Waste dump erosional landform stability – a critical issue for mountain mining

Mining is the largest producer of solid wastes which, when released to land or into waterways, can cause harmful environmental impacts. This is mostly due to fluvial erosion, which is highly increased in mountain areas, due to abrupt slopes. We have analysed this situation at a mountain watershed (192 ha), where steep mined sites and their waste dumps are the main source of sediment in a Natural Park. This problem was tackled by building gabion check dams downstream from the mined sites. We used the DEM of Differences (DoD) method to quantify erosion and sediment yield from three waste dumps (5 ha). Their topography and substrate properties were analysed to understand the erosion problem. The sediment trapped by the check dams was quantified by electrical resistivity tomography (ERT). The rainfall characteristics triggering an episode that filled the check dams with sediment in the winter 2009–2010, were studied to confirm whether it was a case of extreme precipitation conditions. The waste dumps sediment yield (353 ± 95 Mg ha^?1 yr^?1) suggests severe landform instability. Analysis of topographic and substrate properties confirmed long, steep slopes combined with highly erodible materials. The check dams proved to be inefficient in controlling sediment loads, as they had only functioned for four years of 31 of existence, having trapped 13 000 ± 660 m³ of sediment, whereas we estimated that the waste dumps have yielded approximately three times more sediment for the same period. Rainfall analyses showed that neither intense nor extreme conditions (return period of 25 to 35 years) triggered the mobilization of 37 ± 2 Mg ha^?1 in a month. This study highlights the fact that mining operations in similar mountainous settings, with equivalent waste dump construction and reclamation practices, are currently unfeasible. We conclude that landform stability cannot be achieved at this site without landform changes. Copyright © 2017 John Wiley & Sons, Ltd.     

Spatial variation of the vegetative roughness in Mediterranean torrential streams affected by check dams

This study focuses on the spatial variations in vegetative roughness associated with morphological channel adjustments due to the presence of check dams in Mediterranean torrential streams. Manning’s n values were estimated using methods established by previous studies of submerged and non-submerged vegetation in laboratory flume experiments and field work. The results showed a linear decrease in shrub density and rate of variation of the roughness coefficient versus degree of submergence with increasing distance upstream from the check dam, while downstream, the filling of the check dam and the bed incision had the most influence. A regression analysis was applied by fitting the data to different models: relationships between Manning’s n and the flow velocity were found to be of the power type for shrubs in all upstream sections, while relationships of flow velocity versus hydraulic radius in the sections closest to check dams showed a good fit to second-order polynomial equations.     

Intersection and point-to-line solutions for geodesics on the ellipsoid

The paper presents two algorithms for the computation of intersection of geodesics and minimum distance from a point to a geodesic on the ellipsoid, respectively. They are based on the iterative use of direct and inverse problems of geodesy by means of their implementations with machine-precision accuracy in GeographicLib. The algorithms yield the same results as those obtained by Karney’s approach based on the use of auxiliary ellipsoidal gnomonic projections, with the advantage on our side that the algorithms are not limited to distances below 10000 km. This results in our algorithm being the only general solution for the problem of minimum distance from a point to a geodesic on the ellipsoid.     

Spatiotemporal modeling of relative risk of dengue disease in Colombia

Spatiotemporal modeling of relative risk of dengue disease provides useful risk maps for surveillance and forecasting. The objective of the study was to generate smoothed estimates of relative risk applying hierarchical Bayesian spatiotemporal models, including covariates derived from satellite images containing land surface temperature (LST) and normalized difference vegetation index, for the period January 2009–December 2015, in a medium–sized Colombian city. Our models are based on the spatiotemporal interaction modeling framework of relative risk, where the interaction effects are unstructured, temporal, spatial or inseparable, at a small spatial and temporal scales. We fitted the models using Markov chain MonteCarlo Simulations, selecting the best model using leave-one-out cross-validation and widely applicable information criteria. Our best model was the inseparable spatiotemporal interaction-effects plus LST with constant coefficient model. We found a weak, positive association between LST and cases of dengue. We discussed the strengths and weaknesses of our spatiotemporal models given the spatial and temporal resolution selected in the study.     

A Methodology Based on Numerical Simulation to Study River Floods. Application to Lower River Omaña Basin

Water Resources - The river floods happening in populated areas are serious natural risks that give rise to human and economic losses. In order to predict the consequences of river floods and to...     

