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41.
Marie-Françoise André Samuel Etienne Denis Mercier Franck Vautier Olivier Voldoire 《Environmental Geology》2008,56(3-4):677-688
A first application of geomorphological methods to the assessment of sandstone deterioration at Angkor is presented. Damage diagnosis was carried out on the first eastern tier of the central pyramid of the 1,000 year-old Ta Keo temple. Methods combine field observations and measurements at 230 sampling points, high-resolution lasergrammetry and stereophotogrammetry on a 2-m2 test zone, and SEM observations. The first results indicate that decay operates through a synergistic combination of weathering phenomena dominated by scaling and solution, and exhibits a high spatial variability. Percentages of deteriorated surfaces vary from 17.6 to 93.8%, and average stone recession values from 0.00 to 2.71 cm (minimum) and 0.34 to 5.49 cm (maximum). On the test-zone, stereophotogrammetry and 3D-mapping of the present and reconstructed initial states using lasergrammetry indicate that erosion scars up to 6 cm deep have formed since 1963. On the whole, the amount of deteriorated surfaces more than tripled between 1963 and 2008. The degree of implication of salts in stone decay remains unclear for most efflorescences are composed of calcite (CaCO3), with secondary importance of barite (BaSO4) and gypsum (CaSO4·2H2O). Future prospects aim to evaluate the impact on stone decay of the clearing out of the temple from the forest in the 1920s. 相似文献
42.
Spatial variations in grain-size parameters (i.e. grain-size trends) contain information on sediment transport patterns. Analytical procedures have been proposed using the grain-size trend to determine net sediment transport pathways. In the first part of this study, the fundamentals of the theory are presented through methods for analysing 1D and 2D variations. The methods used are critically discussed, while pointing out some severe problems. So far, these methods suffer from limitations leading to serious interpretational errors, making it necessary to take account of two kinds of uncertainties. Inputs uncertainties are linked to the physical sediment properties as well as procedures of sampling and analysis. Model uncertainties are then discussed for each step of the grain-size trend analysis. The validity of Sediment Trend Analysis under natural conditions is tested against published field studies to determine the most appropriate variation trend to use in a specific environment. Proposals are given for each step of the procedure for optimal use of the method using a Quality Assurance (QA) approach. Further developments are proposed, such as integration into a Geographic Information System. 相似文献
43.
The Simpevarp area is one of the alternative sites being considered for the deep geological disposal of high level radioactive waste in Sweden. In this paper, a coupled regional groundwater flow and reactive solute transport model of the Simpevarp area is presented that integrates current hydrogeological and hydrochemical data of the area. The model simulates the current hydrochemical pattern of the groundwater system in the area. To that aim, a conceptual hydrochemical model was developed in order to represent the dominant chemical processes. Groundwater flow conditions were reproduced by taking into account fluid-density-dependent groundwater flow and regional hydrogeologic boundary conditions. Reactive solute transport calculations were performed on the basis of the velocity field so obtained. The model was calibrated and sensitivity analyses were carried out in order to investigate the effects of heterogeneities of hydraulic conductivity in the subsurface medium. Results provided by the reactive transport model are in good agreement with much of the measured hydrochemical data. This paper emphasizes the appropriateness of the use of reactive solute transport models when water-rock interaction reactions are involved, and demonstrates what powerful tools they are for the interpretation of hydrogeological and hydrochemical data from site geological repository characterization programs, by providing a qualitative framework for data analysis and testing of conceptual assumptions in a process-oriented approach. 相似文献
44.
Quantitative sinkhole hazard assessments in karst areas allow calculation of the potential sinkhole risk and the performance
of cost-benefit analyses. These estimations are of practical interest for planning, engineering, and insurance purposes. The
sinkhole hazard assessments should include two components: the probability of occurrence of sinkholes (sinkholes/km2 year) and the severity of the sinkholes, which mainly refers to the subsidence mechanisms (progressive passive bending or
catastrophic collapse) and the size of the sinkholes at the time of formation; a critical engineering design parameter. This
requires the compilation of an exhaustive database on recent sinkholes, including information on the: (1) location, (2) chronology
(precise date or age range), (3) size, and (4) subsidence mechanisms and rate. This work presents a hazard assessment from
an alluvial evaporite karst area (0.81 km2) located in the periphery of the city of Zaragoza (Ebro River valley, NE Spain). Five sinkholes and four locations with features
attributable to karstic subsidence where identified in an initial investigation phase providing a preliminary probability
of occurrence of 0.14 sinkholes/km2 year (11.34% in annual probability). A trenching program conducted in a subsequent investigation phase allowed us to rule
out the four probable sinkholes, reducing the probability of occurrence to 0.079 sinkholes/km2 year (6.4% in annual probability). The information on the severity indicates that collapse sinkholes 10–15 m in diameter
may occur in the area. A detailed study of the deposits and deformational structures exposed by trenching in one of the sinkholes
allowed us to infer a modern collapse sinkhole approximately 12 m in diameter and with a vertical throw of 8 m. This collapse
structure is superimposed on a subsidence sinkhole around 80 m across that records at least 1.7 m of synsedimentary subsidence.
Trenching, in combination with dating techniques, is proposed as a useful methodology to elucidate the origin of depressions
with uncertain diagnosis and to gather practical information with predictive utility about particular sinkholes in alluvial
karst settings: precise location, subsidence mechanisms and magnitude, and timing and rate of the subsidence episodes. 相似文献
45.
