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Assessment of potentially contaminated sites (PCS) can be expensive; hence, simple and less demanding methods and models are required. This work attempts to provide an approach that can aid in selecting the most appropriate model for the PCS. The developed method uses over 100 field site data to evaluate four test models (analytical/empirical) that provide the maximum plume length (L

Characterization of karst systems and forecast of their state variables are essential for groundwater management and engineering in karst regions. These objectives can be met by the use of process-based discrete-continuum models (DCMs). However, results of DCMs may suffer from inversion nonuniqueness. It has been demonstrated that the joint inversion of observations regulated by different natural processes can tackle the nonuniqueness issue in groundwater modeling. However, this has not been tested for DCMs thus far. This research proposes a methodology for the joint inversion of hydro-thermo-chemo-graphs, applying to two small-scale sink-to-spring experiments at Freiheit Spring, Minnesota, USA. In order to address conceptual uncertainty, a multimodel approach was implemented, featuring seven mutually exclusive variants. Spring hydro-thermo-chemo-graphs, for all the variants simulated by MODFLOW-CFPv2, were jointly inverted using a weighted least squares algorithm. Subsequently, models were compared in terms of inversion and forecast performances, as well as parameter uncertainties. Results reveal the suitability of the DCM approach for simultaneous inversion and forecast of hydro-physico-chemical behavior of karst systems, even at a scale of meters and seconds. The estimated volume of the tracer conduit passage ranges from approximately 46–51 m3, which is comparable to the estimate from the flood-pulse method. Moreover, it was demonstrated that the thermograph and hydrograph contain more information about aquifer characteristics than the chemograph. However, this finding can be site-specific and should depend on the analysis scale, the considered conceptual models, and the hydrological state, which are potentially affected by minor unaccountable processes and features.

Groundwater dependency is increasing globally, while millions of potentially contaminated sites are yet to be characterized for contamination levels. In particular, groundwater contamination due to light nonaqueous phase liquids (LNAPLs) continues to be a global challenge. Mathematical approaches (i.e., analytical, semi-analytical, empirical, numerical) are preferred for an initial site assessment to circumvent the high characterization costs and limited site data availability. However, the site-specific nature of contamination restricts the generalization of any single approach. Hence, the requirement is for an easy-to-use computing interface that provides site-specific data management, the selection and use of multiple-model interfaces for computing, and site characterization, with extension for the latest models as they become available. This work provides one such interface called CAST or Contamination Assessment and Site-management Tool. CAST is an open-source browser-based (online/offline) tool that provides an interface for six different analytical models (e.g., BIOSCREEN-AT), a MODFLOW based numerical model, and two empirical models (including a hybrid numerical-analytical model). Additionally, CAST includes interfaces for site data management, their evaluation, and scenario-based modeling. CAST's development is in a modular format, which simplifies the addition of new computing or data interfaces. Furthermore, the entire code-base of CAST is based on open-source (dominantly Python programming) libraries and standards. This further simplifies the modification or extension of this tool. This paper introduces CAST, its different computing, and data management interfaces and provides examples of the tool's functionality primarily for the initial evaluation of contaminated sites.

Gravity-driven infiltration into the shallow subsurface via small-diameter wells (SDWs), i.e., wells with an inner diameter smaller than 7.5 cm (3 inches) and no gravel pack) has proven to be a cost-efficient and flexible tool for managed aquifer recharge (MAR), as it provides relatively high recharge rates with minimal construction effort. SDWs have a significantly smaller open filter area than larger diameter wells with gravel pack, making the infiltration of low-quality waters through these wells more at risk clogging. To investigate their susceptibility for biological and physical clogging, 24 physical models with different well setups were evaluated by infiltrating either nutrient-poor but turbid water or nutrient-rich but clear water. The experiments showed that smaller diameters and the lack of a gravel pack increase the well's susceptibility to both kinds of clogging. However, this effect was observed to be much more pronounced for physical than for biological clogging. Our conclusion is that SDWs show severe disadvantages with respect to the infiltration of highly turbid waters in comparison to large diameter wells with a gravel pack. Nevertheless, this disadvantage is much less severe when it comes to the infiltration of clear but nutrient-rich waters (e.g., treated wastewater). Depending on the economic and geological circumstances of a MAR-project, this disadvantage could be outweighed by the significantly lower construction costs of SDWs.

Land subsidence due to overexploitation of aquifers is often attributed to incoherent public policies. Taking the case of the Mahyar valley in Iran as an example, and based on a mixed-method research design, this study analyses the effects of policy incoherence on well use for agricultural irrigation and the resulting groundwater levels. Results show how an accumulation of policy incoherence over time results in an increased construction of wells, ultimately leading to a groundwater table drawdown, with a significant decrease of 7.61 m in the last 16 years.

Education in the natural and engineering sciences is traditionally taught following a standard template where the instructor stands in front of the classroom presenting statically and linearly the course material. The educational environment can be improved by using innovative didactic concepts with interactive-digital tools that enhance the students’ understanding of the material. Audience response systems promote active learning during lectures, and learning management systems improve students’ self-learning strategies. This contribution demonstrates such adaptations for the lecture series “Groundwater Management with Computer Models” and shares our experiences regarding methods, effort, and benefit. Student performance was significantly improved together with overall positive evaluation. The techniques used for redesign also increase the teaching efficiency because they exhibit a large degree of reusability without significant modifications and are well scalable for larger audiences. In addition, media-enhanced lecture series meet future requirements by students and the industry for higher education in a networked and digitized society.

