Evaluation of groundwater availability and sustainable extraction rate for the Upper Santiago Valley Aquifer,Chile

The use of groundwater as water supply has increased dramatically in Santiago, Chile, during the last decades, and there is a need for accurately estimating the actual groundwater supply capacity in the upper Santiago Valley aquifer. The behavior of this aquifer was studied in order to determine the availability of water and the long-range sustainable extraction rate.Water-table depths were simulated using a numerical model with information on recharge from the last 48 years under different extraction policies. With this series of groundwater level data, groundwater level probability distribution functions were determined and extraction statistics were estimated by fitting time series models and by using the crossing theory. With this information, it has been possible to calculate the risk of being unable to supply groundwater demand because the results verify that only 67% of the water rights granted are able to be extracted on a sustained basis with a 90% exceedance probability. Furthermore, the results obtained demonstrate that the method is adequate for determining exceedance probabilities of groundwater flow.

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Resumen El uso de las aguas subterráneas como fuente de abastecimiento se ha incrementado enormemente en Santiago de Chile durante las últimas décadas, por lo que se necesita estimar de forma adecuada la capacidad actual de suministro del acuífero superior del Valle de Santiago. Se ha estudiado el comportamiento de este acuífero para determinar la disponibilidad de recursos y la tasa de extracción sustentable a largo plazo.Se ha simulado los niveles freáticos del acuífero utilizando un modelo numérico con información de la recarga en los últimos 48 años bajo diferentes regímenes de extracción. Con esta serie de datos de los niveles en el acuífero, se ha determinado la distribución de probabilidad de los niveles de las aguas subterráneas y se ha estimado las estadísticas de las extracciones mediante el ajuste de modelos de series temporales y la teoría de cruce. Con esta información, se ha podido calcular el riego de no satisfacer la demanda de abastecimiento, puesto que los resultados verifican que sólo se podría extraer el 67% de las concesiones de agua existentes de manera sustentable con un 90% de probabilidad de excedencia. Aún más, los resultados obtenidos demuestran que el método es adecuado para determinar las probabilidades de excedencia del flujo de las aguas subterráneas.

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Resumé Lutilisation de leau souterraine pour leau potable sest considérablement accrue à Santiago (Chili) au cours des derniers lustres; cest pourquoi il est maintenant nécessaire destimer avec précision la capacité réelle dalimentation de la nappe de laquifère supérieur de la vallée de Santiago. Le fonctionnement de cet aquifère a été étudié afin de déterminer la disponibilité en eau et le taux dextraction durable à long terme.Les niveaux de la nappe ont été simulés avec un modèle numérique à partir dinformation sur la recharge au cours des 48 dernières années pour différentes politiques dextraction. A partir de cette série de données piézométriques, des fonctions de distribution de probabilité des niveaux de la nappe ont été déterminées et des statistiques dextraction ont été estimées par ajustement de modèles de séries chronologiques en utilisant la théorie du croisement. Avec ces informations, il a été possible de calculer le risque de ne pas pouvoir satisfaire la demande deau souterraine, puisque les résultats vérifient que seulement 67% des droits deau attribués peuvent être extraits sur une base durable avec une probabilité de dépassement de 90%. En outre, les résultats obtenus démontrent que la méthode est adaptée à la détermination des probabilités de dépassement de lécoulement souterrain.

     

Accumulation and distribution of Hg and 210Pb in superficial sediments from a coastal lagoon in the SE Gulf of California associated with urban-industrial and port activities

The Estero de Urías Lagoon (EUL) is an inner shelf barrier coastal lagoon, located in the Mexican Pacific Coast (SE Gulf of California). It is surrounded by Mazatlán City, one of the most important international tourist areas of Mexico. To provide a comprehensive reassessment of the concentration levels and spatial variability of Hg and ²¹⁰Pb in the EUL, 40 surface sediment samples were analyzed for several geochemical variables (e.g. grain size distribution, organic matter and reference element concentrations) that could explain the observed variability of Hg and ²¹⁰Pb. The Hg concentrations ranged from 23 to 214 ng g^?1, whereas ²¹⁰Pb activities varied from 20 to 56 Bq kg^?1. No defined distribution pattern was observed for Hg and ²¹⁰Pb concentrations in the lagoon and no evidence of a common atmospheric delivery route was observed. The sediments from EUL were found contaminated by Hg, and according to international guidelines 48 % of the sampling sites have concentrations that could be harmful to biota.     

A strong flare of the H<Subscript>2</Subscript>O maser in Sagittarius B2(M)

Results of a study of a strong flare of H₂O maser emission in the star-forming region Sgr B2(M) in 2004 are reported. The observations were carried out on the 22-m radio telescope of the Pushchino Radio Astronomy Observatory. The main emission, with its flux density reaching 3800 Jy, was concentrated in a narrow radial-velocity interval (about 3 km/s) and was most likely associated with the compact group r, while the emission at V_LSR > 64 km/s came from group q. After 1994, the variations of the H₂O maser emission in Sgr B2(M) became cyclic with a mean period of 3 years.     

