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Most density-dependent flow and transport models assume homogeneity of natural aquifers, a strong simplification with respect to reality, while subsurface formations are known to have spatially variable properties (e.g. Freeze, 1975). Previous studies of saltwater intrusion in heterogeneous aquifers have considered mainly macro-scale geological structures, but the effects of local heterogeneities on density-dependent flow and transport are known to be highly affected by spatially correlated distributions of hydraulic conductivities (e.g., Dagan and Zeitoun, 1998, Prasad and Simmons, 2003, Li et al., 2022). Moreover, investigations have been performed mainly via numerical modeling and, to the best of our knowledge, only in one case numerical results have been compared with physical evidence from laboratory reproduction of a heterogeneous media (Koch and Starke, 2001).The present work describes the design and the realization activities developed to reproduce a controlled heterogeneous porous media in a laboratory flume, aimed at defining the influence of the hydraulic conductivity spatial variability on the density-dependent transport in coastal phreatic aquifers.The sandbox measures 500 cm long by 30 cm wide by 60 cm high, with 3 cm thick plexiglass walls. Two tanks are located upstream and downstream of the sandbox, with volumes of approximately 0.5 m3 and 2.0 m3, respectively. The upstream tank is filled with fresh-water and is continuously supplied by a small pump, providing fresh-water recharge. The downstream tank is filled with salt-water, previously prepared by adding salt to fresh-water till a proper density is reached, and it represents the sea. In both tanks the level is maintained constant via two spillways, whose height can be adjusted. The discharge through the downstream spillway can be measured.The flume has been used in previous works (Bouzaglou et al., 2018, Crestani et al., 2022), but here the homogeneous porous media has been substituted by three different nominal size ranges of glass beads, equal to 0.3-0.4, 0.4-0.8 and 1.0-1.3 mm respectively, organized in 250 cells, each of size 20x30x5 cm3 to reproduce a prescribed statistical anisotropic structure (Figure 1).Figure 1- Sandbox 3D view from upstream (left side) to downstream (right side)After a preliminary analysis carried out by constant head permeameter tests on each glass beads nominal size range, the hydraulic characterization of the whole heterogeneous formation has been developed considering the filtration process that affects different thicknesses of the aquifer (10, 20, 30, 40 cm) forced by three upstream-downstream head differences (2, 4 and 6 cm).During the saltwater intrusion experiment a water level difference upstream - downstream of 2 cm has been maintained for 8 days, introducing two separate drought periods (about 8 and 10 hours) at the end of the second and of the third days respectively.The findings from the heterogeneous media characterization and the seawater advance-retreat phenomenon are discussed in comparison with the results of a numerical model.This study has been co-funded by the Interreg Italy–Croatia CBC Programme 2014–2020 (Priority Axes: Safety and Resilience) through the ERDF as a part of the projects MoST (AID: 10047742) and SeCure (AID: 10419304).

In the Treviso province (Veneto, Italy) most of the drinking water (nearly 60 %) is supplied from wells located in the northern piedmont area, where agricultural activities are developed using chemical plant protection products (chemical PPPs). In this area the aquifer interested by the groundwater extraction is unconfined, making the subsurface water resource intrinsically vulnerable to any PPP or PPP residue (metabolite) leaching from the agricultural soil to the groundwater table, and raising concerns about the consequences of a possible groundwater contamination on the health of the local inhabitants.To protect the drinking water resource, in 2019 the Veneto Region provided a technical framework for the definition of the wellhead protection areas (WHPAs, Resolution 1621) in accordance with the EU directives 2000/60 and 2006/118, related to the establishment of safeguard zones for the water bodies used for drinking water supply. In the WHPAs the use of PPPs is only allowed when accounting for the vulnerability of the groundwater and the well extracting water for human consumption. To define the vulnerability of wells supplying drinking water, a procedure that considers the tridimensional behavior of a possible contaminant is suggested, taking into account the mobility of the chemical species across the vadose zone, the total amount of PPPs applied on the soil, and combining the probability of contaminant infiltration with the groundwater pathlines reaching the well.An application has been developed in the piedmont area of the Treviso province where a geospatial analysis of the vine-specific PPPs sales data identified over 30 WHPAs potentially affected by the PPPs use. The 3D vulnerability assessment couples the position of the vulnerable WHPAs retrieved from the geospatial analysis with 1) the data related to the infiltration capacity of agricultural and not-agricultural unsaturated soils in the piedmont area of the Treviso province, 2) the mobility of the vine-specific PPPs, and 3) the groundwater pathlines in the superficial phreatic aquifer obtained by physically-based numerical modeling.This research has been funded by the contribution from the UNI-IMPRESA 2021 joint research project (Centre of Hydrology ‘Dino Tonini’ - University of Padua, Alto Trevigiano Servizi Spa, Piave Servizi Spa): Subsurface Water quality and Agricultural pracTices monitoring 2 (SWAT-2).