Locally collected precipitation water can be actively used as a groundwater tracer solution based on four inherent tracer signals: electrical conductivity, stable isotopic signatures of deuterium [δ2 H], oxygen-18 [δ18 O], and heat, which all may strongly differ from the corresponding background values in the tested groundwater. In hydrogeological practice, a tracer test is one of the most important methods for determining subsurface connections or field parameters, such as porosity, dispersivity, diffusion coefficient, groundwater flow velocity, or flow direction. A common problem is the choice of tracer and the corresponding permission by the appropriate authorities. This problem intensifies where tracer tests are conducted in vulnerable conservation or water protection areas (e.g., around drinking water wells). The use of (if required treated) precipitation as an elemental groundwater tracer is a practical solution for this problem, as it does not introduce foreign matters into the aquifer system, which may contribute positively to the permission delivery. Before tracer application, the natural variations of the participating end members' tracer signals have to be evaluated locally. To obtain a sufficient volume of tracer solution, precipitation can be collected as rain using a detached, large-scale rain collector, which will be independent from possibly existing surfaces like roofs or drained areas. The collected precipitation is then stored prior to a tracer experiment.

Many studies have investigated the migration and entrapment processes of source zones from dense non-aqueous phase liquid (DNAPL) contamination under different conditions. However, the characterization of occupying area by source zone (or source shape) in water-saturated aquifers is still rudimentarily considered. In this study, we demonstrated this issue (1) by providing a brief review of existing approaches for source shape consideration, (2) by proposing an approach with simple shape parameters based on the non-uniformity of source widths, and (3) by providing exemplary applications of our proposed approach on shapes already published in previous research works. Our literature review suggested that the source zone in mathematical approaches is generally characterized as simple geometrical shapes (arbitrary lines or rectangles) or system-defined parameters that contrast to complex and discontinuous shapes observed in the real world. But the characterization of such complex shapes is still not possible with acceptable efforts. Therefore, we proposed an approach to parameterize the source shape by considering the variation of width and midpoints over the depth of the entire source zone and formulate four parameters based on population statistics (mean, standard deviation). To illustrate the suitability of our approach, we applied it to the results of lab experiments, and by analyzing these complex shapes, we highlighted the potential for improving the characterization techniques of non-uniformity of the source zones.

The locally focused dissolution of the rock material (e.g., below dolines and dry valleys) in karst systems and in general percolating clusters of fractures in consolidated aquifer systems trigger the development of preferential flow paths in the vadose zone. Rainfall events may initiate rapid mass fluxes via macropores and fractures (e.g., as gravitationally-driven films) that lead to source-responsive water table fluctuations and comparably short residence times within the vadose zone. The degree of partitioning into a slow diffuse infiltration component and a rapid localized part depends, amongst others, on the hydraulic interaction of porous matrix and fracture domain as well as the geometrical characteristics of the fracture systems (e.g., persistence, connectivity) that are often difficult to obtain or unknown under most field conditions. Given their importance in water-resource management, specifically in arid and semi-arid regions (e.g., Mediterranean), it is desirable to recover such infiltration dynamics in porous-fractured systems with physically-based yet not overparameterized models. Here, we simulate water table fluctuations in a karst catchment in southwest Germany (Gallusquelle) using a source-responsive film flow model based on borehole and precipitation data. The model takes into account interfacial connectivity between slow and fast domain as well as phreatic zone discharge via classical recession analysis. This case study shows the potential importance of preferential flows while modeling water table responses in karst systems and recognizes the need for formulations other than those applied for a diffuse bulk fractured domain where infiltration patterns are assumed to be homogeneous without formation of infiltration instabilities along preferential pathways.

The reuse of treated wastewater (e.g. for irrigation) is a common practice to combat water scarcity problems world-wide. However, the potential spread of opportunistic pathogens and fecal contaminants like Enterococci within the subsoil could pose serious health hazards. Additional sources (e.g., leaky sewer systems, livestock farming) aggravate this situation. This study contributes to an understanding of pathogen spread in the environment, using a combined modelling and experimental approach. The impact of quartz sediment and certain wastewater characteristics on the dissemination of Enterococcus faecalis JH2–2 is investigated. The transport processes of advection-dispersion and straining were studied by injecting conservative saline tracer and fluorescent microspheres through sediment packed columns, and evaluating resulting breakthrough curves using models. Similarly, simultaneously occurring reactive processes of microbial attachment, decay, respiration and growth were studied by injecting Enterococcus faecalis JH2–2 suspended in water with or without dissolved oxygen (DO) and nutrients through sediment, and evaluating resulting inlet and outlet concentration curves. The processes of straining, microbial decay and growth, were important when DO was absent. Irreversible attachment was important when DO was present. Sensitivity analysis of each parameter was conducted, and field scale behavior of the processes was predicted, to facilitate future work.

The use of snowmelt as an inexpensive multi-component tracer solution for active aquifer characterization is investigated, creating a valid alternative to existing artificial water isotope labelling using enriched deuterium oxide (2H2O) and water-18O (H218O). The approach directly takes advantage of natural differences between groundwater and precipitation. It is shown, at laboratory-scale and small field-scale, that a direct injection of snowmelt into a porous medium allows for the tracing of water flow and, therefore, for the determination of transport parameters based on the stable isotope signatures (δ2H and δ18O) and on the sum parameter electrical conductivity (EC). The differences in the isotope signature between the snowmelt and groundwater applied in this study were significant, with ∆(δ2H) = 61.0‰ and ∆(δ18O) = 8.2‰, while the EC difference was ~0.5 mS/cm. Stable isotope breakthrough was observed to be almost congruent to sodium chloride (laboratory tracer experiment) and to uranine (field-scale push-drift-pull test), clearly supporting the assumption of conservative transport. A crosscheck of the isotope data in δ2H-δ18O plots revealed no significant biases in the tests. On the other hand, the snowmelt’s EC breakthrough suffered from a slight retardation due to ion exchange and mineral reactions.

