Alluvial Aquifer System Research Articles

Oxygen and hydrogen isotopic composition of waters in a past-mining area of southern Apuan Alps (Italy): Hydrogeological characterization and implications on the fate of potentially toxic elements

The oxygen and hydrogen isotopic composition of stream water, springs, groundwater tapped from irrigation wells and acid mine drainages were determined during two different surveys in 2015 in an area highly impacted by past-mining activity of Apuan Alps (Italy), as a guidance on good practices for water management. The isotopic local meteoric water line (LMWL) was built by monthly collecting rainwater between 2014 and 2018, given by δD = 7.02 ± 0.35 × δ18O + 8.54 ± 2.89. The obtained results indicate that acid mine drainages (AMD) are supplied by freshwater from karst systems which flow throughout the post-mining workings. Such waters contaminate by interactions with sulfides (pyrite) that remained unmined in the ore-bodies. During rainstorms, infiltration rainwater displaces water ponding within mine, sharply increasing the outflow rate of highly-contaminated AMD. Acidic drippings in tunnels show an isotopic shift in both δ18O and δD values attributable to pyrite oxidation and Fe hydrolysis. The data reveal that karst-springs represents the primary supply for the stream. The isotopic data also reveal that waters flowing in the bedrock carbonate aquifer represent the main feeding component for the overlying alluvial aquifer tapped by wells. The prevailing transfer of clean freshwaters from the carbonate aquifer towards the alluvial aquifer system mitigates the possible influence of contaminated water from stream seepage. However, these observations require a monitoring program on water quality to be established.

Critical Zone Assessments of an Alluvial Aquifer System Using the Multi-influencing Factor (MIF) and Analytical Hierarchy Process (AHP) Models in Western Iran

Many arid regions in the world suffer from over-exploitation of local groundwater resources leading to the degradation of freshwater aquifer systems, drying of spring discharges, and other damage to land and infrastructure. The development of groundwater critical zone maps (GCZMs) using the best available data is one important method that can be used by decision makers to develop a justifiable regulatory framework that may ban future use of wells. The multi-influencing factor (MIF) and the analytical hierarchy process (AHP) methods were used to create GCZMs for the Kangavar sub-catchment basin (aquifer system) of western Iran. Seven mapped factors were used as input into the models that included spatial occurrence of geological formations, aquifer lithologies, aquifer thickness, aquifer recharge, annual groundwater discharge (including water use), water-well density, and groundwater quality (degradation). Weighting factors were placed on the input data based on expert opinions, and the created thematic maps were combined using the weighted sum tool within a GIS framework to create two separate GCZMs. It was found that both methods produced acceptable and similar results, but based on a receiver operating characteristic curve analysis of internal error the MIF model (0.82) was > 10% more accurate compared to the AHP model (0.72). Critical and subcritical classification areas within the basin covered areas of 94 and 77.7 km2 in the MIF and AHP maps, respectively. Banning of water-well construction in these areas is therefore technically justifiable and demonstrates the need to use two methods for development and verification of GCZMs with varying assumptions.

Development and Evaluation of Hybrid Artificial Neural Network Architectures for Modeling Spatio-Temporal Groundwater Fluctuations in a Complex Aquifer System