Saltwater intrusion in coastal aquifers is a global problem recently worsened by anthropogenic activities (e.g., aquifer overexploitation, hydraulic reclamation and drainage of low-lying areas) and climate change effects (e.g., severe droughts, sea level rise) that contribute to reduce groundwater natural recharge, water quality, and agricultural production. Many low-lying coastal plains facing the Adriatic Sea are strongly affected by saltwater intrusion with serious consequences on agricultural activities and tourism that may become dramatic in a relatively short time due to climate change. In this framework, this work aims to identify monitoring strategies to characterize the process of saltwater intrusion under the effects of climate change and recommend appropriate countermeasures in two Adriatic low-lying coastal plain: south of the Venice Lagoon (north-eastern Italy), and at the Neretva River mouth (south-eastern Croatia).Geomorphologic, stratigraphic, hydrogeologic, and agricultural data were collected to characterize the aquifer system at both sites and assess the effects of seawater intrusion on agricultural productivity. Saltwater intrusion was monitored and analysed through monitoring systems that provide qualitative and quantitative information on the processes influencing groundwater and surface water dynamics within the two coastal systems. Moreover, laboratory physical models were developed to serve as benchmarks for the numerical models used to simulate the field results. Numerical modelling reliably implements boundary and initial conditions defined in-situ on both sites, simulates existing states, specifies different scenarios, and predicts salinization dynamic changes caused by climate changes.The results of the research activities include the development of specific tools for the management of agriculture-related activities and freshwater resources in coastal areas including vulnerability assessment, mitigation plans, and countermeasures against salt contamination. These results were obtained by integrating the findings gained on both sites, considering differences and peculiarities of the specific areas that are representative of many low-lying plains located on both sides of the Adriatic coast.This study has been funded by the contribution from the EU cofinancing and the Interreg Italy–Croatia Cross Border Collaboration (CBC) Programme 2014–2020 (Priority Axes: Safety and Resilience) through the European Regional Development Fund as a part of the projects MoST (AID: 10047742) and SeCure (AID: 10419304).

The Piedmont region (north-western Italy) is located between the Alps and the Mediterranean area, two territories that are recognized as climate hotspot regions, showing amplified climate change signals and associated with environmental, social and economic impacts.A number of water crisis that affected the Italian territory in the last twenty years exacerbated conflicts in different territories with regard to the priority use of water resource. The recent drought events (2017, 2021, and 2022) have seen areas not normally characterized by this type of phenomenon, such as the Piedmont region, go into crisis, involving all water users and human activities.In this framework, there is a renewed urgency for improved drought monitoring, forecasting and assessment methods, that will allow for better anticipation and preparation and will lead to better management practices, in order to reduce the vulnerability of society to drought and its subsequent impacts.As drought can be defined in a number of ways and the determination of drought magnitude and impacts can be quite complex, the top scientific priority and social challenge are the identification of meteo-hydrological precursors of water crises. This will lead from meteo-hydrological drought to socio-economic drought and drive water management and decision-making with a strong scientific basis.In this work we focused on the Turin area and after identifying the events that have sent in crisis the drinking water supply sources, the meteorological data and appropriate drought indexes have been analyzed. Critical thresholds and parameters have been identified and a first combined index, for developing an operational chain that can alert water utilities, stakeholders and mayors reasonably in advance, is proposed.