Application of numerical models is a common method to assess groundwater resources. The versatility of these models allows consideration of different levels of complexity, but the accuracy of the outcomes hinges upon a proper description of the system behaviour. In seawater intrusion assessment, the implementation of the sea-side boundary condition is of particular importance. We evaluate the influence of the slope of the sea-side boundary on the simulation results of seawater intrusion in a freshwater aquifer by employing a series of slope variations together with a sensitivity analysis by varying additional sensitive parameters (freshwater inflow and longitudinal and transverse dispersivities). Model results reveal a multi-dimensional dependence of the investigated variables with an increasing relevance of the sea-side boundary slope for seawater intrusion (decrease of up to 32%), submarine groundwater discharge zone (reduction of up to 55%), and turnover times (increase of up to 730%) with increasing freshwater inflow or dispersivity values.

At the current time, cities harbor more than 4 billion inhabitants. According to the United Nations’ projections, an increment by 2.5 billion is expected until mid-century. This will create enormous stresses to the water resource management in urban regions, including detrimental impacts on both groundwater quantity and quality. For instance, leakages from aging urban sewer network systems may lead to uncontrolled recharge and contamination. Sewer-borne contaminants cover a broad bandwidth of substances including pathogenic microbiota, nutrients and emerging contaminants. These substances may be highly persistent and accumulate in the subsurface over time. This, in turn, may pose a long-term threat to urban ecosystems. Hence, understanding the spatiotemporal distribution of sewer-borne plumes within the subsurface is of strategic importance. Sewer failures may include, among others, pipe blockades, local collapses and smaller cracks, as well as leaking joints between pipe segments. The intensity of sewer exfiltration to the soil and eventually to the aquifers depends on a variety of influencing factors, including pipe diameter and failure type as well as pipe burial depth and distance to the groundwater table. In this context, this study’s specific aim is to investigate the effect of selected vadose zone and aquifer properties and of failure characteristics on the final shape of sewer contaminant plumes to eventually delineate groundwater contamination characteristics solely from sewer network properties.Results from two numerical studies, employing the HYDRUS 3D software code for variably saturated flow and transport simulation, will be presented. First, a small-scale principal model setup with a single pipe defect was designed to investigate the effect of soil type, colmation layer properties, pipe water level, defect shape and natural groundwater recharge on the shape of the plume in the vadose zone and at the aquifer table. Hereby, the simulations included both constant and varying pipe water levels. To define a de-facto worst-case scenario, continuous water injection as well as conservative transport (i.e., no decay or sorption) were assumed for most simulation runs. Besides the pipe water level, the intensity of precipitation was found to be a major influencing factor on the contaminant plume dimensions. In a second step, an intermediate-scale model involving a long pipe was conducted to further investigate overlay effects of multiple contaminant plumes. Here, multiple defects were positioned along the pipe in various distances, starting from a quasi-continuous line source and ending at a rather broad interval. It was found that the plume shapes on larger scale were very similar for most defect positionings, if the averaged injection rate remains the same. The direction of groundwater flow was altered in addition to the variation of the defects’ positions. Here, the contaminant plumes became slightly skewed.The presentation will also give a short outlook to future works which will include simulations on city district scale employing HPC-capable codes such as ParSWMS, ParFlow and/or OpenGeoSys, and a comparison to simplified modeling approaches.

International audience; Inner boundary conditions describe the interaction of groundwater wells with the surrounding aquifer during pumping and are associated with well-skin damage that limits water production and water derived from wellbore storage. Pumping test evaluations of wells during immediate and early time flow require assignment of inner boundary conditions. Originally, these concepts were developed for vertical well screens, and later transferred to wellbores intersecting highly conductive structures, such as preferential flow zones in fractured and karstic systems. Conceptual models for pumping test analysis in complex bedrock geology are often simplified. Classic analytical solutions generally lump or ignore conditions that limit or enhance well productivity along the well screen at the onset of pumping. Numerical solutions can represent well drawdowns in complex geological settings, such as karst systems, more precisely than many analytical solutions by accounting for additional physical processes and avoiding assumptions and simplifications. Suitable numerical tools for flow simulations in karst are discrete pipe-continuum models that account for various physical processes such as the transient hydraulics of wellbores intersecting highly conductive structures during pumping.

Karst groundwater vulnerability maps are important tools for the development of groundwater management and protection strategies. However, current methodologies do not always match regional characteristics and parameter adaptations are necessary. In addition, other important processes such as dilution and aquifer residence time are not included in vulnerability analysis for the complications of evaluating two or more criteria simultaneously. The integrated karst aquifer vulnerability approach (IKAV) project aims to develop an integrated approach to include these parameters and estimate global change implications in current and future scenarios. As a first step, intrinsic vulnerability methodologies are studied in order to highlight important parameters and the congruence with regional characteristics of the Yucatan karst. Results demonstrate agreement between methods for the evaluation of high and very high vulnerabilities and their relation with fissures and dolines. Moderate vulnerabilities are assigned to more than 50% of the area. However, moderate vulnerabilities, assigned to the coastal area and the Southern hill, are highly questionable. Intrinsic features affecting moderate classes vary according to the method. Parameter sensitivity analysis and overlap analysis demonstrate the influence of depth to the unsaturated zone, soils, precipitation, and slope on moderate values. Therefore, such parameters must be re-evaluated and discretized according to the characteristics of the study area to match Yucatan regional characteristics.