The proper design, development, and appropriate tuning of the Hybrid Neural Network architecture, mainly for its parsimoniousity and optimal training can help practitioners to generate a robust predictive tool for modeling several important hydrological processes within the water resources sector. In this paper, the Feedforward Artificial Neural Network (FFANN) and the hybrid WANN model have been developed, and later, coupled with the Gamma and M-tests (GT) approach for forecasting spatio-temporal groundwater fluctuations in a complex alluvial aquifer system. The performance of these hybrid models were evaluated using goodness-of-fit criteria. An analysis of the modeling results indicates that the GT coupled with the WANN model was able to provide significantly improved results, with lower values of the root mean square error (RMSE) and higher values of the NSE metric for the 1-week and 3-week lead times. Hence, utilizing this hybrid model, the groundwater level prediction tests were extended for 6-week and 12-week lead times with the GT approach, coupled with the WANN hybrid model only. The results showed that the accuracy of the GT-WANN hybrid model was better for the unconfined aquifer system compared to the leaky confined aquifer system. Furthermore, the present study also examined the interdependence between different model inputs and output variables for the selected study sites by means of the Wavelet Coherent Analysis (WCA). These results indicated that all the model’s input variables have a significant effect on the groundwater level of unconfined aquifers, and confirmed the nature of the aquifers tapped within the present study sites. The study finally concludes that the GT-WANN approach can be a robust predictive tool for modeling spatio-temporal fluctuations of groundwater levels.

Trends and probabilistic stability index for evaluating groundwater quality: The case of quaternary alluvial and quartzite aquifer system of India

This study proposed a novel groundwater-quality stability index (GQSI), which considers probabilistic estimate of reliability and resilience based on multi-year dataset. The developed index is validated and optimized adopting optimum index factor approach. The vulnerabilities of different groundwater quality parameters are also computed to provide an insight about the deviations of their concentrations from the safe drinking water limits. The application of the developed stability index is demonstrated through a case study in quaternary alluvial and quartzite aquifer system of India. In addition, trends in the groundwater quality parameters are identified by using variance-corrected Mann-Kendall test, and trends are quantified by using Sen's slope estimation test. Box-whisker plots revealed that EC and TDS mostly exceed their maximum permissible limits prescribed for drinking water in the southern and southwest hard-rock formations. Whereas, most parameters do not cross their maximum desirable limits in the central and northern alluvial formations. Increasing trends of potassium and bicarbonate, and decreasing trends of carbonate, calcium, sulfate, and fluoride are found prominent. The GQSI values indicated high stability of groundwater quality under older alluvium geology and low stability under the gneiss and mica-schist. Results of the GQSI are found in agreement with that of groundwater-quality index (GQI) at 84% sites, which proved adequacy of the developed GQSI. Also, three classes (‘low’/‘poor’, ‘moderate’, and ‘high’/‘good’) of both the GQSI and GQI showed a good coherence at 83, 78, and 87% sites. However, GQSI is more advantageous than GQI due to former's statistical framework, consistency and comparability over different areas. Three optimum index factors, i.e., TDS, pH and nitrate, are found to have the maximum impact on overall groundwater quality with their largest variations. Results of the optimum groundwater-quality stability index (OGQSI) and GQSI closely matched with each other, and a significant linear relationship (R2 = 0.70) existed between them. Therefore, OGQSI is a cost-effective approach for adequate monitoring and satisfactory evaluation of the groundwater quality in low-income nations.

Seasonal microbial variation accounts for arsenic dynamics in shallow alluvial aquifer systems.

Determining the temporal variation of microbial communities in groundwater systems is essential to improve our understanding of hydrochemical dynamics in aquifers, particularly as it relates to the fate of redox-sensitive contaminants like arsenic (As). Therefore, a high-resolution hydrobiogeochemical investigation was conducted in the As-affected alluvial aquifer systems of the Jianghan Plain. In two 25 m-deep monitoring wells, the seasonal variation in the composition of groundwater microbial communities was positively correlated with the change in groundwater level (R = 0.47 and 0.39 in NH03B and NH05B, respectively, P < 0.01), implying that the latter could be a primary driver of the seasonal microbial dynamics. In response to the fluctuating groundwater level, iron (Fe) reducers within the Desulfuromonadales were dominant (9.9 ± 4.7% among different sampling sites) in groundwater microbial communities during the monsoon season and associated with high concentrations of Fe(II) and As, while the predominance (16.7 ± 15.2% among different sampling sites) of iron-oxidizers the Gallionellaceae was accompanied by low Fe(II) and As in the non-monsoon season. These results suggest that microbially-mediated iron reduction/oxidation may have governed the seasonal mobilization/scavenging of As in groundwater. Our results provide new insights into mechanisms responsible for seasonal variations in groundwater As concentrations in similar aquifer systems.