In the last twenty years, the Italian territory has been affected by different water crises, which have affected the main sectors of water use, exacerbating conflicts in different territories between these sectors (concerning the priority use of the resource), and requiring the implementation of emergency procedures for impacts management. The recent drought events of 2017, 2021, and winter 2022 saw areas of the country not typically prone to this type of phenomenon, such as north-western Italy, go into crisis.The term “water crisis” identifies the phenomenon for which the water shortage (a condition resulting from a demand for a resource exceeding the natural availability of renewable resources) reaches a severity demanding a series of management procedures for the phenomenon.Future water security will depend on the magnitude, rate, and regional details of meteo-climatic changes and non-climatic factors such as agricultural practices, water demand, and governance: improving aspects of water management will be a key to winning adaptation measures. Since drought can be defined in several ways, there are potentially different responses under a warming climate depending on the drought type. Beyond a lack of precipitation, changes in evapotranspiration are critical components of drought, because these can lead to soil moisture declines. Under very dry soil conditions, evapotranspiration becomes restricted and plants experience water stress in response to increased atmospheric demand. Human activities and decision-making have a critical impact on drought severity. The discrepancy between water shortage and the unavailability of the water resource to meet water demand is a function of socio-economic vulnerabilities and gaps in water governance.In this framework, uncertainty in future water scarcity forecasting and projections makes water security risk assessment and adaptation strategies a top priority scientific challenge: a bottom-up approach for forecasting and managing water crises is particularly advantageous.Considering the Turin area, Italy, after identifying the events that moved the drinking water supply sources towards crisis, meteorological data and appropriate drought indexes have been analyzed. Critical thresholds and parameters have been identified as a function of water supply sources and response time.A first forecasting chain was tested to provide monthly forecasts to assess the overcoming of these thresholds for operational purposes.

Barrages are low-head dams, used to realize diversion works for irrigation, hydroelectric or human consumption purposes. These in-river structures control the river bed elevation and maintain a prescribed water level upstream, affecting the levees’ elevation too if present. Often, they have been present for a long time (in the examined case centuries) and act as an inherent element of the surrounding environment, representing a constraint for the human activities growing through the years along the river.The Roggia Morlana barrage, which is located across the Serio River in the Province of Bergamo, northern Italy, has for centuries been a fundamental part of the economic life in the area, thanks to the several artificial canals that supply water for irrigation purposes. In the mid-twentieth century, a maximum capacity of 4500 l/s was derived and distributed in an extensive area of about 4200 hectares, while nowadays this barrage keeps an important role also for hydroelectric power production.In October 2020, an event led to the collapse of a part of the barrage and to the subsequent lowering of the river bed and destabilization of the banks. In addition to the stop of the hydropower production and the lack in satisfying the irrigation demand, the retrogressive erosion threatened various fundamental infrastructures crossing the river upstream (a gas pipeline, a water main and a bridge), hence a rapid rehabilitation of the barrage was required.The stability of the restored barrage depends on the flood discharges and on the related scouring phenomena that could take place immediately downstream. With the aim to assess the exposure and vulnerability of this critical infrastructure to the natural hazard, the effects of different riverbed protection configurations are analysed through physical modelling, testing each configuration against flood events.The area downstream the barrage is subdivided in frames delimited by bottom sills, filled with material. The physical model allowed to evaluate the effectiveness in scouring mitigation using different size of natural stones, put in place as loose boulders or wired in groups. To reduce the amount of damages and increase the resilience of the riverbed protection boulders have been substituted by concrete blocks in some frames. By this way, the goal to shift the scouring phenomena downstream, localizing the maximum scour depth far from the barrage foundations, is fulfilled.The cost of the restoration obtained via different riverbed protections, increasing with the resilience of the barrage, is compared with the cost of their failure that can cause complex hazard cascades. This is because a failure of the Roggia Morlana barrage does not have consequences only to the hydropower production and irrigation service, but also on the safety of the infrastructures crossing the river upstream, potentially affected by backward erosion phenomena.