Vegetation species mapping in a coastal-dune ecosystem using high resolution satellite imagery

Vegetation mapping is a priority when managing natural protected areas. In this context, very high resolution satellite remote sensing data can be fundamental in providing accurate vegetation cartography at species level. In this work, a complete processing methodology has been developed and validated in a complex vulnerable coastal-dune ecosystem. Specifically, the analysis has been carried out using WorldView-2 imagery, which offers spatial and spectral resolutions. A thorough assessment of 5 atmospheric correction models has been performed using real reflectance measures from a field radiometry campaign. To select the classification methodology, different strategies have been evaluated, including additional spectral (23 vegetation indices) and spatial (4 texture parameters) information to the multispectral bands. Likewise, the application of linear unmixing techniques has been tested and abundance maps of each plant species have been generated using the library of spectral signatures recorded during the campaign. After the analysis conducted, a new methodology has been proposed based on the use of the 6S atmospheric model and the Support Vector Machine classification algorithm applied to a combination of different spectral and spatial input data. Specifically, an overall accuracy of 88,03% was achieved combining the corrected multispectral bands plus a vegetation index (MSAVI2) and texture information (variance of the first principal component). Furthermore, the methodology has been validated by photointerpretation and 3 plant species achieve significant accuracy: Tamarix canariensis (94,9%), Juncus acutus (85,7%) and Launaea arborescens (62,4%). Finally, the classified procedure comparing maps for different seasons has also shown robustness to changes in the phenological state of the vegetation.     

Gravity modeling of the Muertos Trough and tectonic implications (north-eastern Caribbean)

The Muertos Trough in the northeast Caribbean has been interpreted as a subduction zone from seismicity, leading to infer a possible reversal subduction polarity. However, the distribution of the seismicity is very diffuse and makes definition of the plate geometry difficult. In addition, the compressive deformational features observed in the upper crust and sandbox kinematic modeling do not necessarily suggest a subduction process. We tested the hypothesized subduction of the Caribbean plate’s interior beneath the eastern Greater Antilles island arc using gravity modeling. Gravity models simulating a subduction process yield a regional mass deficit beneath the island arc independently of the geometry and depth of the subducted slab used in the models. This mass deficit results from sinking of the less dense Caribbean slab beneath the lithospheric mantle replacing denser mantle materials and suggests that there is not a subducted Caribbean plateau beneath the island arc. The geologically more realistic gravity model which would explain the N–S shortening observed in the upper crust requires an overthrusted Caribbean slab extending at least 60 km northward from the deformation front, a progressive increase in the thrusting angle from 8° to 30° reaching a maximum depth of 22 km beneath the insular slope. This new tectonic model for the Muertos Margin, defined as a retroarc thrusting, will help to assess the seismic and tsunami hazard in the region. The use of gravity modeling has provided targets for future wide-angle seismic surveys in the Muertos Margin.     

Paleoshoreline reconstruction: A proposed method to approach submerged prehistoric landscapes of Espiritu Santo Island,Baja California Sur,Mexico

When the first Americans inhabited the area now known as Isla Espiritu Santo, around 12.5 and 6 ka, the sea level continuously rose. This resulted in the loss of the coastal territory and the retreat of the human population further inland. Part of the archaeological evidence of this period currently lies over the seafloor and under the seabed. Therefore, reconstructing paleoshorelines is a necessary first step toward submerged precontact archaeology and a broad understanding of the spatial context in which those human populations interacted and how the landscapes changed. Isla Espiritu Santo is of prehistoric importance as it contains numerous Paleocoastal tradition sites as early as ~12,400 Cal B.P. This research aims to reconstruct the changing shoreline positions as sea levels rose around Isla Espiritu Santo between 12.5 and 6.5 ka. We apply numerical modeling to map digital elevation models at 1 ka intervals by estimating the changes in the morphology of the seafloor according to the deposition rates and global sea-level curve. The results show the evolution of coastal morphology and paleoshoreline's position. Three primary geoforms are proposed: (1) coastal plains, (2) tombolo, and (3) a coastal lagoon–island barrier system. This also offers insights into the physical aspect of submerged prehistoric landscapes and the possible resource exploitation options of early societies. In this research, the reconstruction of submerged landscapes seeks to contribute to the long-term goal of locating submerged precontact sites.