Responding to salinity in a rural African alluvial valley aquifer system: To boldly go beyond the world of hand-pumped groundwater supply?

Effective response to groundwater salinity in the developing world may critically safeguard drinking-water supplies. Groundwater resources throughout rural Africa are exploited by a vast and increasing number of hand-pumped boreholes for community supply. Our research in TA Ngabu (Shire Valley), Southern Malawi aims to: define groundwater-salinity problem occurrence within the semi-arid alluvial-valley aquifer, rural developing-world setting; critique current capacity to respond; and, to discuss future response options - in particular considering the need to explore alternative options that boldly go beyond the world of hand-pumped groundwater supply. Salinity problem definition was achieved through survey of 419 hand-pumped boreholes that revealed widespread brackish groundwater leading to non-potable (unpalatable) drinking-water supplies. Persistent non-functionality or abandonment of boreholes was typically ascribed to salinity. Whilst salinity is conceptualised to arise from shallow-groundwater evaporation, formation-evaporite dissolution and faulted-area upwelling, sparse data locally renders attribution of salinity sources to individual boreholes difficult. There is a significant need to better resolve the vertical distribution of salinity and local controlling processes. Problem response capacity was hampered by multiple factors, including, sector inertia, low drilling costs compromising water-point integrity, and lack of technical vision for alternatives. Various recommendations are made to improve response capacity continuing to work at the hand-pump supply scale. However, in areas where salinity is significant, exploring the feasibility of other options is advocated in conjunction with technical capacity development. Groundwater options may utilise high borehole yields possible from alluvial aquifers, grossly under-exploited by hand pumps. Groundwater at depth, albeit of unknown quality typically, or pipeline transfers of probable good-quality groundwater from valley-margin units, should be considered. Surface-water pipeline supplies may be viable for (growing) population centres. Canal-fed irrigation schemes (pending for the area), should be multiple-use, protective of groundwater and embrace pipeline drinking-water supply and managed-aquifer-recharge opportunities. Advancing desalination technologies, although presently unaffordable, should be kept under review.

Flow to a well in an unconfined-fractured and leaky wedge-shaped aquifer system

Wedge-shaped aquifers are usually formed where two linear boundaries intersect. These types of aquifers are commonly seen in river basins and alluvial fans, but have received much less attention in the hydrological sciences community. Fundamental understanding of the effects of lateral boundaries on the hydrodynamic process in such aquifers is quite poor, particularly for unconfined-fractured and leaky wedge-shaped aquifer systems, which will be the concern of this study. Solutions of flow to a well in an unconfined-fractured wedge-shaped two aquifer system are obtained using Laplace, Hankel and Fourier transforms. An infinitesimal radius pumping well partially penetrates the overlying unconfined aquifer. Both aquifer layers are homogeneous and anisotropic bounded by two intersecting linear lateral boundaries of constant-head or barrier types and the aquifer system is semi-infinite in radial direction. The time domain drawdowns are obtained via the Stehfest algorithm and Gaussian Quadrature. The inter-porosity flow in the underlying fracture aquifer, the instantaneous water table drainage, the horizontal and vertical hydraulic conductivity anisotropy and the wedge angle are taken into account. Eliminating the inter-porosity flow in the underlying fractured aquifer, the presented solution reduces to a leaky wedge-shaped aquifer case. The influences of the underlying fractured aquifer hydraulic parameters on the overlying unconfined aquifer for different wedge angles and linear lateral boundaries types are explored using dimensionless drawdown and scaled sensitivity curves. The results of this study can be utilized to obtain hydraulic parameters of an alluvial and river basin unconfined-fractured wedge-shaped aquifer systems. The presented solution can also be used for water budget assessment of river basin aquifers.