Evidence of pesticides leaching due to intense rainfall events was found in two wellhead protection areas (WHPAs) located in the wine-growing areas of the Veneto piedmont area, in Italy. In this territory, the extensive agricultural activities related to the Prosecco production are developed often using pesticides-based vine protection practices. In the same area, numerous wells extract from the phreatic aquifers the drinking water needs of most of the province of Treviso, rising concern on the possibility of groundwater contamination from pesticides and risks for human health. Further experimental surveys – infiltration tests and soil samplings – were developed in the same WHPAs to study the spatial variability of the chemical-physical properties of the soil governing the pesticides leaching. The experimental data collected on areas of 2 hectares comprising both vineyards and non-agricultural areas, highlighted a larger variability of the soil properties inside the vineyards. Moreover, soil infiltration capacity, assumed in our case as the main property governing the pesticide leaching capacity, showed values up to one order of magnitude higher within the areas destined to wine-growing activities than the non-agricultural ones. This information, obtained at the local and at the field scale, were included in a geospatial analysis related to the distribution of vine-specific pesticides at the scale of the Treviso province, to obtain a vulnerability map for all the wells located in area. The geospatial analysis, developed in a geographical information system (GIS), is based on the sale data of pesticides for agricultural activities - also referred to as plant protection products (PPPs) – registered in the province in the period 2012-2019. The units of PPPs (kilograms or liters) collected at the municipal scale (the province of Treviso counts 94 municipalities) were analyzed by: i) identification of the vine-specific products based on the local guidelines for the vine-protection practices, ii) hazard classification of the vine-specific PPPs based on the CLP pictograms and statements (Classification, Labelling and Packaging Regulation, EC/1272/2008). This information, combined with the extension of the wine-growing areas from land use geographical data (Corine Land Cover 2018), allowed to outline, by assuming the use of the PPP in the municipality of sale, a map showing the hazard level of the wine-growing areas. The geospatial analysis based on the level of superimposition obtained between the extension of the wellhead protection areas and the wine-growing areas, led to a vulnerability map for wells. The map, resulting from the definition in different scenarios of the WHPAs extensions based on a geometrical criterion and the PPPs-based hazard of the vineyards, gives a clear picture of the wells that require PPPs-specific actions to minimize the risk for the quality of the water supplied for human consumption.

In coastal aquifers seawater intrusion is a worldwide problem caused by natural processes but significantly worsened by aquifer overexploitation for irrigation and drinking water supply, land subsidence, sea level rise and climate changes, which contribute to the reduction of groundwater natural recharge.Seawater intrusion represents a relevant environmental issue along the coastal aquifers of the Mediterranean Sea, including the coast south of the Venice Lagoon, a peculiar ecosystem characterized by a fragile equilibrium between reclamation and irrigation activities, whereby salinization is significantly reducing the annual local crop production of about the 25% on average.Here, we present the test case of Ca’ Bianca, located near the city of Chioggia - Italy. A numerical flow and transport model has been set up with SEAWAT, aimed at reproducing the complex saltwater intrusion dynamics in the area. To pursue this goal, real field water table and concentration measurements are combined to aid in the calibration and validation of the model. Particular attention is devoted to the evaluation of the dynamics and uncertainty associated with seawater levels, an essential forcing of the model. Then, mitigation strategies, such as drains supplying freshwater in the first layer of soil, are simulated to test their effectiveness against the saltwater intrusion in a way that their application can be reproduced also in other sites affected by the same phenomenon.Results show a good match between the simulations and the data, with errors of about 10 cm for the water table, which is acceptable if we consider the scale of the project and its topographical and stratigraphical uncertainties. Even though matching observed concentrations proved to be more difficult, the model realistically reproduces the saltwater spatio-temporal behaviour. The comparison between the scenarios with and without mitigation strategies shows that, in the latter case, significant enhancement in crop production can be achieved.As a future development, climate change effects on the sea levels will be considered and predictive scenarios will be developed and quantitatively analysed.

Numerical dispersion is a well-known problem that affects solute transport in groundwater simulations and can lead to wrong results, in terms of plume path overestimation and overprediction of contaminant dispersion. Numerical dispersion is generally introduced through stabilization techniques aimed at preventing oscillations, with the side effect of increasing mass spreading. Even though this issue has long been investigated in subsurface hydrology, little is known about its possible impacts on integrated surface–subsurface hydrological models (ISSHMs). In this study, we analyze numerical dispersion in the CATchment HYdrology (CATHY) model. In CATHY, a robust and computationally efficient time-splitting technique is implemented for the solution of the subsurface transport equation, whereby the advective part is solved on elements with an explicit finite volume scheme and the dispersive part is solved on nodes with an implicit finite element scheme. Taken alone, the advection and dispersion solvers provide accurate results. However, when coupled, the continuous transfer of concentration from elements to nodes, and vice versa, gives rise to a particular form of numerical dispersion. We assess the nature and impact of this artificial spreading through two sets of synthetic experiments. In the first set, the subsurface transport of a nonreactive tracer in two soil column test cases is simulated and compared with known analytical solutions. Different input dispersion coefficients and mesh discretizations are tested, in order to quantify the numerical error and define a criterion for its containment. In the second set of experiments, fully coupled surface–subsurface processes are simulated using two idealized hillslopes, one concave and one convex, and we examine how the additional subsurface dispersion affects the representation of pre-event water contribution to the streamflow hydrograph. Overall, we show that the numerical dispersion in CATHY that is caused by the transfer of information between elements and nodes can be kept under control if the grid Péclet number is less than 1. It is also suggested that the test cases used in this study can be useful benchmarks for integrated surface–subsurface hydrological models, for which thus far only flow benchmarks have been proposed.