Karst aquifers are a major source of drinking water with intrinsic features that increase the pollution risk from anthropogenic and natural impacts. In Yucatan, Mexico, groundwater is the sole source of drinking water, also acting as receptor of untreated wastewater due to the low regional coverage of sewer systems. To protect karst groundwater, vulnerability methodologies are widely used. Worldwide, multiple karst vulnerability schemes have been developed and tested; however, none of these consider pollutant residence time or pollutant concentration as core parameters to estimate vulnerability. This work aims to define important considerations regarding the behavior of nitrates (NO3) in a real scenario, to be included in a new integrated vulnerability method. This work has two main objectives: to set up a groundwater model to depict as close as possible the groundwater behavior of the Yucatan karst system, and to introduce a transport model to estimate the behavior of a pollution plume. Model outcomes suggest that pollutants have a short residence time, reaching the coast in the north after 3 years. Well fields are also affected by pollution at variable NO3 concentrations. Results can be further discretized to establish a base and to include these parameters as part of a new integrated groundwater vulnerability approach.

A numerical discrete conduit-continuum model is employed to investigate large-scale groundwater abstraction in karst aquifers. The application of large-scale experiments is one approach to deal with the scale problem in hydraulic parameter assessment, caused by significant contrasts of hydraulic parameters in a karst aquifer. Here, conduit drawdown is evaluated by diagnostic plots and by considering the apparent flow dimension. These tools are frequently used for the interpretation of hydraulic borehole tests by analytical solutions. In contrast to existing analytical solutions, a numerical groundwater model allows the incorporation of the effect of complex parameter distributions. The objective is to demonstrate the application of diagnostic plots and flow dimension analysis for a systematic analysis of the effect of different boundary conditions as well as sink/source terms for idealized two-dimensional mixed karst aquifer systems, which ultimately extends existing analytical solutions and, therefore, contributes to the interpretation of measured field data. The analysis is focused on the apparent flow dimension and shows the extension of the cross-sectional flow area for selected models. The results are used to evaluate the large-scale pumping test of the karstified Cent Fonts catchment (Languedoc, France). The inverse calibration of two realistic, but still simplified, catchment models reveals that the apparent flow dimension supplies useful information about the general flow pattern during the Cent Fonts pumping test. The flow dimension after the end of the storage period can be explained by a large contribution of exchange flow resulting in a strong influence of radial flow on regional, i.e., kilometer scale.

An approach to establish the recharge component of managed aquifer recharge (MAR) has recently been proposed that uses small-diameter shallow wells installed using relatively inexpensive drilling methods such as direct push. As part of further development of that approach, a generalized procedure is presented for a technical and economic assessment of the approach’s potential in comparison to other systems. Following this procedure, the use of small-diameter wells was evaluated both experimentally and numerically for a site located in southern Styria, Austria. MAR is currently done at the site using a horizontal pipe infiltration system, and system expansion has been proposed with a target rate of 12 l/s using small-diameter wells as one possible option. A short-duration single-well field recharge experiment (recharge rate 1.3–3.5 l/s) was performed (recharge by gravity only). Numerical modeling of the injection test was used to estimate hydraulic conductivity (K). Quasi-steady-state, single-well recharge simulations for different locations, as well as a long-term transient simulation, were performed using the K value calibrated from the field injection test. Results indicate that a recharge capacity of 4.1 l/s was achievable with a maximum head rise of 0.2 m at the injection well. Finally, simulations were performed for three different well fields (4, 6 and 8 wells, respectively) designed to infiltrate a target rate of 12 l/s. The experimental and numerical assessments, supported by a cost analysis of the small-diameter wells, indicate that the small-diameter wells are a viable, cost-effective recharge approach at this and other similar sites.

Peri-urban areas are characterized by multifunctional land-use patterns forming a mosaic of built-up and agricultural areas. They are critical for providing food and other agricultural products, livelihood opportunities and multiple ecosystem services, which makes them transformative where urban and rural spaces blend. We analyzed land use changes in a peri-urban micro-watershed in Southern India by using Google Earth data to understand the micro-level spatio-temporal dynamics. This study aims at understanding the peri-urban agriculture and landscape changes as related to the change in use of wastewater and groundwater for irrigation. The temporal dynamics of peri-urban system including the changes in built-up, paragrass, paddy rice and vegetable cultivation, groundwater and wastewater irrigated areas in the watershed were evaluated. The detected changes indicate that, as a consequence of urban pressures, agricultural landscapes are being converted into built-up areas and, at the same time, former barren land is converted to agricultural plots. The mapped land use data are used in landscape change modelling for predicting the peri-urban agricultural dynamics and the driving factors in the watershed. Combined with the mapping and modelling approaches for land use change analysis, our results form the basis for integrated resources management in the wastewater influenced peri-urban systems.