The origins of high concentrations of iron, sodium, bicarbonate, and arsenic in the Lower Mississippi River Alluvial Aquifer

Many alluvial aquifer systems are characterized in part by groundwater rich in sodium (Na) and bicarbonate (HCO3) and elevated concentrations of dissolved iron (Fe) and arsenic (As). However the relationships among Fe and As concentrations and the formation of NaHCO3 waters are unclear. Here we evaluated the formation of NaHCO3 groundwater in the Lower Mississippi River Alluvial Aquifer (LMRAA) in Louisiana, USA, where concentrations of dissolved Fe and As reached values as high as 16 mg/L and 64 μg/L, respectively. Water isotope data showed that groundwater was predominantly recharged via local precipitation outboard of the Mississippi River, while groundwater nearer the river and to the south of the study area was more hydraulically connected to the river. Much of the geochemical data, including water isotopes, calcite saturation index, Na excess, and As correlated to some degree with well depth, highlighting the complex interactions between the shallower recharge from local precipitation and the deeper reaction pathways laterally connected to the Mississippi River and/or vertically connected with regional groundwater. The δ13C(DIC) of groundwater ranged from −17.4 to −11.1‰, likely representing a mixture of microbially- and abiotically-derived alkalinity. Within this context, the production of groundwater rich in NaHCO3 can be explained by reaction pathways involving the weathering of CaNa silicate phases. This weathering, driven in part by the production of microbial CO2 during Fe and sulfate reduction, may continue past the point of calcite saturation. Once calcite reaches saturation the concentration of Ca is buffered, but there is a possibility of further buildup in the concentrations of Na and HCO3. The silicate weathering model serves as an alternative conceptual model to calcite dissolution and clay exchange for the development of NaHCO3 waters. If globally important, this water-rock reaction pathway could place new constraints on the processes influencing the fate and transport of Fe and As in alluvial aquifer systems.

Hydrogeochemical characterization of a shallow alluvial aquifer: 1 baseline for groundwater quality assessment and resource management

Considering the progressive depletion of groundwater quantity and the alteration of superficial and groundwater quality in the Madrid region, a highly populated area with extended urbanizations in the north and agricultural activities in the south, we conducted a monitoring study over a period of 2.5 years (2015–2017). The study was conducted in the Jarama-Tajuña shallow alluvial aquifer system located southeast of Madrid, where the exploitation of the aquifer and the Jarama river have increased exponentially in the last decade being affected by both urban and agricultural activities. Our aims were to provide: i) a geochemical characterization of the surface and groundwater properties; ii) identify the process responsible for the geochemical evolution and mineralization of the waters; iii) assess the water quality (i.e. nitrates, ammonia, sodium and chloride as potential contaminants) and the water suitability for irrigation (SAR, Wilcox, KI and MH indexes); and iv) identify the main sources of contamination in the area.A set of plots, ion ratios, correlation coefficients, multivariate statistical analyses and indexes were performed. Results indicated that rock weathering largely controls the hydrogeochemistry of the system and that wastewater treatment plant discharges and agricultural practices significantly affect the composition of the water, causing an important decline of both surface and groundwater chemical quality. Nonetheless, water suitability for irrigation is admissible. Thus, taking additional measures to increase its quality are not necessary.With this study we aimed to establish a base line to evaluate future changes in the groundwater properties from the Madrid region enabling the planners and policy makers to develop a strategy to mitigate the impact of the exponential increase of urban and agriculture activities on groundwater resources.

