A Modified AVI Model for Groundwater Vulnerability Mapping: Case Studies in Southern Italy

Many methods for evaluating the aquifer’s vulnerability to pollution have been developed in the past four decades by using geographic information system (GIS) tools. However, even if the aquifer vulnerability concept is well defined and the methods have been constantly tested and compared, the problem of the choice of the best “standard” method remains. To meet these objectives, aquifer vulnerability maps are of crucial importance. The choice of method depends on several factors, including the scale of the project, the hydrogeological characteristics of the area, and data availability. Among the many methods, the AVI (Aquifer Vulnerability Index) method has been widely used as it considers only two physical parameters. The AVI Index represents the hydraulic resistance of an aquifer to vertical flow, as a ratio between the thickness of each sedimentary unit above the uppermost aquifer (D, length), and the estimated hydraulic conductivity (K, length/time) of each of these layers. The AVI Index has a time dimension and is divided into five classes. In order to avoid a widespread presence of the higher vulnerability classes, especially in shallow aquifers, the AVI classification has been modified using statistical methods. The study reports the application of the modified AVI method for groundwater pollution vulnerability, in three different areas of southern Italy, highlighting the limitations of the method in alluvial aquifers and the differences with other methods.

Pumping Well Layout Scheme Design and Sensitivity Analysis of Total Critical Pumping Rates in Coral Island Based on Numerical Model

Groundwater on small coral islands exists in the form of freshwater lenses that serve as an important water resource for local inhabitants and ecosystems. These lenses are vulnerable to salinization due to groundwater abstraction and precipitation variation. Determination of the sustainable yield from freshwater lenses is challenging because the uncertainties of recharge and hydrogeological characteristics make it difficult to predict the lens response to long-term pumping. In this study, nine pumping well layout schemes along a line are designed using the orthogonal experimental design method, and an optimal well layout scheme is determined by multi-index range analysis and comprehensive balance analysis method. The total critical pumping rates of the freshwater lens corresponding to different schemes are calculated by numerical simulation, and the sensitivity of the total critical pumping rates to hydrogeological parameters is analyzed. The results show that the calculation of the total critical pumping rates needs to be combined with the specific well layout scheme with consideration to the length of well screens, the number of wells and the distance between wells. The difference in total critical pumping rates between different schemes can be up to three times. The uncertainty of hydrogeological parameters has a great impact on the total critical pumping rates. Within the range of a 30% reduction in parameters, α and K are the key risk factors of pumping; within the range of a 30% increase in parameters, α, ne and K are the key risk factors; α-ne combined changes had the greatest impact. The management of freshwater lenses and the assessment of sustainable yield will continue to be important tasks for coral islands in the future, and this study can help with the sustainable exploitation of island freshwater lenses.

Basics of Calculation and Design of Two-Column Two-Filter Water Intake Wells

The paper provides an overview of the known designs of water wells. A new design of a two-column two-filter water intake well has been also proposed, in which the filters are arranged in two tiers. This will lead to an increase in water intake capacity and will reduce the filtration rate on the approach to the filters. This, in turn, will create conditions for reducing head losses and will make it possible to reduce drawdowns in the well, ensuring a reduction in the cost of produced water. This design combines both working and reserve wells located in one borehole, which increases its reliability, durability and uninterrupted water supply to the consumer. A method for calculating the hydraulic parameters of a two-column two-filter water intake well is presented in the paper. It is based on dependencies for calculating the main geometric dimensions for a given design flow rate and hydrogeological characteristics of an aquifer, as well as formulas for determining a decrease in a well for a given period of operation when one and two pumps operate simultaneously. The basics of designing a well of the proposed design are outlined in the paper. The paper considers an example of calculation for a new well design instead of an existing typical well that has reduced its specific flow rate.

A ConvLSTM Conjunction Model for Groundwater Level Forecasting in a Karst Aquifer Considering Connectivity Characteristics

Groundwater is an important water resource, and groundwater level (GWL) forecasting is a useful tool for supporting the sustainable management of water resources. Existing studies have shown that GWLs can be accurately predicted by combining an artificial neural network model with meteorological and hydrological factors. However, GWL data are typically geographic spatiotemporal series data, and current studies have considered only the spatial distance factor when predicting GWLs. In karst aquifers, the GWL is affected by the developmental degree of the karst, topographic factors, structural features, and other factors; considering only the spatial distance is not enough, and the real spatial connectivity characteristics need to be considered. Thus, in this paper, we proposed a new method for forecasting GWLs in karst aquifers while considering connectivity characteristics using a neural network prediction model. The connectivity of a karst aquifer was analyzed by a multidimensional feature clustering method based on the distance index and hydrogeological characteristics recorded at observation wells, and a convolutional long short-term memory (ConvLSTM) conjunction model was constructed. The proposed approach was validated through GWL simulations and predictions in karst aquifers in Jinan, China, and four experiments were conducted for comparison. The experimental results show that the proposed method provided the most consistent results with the measured observation well data among the analyzed methods. These findings demonstrate that the proposed method, which considers connectivity characteristics in karst aquifers, has a higher simulation accuracy than other methods. This method is therefore effective and provides a new idea for the real-time prediction of the GWLs of karst aquifers.

