Origin of boron from a complex aquifer in southeast of Spain

A study of the boron content alongside Cl ^-, SO ₄ ^2-, and NO ₃ ^- ions has enabled the factors that determine its origin to be distinguished. In carbonate rocks, with their higher saline content, boron is associated with marine intrusion. In the Plioquaternary aquifer, its origin is complex and is associated with three processes: marine intrusion, where there is a high Cl ^- content and the B/Cl ^- ratio is close to that of seawater; anthropogenic pollution, at points with high B and NO ₃ ^- concentrations and where the B/Cl ^- ratio is higher than that of seawater; and the dissolution of evaporite deposits present in the Plioquaternary strata, at a series of sampling points where the SO ₄ ^2-/Cl ^- ratio is elevated and B content is high.     

Matrix hydrodynamic properties of carbonate rocks from the Betic Cordillera (Spain)

Laboratory tests performed on 181 rock samples from boreholes drilled in different areas of the Betic Cordillera allow us to calculate their hydraulic conductivity and open porosity values. Higher values are generally associated with Miocene calcareous sandstones, although hydraulic conductivity reaches its highest values in some isolated limestone and dolostone samples. Lower values were found in marly limestones and marbles. Specific yield ranged from 0 to 0·0798, with a mean value of 0·00579. A total of 79 samples did not release water during the specific yield test, while another 11 samples released water for more than 30 min. Such wide ranges of variation show the great diversity of behaviour that the matrix of the carbonate rocks can have, referring to water storage and transfer, and its influence on pollutants spread, for example. A weak relation between interconnected porosity and hydraulic conductivity was found. The relation between interconnected porosity and specific yield is slightly stronger, except in the case of the dolomites, where a high correlation was found. No dependence on depth was found for hydraulic conductivity and interconnected porosity. Copyright © 2004 John Wiley & Sons, Ltd.     

Analysis of leaky sheetpile by Summary Representation

A numerical technique called Summary Representation was used to solve the problem of seepage through a leaky sheetpile; this particular method was selected owing to its accuracy and computational speed. Seepage parameters were evaluated quantitatively and the influence of the leakiness of sheetpiles in a porous medium underlain by an impervious horizontal stratum was determined. The case of a single sheetpile was first considered, and the effect of the depth of penetration and coefficient of leakiness on the total rate of flow and on the values of the exit gradient was analysed. Next, the flow under an impervious dam was considered to assess the accuracy of the method. Finally, the case of seepage under a dam with leaky sheetpiles at both ends was studied, including the effect of the leaky sheetpiles on the uplift pressure acting along the foundation of the dam. Patterns of seepage through the flow line deformation that is caused by the leakiness of the sheetpiles.     

Differential piscivory of the native Percichthys trucha and exotic salmonids upon the native forage fish Galaxias maculatus in Patagonian Andean lakes

The present paper analyses predation patterns, of Percichthys trucha and salmonid fish upon Galaxias maculatus in five lakes of northern Patagonia with differing community and environmental characteristics. Tank experiments were performed to evaluate relative efficiency of native and exotic predators of G. maculatus under treatments with and without cover (aquatic vegetation). Important differences were found between predators with regards to distribution and consumption of G. maculatus. Salmonids are more efficient than P. trucha in consuming G. maculatus in deep environments with scarcely vegetation; in contrast to native species they frequently use the pelagic environment. Although pelagic habitat might have served in the past as a refuge from native predators in the past, G maculatus now experiences intense predation in the pelagic zone by exotic salmonids. It is suggested that the widespread distribution of G. maculatus in Patagonian lakes may have facilitated the success of salmonids throughout Patagonia.     

Rapid characterisation of the extremely large landslide threatening the Rules Reservoir (Southern Spain)

Landslides - When an active landslide is first identified in an artificial reservoir, a comprehensive study has to be quickly conducted to analyse the possible hazard that it may represent to such...     

An effective combined framework for modelling the time-dependent behaviour of soft structured clays

A constitutive framework for the simulation of the time-dependent behaviour of soft structured clays has been developed from the combination of a number of existing modelling approaches. The formulation accounts, in a natural way, for time-dependent phenomena such as loading rate dependency, stress relaxation, ageing, and creep deformations under constant load. In addition, the effect of structure is accounted for. To demonstrate the potential of the proposed approach, a specific model based on this framework is described and applied to the simulation of a number of relevant laboratory tests from the literature.

