Estimating Tortuosity Coefficients Based on Hydraulic Conductivity

While the tortuosity coefficient is commonly estimated using an expression based on total porosity, this relationship is demonstrated to not be applicable (and thus is often misapplied) over a broad range of soil textures. The fundamental basis for a correlation between the apparent diffusion tortuosity coefficient and hydraulic conductivity is demonstrated, although such a relationship is not typically considered. An empirical regression for estimating the tortuosity coefficient based on hydraulic conductivity for saturated, unconsolidated soil is derived based on results from 14 previously reported diffusion experiments performed with a broad range of soil textures. Analyses of these experimental results confirm that total porosity is a poor predictor for the tortuosity coefficient over a large range of soil textures. The apparent diffusion tortuosity coefficient is more reliably estimated based on hydraulic conductivity.     

Deep Injection of Waste Water in the Western Canada Sedimentary Basin

Injection of wastes into the deep subsurface has become a contentious issue, particularly in emerging regions of oil and gas production. Experience in other regions suggests that injection is an effective waste management practice and that widespread environmental damage is unlikely. Over the past several decades, 23 km³ of water has been injected into the Western Canada Sedimentary Basin (WCSB). The oil and gas industry has injected most of this water but large amounts of injection are associated with mining activities. The amount of water injected into this basin during the past century is 2 to 3 orders magnitude greater than natural recharge to deep formations in the WCSB. Despite this large‐scale disturbance to the hydrogeological system, there have been few documented cases of environmental problems related to injection wells. Deep injection of waste appears to be a low risk activity based on this experience but monitoring efforts are insufficient to make definitive statements. Serious uncharacterized legacy issues could be present. Initiating more comprehensive monitoring and research programs on the effects of injection in the WCSB could provide insight into the risks associated with injection in less developed sedimentary basins.     

Cylindrical cavities and classical rat‐hole theory occurring in bulk materials

The phenomenon of stable cylindrical cavities known as rat‐holes in stockpiles and hoppers is well known but is not properly understood, and existing theory is unsatisfactory, in that it is believed not to properly incorporate actual material properties. Here the classical rat‐hole theory of Jenike and his coworkers is re‐examined, with a view to examining the validity of the so‐called ‘stable rat‐hole equation’, which is widely used in practice. For certain plastic regimes, new exact analytical solutions are determined for two special values of the angle of internal friction. One of the exact results may be used as the basis of an approximate solution valid for small angles of internal friction. Further, these exact and approximate solutions are compared with a full numerical solution of the governing differential equations. One of the approximations used by Jenike and his coworkers is shown to be invalid. Copyright © 2000 John Wiley & Sons, Ltd.     

A dual-porosity model for the study of chemical effects on the swelling behaviour of MX-80 bentonite

Significant chemical influence on the swelling potential of MX-80 bentonite was observed during swelling tests where specimens were hydrated with highly concentrated brine. The maximum swelling pressure for specimens hydrated with brine was about 30% of the maximum swelling pressure for the same specimens hydrated with de-ionized water. The maximum swelling pressure was attained within tens of hours of brine infiltration and further decreased by half within a year. A fully coupled hydro–mechanical–chemical (HMC) dual-porosity model is proposed in this paper to interpret the swelling behaviour of MX-80 when infiltrated with brine. The dependence of hydraulic and mechanical properties on such factors as porosity, salinity and water content was investigated. A nonlinear elastic constitutive model was proposed to correlate the swelling pressure with the variation in the microporosity. The chemical effects on the mechanical behaviour were coupled at the micropore level. A number of relationships have been developed for MX-80, i.e. micropore permeability as a function of void ratio, water retention characteristics of micropores and macropores, micropore dependence on water content and the diffusion coefficients of the two types of pore structure. The proposed model was successful in reproducing both quantitatively and qualitatively the experimental results from two sets of infiltration experiments on compacted MX-80 bentonite.

     

The nature and emplacement of distal aqueous-rich ejecta deposits from Hale crater,Mars

Hale crater formed in the Early to Middle Amazonian and is one of the best preserved large craters on Mars. We focus on the emplacement of previously mapped distal continuous ejecta and newly recognized discontinuous distal ejecta deposits reaching up to 450 km northeast of Hale. The distal continuous ejecta deposits are typically tens of meters thick, likely water-rich, and subsequent dewatering of some resulted in flow along gradients of 10 m km^-1 for distances of tens of kilometers. The discontinuous distal ejecta are typically <10 m thick with volumes generally <0.5 km³ and embay Hale secondaries, which occur up to ~600 km from Hale. Both continuous and discontinuous distal ejecta deposits are typically smooth at scales of tens to hundreds of meters, relatively dark-toned, devoid of eolian bedforms, inferred to be mostly fine-grained, and were likely emplaced within hours to 1–2 days after impact. The occurrence of well-preserved discontinuous distal ejecta at Hale is unusual compared to other large Martian craters and could be due to impact into an ice-rich substrate that enabled their formation and (or) their survival after minimal postimpact degradation relative to older craters. The pristine nature of distal continuous and discontinuous distal deposits at Hale and the preservation of associated secondaries imply (1) low erosion rates after the Hale impact, comparable to those estimated elsewhere during the Amazonian; (2) the impact did not significantly influence long-term global or regional scale geomorphic activity or climate; and (3) the Hale impact occurred after late alluvial fan activity in Margaritifer Terra.     