Preventing Groundwater Pollution Using Vulnerability and Risk Mapping: The Case of the Florina Basin, NW Greece

The alluvial aquifer system of the Florina basin (320 km2) in North Greece is a representative area where irrigated agriculture is applied. Groundwater is the main source of water. The highest and mean nitrate concentrations in groundwater are 67.9 mg/L and 25 mg/L, respectively. High values could be associated with the use of nitrogen fertilizers from agricultural activities. This study deals with the evaluation of the groundwater quality. For this reason, hydrochemical analyses from 29 groundwater samples and water level measurements were performed for the wet and dry periods of 2016. The suitability of groundwater quality for irrigation purposes is examined by using different indices (Chlorinity Index, SAR, Sodium Percentage, Potential Salinity and Kelly’s index). In addition, the DRASTIC method was modified by using statistical methods, land use map and nitrate concentrations and applied in order to assess the groundwater vulnerability to external pollution. Notably, there was no correlation between the standard DRASTIC method and nitrate concentrations. However, the modified version and the obtained risk map showed high correlation with nitrate concentrations (ρ = 0.55) and the Groundwater Quality; hence, it is suggested as the base for a protection plan of the alluvial aquifer.

Identifying local and regional groundwater in basins: chemical and stable isotopic attributes of multivariate classification of hydrochemical data, the Lower Virgin River Basin, Nevada, Arizona and Utah, U.S.A

ABSTRACTIn the Basin and Range Province of the Southwestern U.S.A., deep carbonate groundwater has been suggested as a significant source to many overlying basin-fill alluvial aquifer systems. Notwithstanding, testing this hypothesis is limited by obtaining data from such considerable depths and complex geology.This study uses δ2H and δ18O data from springs, rivers, and wells tapping shallow basin-fill groundwater to test the hydrochemical interpretation of deep regional carbonate groundwater flow into the basin-fill aquifers. Stable isotopic and major ion attributes of hydrochemical facies suggest basin-fill alluvial groundwater of the Lower Virgin River Basin is a mixture of precipitation recharge within the Lower Virgin River Basin or the Clover and Escalante Desert Basin northwards, and the deep carbonate flow. The data support the conclusions that in the Lower Virgin River Basin, deep carbonate groundwater is an important source to the alluvial aquifer system and likely accounts for approximately 50% of the alluvial aquifer groundwater. Na+, K+, and SO42– increase in the basin-fill alluvial groundwaters outside the Virgin River floodplain appears to be related with upwelling of deep regional groundwater, and indicating that the chemical character of the basin-fill alluvial groundwaters are related to the deeper flow systems.

Hydrologic and Geochemical Research at Pinios Hydrologic Observatory: Initial Results

Core Ideas Modeled ETo gradients present variations as a function of altitude, annual cycle, and total amount. A very good match between different soil moisture monitoring devices has been achieved. Groundwater level monitoring revealed dominant hydrodynamic evolution mechanisms. Hydrochemical monitoring supports groundwater hydrology findings and reveals pollution sources. Monitoring the PHO supports accurate hydrologic modeling and sustainable water use. The Pinios Hydrologic Observatory (PHO) is located in the River Pinios basin, which is one of the most productive basins in Greece. The PHO was established to develop deep knowledge of water balance at the river basin scale and to improve understanding of the major hydrodynamic mechanisms to improve hydrological modeling and ultimately sustainable water resource management. The PHO comprises three meteorological stations, 12 groundwater monitoring sites, and one soil moisture monitoring site, which includes frequency domain reflectometry sensors (SoilNet) and a cosmic‐ray neutron sensor (CRNS) probe. Although the PHO was recently established (at the end of 2015), the preliminary findings from data analysis are promising. Calculated reference evapotranspiration (ETo) gradients demonstrate differences regarding their annual cycle, total amount, and altitude level. Moreover, climate analysis indicates nocturnal mountain‐valley winds. Groundwater level spatial distribution indicates the dominant recharge mechanisms to the alluvial aquifer system. These findings are also supported by the hydrochemical data analysis (electrical conductivity and, secondarily, NO3 distribution). Locally elevated NO3 concentrations are attributed to agricultural activities and call for review of the adopted farming practices. Results from the soil moisture monitoring site indicate a very good match between the CRNS probe and the average SoilNet data. Future perspectives of the PHO include geophysical surveys to accurately delineate the geometry of the groundwater system, the expansion of groundwater and soil moisture observation networks, and the application of the mGROWA hydrologic model to accurately simulate the hydrological processes in the PHO and upscale in the entire River Pinios basin. Finally, in support of the local farmers, we plan to develop and implement a distributed irrigation programming protocol in the entire area of the PHO.