Flood hazard delineation combining geomorphological and hydrological methods: an example in the Northern Iberian Peninsula 总被引:2,自引:1,他引:1
Flood mapping requires the combination and integration of geomorphological and hydrological-hydraulic methods; however, despite
this, there is very little scientific literature that compares and validates both methods. Two types of analysis are addressed
in the present article. On the one hand, maps of flood plains have been elaborated using geomorphological evidence and historical
flood data in the mountainous area of northwestern Spain, covering an area of more then 232 km2 of floodplains. On the other hand, a hydrometeorological model has been developed (Clark semidistributed unit hydrograph)
in the Sarria River basin (155 km2, NW Spain). This basin is not gauged, hence the model was subjected to a goodness-of-fit test of its parameter (curve number)
by means of Monte Carlo simulation. The peak flows obtained by means of the hydrological model were used for hydraulic modeling
(one-phase, one-dimensional and steady flow) in a 4 km2 urban stretch of the river bed. The delineation of surface areas affected by floods since 1918, as well as those analyzed
subsequent to the geomorphological study, reveals a high degree of reliability in the delineation of the flooded areas with
frequent recurrence intervals (<50 years). If we compare these flooded surface areas with the estimate obtained by the hydrological-hydraulic
method we can see that the latter method overestimates the extent of the surface water by 144% for very frequent recurrence
intervals (>10 years) and underestimates it as the recurrence interval increases, by up to 80% less floodplain for exceptional
events (>500 years). Finally, a management map is put forth combining the most reliable results available by integrating both
methods.
Originally presented at the Sixth International Conference on Geomorphology. 相似文献
46.
M. Mejías J. Garcia-Orellana J. L. Plata M. Marina E. Garcia-Solsona B. Ballesteros P. Masqué J. López C. Fernández-Arrojo 《Environmental Geology》2008,54(3):521-536
A methodology for the characterization of deep carbonate aquifers has been developed and applied to El Maestrazgo Jurassic
aquifer in Castellón, Spain. Characterization of these aquifer formations, located at more than 300 m deep, consisted of a
previous phase of compilation, analysis and synthesis of the existing information about the area, followed by a coordinated
combination of different speciality studies: geology, stratigraphy, structural analysis, hydrogeology, hydrochemistry, geophysics
and remote sensing. Geological studies included geological mapping, definition of stratigraphical units and facies and structural
analysis. The aim of the hydrogeology study was to define aquifer formations, recharge area, aquifer points inventory and
groundwater flow directions for the establishment of piezometric and water quality observation nets. Special techniques were
applied, like thermal infrared aerial images and the evaluation of submarine groundwater discharge by means of natural radium
isotopes. Hydrochemical techniques, including majority elements characterization and stable isotopes (18O, 2H and 3H) determination, allowed classifying hydrochemical facies and establishing a renewal pattern for water within the system.
Geophysics was useful in determining the aquifer geometry, the features of the basement and the petrophysical characteristics
of the geological formations. Preliminary results show an important tectonic complexity and the possibilities for groundwater
uses in the area of study. 相似文献
47.
Alberto C. Montefinale Liliana A. Masironi Henry M. Papée 《Pure and Applied Geophysics》1963,54(1):207-211
Summary Correlation between some physical and chemical variables, measured at 28 stations of the United States Weather Bureau Network, and seasonal and annual frequencies of precipitation, has been attempted with the aim of gaining insight into the bearing of such variables, on occurrence of precipitation. — Concurrent trends of frequencies with local temperature functions, altitude parameters, precipitable water vapour increments, and some chemical species have been found.Contribution of the «Centro Nucleazione Aerosoli» of the National Research Council of Italy, Via Vettore 4 (Monte Sacro),Roma. 相似文献
48.
T. Németh 《Pure and Applied Geophysics》1966,63(1):205-210
Summary According to the author the reason of the subsistence of the 11 years' sunspot cycle is to be found in the conjunction of the planets. As a result of the investigations it has been stated that from among the nine planets the joint tidal effect of Venus-Jupiter-Earth is a decisive factor in the variations of sunspot activity. The above three planets are every 10.4 years and 12.0 years respectively, in a close conjunction. The mean value (11.2 years) is in an almost full accordance with the average cycle-period. The fluctuations of the period of the cycle come from the fact that the planets' getting into approximately one line takes a different time within each cycle. This time delay is the cause of the stronger or weaker sunspot activity, and of the shorter or longer cycles. 相似文献
49.
50.
P Thoya S Pérez-Jorge GM Okemwa H Mwamlavya A Tuda N Wambiji 《African Journal of Marine Science》2020,42(1):23-33
Ringnet fishing began in the early 20th century and is practised worldwide, mainly to target nearshore pelagic species. The method was introduced to Kenya’s coastal waters by migrant fishers from Tanzania. However, the impacts of this fishing gear remain poorly assessed. We assessed the spatial distribution of ringnet fishing effort and its possible effects on ecosystem components, such as coral reefs, marine megafauna and marine protected areas, on the south coast of Kenya. We tracked 89 ringnet fishing trips made from December 2015 to January 2016 and used spatial multicriteria analysis to determine hotspots of possible environmental risks. The results showed that habitat type and bathymetric profile influenced the spatial distribution of ringnet fishing effort. Mixed seagrass and coral habitats had the highest concentration of the effort. Most of the habitats in the study area were moderately exposed to the impacts of the ringnet fishery. The study identifies high-risk areas that require spatial measures to minimise possible environmental risks of the gear both to habitats and to endangered sea turtles. 相似文献