Analytical study of hydraulic and mechanical effects on tide-induced head fluctuation in a coastal aquifer system that extends under the sea

Head response to sea level fluctuations has been extensively used for characterizing coastal aquifers. When the aquifer is semiconfined and extends for a certain distance . D under the sea, head response results from the superposition of two types of effects: hydraulic (i.e., ground water flow connection through aquifer and aquitard) and mechanical (induced by tidal loading onto the sea floor). Solutions are available for this problem that has been analyzed before, but only for . D zero or infinity. These solutions do not allow analyzing aquifer systems that extends for a finite . D, or identifying them, which is critical for coastal aquifer management. We derive an exact analytical solution that describes separately the mechanical and hydraulic effects. The proposed analytical solution is a generalization of most of existing analytical solutions. A simpler approximate analytical solution is also obtained for soft aquitards with low permeabilities. We find that the impact of the hydraulic component of the aquitard and the mechanical effects in the total head fluctuation at the shoreline is significant, but not very sensitive to the properties of the aquitard. The amplitude of these fluctuations relative to that of the sea tide ranges approximately between 1 (small . D) and 0.5 (large . D). This implies that aquifer penetration under the sea can indeed be identified if it is below a certain threshold, beyond which the system responds as if . D was infinity. Surprisingly, the time lag is close to zero regardless of hydraulic parameters of the aquifer system.Fil: Guarracino, Luis. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; ArgentinaFil: Carrera, Jesús. INSTITUTO DE DIAGNÓSTICO AMBIENTAL Y ESTUDIOS DEL AGUA (IDAEA);Fil: Vázquez Suñé, Enric. INSTITUTO DE DIAGNÓSTICO AMBIENTAL Y ESTUDIOS DEL AGUA (IDAEA)

Groundwater-Gossan interaction and the genesis of the secondarysiderite rock at Las Cruces ore deposit (SW Spain)

Part of the Las Cruces secondary siderite deposit has sparked an interest in the scientific communitybecause of its unique mineralogy. The original gossan formed by goethite and hematite has been replacedby a siderite and galena rock. We postulate that this rock can be formed by the interaction of iron oxideswith groundwater similar in composition to that of the present day. Hydrochemical and isotopic charac-teristics of groundwater support this hypothesis. The negative Eh values, the existence of H2S and the ten-dency toward high sulfate isotope values indicate a reducing groundwater condition. The highammonium, boron and iodine concentrations as well as the low d13C values of dissolved inorganic carbon(DIC) confirm the organic matter oxidation. The reductive dissolution of Pb-bearing goethite at theexpense of Dissolved Organic Carbon (DOC) leads to the precipitation of Fe-sulfides, galena and siderite.The formation of siderite from this process is confirmed by the low amount of dissolved Fe in groundwa-ter (<10 ppb), its low d13C values and thermodynamic calculations. One-dimensional reactive transportmodeling demonstrated that the present-day groundwater flux and chemical composition could formthe siderite rock in less than 1 Ma with no external supply of reactants. Sensitivity analyses revealed thatthe time of formation depends on the structure of the groundwater flux (spaced fractures or pervasive),the flow rate and especially the DOC concentration. In fact, calculations with the highest DOC measuredconcentration resulted in a mineral zonation: one zone formed by Fe-sulfides and other zone formed bysiderite, with galena in both zones. Reactive transport calculations and the similarity of its high d34S val-ues indicate that the sulfur of galena came from the current groundwater. Reactive transport calculationsand the similarity of its high d34S values indicate that the sulfur of galena came from the currentgroundwater

A geological model for the management of subsurface data in the urban environment of Barcelona and surrounding area