Assessing groundwater vulnerability using GIS-based DRASTIC model for Ahmedabad district, India

The present research aims to derive the intrinsic vulnerability of groundwater against contamination using the GIS platform. The study applies DRASTIC model for Ahmedabad district in Gujarat, India. The model uses parameters like depth, recharge, aquifer, soil, topography, vadose zone and hydraulic conductivity, which depict the hydrogeology of the area. The research demonstrates that northern part of district with 46.4% of area is under low vulnerability, the central and southern parts with 48.4% of the area are under moderate vulnerability, while 5.2% of area in the south-east of district is under high vulnerability. It is observed from the study that lower vulnerability in northern part may be mostly due to the greater depth of vadose zone, deeper water tables and alluvial aquifer system with minor clay lenses. The moderate and high vulnerability in central and southern parts of study area may be due to lesser depth to water tables, smaller vadose zone depths, unconfined to semi-confined alluvial aquifer system and greater amount of recharge due to irrigation practices. Further, the map removal and single-parameter sensitivity analysis indicate that groundwater vulnerability index has higher influence of vadose zone, recharge, depth and aquifer parameters for the given study area. The research also contributes to validating the existence of higher concentrations of contaminants/indicators like electrical conductivity, chloride, total dissolved solids, sulphate, nitrate, calcium, sodium and magnesium with respect to groundwater vulnerability status in the study area. The contaminants/indicators exceeding the prescribed limits for drinking water as per Indian Standard 10500 (1991) were mostly found in areas under moderate and high vulnerability. Finally, the research successfully delineates the groundwater vulnerability in the region which can aid land-use policies and norms for activities related to recharge and seepage with respect to existing status of groundwater vulnerability and its quality.

Groundwater quality in the alluvial aquifer system of northwest India: New evidence of the extent of anthropogenic and geogenic contamination

Groundwater depletion has been widely studied in northwest India, but water quality concerns are still poorly constrained. In this study, we explore the hydrochemistry of the top 160m of the aquifer system, through detailed field studies in the Bist-Doab region, considering both anthropogenic and geogenic controls. A detailed comparison is made between sites dominated by urban and agricultural landuse. Salinity, nitrate, chloride and lead concentrations are significantly higher in the shallow (0–50m) groundwater system due to surface anthropogenic contaminant loading from agricultural and urban sources. The widespread occurrence of oxic groundwater within the aquifer system means that denitrification potential is limited and also enhances the mobility of selenium and uranium in groundwater. Geogenic trace elements (e.g. As, Se, F), are generally found at concentrations below WHO guideline drinking water values, however elevated U concentrations (50–70μg/L) are found within the deeper part of the aquifer and shallow urban aquifers associated with higher bicarbonate waters. Higher concentration of Se (10–40μg/L) are found exclusively in the shallow groundwater system where Se is mobilised from soils and transported to depth in the shallow aquifer due to the prevailing oxidising aquifer conditions. New evidence from a range of environmental tracers shows elevated concentrations of anthropogenic contaminants in the deeper part of the aquifer (50–160m deep) and demonstrates vulnerability to vertical migration of contaminants. Continued intensive groundwater abstraction from >100m deep means that water quality risks to the deep aquifer system need to be considered together with water quantity constraints.

