Delimitation of ground failure zones due to land subsidence using gravity data and finite element modeling in the Querétaro valley, México

Sedimentary basins of arid and semiarid zones are often subject to regimes of intense ground-water withdrawal as it is normally the only source of water for development of communities. An associated phenomenon is land subsidence, which can develop to ground failures, and consequently, damage to infrastructure. Aquifer deformation can be analyzed using a stress–strain or a flux–force approach depending on the aquifer material (compact or loose) and on whether the water withdrawal forms a predominant flow direction toward a cone of depression. Geometry of the aquifer system also plays an important role as uneven thickness induces differential compaction and hence, tensional and shear stresses on the ground mass. In this work we present a stress–strain approach to analyze subsidence for an unconfined aquifer of varying thickness; this is done in two steps, namely when the aquifer is in equilibrium, and when it is totally depleted. Using this scheme in a region where ground failure is evident, a portion of the aquifer system of the Querétaro valley is analyzed. The geometry of the hydrologic basement is first modeled using gravity measurements properly correlated with wells and field data. Then a stress analysis is implemented using the finite element method in order to identify probable zones of ground weakness, which are calibrated with known ground failures. The results indicate that both, tensional and shear stress are present, which induce ground failure in the form of surface faults.     

Optimisation of the Operation of an Electrochemical Process To Treat TBT‐contaminated Sediments on a Pilot Scale

Since at least three decades tributyltin had been commonly used in paint formulations to protect ship hulls and submersed surfaces from fouling. This has resulted in negative and Technology, effects to the marine environment due to its high toxicity towards non‐target organisms and to its accumulation in sediments, especially near point sources of pollution. Even if a ban of TBT for its application in anti‐fouling paints is enforced the problem of TBT‐contaminated sediments will remain for the coming years due to the low degradation rates of organotin in sediments. In this work an electrochemical process at a pilot scale to destroy TBT in sediments was investigated. Previous experiences at a laboratory and technical scale have demonstrated the potential of this process to electrolytically degrade organotin species in sediments. This article deals with the optimisation of the pilot plant performance in terms of organotin degradation and operation costs monitoring additionally the effect of the electrochemical treatment on other pollutants such as heavy metals, PCBs, and PAHs. The aim was to investigate by means of a parametric study the range of operating conditions required to destroy TBT down to concentrations lower than 100 μg/kg; to determine the influence of those parameters on the performance of the process; and to evaluate the operation costs associated to the process. It was determined that it was possible to destroy TBT down to 100 μg/kg at current densities in the range of 4.4 to 6.6 mA/cm² and chloride concentrations of least of 0.2 mol/L with operation costs of 13 to 18 EUR/m³.     

Diagnosing drought using the downstreamness concept: the effect of reservoir networks on drought evolution

ABSTRACT

To effectively manage hydrological drought, there is an urgent need to better understand and evaluate its human drivers. Using the “downstreamness” concept, we assess the role of a reservoir network in the emergence and evolution of droughts in a river basin in Brazil. In our case study, the downstreamness concept shows the effect of a network of reservoirs on the spatial distribution of stored surface water volumes over time. We demonstrate that, as a consequence of meteorological drought and recovery, the distribution of stored volumes became spatially skewed towards upstream locations, which affected the duration and magnitude of hydrological drought both upstream (where drought was alleviated) and downstream (where drought was aggravated). The downstreamness concept thus appears to be a useful entry point for spatiotemporally explicit assessments of hydrological drought and for determining the likelihood of progression from meteorological drought to a human-modified hydrological drought in a basin.     

A stochastic programming model for tactical product prepositioning at domestic hunger relief organizations impacted by natural hazards

Natural Hazards - Disaster response involves the planning, coordination, and distribution of supplies in an effective manner to people in need. Recent natural hazards, such as hurricane Harvey,...     

Assessment of business interruption time due to direct and indirect effects of the Chiapas earthquake on September 7th 2017

Natural Hazards - After an earthquake, a business often stops operating temporarily or permanently due to direct effects on the building (Initial security protocols and Physical damage to building...     

