Controls of uncertainty in acid rock drainage predictions from waste rock piles examined through Monte-Carlo multicomponent reactive transport

Stochastic Environmental Research and Risk Assessment - Heterogeneity in waste rock piles (WRPs) determines uncertainty in acid mine drainage (ARD) predictions from these deposits. Numerical...     

3-Dimensional Necklace Flower Constellations

A new approach in satellite constellation design is presented in this paper, taking as a base the 3D Lattice Flower Constellation Theory and introducing the necklace problem in its formulation. This creates a further generalization of the Flower Constellation Theory, increasing the possibilities of constellation distribution while maintaining the characteristic symmetries of the original theory in the design.     

Robust optimization for ship conceptual design

The paper presents an approach for the robust optimization of a bulk carrier conceptual design, subject to uncertain operating and environmental conditions. The uncertainties involved in the optimization process are addressed and a general formulation for robust design is given. Specifically, the uncertainties involved in the decision making process are taken into account by means of their probabilistic distributions. The expected values and the standard deviations of the relevant quantities are assessed and included in the optimization objectives, whereas the constraints are evaluated in the worst case. This leads to a robust design able to keep a good performance in the whole probabilistic operating scenario. A particle swarm optimization algorithm is used for the global minimization process, minimizing the expectation and the standard deviation of the unit transportation cost.     

A recipe for why and how to set up and sustain an experimental catchment

Experimental catchments are fundamental elements in hydrological sciences as they provide key data for putting forward and testing hypotheses, developing theories, constraining models, and making predictions. Significant progress in catchment hydrology stemmed from field measurements but increasing costs and risks associated with field work and the availability of big data based on remote sensing, machine learning, and a plethora of models, as well as observations deriving from previous and current sites, raises questions on whether running an experimental catchment still provides individual and community benefits as in the past. In this commentary, I highlight the advantages of keeping experimental catchments alive and propose a personal 10-step “recipe” to set up a new experimental catchment and manage and sustain it in the long term. These suggestions can be useful both to young and less young researchers who are open to facing the challenge of measuring processes in the field and are willing to offer the scientific community new experimental evidence for advancing our current knowledge in catchment hydrology.     

Three‐fold nature of coastal progradation during the Holocene eustatic highstand,Po Plain,Italy – close correspondence of stratal character with distribution patterns

Although general trends in transgressive to highstand sedimentary evolution of river‐mouth coastlines are well‐known, the details of the turnaround from retrogradational (typically estuarine) to aggradational–progradational (typically coastal/deltaic) stacking patterns are not fully resolved. This paper examines the middle to late Holocene eustatic highstand succession of the Po Delta: its stratigraphic architecture records a complex pattern of delta outbuilding and coastal progradation that followed eustatic stabilization, since around 7·7 cal kyr bp . Sedimentological, palaeoecological (benthic foraminifera, ostracods and molluscs) and compositional criteria were used to characterize depositional conditions and sediment‐dispersal pathways within a radiocarbon‐dated chronological framework. A three‐stage progradation history was reconstructed. First, as soon as eustasy stabilized (7·7 to 7·0 cal kyr bp ), rapid bay‐head delta progradation (ca 5 m year^?1), fed mostly by the Po River, took place in a mixed, freshwater and brackish estuarine environment. Second, a dominantly aggradational parasequence set of beach‐barrier deposits in the lower highstand systems tract (7·0 to 2·0 cal kyr bp ) records the development of a shallow, wave‐dominated coastal system fed alongshore, with elongated, modestly crescent beaches (ca 2·5 m year^?1). Third, in the last 2000 years, the development of faster accreting and more rapidly prograding (up to ca 15 m year^?1) Po delta lobes occurred into 30 m deep waters (upper highstand systems tract). This study documents the close correspondence of sediment character with stratal distribution patterns within the highstand systems tract. Remarkable changes in sediment characteristics, palaeoenvironments and direction of sediment transport occur across a surface named the ‘A–P surface’. This surface demarcates a major shift from dominantly aggradational (lower highstand systems tract) to fully progradational (upper highstand systems tract) parasequence stacking. In the Po system, this surface also reflects evolution from a wave‐dominated to river‐dominated deltaic system. Identifying the A–P surface through detailed palaeoecological and compositional data can help guide interpretation of highstand systems tracts in the rock record, especially where facies assemblages and their characteristic geometries are difficult to discern from physical sedimentary structures alone.     