Assessment of alluvial aquifer heterogeneity and development of stochastic hydrofacies models for the Hat Yai Basin in Southern Thailand

In previous studies, the groundwater flow models formulated for the Hat Yai Basin were conventional and deterministic because the geologic heterogeneity of the alluvial aquifer system in the basin had not yet been assessed. This paper describes an effort to develop hydrofacies models, such that the spatial variability of the aquifer system can be represented in a systematic way. Variogram parameters that characterize the alluvial aquifer heterogeneity were determined. Based on these variogram parameters, an indicator-based geostatistical approach was used to develop hydrofacies models using sequential indicator simulation. The hydrofacies models indicate three distinct aquifer units, namely Hat Yai, Khu Tao, and Kho Hong aquifers, which is in good agreement with a conceptual model, and incorporates spatial variability as observed in field data from borehole logs. The hydrofacies models can be used in groundwater modeling and simulations.

Comparison of groundwater recharge estimation techniques in an alluvial aquifer system with an intermittent/ephemeral stream (Queensland, Australia)

This study demonstrates the importance of the conceptual hydrogeological model for the estimation of groundwater recharge rates in an alluvial system interconnected with an ephemeral or intermittent stream in south-east Queensland, Australia. The losing/gaining condition of these streams is typically subject to temporal and spatial variability, and knowledge of these hydrological processes is critical for the interpretation of recharge estimates. Recharge rate estimates of 76–182 mm/year were determined using the water budget method. The water budget method provides useful broad approximations of recharge and discharge fluxes. The chloride mass balance (CMB) method and the tritium method were used on 17 and 13 sites respectively, yielding recharge rates of 1–43 mm/year (CMB) and 4–553 mm/year (tritium method). However, the conceptual hydrogeological model confirms that the results from the CMB method at some sites are not applicable in this setting because of overland flow and channel leakage. The tritium method was appropriate here and could be applied to other alluvial systems, provided that channel leakage and diffuse infiltration of rainfall can be accurately estimated. The water-table fluctuation (WTF) method was also applied to data from 16 bores; recharge estimates ranged from 0 to 721 mm/year. The WTF method was not suitable where bank storage processes occurred.

Estimating Hydraulic Properties of Alluvial Sand Aquifer in Motloutse River course, Eastern Botswana

A single layered alluvial aquifer in Botswana along the Motloutse River catchment was studied to estimate its hydraulic properties. Ground Penetrating Radar Survey (GPR) was used to determine the thickness and porosity of the aquifer. Specific yield of the aquifer was determined in the laboratory. The hydraulic conductivity of the riverbed sediments were estimated using the Alyamani-Sen empirical formula and the hydraulic conductivity of the river bank sediment was measured using the slug test. Geologically, the area is consists of alluvial deposits overlying granite, which is the bed rock of the area. The geophysical survey, GPR, provided information on the range of the thickness of the alluvium (9 – 12m) and also the porosity of the sediments (40%). The laboratory test resulted in an average specific yield of 13.68% for the riverbed sediments and 8.84% for the river bank sediments. A slug test performed in the riverbank yielded estimates of hydraulic conductivity of 26.43m/day. An average hydraulic conductivity value of 160m/day for the riverbed sediments was determined using the Alyamani-Sen formula. This difference in the hydraulic properties of the riverbed and the riverbank sediments is likely to be a result of sediment heterogeneity as more fine grained sediments is found together with sand in the riverbank sediments. These combined hydraulic properties estimation using empirical formulas, geophysical survey, laboratory tests, and the slug test highly improved the understanding of the hydrologic properties of the single layered alluvial aquifer system in the Motloutse River catchment. In the same area, groundwater resource modelling can be done using these aquifer parameters to determine the groundwater potential of the aquifer.

CROSS-CORRELATION MODELLING OF SURFACE WATER – GROUNDWATER INTERACTION USING THE EXCEL SPREADSHEET APPLICATION

Modelling responses of groundwater levels in aquifer systems, which occur as a reaction to changes in aquifer system boundary conditions such as river or stream stages, is commonly being studied using statistical methods, namely correlation, cross-correlation and regression methods. Although correlation and regression analysis tools are readily available in Microsoft Excel, a widely applied spreadsheet industry standard, the cross-correlation analysis tool is missing. As a part of research of groundwater pressure propagation into alluvial aquifer systems of the Sava and Drava/Danube River catchments following river stages rise, focused on estimating groundwater pressure travel times in aquifers, an Excel spreadsheet data analysis application for cross-correlation modelling has been designed and used in modelling surface water – groundwater interaction. Examples of fi eld data from the Zagreb aquifer system and the Kopacki rit Nature Park aquifer system are used to illustrate the usefulness of the cross-correlation application.