Computing and querying strict,approximate, and metrically refined topological relations in linked geographic data

Geographic entities and the information associated with them play a major role in Web‐scale knowledge graphs such as Linked Data. Interestingly, almost all major datasets represent places and even entire regions as point coordinates. There are two key reasons for this. First, complex geometries are difficult to store and query using the current Linked Data technology stack to a degree where many queries take minutes to return or will simply time out. Second, the absence of complex geometries confirms a common suspicion among GIScientists, namely that for many everyday queries place‐based relational knowledge is more relevant than raw geometries alone. To give an illustrative example, the statement that the White House is in Washington, DC is more important for gaining an understating of the city than the exact geometries of both entities. This does not imply that complex geometries are unimportant but that (topological) relations should also be extracted from them. As Egenhofer and Mark (1995b) put it in their landmark paper on naive geography, topology matters, metric refines. In this work we demonstrate how to compute and utilize strict, approximate, and metrically refined topological relations between several geographic feature types in DBpedia and compare our results to approaches that compute result sets for topological queries on the fly.     

Fish community responses to invasive fish removal and installation of an exclusion barrier at Lake Ohinewai,Waikato

Introduced common carp (Cyprinus carpio) are a recognised threat to New Zealand’s freshwater ecosystems. In 2011, an invasive fish removal programme was undertaken in 16.8 ha Lake Ohinewai, a Waikato riverine lake. Active fish removal using netting and boat electrofishing was supported by installation of a one-way exclusion barrier on the outflow to Lake Ohinewai. The barrier was designed to allow fish passage downstream out of the lake, while preventing adult carp from moving upstream. The estimated carp population was reduced from 8,548 fish (5,863–12,937, 95% confidence limits) in 2011–454 fish (251–889, 95% CL) in 2014. However, by 2016 the carp population had recovered to 2,063 fish (1,070–4,328, 95% CL) with increased abundance in invasive brown bullhead catfish (Ameiurus nebulosus) also observed. This research demonstrates that carp populations can be reduced to low abundances in the short to medium term, but continued removal will be required for on-going control.     

Identifying Common Decision Problem Elements for the Management of Emerging Fungal Diseases of Wildlife

Emerging infectious diseases (EIDs) of wildlife have characteristics that make them difficult to manage, leading to reactive and often ineffective management strategies. Currently, two fungal pathogens, Pseudogymnoascus destructans (Pd) and Batrachochytrium salamandrivorans (Bsal), are causing declines in novel host species. To improve the application of management strategies addressing the risk of these pathogens to North American wildlife, we queried wildlife managers about their concerns regarding managing populations of bats and amphibians potentially impacted by Pd and Bsal. Using these responses, we identified aspects of each decision problem that were shared across pathogens, regions and agencies – and found similarities in decision-problem elements for disease management. Reframing management problems as decisions can enable managers to identify similarities across EIDs, i.e. uncertainties within management actions, and improve reactive responses if proactive management is not possible. Such an approach recognizes context-specific constraints and identifies relevant uncertainties that must be reduced in developing a response.     

Introduction of a new friction routine into the SWAN model that evaluates roughness due to bedform and sediment size changes

The significant loss of wave energy due to seabed interaction in finite depths is a known effect and bottom friction terms are used in the wave models to account for this dissipation. In this paper, a new bottom-interaction function is tested by means of the SWAN model, based on measurements at two field sites, Lake George and Lakes Entrance, both in Australia. The function accounts for dependence of the friction on the formation process of bottom ripples and on the grain size of the sediment. The overall improvement of the model prediction both for the wave height and wave period is demonstrated.     

HiRISE views enigmatic deposits in the Sirenum Fossae region of Mars

HiRISE images together with other recent orbital data from Mars define new characteristics of enigmatic Hesperian-aged deposits in Sirenum Fossae that are mostly 100-200 m thick, drape kilometers of relief, and often display generally low relief surfaces. New characteristics of the deposits, previously mapped as the “Electris deposits,” include local detection of meter-scale beds that show truncating relationships, a generally light-toned nature, and a variably blocky, weakly indurated appearance. Boulders shed by erosion of the deposits are readily broken down and contribute little to talus. Thermal inertia values for the deposits are ∼200 J m⁻² K⁻¹ s^−1/2 and they may incorporate hydrated minerals derived from weathering of basalt. The deposits do not contain anomalous amounts of water or water ice. Deflation may dominate degradation of the deposits over time and points to an inventory of fine-grained sediment. Together with constraints imposed by the regional setting on formation processes, these newly resolved characteristics are most consistent with an eolian origin as a loess-like deposit comprised of redistributed and somewhat altered volcanic ash. Constituent sediments may be derived from airfall ash deposits in the Tharsis region. An origin directly related to airfall ash or similar volcanic materials is less probable and emplacement by alluvial/fluvial, impact, lacustrine, or relict polar processes is even less likely.