A large number of potentially contaminated sites reported worldwide require cost- and time-effective assessment of the extent of contamination and the threats posed to the water resources. A significant risk assessment metric for these sites can be the determination of the maximum (i.e., steady-state) contaminant plume length (Lmax). Analytical approaches in the literature provide an option for such an assessment, but they include a certain degree of uncertainty. Often, the causes of such uncertainties are the simplifications in the analytical models, e.g., not considering the influence of hydrogeological stresses such as recharge, which impact the plume development significantly. This may lead to an over- or underestimation of Lmax. This work includes the influence of the recharge for the effective estimation of Lmax. For that, several two-dimensional (2D) numerical simulations have been performed by considering different aquifer thicknesses (1 m– 4 m) and recharge rates (ranging from 0 to 3.6 mm/day). From the numerical results of this work, it has been deduced that 1) the application of the recharge shortens Lmax, and the recharge entering the aquifer top causes the plume to tilt, 2) the reduction percentage in Lmax depends on the recharge rate applied and the aquifer thickness, and 3) the reduction percentage varies in a non-linear manner with respect to the recharge rate for a fixed aquifer thickness. Based on these results, a hybrid analytical-empirical solution has been developed for the estimation of Lmax with the inclusion of the recharge rate. The proposed hybrid analytical-empirical solution superimposes an empirically obtained correction factor onto an analytical solution. Although extensive confirmation steps of the developed model are required for including the effect of the recharge on aquifer hydraulics, the proposed expression improves the estimation of the Lmax significantly. The hybrid analytical-empirical solution has also been confirmed with a selection of limited field contamination sites data. The hybrid model result (Lhyb) provides a significant improvement in the estimation, i.e., an order of magnitude lower mean relative error compared to the analytical model.

This research presents the first application of a distributed discrete-continuum numerical model for simultaneous inversion of long-term spring flow in conjunction with solute- and heat-transport signatures, in a large-scale karst system. The MODFLOW-2005 CFPv2 code was adopted for this reason, utilizing PEST for automated inversion. Taking the principal of model parsimony into account, simulations were performed at two stages, testing likely conceptual models based on the hydro-geological understandings. At the first stage, simple yet realistic conceptual models were setup considering different probable variants of conduit geometries. Results of this stage highlights the importance of sinkhole-spring dynamics, in the recorded spring signatures; such that, successful simultaneous calibration of all spring signatures could not be obtained unless high linkage of conduits to the sinkholes all over the catchment was adopted. Subsequently, some additional rational complexity was added in order to achieve a more demonstrable model of the karst system, as the second stage. Model selection criteria, fitting statistics and reasonableness of calibrated parameters were assessed, at this stage. Although one of the model variants could statistically represent all observations with reasonable parameter values and high agreement with catchment hydrogeological perspective, it still cannot be approved as a predictive tool, unless field measurements on conduit system characteristics and matrix hydraulic parameters, as well as long-term observation of aquifer physicochemical signatures be collected for further validation/improvement of conceptual and numerical model. Achieved simultaneous inversion results can serve as a proof of concept for applicability of physically based discrete-continuum modeling approach for flow and transport modeling in karst.

The development of vulnerability maps is considered to be the first step in promoting awareness, development of protection strategies and sustainable use of karst aquifers. Nevertheless, high subjectivity of current methodologies for groundwater vulnerability assessment leads to contradictory results when different models are applied over the same area. This makes it difficult for water institutions and decision makers to determine a method to be used on a specific karst area. Four European methods (EPIK, PI, COP and PaPRIKa) were applied for the Yucatan karst to estimate groundwater vulnerability and determine if any of these European methods display vulnerability outcomes in correspondence with regional characteristics such as sinkhole alignments and the shallow water table. Agreement between methodologies was evaluated according to the spatial match on vulnerability rates displayed by final maps; intrinsic features influencing such match and divergent factors were highlighted. Similar vulnerabilities, with more than 52% in average of spatial agreement, were found between COP, PI and EPIK maps. A considerable average up to 33% of match in moderate vulnerability between these three methods was analysed. However, despite the methods displaying similarities regarding moderate vulnerability, these methodologies show no congruence with regional characteristics. A result of a moderate vulnerability on Yucatan coastal and central areas, where the unsaturated zone reaches just a couple of metres, is not an accurate outcome for the shallow water table. Adaptations of these methods or a new integrated methodology would be necessary to estimate groundwater vulnerability in the Yucatan karst.

Detailed analysis of Land Use/Land Cover (LULC) using remote sensing data in complex irrigated basins provides complete profile for better water resource management and planning. Using remote sensing data, this study provides detailed land use maps of the Lower Chenab Canal irrigated region of Pakistan from 2005 to 2012 for LULC change detection. Major crop types are demarcated by identifying temporal profiles of NDVI using MODIS 250 m × 250 m spatial resolution data. Wheat and rice are found to be major crops in rabi and kharif seasons, respectively. Accuracy assessment of prepared maps is performed using three different techniques: error matrix approach, comparison with ancillary data and with previous study. Producer and user accuracies for each class are calculated along with kappa coefficients (K). The average overall accuracies for rabi and kharif are 82.83% and 78.21%, respectively. Producer and user accuracies for individual class range respectively between 72.5% to 77% and 70.1% to 84.3% for rabi and 76.6% to 90.2% and 72% to 84.7% for kharif. The K values range between 0.66 to 0.77 for rabi with average of 0.73, and from 0.69 to 0.74 with average of 0.71 for kharif. LULC change detection indicates that wheat and rice have less volatility of change in comparison with both rabi and kharif fodders. Transformation between cotton and rice is less common due to their completely different cropping conditions. Results of spatial and temporal LULC distributions and their seasonal variations provide useful insights for establishing realistic LULC scenarios for hydrological studies.