Basin-scale hydrogeological, geophysical, geochemical and isotopic characterization: an essential tool for building a Decision Support System for the sustainable management of alluvial aquifer systems within the provinces of Milan and Monza-Brianza

CAP Group is a public company, supplying the municipalities within the provinces of Milan and Monza/Brianza (Northern Italy) with the integrated water service: 197 municipalities and more than 2 million users served, 887 wells, 154 wall-mounted tanks and hubs, a water supply network of over 7500 km, from which approximately 250 million cubic metres of water per year are withdrawn. The drinking water supply comes exclusively from groundwater resources, circulating in several overlapping aquifer systems. Basin-scale water resource management, as required by the European Water Framework Directive (2000/60/EC), is an extremely complex task. In view of this backdrop, CAP is currently developing a project called Infrastructural Aqueduct Plan that relies on a Decision Support System approach. The paper describes the preliminary steps concerning the design of a prototype Decision Support System aiming at the management of groundwater resources on a basin scale (Ticino and Adda rivers area). CAP Group Decision Support System is intended to be a package allowing for water resource assessment, identification of boundary conditions, climatic driving forces and demographic pressures, simulation and investigation of future forecasts and comparison of alternative policy measures. The project has been designed in steps including Geodatabase building, geographic information system (GIS) analysis (including multilayer analysis) and numerical modelling. The data collected in the geodatabase were analyzed to design GIS quantitative and qualitative thematic maps in order to perform the multilayer analysis of current and future state and impacts, for providing the decision maker with a comprehensive picture of the water system. The multilayer analysis relies on specific indicators based on some quantitative and qualitative data: hydrogeological, chemical, isotopic, soil use and hazards, climatic and demographic. Each parameter belonging to these macro areas were classified by 7-criticality classes scale and weights were assigned to each of them. For each macro area a synthetic index was calculated by multiplying class values with weights. These synthetic indexes were managed with a multilayer approach and compared with other models and tools (e.g. geological model, numerical groundwater model, distribution network model) in order to obtain criticality indexes. The assessment of these criticality indexes allow to evaluate alternative and strategic solutions to achieve a more efficient and sustainable water system management using a best choice approach. Currently the project team is working on multilayer analysis. The next task will be the implementation of groundwater numerical model.

The recharge process in alluvial strip aquifers in arid Namibia and implication for artificial recharge

Alluvial strip aquifers associated with ephemeral rivers are important groundwater supply sources that sustain numerous settlements and ecological systems in arid Namibia. More than 70 % of the population in the nation’s western and southern regions depend on alluvial aquifers associated with ephemeral rivers. Under natural conditions, recharge occurs through infiltration during flood events. Due to the characteristic spatial and temporal variability of rainfall in arid regions, recharge is irregular making the aquifers challenging to manage sustainably and they are often overexploited. This condition is likely to become more acute with increasing water demand and climate change, and artificial recharge has been projected as the apparent means of increasing reliability of supply. The article explores, through a case study and numerical simulation, the processes controlling infiltration, significance of surface water and groundwater losses, and possible artificial recharge options. It is concluded that recharge processes in arid alluvial aquifers differ significantly from those processes in subhumid systems and viability of artificial recharge requires assessment through an understanding of the natural recharge process and losses from the aquifer. It is also established that in arid-region catchments, infiltration through the streambed occurs at rates dependent on factors such as antecedent conditions, flow rate, flow duration, channel morphology, and sediment texture and composition. The study provides an important reference for sustainable management of alluvial aquifer systems in similar regions.