DInSAR analysis of ALOS PALSAR images for the assessment of very slow landslides: the Tena Valley case study

In this work we analyse the performance of advanced land observing satellite (ALOS) phased array type L-band syntetic aperture radar (PALSAR) images for mapping and monitoring of very slow landslides using conventional differential interferometry in the Tena Valley (Central Pyrenees, Spain). These results are compared with those retrieved in previous works where multi-band advanced differential interferometric synthetic aperture radar (DInSAR) analysis was performed for the same area using PSI techniques. The study area is largely underlain by slates (ca. 80 %) where large deep-seated very slow earth flows are dominant. The results reveal that DInSAR analysis is able to measure displacements of landslides with a greater spatial coverage than PSI analysis, but for a lower amount of them (nine against 51). Overall, the combination of the DInSAR and multi-band PSI analysis permitted to map and monitor 68 % of the landslides in Tena Valley. From this amount, 63 landslides are considered as active. The main advantage of DInSAR with respect to PSI analysis is the capability to detect faster movements (up to 145 cm?year^?1) derived from the 46 days interferograms. That is the case of Sextas and La Selva landslides where an acceleration of the moving mass was measured after intense rainfall periods producing major damages to linear infrastructures. The combination of measured displacement from ALOS interferograms, with the observed damages on the A-136 road, was useful to assess the potential damage that could cause these slow movements. In general, it is demonstrated that even though PSI analysis provides a better performance in terms of landslide mapping, L-band DInSAR analysis provides an added value for landslide hazard assessment through radar remote sensing. For this reason it is necessary to encourage the launch of new satellite missions similar to ALOS PALSAR that could operate with shorter revisiting time periods.     

Upscaling Hydraulic Conductivities in Cross-Bedded Formations

Modern geostatistical techniques allow the generation of high-resolution heterogeneous models of hydraulic conductivity containing millions to billions of cells. Selective upscaling is a numerical approach for the change of scale of fine-scale hydraulic conductivity models into coarser scale models that are suitable for numerical simulations of groundwater flow and mass transport. Selective upscaling uses an elastic gridding technique to selectively determine the geometry of the coarse grid by an iterative procedure. The geometry of the coarse grid is built so that the variances of flow velocities within the coarse blocks are minimum. Selective upscaling is able to handle complex geological formations and flow patterns, and provides full hydraulic conductivity tensor for each block. Selective upscaling is applied to a cross-bedded formation in which the fine-scale hydraulic conductivities are full tensors with principal directions not parallel to the statistical anisotropy of their spatial distribution. Mass transport results from three coarse-scale models constructed by different upscaling techniques are compared to the fine-scale results for different flow conditions. Selective upscaling provides coarse grids in which mass transport simulation is in good agreement with the fine-scale simulations, and consistently superior to simulations on traditional regular (equal-sized) grids or elastic grids built without accounting for flow velocities.     

Self-Similar and Self-Affine Properties of Two-Dimensional Fracture Patterns in Rocks

In this paper, we investigate the fractal properties of binary maps of rock fractures at different scales and different geological types, as well as different families of fracture patterns obtained from a two-dimensional Laplacian growth model (LGM). From these analyses we figure out which families of the LGM patterns match the structural properties of the fracture binary maps. The LGM is defined in terms of a nonlinear map that depends on two parameters, λ and \mathfraka\mathfrak{a}, that respectively define the area and shape of the elements of the aggregate that conforms the patterns. The fractal dimension and roughness exponent of the LGM patterns are found to depend on \mathfraka\mathfrak{a}, with 0 < \mathfrak a < 10<\mathfrak {a}<1. From a detailed statistical analysis of these patterns we found that the fractal dimensions of capacity, correlation and information decrease monotonically as \mathfraka\mathfrak{a} increases. We also found that the values of these three fractal dimensions tend to collapse on top of each other as \mathfraka\lessapprox1\mathfrak{a}\lessapprox1. Remarkably, the fractal properties of rock fractures in the scales from millimeters up to a few meters appear to be well represented by the fractal structure of the LGM families of patterns with \mathfraka=0.15\mathfrak{a}=0.15 and 0.30, while the fractal properties of rock fractures in the scale of kilometers seems to be well represented by the LGM family with \mathfraka=0.90\mathfrak{a}=0.90. In addition, the three fractal dimension values of fracture binary maps in the scales from millimeters up to meters were found to be different between them. Nonetheless, for fractures in the scale of kilometers, the values of the three fractal dimensions are very close to each other as an indication of self-similar behavior. Analysis of the corrections to the scaling of the roughness exponent, ζ, suggests that they are negligible for the LGM family of fracture patterns with \mathfraka=0.9\mathfrak{a}=0.9. This finding points to a self-affine structure for this family of patterns. In fact, the calculated roughness exponent results are in the range of values characteristic of rock fractures.     

Emergence and evolution of active and ephemeral regions: Comparison between observations and models

This work aims to describe some aspects relevant to the emergence of magnetic structures on the solar surface. Using high resolution photospheric and chromospheric data, besides than EUV images acquired by space telescopes, the dynamics of rising flux tubes is studied. It is shown that, for both long-lived and short-lived magnetic regions, the flux tubes are initially characterized by a high rising velocity, which eventually decreases as the region develops. Other results concern the timeline of the active regions appearance in the atmospheric layers and the asymmetries in plasma downflows between preceding and following legs of the flux tubes. These results are briefly discussed in the light of most recent models.     

Multi-wavelength observations of flares and eruptive filaments

In this paper we report some results obtained from multi-wavelength observations carried out to study the mechanisms operating in flares and filament eruptions. Most of these studies have given indication of the presence of phenomena that might be considered signatures of magnetic reconnection, while others have pointed out the important role played by magnetic helicity transport in corona before the eruptive phase.