Summary Reallocation of water resources in any irrigation scheme is only possible by detailed assessment of current irrigation performance. The performance of the Lower Chenab Canal (LCC) irrigation system in Pakistan was evaluated at large spatial and temporal scales. Evaporative Fraction (EF) representing the key element to assess the three very important performance indicators of equity, adequacy and reliability, was determined by the Surface Energy Balance Algorithm (SEBAL) using Moderate Resolution Imaging Spectroradiometer (MODIS) images. Spatially based estimations were performed at irrigation subdivisions, lower and upper LCC and, whole LCC scales, while temporal scales covered months, seasons and years for the study period from 2005 to 2012. Differences in consumptive water use between upper and lower LCC were estimated for different crops and possible water saving options were explored. The assessment of equitable water distribution indicates smaller coefficients of variation and hence less inequity within each subdivision except Sagar (0.08) and Bhagat (0.10). Both adequacy and reliability of water resources are found lower during kharif as compared to rabi with variation from head to tail reaches. Reliability is quite low from July to September and in February/March. This is mainly attributed to seasonal rainfalls. Average consumptive water use estimations indicate almost doubled water use (546 mm) in kharif as compared to (274 mm) in rabi with significant variability for different cropping years. Crop specific consumptive water use reveals rice and sugarcane as major water consumers with average values of 593 mm and 580 mm, respectively, for upper and lower LCC, followed by cotton and kharif fodder. The water uses for cotton are 555 mm and 528 mm. For kharif fodder, corresponding values are 525 mm and 494 mm for both regions. Based on the differences in consumptive water use, different land use land cover change scenarios were evaluated with regard to savings of crop water. It is found that such analyses need to be complemented at more fine spatial resolutions (i.e. irrigation subdivisions).

Irrigation water for agriculture in Pakistan is an issue due to a significant difference between rainfall and crop water needs. Irrigation water is either coming from snowmelt and rainfall in the northern mountains, or being pumped from groundwater. Canal water is limited, and water distribution using the warabandi system, a fixed canal water rotation system among water users on a particular irrigation channel, is not adequate and flexible. The result is overdependence on groundwater, which has impaired crop growth, notably in regions of bad groundwater quality.

In recent years, extensive competition for groundwater use among different consumers has exploited major freshwater aquifers in Pakistan. There is an urgent need for appraisal of this precious resource followed by some mitigation strategies. This modelling study was conducted in the mixed cropping zone of the Punjab, Pakistan. Both remote sensing and secondary data were utilized to achieve objectives of this study. The data related to piezometric water levels, canal gauges, well logs, meteorological and lithological information were collected from Punjab Irrigation Department (PID), Water and Power Development Authority (WAPDA). Groundwater flow models for both steady and transient conditions were set-up using FEFLOW-3D. Water balance components and recharge were estimated using empirical relations and inverse modelling approaches. Both manual and automated approaches were utilized to calibrate the models. Moreover, sensitivity analysis was performed to see the response of model output against different model input parameters. Followed by calibration and validation, the model was run for different management scenarios, including lining of canal sections, minimization of field percolation, and change of groundwater abstraction. The study results show a drop in groundwater levels for almost all scenarios. The highest negative change was observed for the 4th scenario (i.e. 25% increase in groundwater pumping over a 10-year period), with a value of 3.73 m, by ignoring very wet summer and winter seasons. For normal weather conditions, the highest negative change was observed for the 4th scenario with a value of 2.91 m followed by 2.68 m for the 3rd scenario (i.e. 50% reduction in canal seepage and field percolation over a 10-year period). For very wet summer and winter seasons, only one positive change was observed, for the 5th scenario (i.e. 25% decrease in groundwater pumping during 10 years period), with a value of 1.17 m. The changes for all other scenarios were negative. The mitigation strategy may include less groundwater pumping, by supporting cultivation of low delta crops and adjusting cropping patterns considering canal water supplies. It is further suggested to support current modelling results by incorporating more detailed information on cropping and by exploring the effect of climate change. Keywords : numerical modelling, sensitivity analysis, FEFLOW, scenario analysis, Pakistan

Groundwater is inevitable for agricultural production in the Indus Basin of Pakistan. Its management on sustainable basis is only possible by careful appraisal of its recharge potential and dynamics. This study aimed at exploring pixel-based groundwater recharge at 1 km2 spatial resolution using remote sensing data through water balance method. Moreover, spatially distributed groundwater abstractions are estimated by new approach with the aid of remote sensing data and results are compared with the conventional utilization factor method. Groundwater abstraction estimation from conventional utilization factor method overstates results both for kharif and rabi cropping seasons. Recharge results obtained from water balance method and water table fluctuation approach are comparable both at irrigation subdivision and 1 km2 spatial scales. During the kharif cropping seasons, rainfall is the main source of recharge followed by field percolation losses while for rabi cropping seasons, canal seepage remains the major source. Net groundwater recharge is mainly positive during all kharif seasons. A gradual increase in groundwater level is observed in major parts of the study area. Improvement in results from water table fluctuation method is possible by better distribution and increased intensity of piezometers while for water balance approach, it is possible by adopting alternative buffer zones for canal seepage. Detailed sensitivity and uncertainty analyses of input/output variables are needed to present the results with confidence interval and hence to support sustainable and economical operation of irrigation system.