Relationship Between Hydrothermal Alteration Index and Geological Attributes at Chuquicamata Cu–Mo Porphyry Deposit,Chile

The distribution of mineral zones, hydrothermal alteration assemblages and ore associations are important geological attributes of the Chuquicamata Porphyry Cu–Mo deposit. The development and morphology of these attributes were influenced by syn‐mineralization structures with later modification of post‐mineralization tectonism to yield the present day form. In this work we evaluate the elemental mass transfer index due to hydrothermalism by using Pearce Element Ratios, using a database of 1110 samples consisting of elemental concentrations by chemical analysis. We study the relationship of the aforementioned index with the geological attributes in the porphyry as well as evaluate the type of information that the index provides according to its distribution, magnitude and variability. The magnitudes of the alteration index are organized into deciles, each of which represents a source of information, or macrostate. Within these, the geological attribute, or microstate, has a probability to participate that depends on the possible categorization of a particular attributes. The amount of information or uncertainty that each geological attribute provides to each decile of the distribution of the alteration index is determined by measuring the value of entropy. The results indicate that this distribution is controlled by the geometric–kinematic properties of syn‐mineralization structures that generate the primary pattern related to potassic alteration that develops in the hanging wall of the East Shear Zone. Subsequently the shape of the potassic alteration is modified by the kinematic effect imposed by the Americana and Estanques Blancos faults, and this broadly defines the geometry of the Qz–Mo event and the shape of the phyllic alteration. In addition, the sinistral‐inverse shear of the West Fault Zone allows the construction of an enriched blanket and also generates the drag fold that is characteristically observed in the south wall of the mine. All of the above events combine to yield the final geometry of the geological attributes that controls the shape and magnitude of the alteration index in the porphyry. The magnitude of the alteration index is mainly driven by the potassic and phyllic alteration stages. Potassic alteration is dominant in the first four deciles, while phyllic alteration is dominant in the last six deciles. Supergene mineralization attributes contribute discreetly to the average magnitude of the alteration index for each decile. The distribution of the probability of participation of the geological attributes in the distribution of the alteration index suggests that in the potassic alteration, biotite and green‐gray sericite facies contribute to strengthen the index in an associated manner, while in the phyllic alteration, the Qz–Ser textural type is the most significant.     

Dimensionality reduction for production optimization using polynomial approximations

The objective of this paper is to introduce a novel paradigm to reduce the computational effort in waterflooding global optimization problems while realizing smooth well control trajectories amenable for practical deployments in the field. In order to overcome the problems of slow convergence and non-smooth impractical control strategies, often associated with gradient-free optimization (GFO) methods, we introduce a generalized approach which represent the controls by smooth polynomial approximations either by a polynomial function or by a piecewise polynomial interpolation, which we denote as function control method (FCM) and interpolation control method (ICM), respectively. Using these approaches, we aim to optimize the coefficients of the selected functions or the interpolation points in order to represent the well-control trajectories along a time horizon. Our results demonstrate significant computational savings, due to a substantial reduction in the number of control parameters, as we seek the optimal polynomial coefficients or the interpolation points to describe the control trajectories as opposed to directly searching for the optimal control values (bottom hole pressure) at each time interval. We demonstrate the efficiency of the method on two and three-dimensional models, where we found the optimal variables using a parallel dynamic-neighborhood particle swarm optimization (PSO). We compared our FCM-PSO and ICM-PSO to the traditional formulation solved by both gradient-free and gradient-based methods. In all comparisons, both FCM and ICM show very good to superior performances.     

