Applying the Principal Component Analysis for a deeper understanding of the groundwater system: case study of the Bacchiglione Basin (Veneto, Italy)

In hydrogeology, it is often difficult to fully understand the hydraulic factors affecting the recharge of groundwater systems. Particularly, at a regional scale, the groundwater system can have different drivers depending on the considered area, i.e., soil permeability, paleochannels, and precipitation. Chemicalphysical (i.e. temperature) or hydrogeochemical data can help such understanding. However, this type of information is usually sparse at the regional scale, whereas extended groundwater piezometric head monitoring is more common. This study aims at exploiting these longitudinal observations of the hydraulic head to validate (and possibly bring more insights into) the geological structural model of aquifer systems. Clustering control points based on the piezometric head average annual variations can help the system conceptualization in two ways: (i) clusters can geographically identify areas with similar hydrogeological behavior; and (ii) the typical cluster annual variation with its ups and downs can bring insights on the recharge component of an aquifer system. Nevertheless, visual clustering can be a long and subjective procedure, thus this study suggests the use of the Principal Component Analysis to cluster the control points with a similar average annual variation of their recorded time series. This study supports the proposed analysis by applying it to the monitoring data of the Bacchiglione basin resulting in (i) clusters identified based on the number, moment, and lengths of groundwater level peaks and minima, (ii) wellgathered clusters in space, underpinning the groundwater hydrograph dependence on local driving factors. Furthermore, the investigation of clustering anomalies highlighted the relevance of the presence of time series with different recording periods pinpointing, however, the method's capacity to spot a change in the hydrogeological cycle over the years

Sistema integrato di previsione delle piene in tempo reale nel bacino idrografico Brenta-Bacchiglione

-Modello idrologico-idrodinamico per la previsione delle piene in tempo reale nel Brenta-Bacchiglione. -Interfaccia grafica GIS funzionale alla gestione delle emergenze in corso di evento. -Limitazione dell\u2019incertezza delle condizioni iniziali forzando il modello con misure di precipitazione e di livello. -Buona precisione e affidabilit\ue0 del sistema confermate dalle simulazioni di eventi passati

Modello matematico di flusso nei sistemi acquiferi del Veneto Centrale

For the last thirty-five years, the aquifer system of Central Veneto (Italy) has been involved by an increasing demand of water for domestic and private use and by a relevant reduction of groundwater heads. The regional groundwater model developed is a large scale model taking origins from detailed studies of the hydrogeological system. Its purpose is to provide boundary conditions for the study of flow and transport models at smaller scale and to predict the behaviour of the aquifers in conditions different from the present-day ones (changes in rainfall trend, rivers regime, soil use). The three-dimensional flow model of the aquifer systems is based on a large number of experimental data, concerning both groundwater balance (measured rain in pluviometric stations, water flux dispersed by rivers and irrigation channels, water flux springing out of the springs, water withdrawal from a large number of private and public wells) and hydraulic permeability of aquifers. A three-dimensional geological model of the system has been created by means of geological sections and stratigraphies. The flow simulations are performed using a tetrahedral finite element code. The model is calibrated on the basis of real piezometric heads and is used to analyze the interaction between the unconfined aquifer, located in the northern part of the study area, and the multiaquifer system that originates in this area and proceeds towards the sea. The model simulates reasonably well the water flow aquifers system of Central Veneto and permits to simulate the effects of changes in withdrawal policies and/or boundary conditions relevant to the complex aquifer system. The model will allow the establishment of causal relationships between withdrawal of water (whatever the production layer, and the extracted flow rates) and the fluctuations of piezometric heads anywhere in the system. We have investigated the robustness of the model towards variations of the geological model and towards variations of the hydraulic permeability of aquifers and low permeability lenses. The implemented 3D flow model has allowed to improve the understanding of the regional groundwater system and of its hydrogeological properties. The model permits to predict the response of the system to overpumping, fluctuations in recharges, relevant land use changes, new public derivations: so it is deemed of central importance for the management of water resources in the area

Stochastic analysis of groundwater temperature timeseries for characterizing check dams efficiency: case study on a Managed Aquifer Recharge site (Veneto, Italy)