Understanding the effects of major hydrogeological controls on hyporheic exchange and bank storage is essential for river water management, groundwater abstraction, restoration and ecosystem sustainability. Analytical models cannot adequately represent complex settings with, for example, transient boundary conditions, varying geometry of surface water–groundwater interface, unsaturated and overland flow, etc. To understand the influence of parameters such as (1) sloping river banks, (2) varying hydraulic conductivity of the riverbed and (3) different river discharge wave scenarios on hyporheic exchange characteristics such as (a) bank storage, (b) return flows and (c) residence time, a 2-D hydrogeological conceptual model and, subsequently, an adequate numerical model were developed. The numerical model was calibrated against observations in the aquifer adjacent to the hydropower-regulated Lule River, northern Sweden, which has predominantly diurnal discharge fluctuations during summer and long-lasting discharge peaks during autumn and winter. Modelling results revealed that bank storage increased with river wave amplitude, wave duration and smaller slope of the river bank, while maximum exchange flux decreased with wave duration. When a homogeneous clogging layer covered the entire river–aquifer interface, hydraulic conductivity positively affected bank storage. The presence of a clogging layer with hydraulic conductivity < 0.001 m d−1 significantly reduced the exchange flows and virtually eliminated bank storage. The bank storage return/fill time ratio was positively related to wave amplitude and the hydraulic conductivity of the interface and negatively to wave duration and bank slope. Discharge oscillations with short duration and small amplitude decreased bank storage and, therefore, the hyporheic exchange, which has implications for solute fluxes, redox conditions and the potential of riverbeds as fish-spawning locations. Based on these results, river regulation strategies can be improved by considering the effect of certain wave event configurations on hyporheic exchange to ensure harmonious hydrogeochemical functioning of the river–aquifer interfaces and related ecosystems.

Wastewater irrigation is a common livelihood practice in many parts of the developing world. With the continuous irrigation supply, groundwater systems in these regions perceive adverse impacts due to inadequate infrastructure to treat the wastewater. The current study area, Musi River irrigation system, is one such case study located in the peri-urban Hyderabad of South India. The Musi River water, which is used for irrigation, is composed of untreated and secondary treated wastewater from Hyderabad city. Kachiwani Singaram micro-watershed in the peri-urban Hyderabad is practicing wastewater irrigation for the last 40 years. The current quality of (untreated) wastewater used for irrigation is expected to have adverse impacts on the local aquifers, but detailed investigations are lacking. To elucidate the groundwater quality dynamics and seasonality of the wastewater irrigation impacts on the peri-urban agricultural system, we analyzed the groundwater quality on a monthly basis for one hydrological year in the wastewater and groundwater irrigated areas, which exist next to each other. The spatio-temporal variability of groundwater quality in the watershed was analyzed with respect to wastewater irrigation and seasonality using multivariate statistical analysis, multi-way modeling and self-organizing maps. This study indicates the significance of combining various statistical techniques for detailed evaluation of the groundwater processes in a wastewater irrigated agricultural system. The results suggest that concentrations of the major ionic substances increase after the monsoon season, especially in wastewater irrigated areas. Multi-way modeling identified the major polluted groundwaters to come from the wastewater irrigated parts of the watershed. Clusters of chemical variables identified by using self-organizing maps indicate that groundwater pollution is highly impacted by mineral interactions and long-term wastewater irrigation. The study recommends regular monitoring of water resources and development of sustainable management strategies to mitigate the aquifer pollution in wastewater irrigation systems.

The International Water Research Alliance Saxony (IWAS) is addressing the global challenges concerning water quality in the areas of drinking water and sanitation, agricultural irrigation and the quality of surface and ground waters, as well as developing specific ecosystem-relevant services to be implemented on an exemplary basis in selected model regions. Locations (model regions) have been selected in Eastern Europe (R1), Central and Southeast Asia (R2 and R3), the Middle East (R4) and Latin America (R5) that are representative international regions with respect to climate, land use and demographic change (Ibisch et al., Helmholtz Centre for Environmental Research—UFZ, Department of Aquatic Ecosystem analysis and management, 2013). The causes of water problems and the relevant boundary conditions vary from region to region (Borchardt and Ibisch, Integrated water resources management in a changing world : lessons learnt and innovative perspectives, pp 225, 2013). Mongolia and Vietnam were selected model regions in the first IWAS phase; the research was transferred and continued in one of the cross-cutting projects in IWAS II (Vietnam → capacity development) or in the frame of related project activities in Central Asia (R2 Mongolia, Karthe et al., Environ Earth Sci, doi: 10.1007/s12665-014-3789-1 , 2014). The IWAS consortium exists on scientific institutions like the Technische Universitat Dresden and the Helmholtz Centre for Environmental Research—UFZ, Leipzig, as well as partners from industry like the Stadtentwasserung Dresden GmbH (SE-DD), DREBERIS—Dresden consulting for international strategies, and itwh—institute for technical-scientific Hydrology, Hanover. This thematic issue compiles the most important scientific results of the second phase of the IWAS project. The project itself and findings of the first phase were already introduced in a previous special issue by Kalbus et al. (Environ Earth Sci 65:1363–1366, 2012). Main results: The IWAS project is structured by the model regions (R) as well as by cross-cutting activities scenario analysis (Q1), technology development (Q2), governance (Q3) and capacity development (Q4).