Diffuse urban pollution is a significant factor in compromising receiving water and groundwater standards required by the EU Water Framework Directive. Many studies (e.g., Ashley et al., 2005; McGrane, 2016) show that changes in the built environment and climatic forces contribute to the increase of combined sewer system overflows and of stormwater directly conveyed to nearby water bodies. These discharges are responsible for receiving water contamination, as a result of high concentrations of pathogens, BOD, suspended solids (SS), hydrocarbons, heavy metals and nutrients, thus being a significant source of water bodies’ pollution.To mitigate/eliminate pathogens and BOD contamination sources, the combined drainage system is usually split into separated sanitary sewer and stormwater systems, although difficulties related to economic and technical feasibility may be relevant. Nevertheless, this solution does not solve completely pollution due to SS, hydrocarbons, heavy metals from urban areas runoff and nutrients from rural drainage.Sustainable Drainage Systems (SuDS) deal with stormwater at source, helping infiltration and storage of water, increasing groundwater recharge, and reducing peak flood and volume in the drainage system. Moreover, filtration processes through porous media may reduce pollutants driven by first flush, usually controlled by stormwater tanks and sewer system spillways. However, clogging phenomenon limits drainage efficiency in the long-term, making sometimes porous media itself a source of contamination.In the following, a PhD project focusing on the urban area of Treviso is illustrated. Treviso is crossed by the river Sile, one of the longest (95 km) European wellspring rivers, part of a protected area. The Sile river is polluted by discharges from both the existing combined sewer system and rural drainages.While responsible agricultural practices will be promoted to mitigate the pollution originating from rural areas, a project aims to separate the combined system, developing a new pipe network for sanitary wastewater. When properly applied in the present drainage system devoted to the stormwater control only, SuDS solutions are able to mitigate pollution coming from wash-off and reduce flood peaks.Discharge measurement stations will be realised on the Sile river upstream and downstream the Treviso town, to quantify drainage system outflows of the urban area during rainfall events and in dry conditions. Sampling for qualitative analysis will give a measure of the pollutants’ concentration.SuDS solutions, e.g. porous pavements, infiltration trenches and vegetated swales, will be tested with laboratory equipment (6×2 m2) capable of considering the runoff and underground drainage in a fully controlled environment subjected to a prescribed rainfall intensity. By this way it will be possible to analyse the main physical processes and assess the SuDS solutions’ efficiency both in the short and long-term, using advanced mathematical models for the interpretation of results.If the laboratory model will provide satisfactory results, a full-scale test will be developed on an experimental site in Treviso town. The installed qualitative and quantitative monitoring system will allow to determine the effectiveness of the solutions adopted.