     

Evolution of the Galicia Interior Basin over the last 60 ka: sedimentary processes and palaeoceanographic implications

The Galicia Interior Basin (GIB; NW Iberian Peninsula) is located near a critical transition between the subtropical (temperate) and subpolar (cold) gyres of the North Atlantic. It therefore witnesses oceanographic changes driven by global climatic events. This study reports on the recent (latest Pleistocene) sedimentary, palaeoceanographic and palaeoclimatic history of the basin. We integrated analysis of deep‐sea sediment cores retrieved from an E–W transect across the GIB. The analysis indicated three types of sedimentary processes recording glacial (Marine Isotope Stage 2–4) and deglacial events: along‐slope bottom currents (forming contourite deposits), pelagic and hemipelagic sedimentation, and gravitational dislocation. Variation in depositional patterns and sedimentation rates indicate distinctive transport (along‐slope and down‐slope) and depositional processes. These in turn reflect climatic and oceanographic drivers. We interpret changes in sea level from core evidence showing changes in sediment supply. The cores exhibited conspicuous sedimentary evidence of Heinrich events (HEs). The stratigraphic intervals associated with HEs showed significant lateral variation. We suggest that the lateral variation may result from the development of an oceanographic boundary between surface water masses with different temperature and salinity parameters or changes in surface currents which may have introduced relatively warmer water into the GIB during the last glacial period.     

Calibration of imperfect models to biased observations

The problem of assimilating biased and inaccurate observations into inadequate models of the physical systems from which the observations were taken is common in the petroleum and groundwater fields. When large amounts of data are assimilated without accounting for model error and observation bias, predictions tend to be both overconfident and incorrect. In this paper, we propose a workflow for calibration of imperfect models to biased observations that involves model construction, model calibration, model criticism and model improvement. Model criticism is based on computation of model diagnostics which provide an indication of the validity of assumptions. During the model improvement step, we advocate identification of additional physically motivated parameters based on examination of data mismatch after calibration and addition of bias correction terms. If model diagnostics indicates the presence of residual model error after parameters have been added, then we advocate estimation of a “total” observation error covariance matrix, whose purpose is to reduce weighting of observations that cannot be matched because of deficiency of the model. Although the target applications of this methodology are in the subsurface, we illustrate the approach with two simplified examples involving prediction of the future velocity of fall of a sphere from models calibrated to a short-time series of biased measurements with independent additive random noise. The models into which the data are assimilated contain model errors due to neglect of physical processes and neglect of uncertainty in parameters. In every case, the estimated total error covariance is larger than the true observation covariance implying that the observations need not be matched to the accuracy of the measuring instrument. Predictions are much improved when all model improvement steps were taken.     

A parsimonious distributed model for simulating transient water flow in a high-relief karst aquifer

A mathematical model of a highly heterogeneous functioning karst aquifer is described. The aquifer is in a high-relief karst massif and, as is common for such locations, data are scarce and there are no borehole, piezometer or pumping-test data. The scarcity of data in this case required a parsimonious approach to ensure that the level of complexity of the model was commensurate with the amount, type and quality of the available data. Parsimony also requires the model to include the minimum essential components that account adequately for the data, which in this and similar cases are the functional dualities of the karst system: duality in recharge, flow and discharge. The model is three-dimensional (3D) in the sense that the aquifer is discretized into 3D voxels, although the flow is one-dimensional (1D) and vertical in the vadose zone, and horizontal and two-dimensional (2D) in the saturated zone. The parsimonious model was designed by coupling a 1D unsaturated gravity-driven flow along the vertical (along each column of voxels that discretize the aquifer) and a 2D unconfined Darcy flow in the saturated zone. In the context of this type of aquifer, preferential recharge through the network of karst conduits implies a rapid rise in the water table, the location and extension of which are model parameters. The karst springs are simulated by drains. The methodology, which is completely general, is illustrated by application to the karst aquifer in the Sierra de las Nieves mountains in southern Spain.     

Petrological,geochemical, isotopic,and geochronological constraints for the Late Devonian–Early Carboniferous magmatism in SW Gondwana (27–32°LS): an example of geodynamic switching

International Journal of Earth Sciences - We report a study integrating 13 new U–Pb LA-MC-ICP-MS zircon ages and Hf-isotope data from dated magmatic zircons together with complete...