The overdevelopment of cities since the industrial revolution has shown the need to incorporate a sound geological knowledge in the management of required subsurface infrastructures and in the assessment of increasingly needed groundwater resources. Additionally, the scarcity of outcrops and the technical difficulty to conduct underground exploration in urban areas highlights the importance of implementing efficient management plans that deal with the legacy of heterogeneous subsurface information. To deal with these difficulties, a methodology has been proposed to integrate all the available spatio-temporal data into a comprehensive spatial database and a set of tools that facilitates the analysis and processing of the existing and newly added data for the city of Barcelona (NE Spain). Here we present the resulting actual subsurface 3-D geological model that incorporates and articulates all the information stored in the database. The methodology applied to Barcelona benefited from a good collaboration between administrative bodies and researchers that enabled the realization of a comprehensive geological database despite logistic difficulties. Currently, the public administration and also private sectors both benefit from the geological understanding acquired in the city of Barcelona, for example, when preparing the hydrogeological models used in groundwater assessment plans. The methodology further facilitates the continuous incorporation of new data in the implementation and sustainable management of urban groundwater, and also contributes to significantly reducing the costs of new infrastructures.Peer ReviewedPostprint (published version

An open source Python library for environmental isotopic modelling

Altres ajuts: from the Balearic Island Government through the Margalida Comas postdoctoral fellowship programme (PD/036/2020).Isotopic composition modelling is a key aspect in many environmental studies. This work presents Isocompy, an open source Python library that estimates isotopic compositions through machine learning algorithms with user-defined variables. Isocompy includes dataset preprocessing, outlier detection, statistical analysis, feature selection, model validation and calibration and postprocessing. This tool has the flexibility to operate with discontinuous inputs in time and space. The automatic decision-making procedures are knitted in different stages of the algorithm, although it is possible to manually complete each step. The extensive output reports, figures and maps generated by Isocompy facilitate the comprehension of stable water isotope studies. The functionality of Isocompy is demonstrated with an application example involving the meteorological features and isotopic composition of precipitation in N Chile, which are compared with the results produced in previous studies. In essence, Isocompy offers an open source foundation for isotopic studies that ensures reproducible research in environmental fields

Quantitative comparison of impeller-flowmeter and particle-size-distribution techniques for the characterization of hydraulic conductivity variability

Hydraulic conductivities associated with measurement scale of the order of 10&ndash;1&nbsp;m and collected during an extensive field campaign near T&uuml;bingen, Germany, are analyzed. Estimates are provided at coinciding locations in the system using: (1) the empirical Kozeny-Carman formulation, providing conductivity values,&nbsp;K&nbsp;GS, based on particle-size distribution, and (2) borehole impeller-type flowmeter tests, which infer conductivity,&nbsp;K&nbsp;FM, from measurements of vertical flows within a borehole. Correlation between the two sets of estimates is virtually absent. However, statistics of the natural logarithm of&nbsp;K&nbsp;GS&nbsp;and&nbsp;K&nbsp;FM&nbsp;at the site are similar in terms of mean values (averages of&nbsp;ln K&nbsp;GS&nbsp;being slightly smaller) and differ in terms of variogram ranges and sample variances. This is consistent with the fact that the two types of estimates can be associated with different (albeit comparable) measurement (support) scales. It also matches published results on interpretations of variability of geostatistical descriptors of hydraulic parameters on multiple observation scales. The analysis strengthens the idea that hydraulic conductivity values and associated key geostatistical descriptors inferred from different methodologies and at similar observation scales (of the order of tens of cm) are not readily comparable and should not be embedded blindly into a flow (and eventually transport) prediction model

Quantitative comparison of impeller flowmeter and particle-size dsitribution techniques for the characterization of hydraulic conductivity variability

Basic univariate statistics and key geostatistical parameters of estimates of hydraulic conductivity obtained at the decimeter scale by two different methods are presented and compared. The two estimates are based on (1) the empirical Kozeny-Carman formulation, and (2) impeller flowmeter tests. The former provides values of conductivity, KGS, based on particle size distributions. Impeller flowmeter techniques allow inferring conductivities, KFM, from measurements of vertical flows within a borehole. Data obtained during an extensive monitoring campaign at an experimental site located near the city of Tübingen, Germany, are considered. Statistics of the natural logarithm of KGS and KFM at the site are similar in terms of mean values (with averages of ln KGS being slightly smaller than those of ln KFM) and differ in terms of variogram ranges and sample variances. The correlation between the two sets of estimates is virtually absent. Additional data from two different sites already presented in the literature allow comparing conductivity estimates from flowmeter and grain-size distributions (or permeameter measurements) taken at adjacent wells and support the finding that KGS and KFM lack correlation. The analysis highlights the difficulty in obtaining meaningful quantitatively comparable hydraulic conductivity data at the decimetric scale.Peer ReviewedPostprint (published version