Initial assessment of the groundwater flow and budget using Geographic Information System, MODFLOW-2005 and the FREEWAT modeling tool in Bouteldja coastal aquifer (Northern East of Algeria)

The Bouteldja coastal aquifer is one of the most important groundwater resources in North eastern of Algeria. The region is under a sub-humid climate with an average rainfall of 600-880 mm/y. The unconfined aquifer is constituted of Quaternary sands formations. The hydrogeological characteristics were determined based on previous reports. A very important inflow recharges the sandy aquifer in the Southeastern boundary, in relation to a fault network system linking the aquifer and the Obeira Lake area. Another inflow is observed at the Southern boundary in relation to the exchanges with the alluvial aquifer of Bouteldja. The purpose of the present study is to provide an initial assessment of the groundwater flow and water budget of this aquifer. To achieve this goal, a one-layer groundwater flow numerical model was developed using the MODFLOW-2005 code and the FREEWAT software, using the available data. The model was run in steady state conditions. Calibration was achieved using the piezometric measurements of May 2018 as calibration target. After several trials of manual calibrations, the model successfully simulated the groundwater flows directions and heads. Calibration efforts lead to an acceptable concordance (for the purpose of this study) between the estimated and calculated hydraulic conductivity and piezometric heads, except at the Eastern border. The analyses of the simulated inflow budget shows that aside the rainfall infiltration, exchanges with surface water bodies, the adjoining alluvial aquifer and the fault system provide a relevant amount of water. This significant recharge needs additional investigations. This numerical modeling exercise using MODFLOW, the FREEWAT software and GIS reached the objective of a preliminary description of the groundwater flow and it represents an acceptable starting point for more thorough hydrodynamic characterization of the Bouteldja coastal aquifer.

A hydrological framework for persistent river pools

Persistent surface water pools along non-perennial rivers represent an important water resource for plants, animals, and humans. While ecological studies of these features are not uncommon, these are rarely accompanied by a rigorous examination of the hydrological and hydrogeological characteristics that create or support the pools. Here we present an overarching framework for understanding the hydrology of persistent pools. We identified perched water, alluvial through flow and groundwater discharge as mechanisms that control the persistence of pools along river channels. Groundwater discharge is further categorized into that controlled by a geological contact or barrier (not previously described in the literature), and discharge controlled by topography. Emphasis is put on clearly defining through-flow pools and the different drivers of groundwater discharge, as this is lacking in the literature. A suite of diagnostic tools (including geological mapping, hydraulic data and hydrochemical surveys) is generally required to identify the mechanism(s) supporting persistent pools. Water fluxes to pools supported by through-flow alluvial and bedrock aquifers can vary seasonally and resolving these inputs is generally non-trivial. This framework allows the evaluation of the susceptibility of persistent pools along river channels to changes in climate or groundwater withdrawals. Finally, we present three case studies from the Hamersley Basin of north-western Australia to demonstrate how the available diagnostic tools can be applied within the proposed framework.

Mapping Potential Zones for Groundwater Recharge Using a GIS Technique in the Lower Khwae Hanuman Sub-Basin Area, Prachin Buri Province, Thailand

The lower Khwae Hanuman sub-basin in Thailand suffers from water shortage during each dry season. As such, groundwater resources are an additional freshwater source in this region, in particular for cultivating activities. Thus, an understanding of the volume of groundwater recharge into the saturated zone is required. The objective of the study is to assess the groundwater recharge potential (GRP) using the weighted overlay analysis method by geographic information system (GIS) and finally checking the reliability of GRP map using observed specific capacity carried out by the Department of Groundwater Resources (DGR). The geological and hydrogeological features that affect groundwater potential are the lithology, land use, lineaments, drainage, slope, and soil. The weighting and rating of these six influencing factors were determined by assessing the interrelationship of the main and minor influences of each factor based on several literature reviews, followed by a weighted overlay analysis with GIS, in association with groundwater recharge. The GRP can be classified in descending order: high, moderate, low, and very low, where about 33.9 km2 (2.26% of the total area of 1,500 km2) had high recharge potentiality, located at the center of the area. Only 12.8% of the total precipitation (271.75 million m3/y or approximately 181.2 mm) infiltrated the groundwater aquifer, while the rest was lost by either surface runoff or evapotranspiration. Based on GRP sensitivity analysis index, lithology was the most efficient influencing factor in GRP mapping. Most groundwater wells (>96% or 369 wells) were classified into the classes of low and moderated, which agree to the GRP zones. The results of calculating the area under the curve (AUC) of the receiver operating characteristic (ROC) curve were 86.0 percent, with relatively good predictive accuracy. The stable baseflow analysis would be used to confirm the amount of GRP by weighting overlay technique. Therefore, the GRP method can be applied in other areas, particular in similar hydrogeological characteristics. The first-hand recharge potential map and groundwater recharge information in this area can be used to establish an effective groundwater exploration program for agricultural activities; it is also used to appropriate sustainable yields from each groundwater basin to provide groundwater over the long-term, without negatively impacting the environment and without affecting the groundwater balance as it has recharge in the rainy seasons, which can use groundwater sustainably. It is in line with the sustainable development goals (SDGs) in goal number six of the UN.