Summary Aquifer storage and recovery (ASR) methods are increasingly used to overcome the temporal imbalance between water demand and availability. Common ASR recharge methods utilize large-diameter injection wells or surface infiltration basins and trenches, and can be costly to implement. A new low-cost ASR recharge method is currently being developed. This approach is based on recharge via gravity in small-diameter wells installed with direct-push (DP) technology. Numerical modeling is used here to assess the potential of this new approach under conditions commonly faced in field settings. The primary objective is to investigate if a battery of small-diameter DP wells can serve as a viable alternative to a surface basin under typical field conditions, while the secondary objective is to assess which subsurface parameters have the greatest control on DP well performance. Simulation results indicate that gravity recharge via small-diameter wells appears to have a distinct advantage over recharge via surface infiltration basins. For example, two 0.05-m shallow vadose-zone wells with 9-m screens can recharge water at a greater rate than a 60 m 2 basin. Also, results reveal that, contrary to an infiltration basin, the recharge rate in a DP well has a much stronger dependence on the horizontal component of hydraulic conductivity than on the vertical component. Moreover, near-surface layers of low hydraulic conductivity, which can significantly reduce the recharge capacity of a surface basin, have a relatively small impact on the recharge capacity of a well as long as a significant portion of the well screen is installed below those layers. Given that installation and operation costs can be low in comparison to common ASR recharge methods, this new approach appears to have great potential for recharging good quality water in shallow unconsolidated aquifers. A field investigation has recently been initiated to follow up the findings of this simulation assessment.

This paper evaluates the remediation potential of a salinized coastal aquifer by utilizing a scenario simulation. Therefore, the numerical model OpenGeoSys is first validated against analytical and experimental data to represent transient groundwater level development and variable density saline intrusion. Afterwards, a regional scale model with a three-dimensional, heterogeneous hydrogeology is calibrated for a transient state and used to simulate a best-case scenario. Water balances are evaluated in both the transient calibration and scenario run. Visualization techniques help to assess the complex model output providing valuable insight in the occurring density-driven flow processes. Furthermore, modeling and visualization results give information on the time scale for remediation activities and, due to limitations in data quality and quantity reveal potential for model improvement.

In this study the suitability of precipitation waters as semi-artificial and multi-component groundwater tracers is investigated and potential applications as well as limitations are discussed. Specifically, we analyzed their migration behavior during laboratory-scale experiments with groundwater-saturated porous media. Artificially 2H- and 18O-labelled water as well as natural precipitation waters were injected into sediment-packed columns and traced via stable isotope analysis. Their migration behavior was compared to that of widely used tracers. These flow-through experiments were underpinned by a batch reactor study and by hydrogeochemical modeling. While most artificial isotope applications showed a high stability and conservative transport behavior for all tested sediments, the breakthrough curves observed in some experiments with rain and snowmelt were unsteady. This was most likely caused by the small ratio between the tracer’s isotopic difference compared to the background signal and the available analytical precision. The minimum ratio required for effectively reducing uncertainties during data evaluation showed to depend significantly on experimental conditions but should not decrease below ∼10 during peak breakthrough and preferably be higher. Furthermore, our study illustrates that measurements based on using the precipitation waters’ inherent low electrical conductivity can be significantly biased by water-sediment reactions. The batch study and reactive transport simulations confirmed this observation while revealing mineral reactions and, to a minor extent, also ion exchange as the underlying processes.

We present a novel approach for the numerical simulation of the gelation of silicate solutions under density-dependent flow conditions. The method utilizes an auxiliary, not density-dependent solute that is subject to a linear decay function to provide temporal information that is used to describe the viscosity change of the fluid. By comparing the modeling results to experimental data, we are able to simulate the behavior and the gelation process of the injected solute for three different compositions, including long-term stability of the gelated area, and non-gelation of low concentrations due to hydro-dynamic dispersion. This approach can also be used for other types of solutes with this gelling property and is useful in a variety of applications in geological, civil and environmental engineering.

A groundwater model characterized by a lack of field data about hydraulic model parameters and boundary conditions combined with many observation data sets for calibration purpose was investigated concerning model uncertainty. Seven different conceptual models with a stepwise increase from 0 to 30 adjustable parameters were calibrated using PEST. Residuals, sensitivities, the Akaike information criterion (AIC and AICc), Bayesian information criterion (BIC), and Kashyap's information criterion (KIC) were calculated for a set of seven inverse calibrated models with increasing complexity. Finally, the likelihood of each model was computed. Comparing only residuals of the different conceptual models leads to an overparameterization and certainty loss in the conceptual model approach. The model employing only uncalibrated hydraulic parameters, estimated from sedimentological information, obtained the worst AIC, BIC, and KIC values. Using only sedimentological data to derive hydraulic parameters introduces a systematic error into the simulation results and cannot be recommended for generating a valuable model. For numerical investigations with high numbers of calibration data the BIC and KIC select as optimal a simpler model than the AIC. The model with 15 adjusted parameters was evaluated by AIC as the best option and obtained a likelihood of 98%. The AIC disregards the potential model structure error and the selection of the KIC is, therefore, more appropriate. Sensitivities to piezometric heads were highest for the model with only five adjustable parameters and sensitivity coefficients were directly influenced by the changes in extracted groundwater volumes.

The impact of source thickness on steady-state plume length is studied using modifications of the analytical expressions provided in Liedl et al. (2005, 2011) for 2D and 3D scenarios. For comparison, 2D and 3D numerical experiments were performed, and the following three important conclusions were obtained: first, the modified expressions overestimate the plume length only up to a factor of 2 when the source thickness (M s ) is at least 50 % of the aquifer depth (M). Second, overestimates do not exceed plume length by a factor of 10 (2D scenario) or 5 (3D scenario) for 25 % 50 %. As far as the numerical experiments are concerned, it is important to note that the employed finite element approach was applied to the transformed transport equation provided in both Liedl et al. works. This transformation, which can also be applied to more complex scenarios than those studied here, eliminates reaction terms from the model equations and therefore largely facilitates numerical computations.