Kinematic soil-structure interaction effects on maximum inelastic displacement demands of SDOF systems

This paper presents a statistical study of the kinematic soil-foundation-structure interaction effects on the maximum inelastic deformation demands of structures. Discussed here is the inelastic displacement ratio defined as the maximum inelastic displacement demands of structures subjected to foundation input motions divide by those of structures subjected to free-field ground motions. The displacement ratio is computed for a wide period range of elasto-plastic single-degree-of-freedom (SDOF) systems with various levels of lateral strength ratios and with different sizes of foundations. Seventy-two earthquake ground motions recorded on firm soil with average shear wave velocities between 180 m/s and 360 m/s are adopted. The effects of period of vibration, level of lateral yielding strength and dimension of foundations are investigated. The results show that kinematic interaction will reduce the maximum inelastic displacement demands of structures, especially for systems with short periods of vibration, and the larger the foundation size the smaller the maximum inelastic displacement becomes. In addition, the inelastic displacement ratio is nearly not affected by the strength ratio of structures for systems with periods of vibration greater than about 0.3 s and with strength ratios smaller than about 3.0. Expressions obtained from nonlinear regression analyses are also proposed for estimating the effects of kinematic soil-foundation-structure interaction from the maximum deformation demand of the inelastic system subjected to free-field ground motions.     

Controls on sand ramp formation in southern Namibia

Sand ramps have the potential to provide rich palaeoenvironmental information in dryland regions where proxy records are typically scarce. However, current knowledge of the geomorphic controls and processes of sand ramp formation is limited. This study provides a data‐rich examination of the key factors controlling sand ramp formation. The location and morphology of 75 sand ramps in southern Namibia are examined. The sediments and chronologies of 10 sand ramps are studied in detail using 51 OSL dates and 83 grain‐size and LOI samples. Heavy mineral assemblages are used to determine the provenance of 10 samples and OSL sensitivity is used to explore geomorphic processes of eight samples. Sand ramp morphology can be grouped into one of four classes of increasing size and complexity and is closely linked to the available accommodation space. Heavy mineral assemblages indicate local sediment sources and all 75 studied sand ramps are within 4 km of a large ephemeral river channel or within 5.5 km of a dune field. Therefore, accommodation space and sediment supply are identified as the primary controls of sand ramp formation. Sedimentology and OSL sensitivity suggest a complex interplay of aeolian, fluvial and colluvial processes contribute to sand ramp formation with large variability observed between ramps. Three of the ten dated sand ramps have been present in the Namibian landscape for >100 ka. Eight sand ramps show episodic deposition between >75–12 ka and five show evidence of surface reworking over the past 2 ka. Environmental sensitivity is probably linked to the size and availability of the accommodation space. Therefore, individual sand ramps are expected to reflect local environmental conditions, recording when an abundant sediment supply coincided with available accommodation space, while a regional analysis of multiple sand ramps with chronometric data offers the potential to identify larger scale palaeoenvironmental controls of sediment supply. © 2017 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.     

Formation and dynamics of vegetated fluvial landforms follow the biogeomorphological succession model in a channelized river

Feedback between hydrogeomorphological processes and riparian plants drives landscape dynamics and vegetation succession in river corridors. We describe the consequences of biogeomorphological feedback on the formation and dynamics of vegetated fluvial landforms based on observations from the channelized Isère River in France. The channel was laterally confined with embankments and mostly straightened. From the beginning of the 1970s to the end of the 1990s, alternate bars were progressively but heavily colonized by vegetation. This context presented an exceptional opportunity to analyse temporal adjustments between fluvial landforms and vegetation succession from bare gravel bars to mature upland forest as the consequence of biogeomorphological interactions. Based on a GIS analysis of aerial photographs (between 1948 and 1996), we show that the spatiotemporal organization of vegetated bars within the river channel observed in 1996 resulted from a bioconstruction and biostabilization effect of vegetation and interactions between bars of varying age, size and mobility. Field measurements in 1996 reflected how a strong positive feedback between sedimentary dynamics and riparian vegetation succession resulted in the construction of the vegetated bars. A highly significant statistical association of geomorphological and vegetation variables (RV of co-inertia analysis = 0.41, p < 0.001) explained 95% of the variability in just one axis, supporting the existence of very strong feedback between geomorphological changes (i.e. the transformation of small bare alternate bars to fluvial landforms covered by mature upland forest, and vegetation succession). Such dynamics reflect the fluvial biogeomorphological successions model, as described by the authors earlier. © 2020 John Wiley & Sons, Ltd.