A sequence stratigraphic based geological model for constraining hydrogeological modeling in the urbanized area of the Quaternary Besòs delta (NW Mediterranean coast, Spain)

The Quaternary Besòs delta is located on the Mediterranean coast in NE Spain. The Besòs Delta Complex includes 3 aquifers constituted by 3 sandy and gravelly bodies, separated by lutitic units. These aquifers supply water for domestic and industrial use in this area. Management of groundwater has been problematic in the Besòs delta since the 1960s, and continues to pose major problems for subsurface engineering works in this highly urbanized region. This study seeks to demonstrate the advantages of detailed geological characterization and modeling for designing and constructing a hydrogeological model. Available information of the subsurface was compiled, integrated and homogenized in a geospatial database. The interpretation of these data enabled us to delimit geological units by means of a sequence stratigraphic subdivision. A three-dimensional facies belt-based model of the Besòs delta was built on the basis of this geological characterization. This model was used to constrain the distribution of hydraulic parameters and thus to obtain a consistent hydrogeological model of the delta, which was calibrated by data of water management and production over the last hundred years. The resulting hydrogeological model yielded new insights into water front displacements in the aquifer during the time-span considered, improving predictions in an attempt to optimize aquifer management

Insights on the hydrological cycle and its interaction with anthropic pressures: the Katari basin and minor Titicaca lake

The hydrologic cycle behaviour in the Bolivian Altiplano and how it interacts with human activity are still not fully understood. The hydraulic cycle is examined in a novel way in this work by considering extended time series of associated hydrologic and climatic data. Results show that human exploitation and losses from the sewage and water supply networks in the urban areas might cause an hydraulic imbalance in the region. These anthropogenic incomes, at the same time, increase concentrations of different pollutants. Water isotopic analysis reinforces the conceptual model showing that the groundwater sampled are mainly from precipitation. Workshops with local municipalities supported and defined the most relevant anthropic pressures in the basin. This information supports a vulnerability analysis in collaboration among them. The decision-making process for government entities might be strengthened by this study, which would help to develop long-term strategies to prevent and mitigate the issues found in the evaluation of water vulnerability in the region.</p

Hydrogeological impact assessment by tunnelling at sites of high sensitivity

A tunnel for the High Speed Train (HST) was constructed in Barcelona with an Earth Pressure Balance (EPB) Tunnel Boring Machine (TBM). The tunnel crosses Barcelona and passes under some famous landmarks such as the Sagrada Familia and the Casa Mill Both monuments are UNESCO world heritage sites and a committee appointed by the UNESCO acted as external observers during the construction. Concerns about soil settlements and the hydrogeological impacts of the construction were raised. These concerns were addressed during the design stage to forestall any unexpected events. The methodology consisted of 1) characterising the geology in detail, 2) predicting the impacts caused in the aquifer, 3) predicting the soil displacements due to water table oscillations produced by the construction, and 4) monitoring the evolution of groundwater and soil settlements. The main estimated impact on groundwater was a moderate barrier effect. The barrier effect, the magnitude of which matched the predictions, was detected during construction. The monitoring of soil settlements revealed short and long term movements. The latter movements matched the analytical predictions of soil displacements caused by the groundwater oscillations. This paper proposes a realistic procedure to estimate impacts on groundwater during tunnel construction with an EPB. Our methodology will considerably improve the construction of tunnels in urban areas. (C) 2015 Elsevier B.V. All rights reserved.Peer ReviewedPostprint (author's final draft