In the two-year period 2018-2020 the Centre of Hydrology ‘Dino Tonini’ of the University of Padova developed the UNI-Impresa research project SWAT (Subsurface Water quality and Agricultural pracTices monitoring) to study the interactions between agricultural practices, mainly those involved in the production of Prosecco, and the wellhead protection areas in the province of Treviso (Italy). Specific experimental activities, integrated by a modelling analysis of the collected data, were developed to understand the processes affecting the vertical evolution of a glyphosate-based pesticide in the unsaturated soil up to a depth of 0.70 m BGL. The pesticide, along with a non-reactive tracer (potassium bromide), was applied in November 2018 in two experimental sites (Settolo-Valdobbiadene and Colnù-Conegliano) organized nearby well-fields supplying public water systems. Its evolution subjected only to the natural hydrological forcing compared to the infiltration dynamics of the tracer was locally monitored by collecting and analyzing soil and water samples along six months. Both the application and the monitoring activities were carried out in each experimental site on two 25 m2 parcels located at reciprocal distances of 30 m (Settolo) and 115 m (Colnù), obtaining a detailed information about the glyphosate vertical evolution. Each point-wise analysis highlights a strong tendency of the pesticide and its principal metabolite (AMPA) to be adsorbed to the soil matrix rather than to be dissolved in the infiltrated rainwater and carried toward the deeper layers of the soil. However, high concentrations of the pesticide spotted at the depth of -0.70 m suggest that preferential pathways and more intense precipitation events enhance the downward movement of the glyphosate, either dissolved in water or adsorbed to microscopic particles. Differences in the pesticide spatio-temporal evolution were observed between parcels belonging to the same site. Despite the decay analyzed during the experiments is related to both the chemical-physical properties of the soil, the potential movement is dominated by the heterogeneity of the hydraulic properties of soil. Hence, the evaluation of the infiltration capacity was considered a low-cost proper method to extend the analysis to the field scale (~102 m characteristic length). In the experimental site of Colnù, the spatial variability of the soil infiltration capacity (mm/min) and dynamics has been assessed developing a series of tests using the double ring infiltrometer in 17 different positions within an area of 1.75 ha. The investigated area extends over two contiguous vineyards inside the wellhead protection area. Two tests positions correspond to the site parcels while the remaining were spatially distributed maintaining reciprocal distances ranging between 15 and 50 meters. The measured soil infiltration capacity shows a large spatial variability, up to two orders of magnitude. The geostatistical interpolation (kriging) of the achieved data gives a quantitative estimation of the soil vulnerability at the field scale based on the potentially infiltrating pesticide.

This work describes a project that aims to assess and forecast the groundwater balance and the spatiotemporal behavior of fluxes in a regional aquifer located in the middle-high venetian plain between rivers Brenta and Piave (Italy) to analyze the impact of future irrigation policies and to define at regional scale the risk of contamination.The area is widely exploited for agricultural purposes and over time many wells (owned by Water Service Companies and private bodies) have been drilled for the supply of drinking water. A dense network of ditches, that still guarantee most agricultural requirements by border irrigation, is replaced year by year with pressurized systems (sprinkler and drip). This change shows positive effects, reducing the amount of diverted water from rivers helping the Ecological Flows (Eflows) requirements (EU Guidance Document No. 31 2015). On the other hand, it actually reduces the infiltrated volumes (acting as artificial recharge) that sustain the groundwater reserve since centuries ago. Together with the growing number of active and potential sources of pollution, all this jeopardizes the water supply from wells intended for human consumption.This situation requires proper knowledge and tools to anticipate consequences of a changing environment and to suggest policies for an appropriate management and sustainable use of groundwater.The study area develops north to south from the Prealps to the middle of the plain, between Brenta River (west) and Piave River (east). Evidences from geological surveys show a sand and gravel aquifer extending from uplands in the north piedmont region to the southern one where a layered system of nine aquifers can be recognized. The hypothetical separation takes place along alluvial springs that origin the river Sile, that acts as a drain for the upper aquifer of the whole area.A numerical model of the aquifer is under development using Feflow® by DHI, a finite element software able to reproduce the subsurface flow field and transport phenomena. Geological description and vertical stratigraphy of boreholes were used to build the geo-structural model, whose spatial extent was also chosen on the availability of data – water table, piezometric levels and/or fluxes – to be imposed on the boundaries. Rainfall, irrigation, evapotranspiration and water withdrawal artificially from wells or naturally from springs, as well as the flow interchange across the section of rivers, are the external forcing varying in time and controlling the water table and piezometric levels behaviors.Water table and piezometric level information are fundamental in the calibration of the subsurface hydraulic parameters. The actual monitoring network, that considers sensors in wells property of Regional Environmental Agency and different Water Service Companies, has been improved to mitigate its non-uniform spatial distribution instrumenting 25 new positions to reach in the whole area (about 900 km2) a total number of 84 monitored wells (density of about 1 sensor every 10 km²).Information about historical evolution of different irrigation techniques have been gathered from the three Land Reclamation Authorities managing the investigated area to reproduce the present situation and forecast future different scenarios.

