exploitive use (including the Water Framework Directive’s River Basin Management Plan’s Water Exploitation Index (WEI+)) can help identify aquifer systems that may need an immediate policy, conservation, or mitigation interventions, and others that may be self-sustaining for a longer period of time. The authors would like to acknowledge the financial support FCT through project UIDB/50019/2020 – IDL.

How to cite: Malmgren, K. and Neves, M. D. C.: Computing a Groundwater Sustainability Index for coastal aquifers in Portugal and California to foster sustainable groundwater management, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15728, https://doi.org/10.5194/egusphere-egu21-15728, 2021.

Groundwater represents an important source of drinking water for 25% of the population in the province of Quebec (Canada) and for 80% of its rural population. The deployment of the Quebec Groundwater Observation Network (Réseau de suivi des eaux souterraines du Québec – RSESQ) since the start of the millennia provides important data on the dynamics of piezometric heads throughout southern Quebec. This study aims to use the wealth of available groundwater data available to better understand the resilience of groundwater resources to changes in meteorological and hydrological conditions. The study area is located between the St. Lawrence River and the Canada-USA border, and between the Quebec-Ontario border and Quebec City (36,000 km²). Available data consist of groundwater level time series from 81 observation wells (2000-2018; 43 in confined aquifers, 15 in semi-confined aquifers and 23 in unconfined aquifers), total flow rates from 179 hydrometric stations (1960-2017), and meteorological data from a spatially interpolated 10 km x 10 km grid (1960-2017). Statistical analyses (Mann Kendall and Sen’s slope) were used to understand if groundwater levels and flow rates are declining or rising, what is their short-, medium- and long-term memory and what are the geomorphological, land use, and climate controls of this reactivity. The results show that groundwater levels since 2007 exhibit statistically significant negative annual trends for most observation wells. Since 1960, river flow rates, total precipitation and air temperature all show significant increases. Trends calculated on five-year sliding windows confirm that groundwater levels and river flow rates are significantly correlated to the climate indices Southern Oscillation index (SOI), NINO-3 and Pacific Decadal Oscillation index (PDO). Autocorrelations of flow rates and groundwater level data indicate that rivers and aquifers have a short hydrological memory rarely extending beyond the hydrological year. Cross-correlations of flow rates and groundwater levels with temperature show high correlation coefficients with a lag of up to 60 days, indicating a season-long effect of temperature changes. As expected, cross-correlation analysis of the two data sets with precipitation shows smaller correlation coefficients and a shorter reaction time (10 days). Standard deviations of daily groundwater levels are significantly higher in shallower wells and in wells where groundwater levels are closer to the ground. This confirms the presence of highly dynamic shallow aquifers reacting rapidly to surface processes.  Analyses are under way to test if spatially distributed parameters (e.g., geological setting, slope, land use) and well-related parameters (e.g.: depth, confined or unconfined) are explaining factors of trends and variations in groundwater levels and flow rates. One key observation from this study is that the RSESQ is highly valuable to understand groundwater dynamics and should be maintained on a long-term horizon. This detailed analysis has allowed to identify external influences (e.g., pumping) on some observation wells that do not reflect natural conditions and could be removed from the observation network. Recommendations also include the need for new observation wells in specific locations to improve the representativity of groundwater flow conditions in the study area.

How to cite: Vu, T. A., Larocque, M., Gagné, S., and Bourgault, M.-A.: Reactivity of southern Quebec aquifers to meteorological and hydrological conditions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13242, https://doi.org/10.5194/egusphere-egu21-13242, 2021.