System reliability analysis for near-surface radioactive waste disposal facilities     

S. Sujitha 《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2017,11(4):315-322

The low- and intermediate-level radioactive wastes are generally disposed in near-surface disposal facility (NSDF). The NSDF is composed of engineered barriers. The probabilistic safety assessment model has been developed to analyse the performance of NSDF. The endpoints of the assessment are the concentration of the radionuclide in the groundwater and the corresponding dose rate of the radionuclide. The barrier system can have multiple failure modes but practically the possible failure modes are failure of top cover, failure of waste container, degradation of waste form and failure of bottom cover, which are usually considered as independent failure events. Through a sensitivity analysis, the most critical parameters affecting the design reliability for failure criteria are identified as the groundwater velocity and distribution coefficient. The study shows that for the NSDF considered, there is a high degree of dependence between the failure modes, and demonstrates the probability of the simultaneous occurrence of failures. Thus, the need to consider the system reliability in the NSDF is highlighted. The study also advocates the use of optimisation techniques to evaluate the probability of failure, which provides a better estimate of the probability of failure, as validated from the results obtained from Monte Carlo simulations.  相似文献   

Antifoulant concentrations at the site of the Bunga Teratai Satu grounding,Great Barrier Reef,Australia   总被引：1，自引：0，他引：1  

Haynes D  Christie C  Marshall P  Dobbs K 《Marine pollution bulletin》2002,44(9):968-972

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Contradicting Barrier Reef relationships for Darwin’s Evolution of reef types     

Edward G. Purdy  Edward L. Winterer 《International Journal of Earth Sciences》2006,95(1):143-167

The Darwinian progressive subsidence model for the evolution of fringing reefs, barrier reefs and atolls has been generally accepted following the indisputable proof of subsidence provided by drilling results in the Pacific. Nonetheless, there are data that do not fit the expectations of the model, such as the similar lagoon depths of barrier reefs and atolls as opposed to the subsidence theory’s implicit prediction that atolls should have significantly greater depths. In contrast, a great deal of evidence supports the influence of meteoric solution on barrier reef morphology. For example, the maximum lagoon depth of 56 modern barrier reefs is statistically correlated with the lagoon catchment area for modern annual rainfall. These modern rainfall patterns would seem to be a reasonable proxy for relative geographic differences in glacial lowstand rainfall, even though the absolute amounts of such rainfall are unknown. The correlation therefore suggests the importance of Pleistocene subaerial solution in contributing to barrier reef morphology. Further support for antecedent influence occurs in the form of barrier reef passes in which the depth of the reef pass is correlated with onshore drainage volumes. On a larger scale, the Cook Island of Mangaia provides evidence that solution can produce barrier reef morphology independent of reef development. In contrast, there are no examples of the subsidence-predicted lagoon transition of fringing reefs to barrier reefs to atolls. Moreover, the common occurrence of fringing reefs within barrier reefs negates subsidence as a causal factor in their ‘presumed progressive evolutionary development. Consequently, the evidence to date suggests that a solution morphology template has been accentuated by reef construction to produce the diagnostic barrier reef morphology we see today. The importance of subsidence would seem to be in accounting for the overall thickness of the resulting carbonate caps of oceanic examples and in contributing to lagoon depth variation among the larger continental entities.

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Coastal resilience and late Holocene tidal inlet history: The evolution of Dungeness Foreland and the Romney Marsh depositional complex (U.K.)   总被引：1，自引：1，他引：1  

A.J. Long  M.P. Waller  A.J. Plater 《Geomorphology》2006,82(3-4):309-330

Dungeness Foreland is a large sand and gravel barrier located in the eastern English Channel that during the last 5000 years has demonstrated remarkable geomorphological resilience in accommodating changes in relative sea-level, storm magnitude and frequency, variations in sediment supply as well as significant changes in back-barrier sedimentation. In this paper we develop a new palaeogeographic model for this depositional complex using a large dataset of recently acquired litho-, bio- and chrono-stratigraphic data. Our analysis shows how, over the last 2000 years, three large tidal inlets have influenced the pattern of back-barrier inundation and sedimentation, and controlled the stability and evolution of the barrier by determining the location of cross-shore sediment and water exchange, thereby moderating sediment supply and its distribution. The sheer size of the foreland has contributed in part to its resilience, with an abundant supply of sediment always available for ready redistribution. A second reason for the landform's resilience is the repeated ability of the tidal inlets to narrow and then close, effectively healing successive breaches by back-barrier sedimentation and ebb- and/or flood-tidal delta development. Humans emerge as key agents of change, especially through the process of reclamation which from the Saxon period onwards has modified the back-barrier tidal prism and promoted repeated episodes of fine-grained sedimentation and channel/inlet infill and closure. Our palaeogeographic reconstructions show that large barriers such as Dungeness Foreland can survive repeated “catastrophic” breaches, especially where tidal inlets are able to assist the recovery process by raising the elevation of the back-barrier area by intertidal sedimentation. This research leads us to reflect on the concept of “coastal resilience” which, we conclude, means little without a clearly defined spatial and temporal framework. At a macro-scale, the structure as a whole entered a phase of recycling and rapid progradation in response to changing sediment budget and coastal dynamics about 2000 years ago. However, at smaller spatial and temporal scales, barrier inlet dynamics have been associated with the initiation, stabilisation and breakdown of individual beaches and complexes of beaches. We therefore envisage multiple scales of “resilience” operating simultaneously across the complex, responding to different forcing agents with particular magnitudes and frequencies.  相似文献   