Modeling the effects of pulsed versus chronic sand inputs on salmonid spawning habitat in a low‐gradient gravel‐bed river

It is widely recognized that high supplies of fine sediment, largely sand, can negatively impact the aquatic habitat quality of gravel‐bed rivers, but effects of the style of input (chronic vs. pulsed) have not been examined quantitatively. We hypothesize that a continuous (i.e. chronic) supply of sand will be more detrimental to the quality of aquatic habitat than an instantaneous sand pulse equal to the integrated volume of the chronic supply. We investigate this issue by applying a two‐dimensional numerical model to a 1 km long reach of prime salmonid spawning habitat in central Idaho. Results show that in both supply scenarios, sand moves through the study reach as bed load, and that both the movement and depth of sand on the streambed mirrors the hydrograph of this snowmelt‐dominated river. Predictions indicate greater and more persistent mortality of salmonid embryos under chronic supplies than pulse inputs, supporting our hypothesis. However, predicted mortality varies both with salmonid species and location of spawning. We found that the greatest impacts occur closer to the location of the sand input under both supply scenarios. Results also suggest that reach‐scale morphology may modulate the impact of sand loads, and that under conditions of high sand loading climate‐related increases in flow magnitude could increase embryo mortality through sand deposition, rather than streambed scour. Copyright © 2013 John Wiley & Sons, Ltd.     

Representivity of incompletely sampled fall deposits in estimating eruption source parameters: a test using the 12–13 January 2011 lava fountain deposit from Mt. Etna volcano,Italy

The Southeast Crater (SEC) of Mt. Etna, Italy, is renowned for its high activity, mainly long-lived eruptions consisting of sequences of individual paroxysmal episodes which have produced more than 150 eruptive events since 1998. Each episode typically forms eruption columns followed by tephra fallout over distances of up to about 100 km from the vent. One of the last sequences consisted of 25 lava fountaining events, which took place between January 2011 and April 2012 from a pit-vent on the eastern flank of the SEC and built a new scoria cone renamed New Southeast Crater. The first episode on 12–13 January 2011 produced tephra fallout which was unusually dispersed toward to the South extending out over the Mediterranean Sea. The southerly deposition of tephra permitted an extensive survey at distances between ~1 and ~100 km, providing an excellent characterization of the tephra deposit. Here, we document the stratigraphy of the 12–13 January fallout deposit, draw its dispersal, and reconstruct its isopleth map. These data are then used to estimate the main eruption source parameters. The total erupted mass (TEM) was calculated by using four different methodologies which give a mean value of 1.5?±?0.4?×?10⁸ kg. The mass eruption rate (MER) is 2.5?±?0.7?×?10⁴ kg/s using eruption duration of 100 min. The total grain-size (TGS) distribution, peaked at ?3 phi, ranges between ?5 and 5 phi and has a median value of ?1.4 phi. Further, for the eruption column height, we obtained respective values of 6.8–13.8 km by using the method of Carey and Sparks (1986) and 3.4?±?0.3 km by using the methods of Wilson and Walker (1987), Mastin et al. (2009), and Pistolesi et al. (2011) and considering the mean value of MER from the deposit. We also evaluated the uncertainty and reliability of TEM and TGS for scenarios where the proximal and distal samples are not obtainable. This is achieved by only using a sector spanning the downwind distances between 6 and 23 km. This scenario is typical for Etna when the tephra plume is dispersed eastward, i.e., in the prevailing wind direction. Our results show that, if the analyzed deposit has poorer sample coverage than presented in this study, the TEM (3.4?×?10⁷ kg) is 22 % than the TEM obtained from the whole deposit. The lack of the proximal (<6 km) deposit may cause more significant differences in the TGS estimations.     

One‐dimensional and two‐dimensional hydrodynamic modeling derived flow properties: impacts on aquatic habitat quality predictions

Studies of the effects of hydrodynamic model dimensionality on simulated flow properties and derived quantities such as aquatic habitat quality are limited. It is important to close this knowledge gap especially now that entire river networks can be mapped at the microhabitat scale due to the advent of point‐cloud techniques. This study compares flow properties, such as depth and velocity, and aquatic habitat quality predicted from pseudo‐2D and fully 2D hydrodynamic modeling. The models are supported by high‐resolution, point‐cloud derived bathymetries, from which close‐spaced cross‐sections were extracted for the 1D modeling, of three morphologically and hydraulically different river systems. These systems range from small low‐gradient meandering pool–riffle to large steep confined plane‐bed rivers. We test the effects of 1D and 2D models on predicted hydraulic variables at cross‐sections and over the full bathymetry to quantify the differences due to model dimensionality and those from interpolation. Results show that streambed features, whose size is smaller than cross‐sectional spacing, chiefly determine the different results of 1D and 2D modeling whereas flow discharge, stream size, morphological complexity and model grid sizes have secondary effects on flow properties and habitat quality for a given species and life stage predicted from 1D and 2D modeling. In general, the differences in hydraulic variables are larger in the bathymetric than in the cross‐sectional analysis, which suggests that some errors are introduced from interpolation of spatially disaggregated simulated variables with a 1D model, instead of model dimensionality 1D or 2D. Flow property differences are larger for velocity than for water surface elevation and depth. Differences in weighted usable area (WUA) derived from 1D and 2D modeling are relatively small for low‐gradient meandering pool–riffle systems, but the differences in the spatial distribution of microhabitats can be considerable although clusters of same habitat quality are spatially comparable. Copyright © 2014 John Wiley & Sons, Ltd.