Seawater intrusion in coastal aquifers is a worldwide problem caused by natural processes but significantly worsened by aquifer overexploitation for drinking water supply and irrigation, land subsidence, sea levels rise, and climate changes, which contribute to the reduction of groundwater natural recharge.Within the framework of an Interreg Italy-Croatia collaboration project (Italy – Croatia 2014 – 2020 CBC Programme), MoST (MOnitoring Sea-water intrusion in coastal aquifers and Testing pilot projects for its mitigation), a study area located at Ca’ Pasqua, in the southern part of the Venice lagoon, Italy, is used as a pilot site to develop and test possible solutions to issues of coastal seawater intrusion. The project consists of two main phases. The first phase is devoted to the collection of hydro-geophysical information and data in the study area and to mimic the dynamics of the relevant processes in laboratory experiments. In the second phase, appropriate countermeasures (e.g., underground barriers, recharge wells, recharge drains, cut-off walls) will be considered to limit or mitigate the seawater intrusion/contamination and their efficiency will be tested. These activities will be carried out with the involvement of local populations and authorities, which will benefit the most by these actions, thanks to their final implications in terms of enhanced crop productivity and touristic activities.Within the context of this project, we present the results of a numerical modeling study, whereby a finite difference model, SEAWAT, is used to test the potential effects of one of the aforementioned countermeasures, a recharge drain located in a sandy paleochannel which seems to represent a preferential pathway for saline intrusion but can also be used to convey freshwater to reduce soil salinization. The model is set up by integrating information derived from in-situ monitoring and observations of precipitation, rivers hydrometric heads, evapotranspiration and tide levels for a period of about 10 years. A number of different scenarios are modelled and compared, allowing us to predict the resulting seawater intrusion mitigation and its uncertainty.

Saltwater intrusion is a worldwide problem increasingly affecting coastal aquifers, due to climate changes and growing demand of freshwater for irrigation and human consumption. Therefore, research efforts on this topic have been intensified, aiming to achieve better predictions of the saltwater wedge evolution and design suitable countermeasures to limit the saltwater intrusion. Both physical and numerical models are essential for these purposes. This work presents a laboratory facility designed and built to simulate saltwater intrusion in coastal aquifers, with the overall goal of providing benchmarks for numerical models by means of different measurement techniques. The laboratory facility has been specifically designed to limit errors and provide redundant evaluation in the measurement of hydraulic heads and discharged flow rates. Moreover, the size of the facility allows us to monitor the saltwater wedge evolution by electrical resistivity tomography (ERT). A specifically designed ERT monitoring system was developed and verified by comparison with photos of the saltwater wedge collected at regular intervals during an experiment in a homogeneous porous medium. The experiment consisted of two phases: for the initial 24 h, the saltwater wedge evolved without any external forcing, while in the following 12 h, freshwater was pumped out through a channel drain, to simulate aquifer exploitation. The SUTRA code was adopted to reproduce the experimental results, by calibrating only the longitudinal and transversal dispersivities. Overall, the agreement between observed data, numerical simulations, and ERT results, albeit preliminary, demonstrates that the proposed laboratory facility can provide valuable benchmarks for future studies of seawater intrusion, even in more complex settings.

The significance of estimating the spatial variability of the hydraulic conductivity K in natural aquifers is relevant to the possibility of defining the space and time evolution of a non-reactive plume, since the transport of a solute is mainly controlled by the heterogeneity of K. At the local scale, the spatial distribution of K can be inferred by combining the Lagrangian formulation of the transport with a Kalman filter-based technique and assimilating a sequence of time-lapse concentration C measurements, which, for example, can be evaluated on-site through the application of a geophysical method. The objective of this work is to compare the ensemble Kalman filter (EnKF) and the ensemble smoother (ES) capabilities to retrieve the hydraulic conductivity spatial distribution in a groundwater flow and transport modeling framework. The application refers to a two-dimensional synthetic aquifer in which a tracer test is simulated. Moreover, since Kalman filter-based methods are optimal only if each of the involved variables fit to a Gaussian probability density function (pdf) and since this condition may not be met by some of the flow and transport state variables, issues related to the non-Gaussianity of the variables are analyzed and different transformation of the pdfs are considered in order to evaluate their influence on the performance of the methods. The results show that the EnKF reproduces with good accuracy the hydraulic conductivity field, outperforming the ES regardless of the pdf of the concentrations.