In order to investigate hydraulic connections between the Brenta river and its groundwater aquifers, this work performs a stochastic analysis of measured groundwater temperature timeseries. The aim is to compare their trends to verify their mutual influence in stream seepage pathways. Additionally, the study wants to assess whether a large check dam, built across the river to increase aquifer recharge, is working properly. Field data were obtained by a water gauge placed directly into the stream, by two riverbank control points and by a monitoring well representing the regional groundwater thermal trend. Timeseries were evaluated by applying three different analyses - Fourier analysis, autocorrelation and sliding time-window Pearson correlation. Control points results were compared to the inflows to sort whether the aquifer is locally more affected by river dispersion or by regional groundwater flow. The three considered methods substantially agree in showing an increase of the seepage area upstream of the check dam and, at the same time, a marked reduction of groundwater recharge after few years of operation

Comparison of Three Imputation Methods for Groundwater Level Timeseries

This study compares three imputation methods applied to the field observations of hydraulic head in subsurface hydrology. Hydrogeological studies that analyze the timeseries of groundwater elevations often face issues with missing data that may mislead both the interpretation of the relevant processes and the accuracy of the analyses. The imputation methods adopted for this comparative study are relatively simple to be implemented and thus are easily applicable to large datasets. They are: (i) the spline interpolation, (ii) the autoregressive linear model, and (iii) the patched kriging. The average of their results is also analyzed. By artificially generating gaps in timeseries, the results of the various imputation methods are tested. The spline interpolation is shown to be the poorest performing one. The patched kriging method usually proves to be the best option, exploiting the spatial correlations of the groundwater elevations, even though spurious trends due to the the activation of neighboring sensors at times affect their reconstructions. The autoregressive linear model proves to be a reasonable choice; however, it lacks hydrogeological controls. The ensemble average of all methods is a reasonable compromise. Additionally, by interpolating a large dataset of 53 timeseries observing the variabilities of statistical measures, the study finds that the specific choice of the imputation method only marginally affects the overarching statistics

Assessing the long-term sustainability of the groundwater resources in the Bacchiglione basin (Veneto, Italy) with the Mann-Kendall test: suggestions for higher reliability

The social, economic, and ecological importance of the aquifer system within the Bacchiglione basin (Veneto, IT) is noteworthy, and there is considerable disagreement among previous studies over its sustainable use. Investigating the long-term quantitative sustainability of the groundwater system, this study presents a statistical methodology that can be applied to similar cases. Using a combination of robust and widely used techniques, we apply the seasonal Mann-Kendall test and the Sen's slope estimator to the recorded groundwater level timeseries. The analysis is carried out on a large and heterogeneous proprietary dataset gathering hourly groundwater level timeseries at 79 control points, acquired during the period 2005-2019. The test identifies significant decreasing trends for most of the available records, unlike previous studies on the quantitative status of the same resource which covered the domain investigated here for a slightly different period: 2000-2014. The present study questions the reason for such diverging results by focusing on the method's accuracy. After carrying out a Fourier analysis on the longest available timeseries, for studies of groundwater status assessment this work suggests applying the Mann-Kendall test to timeseries longer than 20 years (because otherwise the analysis would be affected by interannual periodicities of the water cycle). A further analysis of two 60-year-long monthly timeseries between 1960 and 2020 supports the actual sustainable use of the groundwater resource, the past deployment of the groundwater resources notwithstanding. Results thus prove more reliable, and meaningful inferences on the long-term sustainability of the groundwater system are possible

Alternative conceptual models and the robustness of groundwater management scenarios in the multi-aquifer system of the Central Veneto Basin, Italy

none6A three-dimensional (3D) groundwater flow model of the deep multi-aquifer Quaternary deposits of the Po plain sedimentary basin, within a 3,300-km(2) area (Veneto, Italy), is developed, tested and applied to aid sustainable large-scale water-resources management. Integrated mathematical modelling proves significantly successful, owing to an unusual wealth of available geological, geophysical, and hydrologic data and to state-of-the-art numerical tools. Of particular interest is the evaluation of the influence of alternative conceptual models; that is, of reconstructed representations of the 3D geological model of the structure of the aquifers. The reference conceptual model is set up by means of extended geological sections and stratigraphic records, and is used to create a large, unstructured 3D finite element grid. By analyzing the effects on piezometric surfaces and on the overall water budget of geometrical perturbations from the reference structure, alternative geo-structural models, obtained by systematically shifting the pinch-out of the aquitards, are compared. Interestingly, the impacts of aquitard pinch-out prove far from negligible. The results suggest the critical importance of reliable geological models even for large, complex 3D models. The good practice of iteratively testing numerically the impact of surprises on the conceptual model, as more field information is collected, is thus supported.noneG. Passadore; M. Monego; L. Altissimo; A. Sottani; M. Putti; A. RinaldoPassadore, Giulia; M., Monego; L., Altissimo; A., Sottani; Putti, Mario; Rinaldo, Andre