Evolution of an incised valley coastal plain estuary under low sediment supply: a ‘give‐up’ estuary     

J. ANDREW G. COOPER  ANDREW N. GREEN  C. IAN WRIGHT 《Sedimentology》2012,59(3):899-916

The literature on incised river valley sedimentology is dominated by studies of sediment‐rich systems in which the valley has been filled during and/or shortly after drowning. In contrast, the Holocene evolution of the Kosi Lagoon, South Africa (an incised coastal plain river valley) took place under very low sedimentation rates which have produced a distinctive stratigraphy and contemporary sedimentary environments. The findings are based on a synthesis of the results of studies of seismic stratigraphy, sediment distribution, morphodynamics and geomorphology. Barrier migration was prevented by a high pre‐Holocene dune barrier against which Holocene coastal deposits accumulated in an aggradational sequence. Holocene evolution of the back barrier involved: (i) drowning of the incised valley; (ii) wave‐induced modification of the back‐barrier shoreline leading to segmentation during the highstand; and (iii) marine sedimentation adjacent to the tidal inlet. Segmentation has divided the estuary into a series of geochemically and sedimentologically distinctive basins connected by channels in the estuarine barriers. The seismic stratigraphy of the back barrier essentially lacks a transgressive systems tract, shoreline modification and deposition having been accomplished during the highstand. The lack of historical geomorphological change suggests that the system has achieved morphological equilibrium with ambient energy conditions and low sediment supply. This study presents a classification for estuarine incised valley fills based on the balance between sea‐level rise and sedimentation in which Kosi represents a ‘give‐up’ estuary where much of the relict incised channel form is drowned and preserved. It exhibits a fundamentally different set of evolutionary processes and stratigraphic sequences to those of the better known incised valley systems in which sedimentation either keeps pace with sea‐level (‘keep‐up’ estuaries) or occurs after initial drowning (‘catch‐up’ estuaries).  相似文献   

Spectral features of the New Zealand deep‐water ocean wave climate     

Kevin C. Ewans  Alick C. Kibblewhite 《新西兰海洋与淡水研究杂志》2013,47(3-4):323-338

The wave climate at the Maui site off the west coast of the North Island and off the east coast of Great Barrier Island to the east of the North Island are examined. This is done by means of average wave spectra derived from a 2‐year database, acquired from Waverider buoy measurements made over 1980 and 1981. The average spectra provide information about the individual sea states which characterise the wave climate, and show that on average the sea state on the east coast is less energetic than it is on the west coast. Further, it is seen that this difference results largely from a dominant and persistent long‐period south‐westerly swell of 12.4 s period which is present at the Maui location but absent from the Great Barrier Island seas.  相似文献   

Algivory in hawksbill turtles: Eretmochelys imbricata food selection within a foraging area on the Northern Great Barrier Reef     

Ian Bell 《Marine Ecology》2013,34(1):43-55

This paper describes the food selection of hawksbill turtles, Eretmochelys imbricata, using reefs of the Far Northern Section of the Great Barrier Reef Marine Park (nGBR) during 2006 and 2007. A total of 467 gastric lavage and 71 buccal cavity ingesta items were collected from 120 individual E. imbricata, comprising adult female and immature turtles of both sexes. Nineteen E. imbricata that were captured in 2006 were recaptured and sampled again in 2007. Within the total pooled buccal and lavage sample (n = 538), the occurrence of food items was dominated (72.7%) by only three algal taxonomic divisions: Rhodophyta (red algae; 53.7%, n = 289); Chlorophyta (green algae; 11.0%, n = 59) and algae from the division of Phaeophyceae (brown algae; 8.0%, n = 43). The remaining total (buccal and lavage) ingesta sample comprised sponges (10.4%, n = 56), soft corals and a wide variety of possibly nutritionally important invertebrate species (12.6%, n = 68), and a small percentage (5.4%, n = 22) of inorganic material. Generally, E. imbricata were considered to be primarily a sponge‐feeding specialist and secondarily an omnivorous species; within coral reef habitats and in various parts of the world this is the case. However, this study has shown that E. imbricata found foraging on reefs of the nGBR are primarily algivorous and secondarily omnivorous. A feeding strategy that relies on a predominantly algal diet may infer important benefits to the species if the impacts of climate change and ocean acidification inhibit coral growth, while promoting algal density and distribution within the Great Barrier Reef ecosystem.  相似文献